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Modeling and Sliding Mode Control Based on Inverse Compensation of Piezo-positioning System
智斌 李, 源泽 辛, 建强 张, 崇尚 孙
 doi: 10.37188/CO.2024-0012
Abstract(16) PDF 3163KB(0)
为了提高压电定位系统(Piezo-positioning system)的控制性能,对迟滞特性产生的影响及其补偿控制方法进行了研究。利用Hammerstein模型表征压电陶瓷定位器的动态迟滞非线性特性,分别以Prandtl-Ishlinskii(P-I)模型和Hankel矩阵系统辨识法求得的模型表示Hammerstein模型的静态非线性部分和动态线性部分。此模型对于200 Hz以内的典型输入频率具有较好的泛化能力。提出了基于P-I逆模型与积分增广的滑模逆补偿跟踪控制策略,实验结果表明,相较于PID逆补偿控制和无逆补偿的滑模控制,滑模逆补偿控制具有更加理想的阶跃响应,无超调且调节时间仅为6.2 ms,在频域内系统闭环跟踪带宽达到119.9 Hz,且扰动抑制带宽达到86.2 Hz。所提控制策略实现了迟滞非线性的有效补偿,提高了压电定位系统的跟踪精度与抗扰性能。
Influence of SA recovery time on orthogonally polarized dissipative solitons
HE Xiao-ying, ZHANG Chuan, ZHANG Yin-dong, RAO Lan
 doi: 10.37188/CO.EN-2023-0032
Abstract(37) FullText HTML(29) PDF 3907KB(5)

Polarization is a crucial factor in shaping and stabilizing mode-locking pulses. We develop an orthogonally polarized numerical modeling of passive mode-locked graphene fiber lasers for generating orthogonally polarized dissipative solitons (DSs). The focus is on analyzing the influence of orthogonal polarization in this net-normal dispersion birefringent cavity caused by the polarization-dependent graphene microfiber saturable absorber. The research results demonstrate that the recovery time of such saturable absorbers significantly affects the characteristics of the orthogonally polarized DSs’ output pulses, including energy, pulse width, time-bandwidth product, and chirps. Results show that its recovery time of 120 fs is optimal, producing two orthogonally polarized narrow dissipative soliton pulses with large chirps of about 7.47 ps and 8.06 ps. This has significant implications for the development of compact, high-power, polarized dissipative soliton fiber laser systems.

Lightweight and optimized U-frame design for space-borne two-dimensional turntable
WEI Yu-xuan, WANG Zhen-yu, LI Zhi-guo, HUANG Le-hong, YANG Kai, MA Yu-bao
 doi: 10.37188/CO.2023-0227
Abstract(16) FullText HTML(7) PDF 5070KB(1)

Space-borne two-dimensional turntables are the main bearing mechanism of space cameras and other optoelectronic equipment, and the U-frame is the key supporting part of these turntables. In order to optimize the structure and lightweight design of the U-frame of the two-dimensional rotary table and to develop a lightweight two-dimensional rotary table with a high load-bearing ratio, this paper designs a carbon fiber composite U-frame for the two-dimensional rotary table. First, a variable cross-section tubular structure U-frame was designed using carbon fiber composites instead of titanium alloy material, combined under consideration of manufacturability. Then, according to the finite element modeling method based on the lay-up process, the carbon fiber U-frame was subjected to finite element modeling and simulation analysis. Then, a prototype U-frame was fabricated, and modal tests verified the accuracy of the finite element model. Finally, a three-level optimization method combining theoretical analysis, genetic algorithm, and the finite element method was proposed to optimize the design of carbon fiber U- frame ply angle, ply thickness, and ply sequence. The results indicate that the vibration patterns of the U-frame obtained from the modal test and simulation are identical and that the frequency difference is less than 5%. The initial design of the carbon fiber U-frame was 45.7% lighter than the titanium U-frame. Through the secondary optimization of the composite layup, the U-frame was further reduced in weight by 13.8%. Additionally, the intrinsic frequency of the U-frame was improved by 10.14%. The composite modeling and optimization methods used in this paper are correct, and the designed carbon fiber U-frame meets the lightweight design requirements of two-dimensional rotary tables.

Adjusting the compactness and hydrophobicity of color filters to decrease gas release during TFT-LCD fabrication
LI Ji, ZHANG Xia, FENG Yi, LIAO Chang, ZHANG Jie, YIN Yong-ming, MENG Hong
 doi: 10.37188/CO.EN-2023-0029
Abstract(99) FullText HTML(75) PDF 5142KB(18)

The TFT-LCD industry is moving towards high efficiency and low costs. During the manufacturing process, it has been found that various photoresists require different vacuum drying times. To reduce manufacturing time and increase panel yields, clarifying the factors that can influence and reduce the vacuum time is necessary. This paper explored the relationship between pumping time and the properties of photoresist materials. It finds that the thermal stability of the photoresist has a negligible relationship with the pumping time. The compactness and hydrophobicity of the photoresist correlated strongly with the vacuum drying time. High compactness and high hydrophobicity can effectively prevent water vapor intrusion and storage in the photoresist during fabrication and consequently reduce pumping times. Overall, this work could guide the future development of new photoresists for the TFT-LCD industry.

Advances in data simulation for space-based situational awareness
LUO Xiu-juan, HAO Wei
 doi: 10.37188/CO.2023-0156
Abstract(235) FullText HTML(90) PDF 3788KB(68)

The data simulation for Space Situational Awareness (SSA) can provide critical data support for the development, testing, and validation of space surveillance equipment and situational awareness algorithms (including detection, tracking, recognition, and characterization of space object), playing a significant role in building SSA capabilities. Taking the optical data simulation for space-based situational awareness as the research subject, the purpose and main research content of SSA data simulation are presented, and the typical research methods and processes of SSA optical imaging simulation are set forth. The current research status and progress in domestic and foreign related research are introduced, covering the imaging modeling and simulation achievements of different optical sensing systems such as binocular vision sensors, LiDAR, infrared sensors, visible light telescopes, and star trackers. The development trend of SSA data simulation research is analyzed, providing reference for future research ideas and approaches of SSA data simulation.

Indistinguishable points attention-aware network for infrared small object detection
WANG Bo-xiao, SONG Yan-song, DONG Xiao-na
 doi: 10.37188/CO.2023-0178
Abstract(216) FullText HTML(84) PDF 4195KB(24)

As aircraft maneuverability increases, multi-frame infrared small target detection methods are becoming insufficient to meet detection requirements. In recent years, significant progress has been achieved in single-frame infrared small-target detection method based on deep learning. However, infrared small targets often lack shape features and have blurred boundaries and backgrounds, obstructing accurate segmentation. According to the problems, an indistinguishable points attention-aware network for infrared small object detection was proposed. First, potential target areas were acquired through a point-based region proposal module while filtering out redundant backgrounds. Then, to achieve high-quality segmentation, the mask boundary refinement module was utilized to identify disordered, non-local indistinguishable points in the coarse mask. Multi-scale features of these difficult points were then fused to perform pixel-wise attention modeling. Finally, A fine segmentation mask was generated through re-predicting the indistinguishable points attention-aware features by point detection head. The mAP of the proposed method reached 87.4 and 63.4 on the publicly available datasets NUDT-SIRST and IRDST, and the F-measure reached 0.8935 and 0.7056, respectively. It can achieve accurate segmentation in multi-detection scenarios and multi-target morphology, suppressing false alarm information while controlling the computational overhead.

Simulation and experiment of weak multi-target laser detection in complex hydrology
ZONG Si-guang, YANG Shao-peng, ZHANG Xin, PENG Dan, DUAN Zi-ke, CHEN Bao
 doi: 10.37188/CO.2023-0141
Abstract(120) FullText HTML(91) PDF 5826KB(15)

Investigating the impact of water quality, target characteristics, and target distance on underwater laser detection is crucial to assessing the effectiveness of laser detection for weak targets in complex coastal water bodies. We examine the theoretical and practical significance of understanding these factors in underwater laser detection. In this study, a laser detection model for detecting weak underwater targets is established. Verify the detection performance of weak multi-target laser ranging under different turbidities. Monte Carlo simulation is used to verify the detection. The laser backscattering echo signals of weak targets at different distances are simulated, and the backscattering echo characteristics of multiple targets with various reflection coefficients are analyzed. Additionally, a smart and portable laser detection system for detecting weak underwater targets has been designed and developed. Laboratory and field lake environment tests were conducted to detect and range for multi-target. In a near-shore lake with a turbidity of 12.87 NTU, the system can effectively detect 3−4 mixed small target groups. These groups have different low reflection coefficients and diameters varying from 80 to 400 μm, all within a range of 10 meters. The average measurement error is ±0.11 m, which is consistent with the theoretical simulation results. The research results serve as a guide for computing links, designing systems, and optimizing parameters for detecting weak underwater multi-targets using blue and green lasers. Furthermore, the results assist in the engineering practice of detecting underwater obstacles in offshore turbid waters.

Resistive plasmonic absorbing structures for stability enhancement of broadband absorption
SHEN Yang, LU Zhi-feng, GUO Ya-kun, LONG Yun-fei, HE Rui, Zhang Zhe-rui
 doi: 10.37188/CO.EN-2023-0022
Abstract(90) FullText HTML(37) PDF 2735KB(9)

Broadband absorption performance in resistive metamaterial absorbers (MA) has always been disturbed by its ohmic sheet element. We propose a comprehensive scheme based on integrating resistive MA and plasmonic structure (PS) to enhance the stable absorption performance. Theoretical investigation indicated that the PS can inspire multi-resonance based on dispersion engineering, and that the localized electric field takes effect on the surface of the ohmic sheet accordingly. Simulation and experimental measurement demonstrated that the proposed resistive plasmonic absorbing structures (PAS) can achieve stable and highly efficient absorption within the frequency band from 7.8 to 40.0 GHz with the ohmic sheet ranging from 100 to 250 Ω/sq. In conclusion, the proposed integration of PS and resistive MA provides an efficient pathway to optimize performance for various applications.

A point cloud classification downsampling and registration method for cultural relics based on curvature features
ZHU Jing-yi, YANG Peng-cheng, MENG Jie, ZHANG Jin-jing, CUI Jia-bao, DAI Yang
 doi: 10.37188/CO.2023-0115
Abstract(162) FullText HTML(62) PDF 3394KB(19)

3D reconstruction is crucial for digitization of cultural relics, and the accuracy of 3D point cloud registration is a significant metric for evaluating the reconstruction quality. In practice, cultural relics point cloud data includes numerous details, and using conventional downsampling methods may result in the loss of such details, thereby affecting registration accuracy. We propose a point cloud classification downsampling and registering method for cultural relics based on curvature features. First, 3D point clouds data of cultural relics are obtained using linear matrix laser measurement. Next, the curvature values of all points are calculated, and a curvature threshold is set for point cloud classification. Different point sets are carried out downsampling with different weights according to their feature attributes to retain the shape features and details of the point cloud as much as possible. Finally, point cloud registration is achieved through calculating the rigid transformation model. Compared to the traditional global downsampling ICP method, the point cloud data of the downsampling processing before point cloud registration reduces to 1/3 of the original size. The average distance decreases from approximately 0.89 mm to 0.59 mm, while the standard deviation decreases from about 0.29 mm to 0.18 mm. This approach guarantees the accuracy of downsampling and registration and is applicable to various cultural relics point cloud data.

Omnidirectional spatial monocular vision indoor localization measurement based on a two-degree-of-freedom rotary platform
WU Jun, WANG Hao-shuang, SHAN Teng-fei, GUO Run-xia, ZHANG Xiao-yu, CHEN Jiu-sheng
 doi: 10.37188/CO.2023-0106
Abstract(126) FullText HTML(78) PDF 3471KB(24)

To address the problem of limited field of view measurement in traditional monocular vision measurement systems, we propose an omnidirectional spatial monocular vision measurement method based on a two-degree-of-freedom rotary platform. First, the rotating axis parameters of the double-degree-of-freedom rotary platform are calibrated. Then, the pictures of the checkerboard calibration plate fixed with the two-degree-of-freedom rotary platform are captured by using an auxiliary camera. Position coordinates of the checkerboard corner points are extracted and converted to the same camera coordinate system. The direction vector of the rotating axis parameters in the initial position is obtained through PCA (principal component analysis) plane fitting, and the position parameter of the rotating axis parameters in the initial position is determined using the method of spatial least squares circle fitting. The camera data acquired at various angles is transformed into the same coordinate system using the rotation angle of the rotary platform and the Rodrigues formula. This enables measurement of the target in the horizontal and vertical omnidirectional space. Finally, the measurement accuracy of the proposed method is verified using a high-precision laser rangefinder. Additionally, experiments comparing the omnidirectional spatial measurement ability of the proposed method with the binocular vision measurement system and wMPS measurement system are conducted. The results indicate that the method achieves a measurement accuracy comparable to that of a binocular vision system. However, it also surpasses the binocular vision system in term of measurement range, making it applicable for omnidirectional spatial measurements.

A simplified method for high temperature calibration in the visible light band
LI Yun-long, LI Zhou, SUN Zhi-yuan, YANG Guo-qing
 doi: 10.37188/CO.2023-0122
Abstract(187) FullText HTML(135) PDF 2273KB(26)

To improve the efficiency of high temperature calibration in the visible light band (0.3 μm~0.9 μm), a simplified method for high-temperature calibration is proposed. Firstly, a high-temperature calibration model in the visible light band with exposure time variable is proposed. Based on a large number of experimental data, it is found that the gray value of each channel of an RGB camera varies linearly not only with the increase of exposure time, but also with the increase of black-body radiation brightness. Thus, a specific form of high-temperature calibration model in the visible light band is determined. To solve the unknowns in the simplified high-temperature calibration model in the visible light band, image data at two different exposure times are collected under two levels of black-body radiation brightness, and then the image data is processed to obtain the high-temperature calibration curve of the RGB camera under any exposure time. Finally, the simplified visible light band high-temperature calibration method proposed in this article is compared to the conventional visible light band high-temperature calibration method based on exposure time. The experimental results show that the maximum relative error between the calculated value of the R channel, G channel, B channel and the calibrated values are 3.38%, 2.56%, −1.14%. Moreover, the relative error between the calculated and the calibrated values for each channel does not exceed 3.50%. The mathematical model proposed in this article can effectively simplify the conventional high-temperature calibration method, resulting in a reduced high-temperature calibration time and improving the calibration efficiency.

Design and application of CCD/EMCCD photoelectronic parameter test system
SHEN Ji, VIACHESLAV V. Zabudsky, CHANG Wei-jing, NA Qi-yue, JIAN Yun-fei, OLEG V. Rikhalsky, OLEKSANDR G. Golenkov, VOLODYMYR P. Reva
 doi: 10.37188/CO.EN-2023-0016
Abstract(235) FullText HTML(69) PDF 5116KB(39)

A photoelectrical parameters test system for testing CCD and electron-multiplying charge-coupled device (EMCCD) chips is designed. The test system has automatic and manual modes, and it can test the dark currents, the output amplifier’s responsivity, charge transfer efficiency, charge capacity and other parameters. According to different specifications and structures of CCD/EMCCD devices, we complete the parameter test of wafer or packaged product. The developed system can be used for the testing and sorting for 576 × 288, 640 × 512, 768 × 576, 1024 × 1024, 1280 × 1024 CCD and EMCCD chips.

Design of large-aperture multi-band beam quality detection system
LIU Cai, YU Xin, PAN Guo-tao, HE Guo-qiang, NI Xiao-long, BAI Su-ping
 doi: 10.37188/CO.2023-0228
Abstract(14) FullText HTML(7) PDF 8469KB(0)

Spectral synthesis technology is an important technical approach to achieving high-energy laser output. Ensuring high-quality laser output under the premise of high-power output has become the most urgent goal in further developing spectral synthesis technology. This paper addresses the challenge of parameter detection of 155 mm × 140 mm rectangular aperture, 1064 ± 3 nm, 1030 ± 3 nm, and 635 ± 5 nm band beams by designing a large-aperture multi-band multi-parameter detection system. The wavefront detection unit is based on Kepler’s telescopic structure, the conjugate relationship between the deformable mirror and the microlens is constructed, and the compressed beam matches the detector size. The front group objective lenses adopt a Cassegrain structure to solve the problem of color difference correction in large-aperture and multi-band. The rear group of mirrors adopts a three-piece apochromatic refractor group, which compensates for the color difference while accounting for the non-thermal design and compensates for the residual thermal difference between the front group of objectives and the rear group of mirrors. After passing through the wavefront detection unit, the beam quality and beam uniformity can be measured. In order to improve the environmental adaptability of the system, it was designed through an optical passive anthermic method at 20 °C±10 °C. Finally, the system was installed and tested, and the wavefront image collected by the wavefront detection camera was restored using the Zernike wavefront restoration method. The measured RMS value of the wavefront of the system is better than 0.0524λ (λ=632.8 nm), the beam uniformity is better than 0.893, and the beam quality β factor is better than 1.26 times the diffraction limit at 10 °C−30 °C.

Underwater calibration image enhancement based on image block decomposition and fusion
CHANG Zhi-wen, WANG Li-zhong, LIANG Jin, LI Zhuang-zhuang, GONG Chun-yuan, WU Zhi-hui, XU Jian-ning
 doi: 10.37188/CO.2023-0218
Abstract(12) FullText HTML(7) PDF 8601KB(0)

Aiming at the loss of target point information caused by the degradation of underwater calibration images collected by camera calibration in underwater visual measurement, an underwater calibration image enhancement algorithm based on image block decomposition and fusion is proposed. First, given the difficulty of image dehazing caused by uneven illumination of underwater calibration images, image segmentation is implemented based on homomorphic filtering to calculate the global background light intensity and to achieve image dehazing. Then, given the problems such as noise, blur, and uneven illumination that still exist after the underwater image is dehazed, contrast enhancement and detail information enhancement are performed to obtain two complementary enhanced images. The complementary images are divided into multiple image blocks, and the image blocks are decomposed into. There are three independent components, each of which is of average intensity, signal intensity, and signal structure. The three components are separately fused and solved for the final enhanced image. Finally, subjective and objective evaluation and target point detection experiments are used to evaluate the enhanced quality of the underwater calibration image. Experimental results indicate that this method produces higher visual effects and evaluation scores than UDCP, MSR, and ACDC methods. When the turbidity is 7.6 NTU, 11.4 NTU, 15.7 NTU, and 18.4 NTU, the number of detected target points increases by 2.0%, 2.3%, 9.3%, and 21.2%. Therefore, this paper presents a reliable and effective method to improve the quality of underwater calibration images and provides a stable and reliable underwater calibration image enhancement method for underwater visual measurement.

 doi: 10.37188/CO.2024-0065
Abstract(19) PDF 715KB(0)
 doi: 10.37188/CO.2024-0037
Abstract(20) PDF 728KB(2)
为了实现强流脉冲电子束对材料表面改性的工业化应用,需要对电子束的作用过程进行实时微扰监测。电场强度是反映电子束特性的关键参数之一,基于Stark效应的激光暗荧光光谱可实现对环境电场的微扰测量。因此,开展激光功率密度对环境电场的影响研究,对此类电场测量方法的参数设置和结果判断具有重要的理论和应用价值。方法:通过理论分析和计算得出电场测量微扰状态下的激光功率密度与试验环境的关系模型;基于上述关系模型,搭建测试平台,实验验证激光功率密度对电场测量微扰的情况。结果:实验结果表明:在示踪气体氙气压强为1.0×10^(-4) mbar、电场强度在2kV/cm及以下的条件下,对电场测量微扰的激光功率密度值为5MW/cm2,与理论计算值基本一致。结论:研究结果填补了激光暗荧光光谱诊断方法中激光功率密度对电场影响定量分析方法的空白,可应用在同类电场测量方法中,为激光功率密度与实验参数的设置提供依据和参照,支撑电场测量实验的开展,有效提升电场测量的准确性。
Realization and error analysis of geographical guidance for roll-pitch electro-optical pod
DONG Qi-lin, ZHANG Wei-guo, ZHAO Chuang-she, WANG Chao, YUAN Yi-jie, YI Xing-guo, LIU Wan-gang, CHENG Yong-dong
 doi: 10.37188/CO.2023-0188
Abstract(130) FullText HTML(72) PDF 4516KB(16)

In order to improve the accuracy and success rate of geographical guidance, according to the structural characteristics of the roll-pitch electro-optical pod, a mathematical model of geographical guidance was developed through three steps: first, establishing the coordinate system; second, solving the target coordinates; and third, calculating the frame angle. Speed forward feed and small domain search modes were introduced on this basis. The frame angle calculation error affected by inertial navigation measurement error and target distance was simulated, and the results show that the longitude, latitude, and heading angle errors had a greater influence on the pitch angle calculation error; nonetheless, the errors of elevation and horizontal attitude angle had a greater influence on the calculation error of the roll angle. Improving the positioning accuracy of inertial navigation can further reduce the frame angle calculation error and improve the geographical guidance accuracy. However, when the heading angle decreases below 0.1 degrees and the horizontal attitude angle decreases below 0.05 degrees, then the influence weight of the attitude angle error also decreases. The improvement in guidance accuracy is no longer evident when attitude angle errors are reduced. Increasing target distance sharply decreases the error of frame angle calculation. Finally, the guidance test with pitch and roll mean square errors of less than 0.12 degrees shows the algorithm's accuracy and the simulation analysis's effectiveness.

Design of miniature head-mounted fluorescence microscope based on metalens
ZHANG Zhi-miao, WANG Cheng-miao, XIE Mian, LIN Yu, HAN Ye-ming, DENG Yong-bo, GUO Chang-liang, FU Qiang
 doi: 10.37188/CO.2023-0237
Abstract(89) FullText HTML(60) PDF 25553KB(18)

The recent advent of miniature head-mounted fluorescence microscopes has revolutionized brain science research, enabling real-time imaging of neural activity in the brains of free-moving animals. However, the pursuit of miniaturization and reduced weight often results in a limited field of view, constraining the number of neurons observable. While larger field-of-view systems exist, their increased weight can impede the natural behaviors of the subjects. Addressing these limitations, a novel design utilizing a metalens schematic is proposed. This approach offers the benefits of being ultra-light, ultra-thin, and capable of high-quality imaging. By deriving the aberration formula specific to hyperbolic phase metalens and using it as a foundation, a design for a miniature fluorescence microscope was developed. This microscope boasts a 4 mm×4 mm field of view and a numerical aperture (NA) of 0.14, effectively correcting seven primary aberrations. The resulting prototype, weighing a mere 4.11 g, achieves a resolution of 7.8 μm across the entire field of view. This performance is sufficient to image neural activity in the brains of freely moving mice with single-cell resolution.

Magnetic field sensor utilizing U-Shaped Cavity based on in-fiber Mach–Zehnder interferometer
FAN Peng-cheng, JIANG Xue-zhai, Tian De-qiang, Zhang Guang-qiang
 doi: 10.37188/CO.EN-2023-0015
Abstract(221) FullText HTML(56) PDF 3870KB(27)

An optical fiber magnetic field sensor is proposed and experimentally demonstrated by using a U-shaped cavity based on in-fiber Mach-Zehnder interferometer (MZI) coated with magnetic fluid (MF). The magnetic field sensor is manufactured by splicing a section of single-mode fiber (SMF) between two sections of SMF with designed fiber geometric relationships. As the geometric symmetry MZI is strongly sensitive to the surrounding refractive index (RI) with a high sensitivity up to −13588 nm/RIU and MF’s RI is sensitive to magnetic field, the magnetic field sensing function of the proposed structure is realized. The results show that the magnetic field sensitivity reaches as high as 137 pm/Oe, and the magnetic field range is almost linear from 0 to 250 Oe. The proposed magnetic field sensor has the advantages of small size, low cost, easy to manufacture, robustness, high sensitivity, good repeatability and easy to integrate with fiber optic systems.

Rotary error modeling and assembly optimization of parallel structure shafting
DONG Yi-ming, JIANG Bo, LI Xiang-yu, XIE You-jin, LV Tao, RUAN Ping
 doi: 10.37188/CO.2023-0171
Abstract(121) FullText HTML(42) PDF 3018KB(12)

In order to improve the shafting motion accuracy of two-dimensional turntables such as photoelectric theodolites, we establish a mathematical model considering both the structural error of parts and the coupling amplification effect based on Jacobian-Torsor theory. Aiming at a shafting structure with one fixed end and one swimming, an analysis method of partial parallel structure was proposed. Through numerical simulation analysis, the impact of each part’s structural errors on the motion accuracy of the shafting and the optimal shafting assembly scheme were obtained. The results of assembly and adjustment of a photoelectric theodolite with an optical diameter of 650 mm show that assembly optimization improved the motion accuracy of the shaft system by 32.1%. The precision model and optimization method of shafting motion provide a theoretical basis for the shafting adjustment and tolerance design of two-dimensional turntables such as photoelectric theodolites.

Capillary liquid-core optical fiber temperature sensor based on fluorescence intensity ratio
ZHANG Ye-yu, LIU Ting, HUANG Jian-wei, HUANG Xue-zhi, CHEN Ming-jie
 doi: 10.37188/CO.2023-0160
Abstract(110) FullText HTML(51) PDF 3436KB(18)

Aiming to the problem of the complicated preparation of existing optical fiber fluorescence temperature sensing probes, we propose a simple, cost-effective, and high-performance optical fiber fluorescence temperature sensor based on a capillary liquid core. Firstly, a mixed solution consisting of temperature-sensitive rhodamine B and temperature-insensitive rhodamine 123 was used as the temperature-sensitive material and encapsulated in a stainless-steel capillary to prepare a sensing probe. The ratio of the fluorescence emission peak intensities of the two dyes was utilized for temperature sensing. Subsequently, the sensing probe’s mixed solution concentration and capillary structural parameters were optimized. Then, the performance of the sensor was tested. Finally, the sensor was applied to real-life temperature measurements. The experimental results demonstrate that the sensor has a temperature response range of 30−70 °C and that there is a quadratic correlation between the fluorescence intensity ratio and the temperature, with the fitted correlation coefficient as high as 0.9984. The sensor exhibits excellent accuracy, repeatability, and stability, with more than three months of service time. Moreover, it can be well-utilized to detect temperature in daily life. The optical fiber fluorescence temperature sensor shows significant potential for real-time monitoring and remote detection applications.

Optical design and spectral optimization of Philips prism 3CMOS camera
CHEN Su-hao, LV Bo, LIU Wei-qi
 doi: 10.37188/CO.2023-0155
Abstract(165) FullText HTML(75) PDF 4687KB(38)

According to the demand for high imaging quality and high chromaticity in color digital cameras, we investigated the optical system design and camera spectral optimization methods of 3CMOS cameras based on Philips prisms. By constructing the model of the optical path of the Philips prism, the structural parameters of the prism were optimized. The volume of the system was reduced while ensuring total internal reflection and exit window size. Based on this method, the Philips prism 3CMOS camera optical system was designed, with a field of view angle of 45 ° and a relative aperture of 1/2.8. The system's MTF was greater than 0.4 in the full field of view and full band at Nyquist sampling frequency of 110 lp/mm. Subsequently, based on the fundamental principles of chromaticity, a vector imaging model for Philips prism cameras was established. The problem of thin film spectral shift caused by changes in light incidence angle was analyzed, and a correction model for spectral shift under wide beam conditions was proposed. Four sets of optical thin films in the camera were designed and optimized using this model. Through optical path simulation experiments and color error analysis, based on the optimized camera spectrum, the average color error of the system was reduced by 15.8%, and the color non-uniformity of the image plane was reduced by 60%. The results indicate that the designed optical system has good imaging quality, and the optimized camera spectrum achieves good color performance and uniformity.

Binocular 3D reconstruction method based on interpolation super-resolution
LIU Yuhao, WU Fupei, WU Shuzhuang, WANG Rui
 doi: 10.37188/CO.2023-0214
Abstract(17) FullText HTML(9) PDF 4854KB(0)

The reconstruction of the three-dimensional surface morphology of objects based on binocular stereo matching is constrained by physical conditions such as sensor size, lens focal length, and environmental light. A binocular surface three-dimensional reconstruction method based on interpolation super-resolution is proposed in response to this issue. First, at the image preprocessing stage, an image enhancement method based on wavelet transform and dual histogram equalization fusion is established to overcome the problems of traditional binocular vision limited by complex environmental light interference. Second, a super-resolution algorithm based on Lagrange and cubic polynomial interpolation is constructed to increase the image's pixel density and add image details to the binocular matching cost calculation stage, thereby improving the matching accuracy. Finally, a simple linear iterative clustering (SLIC) method is used to segment the target image, and a secondary surface fitting is performed for each segmented area to obtain a height curve that is more closely aligned with the actual surface of the object, which can reduce the reconstruction error and improve the reconstruction accuracy. The experimental results show that the average relative error of the global height measurement of 5 sets of measurement samples is ±2.3%, the average measurement time of the experiment is 1.8828 s, and the maximum time is 1.9362 s. This is a significant improvement over traditional methods. Experimental analysis results verify the effectiveness of the proposed algorithm.

Study on beam quality of DF laser with inner cavity unstable resonator
RUAN Peng, WANG Yu-hai, PAN Qi-kun, SHAO Chun-lei, CHEN Fei, GUO Jin
 doi: 10.37188/CO.2023-0210
Abstract(14) FullText HTML(9) PDF 1803KB(0)

Laser beam quality is one of the key indicators considered when measuring the performance of laser applications. To meet the application requirements of long-distance optoelectronic countermeasures, this paper researches the design of unstable resonators and beam quality improvement techniques for non-chain DF lasers. Three sets of positive branch confocal unstable resonators with different magnifications are designed. An experimental setup for an unstable inner cavity resonator is constructed with two convex mirror structures: transverse support and longitudinal support. The transverse support structure is equipped with a circulating water-cooling channel. Using 86.5% surrounding energy to define laser beam diameter, the laser beam quality is evaluated with beam quality factor β, and the energy and beam divergence for two support types of convex mirrors are compared. Research has found that, under the same conditions, the laser energy of unstable resonators with longitudinal support is 6% higher than that of the transverse support structure. Still, the far-field divergence angle is 9% larger than that of the transverse support structure. Although the water-cooled transverse support structure has energy shielding, its high thermal stability significantly improves the quality of the laser beam. A beam divergence of θ0.865 = 0.63 mrad with beam quality factor β=1.83 is obtained at M=2.25 with a transverse support unstable resonator. The laser energy under this condition is 2.34 J, the laser pulse width is 88.2 ns, and the peak power reaches 26.5 MW.

Shared secret-key generation from atmospheric MIMO optical channel
CHEN Chun-yi, CAI Jin-xiang, LI Qiong
 doi: 10.37188/CO.2023-0202
Abstract(23) FullText HTML(9) PDF 2380KB(2)

Shared secret-key extraction from random channel characteristics is an effective approach to ensuring the physical layer security of atmospheric optical channels. The secret-key generation rate and disagreement rate are two issues that attract a lot of attention. Using the random characteristics of atmospheric turbulent optical channels as a shared source of randomness, a secret-key extraction scheme for multiple-input multiple-output (MIMO) atmospheric optical channels is proposed. The alternative singular value decomposition is used to decompose the channel matrix; the correlation between the two channel characteristic sequences obtained by the two legitimate parties is enhanced by carrying out a simple moving average; a channel quantization alternating scheme with a single threshold is used to quantize the resultant channel characteristic sequences. The two legitimate parties generate random controlling sequences for coding mapping based on differential diversity values, which are used in performing coding mapping of the quantized bits of the channel characteristic sequences generated by the channel quantization alternating scheme with a single threshold. The experimental results show that our scheme’s initial key disagreement rate can reach 5.2×10−4 at a signal-to-noise ratio of 30 dB, and that the generated random bit sequences have passed the National Institute of Standards and Technology (NIST) randomness test. This paper’s results are useful in the implementation of secret-key extraction from atmospheric MIMO optical channels.

Real-time cascaded microring resonators spectral envelope fitting
ZHAO Kai-hao, LI Ming yu, WANG Zhao-yu, CHEN Xin, GUAN Bo-ren, HE Jian Jun, LIN Chu-yue, DONG Wen-fei
 doi: 10.37188/CO.2023-0195
Abstract(14) FullText HTML(10) PDF 4850KB(1)

Cascaded Microring Resonators (CMRR), a new type of optical sensor, are widely used in biology, medicine, and other fields because of their high sensitivity, easy integration, and low power consumption. This paper proposes a Python-based envelope fitting method for real-time CMRR sensor output spectrum to achieve real-time data analysis and processing of the CMRR sensor output spectrum. First, different fitting models were used to fit the output spectrum of the CMRR sensor. Then, the fitting errors of different fitting models were compared by sensitivity error percentage, and it was concluded that the smooth spline fitting method performed best in real-time processing of the output spectrum of the CMRR sensor. Finally, NaCl solution with different concentrations was used for real-time acquisition and processing of the output spectrum. The reliability of the real-time acquisition and processing program for the CMRR sensor output spectrum is verified. The experimental results show that the wavelength drift of the CMRR sensor is linearly related to the concentration of the solution. It can be seen from the calculation that the sensitivity of the CMRR sensor for brine is about 671.03529 nm/RIU.

High-precision spherical wavefront calibration method for shack-hartmann wavefront sensor
BAO Ming-di, SHI Guo-hua, XING Li-na, HE Yi
 doi: 10.37188/CO.2023-0148
Abstract(157) FullText HTML(99) PDF 4629KB(35)

To address the issues of low measurement accuracy and insufficient stability in traditional calibration methods for Shack-Hartmann wavefront sensors (SHWFS), we propose a high-precision absolute calibration method using spherical waves generated by sensor. A high-precision calibration method for spherical waves was obtained through theoretical derivation. Combined with the constructed spherical wave calibration experimental device, high-precision calibration was performed on the SHWFS with sub apertures of 128×128. The structural parameters of the SHWFS (f, w, and L0) are calculated precisely. The measurement accuracy of the SHWFS is verified after calibration. The experimental results demonstrate that by using this method to calibrate the SHWFS, its wavefront recovery accuracy reaches a PV of 1.376×10−2λ and an RMS of 4×10−3λ (where λ=625 nm), respectively. Additionally, its repeatability accuracy reaches a PV of 3.2×10−3λ and an RMS of 9.76×10-4λ (where λ=625 nm), respectively. These findings suggest that this method is suitable for enhancing the measurement accuracy of high-precision calibration of SHWFS with large aperture.

Optical system design of hyperspectral imaging spectrometer for trace gas occultation detection
KONG Xiang-jin, LI Bo, LI Han-shuang, WANG Xiao-xu, GU Guo-chao, JIANG Xue
 doi: 10.37188/CO.2023-0153
Abstract(119) FullText HTML(81) PDF 5376KB(25)

Trace gases, as important constituents of the atmosphere, play an important role in the ecology of the planet. In order to realize the requirements of wide-band, hyperspectral and all-weather continuous measurement, a hyperspectral imaging spectrometer operating in occultation detection mode is designed in this paper. The system is a dual-channel structure with a common slit, the UV-visible channel adopts a single concave grating, and the infrared channel adopts a structure combining Littrow and immersion grating, which effectively reduces the volume. The software is used to optimize the optical structure, and the optimization results show that the spectrometer operates in the range of 250−952 nm wavelengths, of which the UV-visible channel operates in the wavelength range of 250−675 nm, the spectral resolution is better than 1 nm, the MTFs are all higher than 0.58 at a Nyquist frequency of 20 lp/mm, and the RMS values at various wavelengths of the full-field-of-view are all less than 21 μm; the infrared channel operates in the wavelength band of 756−952 nm, the spectral resolution is better than 0.2 nm, the MTF is higher than 0.76 at the Nyquist frequency of 20 lp/mm, and the RMS value at each wavelength in the whole field of view is less than 6 μm, all of them meet the design requirements. It can be seen that the hyperspectral imaging spectrometer system can realize the occultation detection of trace gases.

Influence of flow channel structure on characteristics of Laser diode pumped flowing-gas rubidium vapor laser
PAN Li, HE Yang, MA Li-guo, JI Yan-hui, LIU Jin-dai, CHEN Fei
 doi: 10.37188/CO.2023-0174
Abstract(124) FullText HTML(74) PDF 3859KB(25)

In order to study the influence of the gas flow channel structure on the output performance of the flowing-gas diode pumped alkali vapor laser (FDPAL), we established the FDPAL theoretical model based on the gas heat transfer, fluid mechanics, and laser dynamics process in FDPAL using side pumping Rb vapor FDPAL (Rb-FDPAL) as the simulation object. The impacts of the gas flow direction, the cross-sectional area and the shape of the runner on the Rb-FDPAL’s output performance were analyzed. The results show that with the horizontal flow method and by increasing the cross-sectional area of the flow channel and setting a masonry structure as the connection between the gas flow channel and the steam pool, we effectively suppress the vortex in the vapor, increase the gas flow rate, and decrease the thermal effect of the steam pool. Rb-FDPAL's laser output power and slope efficiency are higher, and the simulation results are consistent with the experiment.

Error modeling of polarization devices in simultaneous phase-shifted lateral shearing interferometry
ZHANG Yu-wen, LIU Bing-cai, WANG Hong-jun, TIAN Ai-ling, REN Ke-xin, WANG Kai
 doi: 10.37188/CO.2023-0152
Abstract(102) FullText HTML(59) PDF 2748KB(8)

To provide a reliable theoretical basis for the selection, mounting, and error compensation of the polarization device in the synchronous phase-shift transverse shear interference system, based on the Jones matrix principle, we construct an error model reflecting the degree of influence of the errors of quarter-waveplate and polarizer array on the measurement results in the system. Then, we quantitatively analyze how the measurement results are influenced by the following factors: the phase delay error of quarter-waveplate, fast-axis azimuthal angle error, and transmission-axis azimuthal angle error of the polarizer array. The simulation results show that the wavefront measurement errors are 0.00002λ(PV) and 0.000062λ(RMS) when the phase delay error of the quarter-waveplate is within ±1°, 0.0001λ(PV) and 0.00006λ(RMS) when the adjustment accuracy of the quarter-waveplate is within ±2°, and 0.003λ(PV) and 0.001λ(RMS) when the azimuthal angle error of the polarizer array is within ±1°. According to the simulation results, the polarization components in the measurement system were selected. At the same time, two polarization components with different levels of accuracy were chosen for comparison experiments. The experimental results indicate the following conclusions: the deviations of the residual values of the experimental results from the residual values of the simulation results in terms of the PV and the RMS values are less than λ/20, and the validity of the model can be verified to a certain extent. The mathematical model proposed in this paper can provide a reliable theoretical basis for the selection of polarization devices in synchronous phase-shifted transverse shear interference systems.

Infrared reflection characteristics of the wall solved by improved whale optimization algorithm
ZHANG LU, FAN Jin-hao, LU Yu-xuan, ZHANG Lei, FU Li
 doi: 10.37188/CO.2023-0095
Abstract(89) FullText HTML(48) PDF 4610KB(6)

The infrared reflection characteristics of the wall are characterized and solved by the bidirectional reflectance distribution function (BRDF). BRDF measurement currently has two problems to be addressed: it requires much experimental data and accuracy is not high enough. By constructing the reflection characteristic test platform of the wall target, an MR170 Fourier infrared spectroradiometer was used to obtain the target radiance at the incident angle and each reflection angle in the 2−15 μm band. For the stealth target, the RBF network was used to fit the radiance at the bands of 3−5 μm and 8−14 μm to eliminate atmospheric interference. Then, the BRDF values of the stealth targets in the above two bands were obtained. To improve the accuracy of the BRDF model, an improved whale optimization algorithm (IWOA) was proposed to invert BRDF model parameters, and a reflectivity-solving method based on BRDF was designed. The IWOA has a good effect on the parameter inversion of the BRDF calculation model. According to the reflection method and applying the obtained BRDF data, the reflectance 0.5496 and the relative error 6.17% are obtained, which meet the engineering requirements.

Detection method of solar position using a biomimetic polarized light compass
YANG Jiang-tao, WANG Ming-kai, LIU Si-tuo, LIANG Lei, LIU Zhi, GUO Yue
 doi: 10.37188/CO.2023-0192
Abstract(95) FullText HTML(40) PDF 5974KB(11)

Aiming at the requirement of polarized light navigation for accurate position information of feature points in the sky, an accurate detection method for the solar position of imaging system based on all sky polarization mode is proposed. Compared with the traditional detection method of the solar position based on spot, we use the inherent polarization information in the atmosphere to complete the accurate measurement of the solar position, which has the characteristics of simple, high accuracy and wide application range. The optical acquisition system consists of three micro large-field-of-view camera modules and polarizers, which makes the structure more compact, smaller and lower in height. Starting from the principle, the algorithm of solving the solar position is simulated first, and then the algorithm is verified in three weather environments (sunny, occluded, and aerosol) using the optical acquisition system. It can be seen that when the weather is clear, the sun is detected at different times of the same day, and the accuracy of the measured sun's altitude and azimuth are 0.024° and 0.03° respectively; when the sun is blocked by high-rise buildings, the accuracy of the measured sun's altitude and azimuth are 0.08° and 0.05°; when the sun is blocked by the branches and leaves of trees, the accuracy of the measured sun's altitude and azimuth are 0.3° and 0.1° respectively. Only when the aerosol concentration exceeds a certain amount will the Rayleigh distribution mode of polarized light be destroyed, which will affect the detection accuracy of solar position. The experimental results show that this new detection method can not only meet the needs of polarized light navigation for the solar position, but also provide a new way of exploration for fans who like to explore the mysteries of the universe.

Effect of GaInP and GaAsP inserted into waveguide/barrier interface on carrier leakage in InAlGaAs quantum well 808 nm laser diode
梦洁 付, 海亮 董, 志刚 贾, 伟 贾, 建 梁, 并社 许
 doi: 10.37188/CO.2024-0006
Abstract(29) PDF 184KB(4)
There is nonradiative recombination in waveguide region owing carrier leakage, which in turn reduces output power and wall-plug efficiency. In this paper, we designed a novel epitaxial structure, which suppresses carrier leakage by inserting n-Ga0.55In0.45P and p-GaAs0.6P0.4 between barriers and waveguide layers, respectively, to modulate the energy band structure and to increase the height of barriers. The results showed that leakage current density reduced by 87.71%, compared to traditional structure. The output power reached 12.80 W with wall-plug efficiency of 78.24% at an injection current density 5 A/cm2 at room temperature. In addition, temperature drift coefficient of center wavelength was 0.206 nm/°C at the temperature range from 5 to 65 °C. The novel epitaxial structure provides a theoretical basis for achieving high-power laser diode.
 doi: 10.37188/CO.2024-0031
Abstract(23) PDF 804KB(0)
 doi: 10.37188/CO.2024-0015
Abstract(26) PDF 739KB(1)
为了能对飞秒激光系统的群延迟色散(group-delay dispersion,GDD)进行调控,设计并制备了相位延迟反射镜。本文系统的研究了相位延迟反射镜补偿群延迟色散的原理,使用Nb2O5和SiO2作为高低折射率材料,并通过将相位延迟反射镜与其互补镜配对的方式平缓了群延迟色散曲线。最后,制备出了相位调控数据为-800fs^2GDD的相位延迟的反射镜,在900nm-1100nm范围内,反射率达到99%以上。解决了飞秒激光系统带宽调节的问题,满足飞秒激光器的使用要求。
 doi: 10.37188/CO.2024-0010
Abstract(21) PDF 626KB(2)
 doi: 10.37188/CO.2024-0008
Abstract(22) PDF 1349KB(0)
 doi: 10.37188/CO.2024-0007
Abstract(25) PDF 1289KB(0)
 doi: 10.37188/CO.2023-0225
Abstract(15) PDF 1025KB(0)
Research on laser online monitoring equipment for high-temperature corrosive gas in coal-fired boilers
LI Long, SHI Shuai, GONG Ting, TIAN Ya-li, GUO Gu-qing, QIU Xuan-bing, XIONG Xiao-he, LI Chuan-liang
 doi: 10.37188/CO.2023-0209
Abstract(21) FullText HTML(11) PDF 3557KB(3)

The coal-fired boiler combustion process's economic, safety, and environmental performance holds great significance when constructing smart power plants. In coal-fired boiler combustion, H2S and CO are the two main high-temperature corrosive gases. They not only corrode the boiler near the wall surface but also pose severe harm to the atmospheric environment through their exhaust gases. Based on the near-infrared tunable diode laser absorption spectroscopy technology, combined with wavelength modulation spectroscopy and frequency division multiplexing technology, an unstaffed online real-time monitoring instrument for H2S and CO gas concentrations in the main combustion zone of coal-fired boilers was developed. Gas absorption spectroscopy in the 6335−6341 cm−1 range was simulated, and two near-infrared lasers near 1.5 μm were selected as the laser source. A high-temperature and corrosion-resistant Herriott-type multi-pass cell was developed to attain an effective optical path length of 15 m for the interaction between laser and gas. Hardware circuits and corresponding firmware programs were developed to attain secondary demodulation of the absorption spectroscopy signals of H2S and CO and concentration inversion. The linearity and Allan variance experiments showed linear fitting correlation coefficients of 0.9998 and 0.9995. At 73 s and 53 s integration times, the minimum detection limits for H2S and CO were 0.2×10−6 mol/mol and 0.344×10−6 mol/mol, respectively. Finally, the developed instrument was applied in the combustion atmosphere of the main combustion zone of a 300 MW coal-fired boiler under a four-corner tangential firing system, and synchronous measurements of H2S and CO near the water-cooled wall were conducted. The results indicated a positive correlation between the concentrations of H2S and CO in the boiler, with anaerobic combustion leading to an increase in the content of these gases and causing corrosion to the water-cooled wall.

Fully complex optical neural network with insertion-loss robustness
CHEN Hui-bin, TANG Kai-fei, YOU Zhen-yu
 doi: 10.37188/CO.2023-0198
Abstract(29) FullText HTML(12) PDF 4941KB(3)

Linear optical processors based on the cascading of Mach-Zehnder Interferometer (MZI) topologies have been demonstrated to be an important way of implementing optical neural networks, but several practical challenges still need resolution. To solve problems arising from chip manufacturing and testing processes that could lead to phase errors and insertion losses, we conducted experiments and theoretical simulations for various reconfigurable optical processors. We found that using arbitrary unitary matrices instead of arbitrary matrices achieved by a single N×N Clements unit can substantially reduce the optical depth and enhance robustness against insertion losses. This approach allows for the construction of fully complex optical neural networks. Additionally, due to the limited degrees of freedom, we introduced a phase-shift layer before each layer of the Clements unit. Particularly in multi-layer optical neural networks, this design aids in mapping classification data to higher-dimensional spaces, facilitating faster neural network convergence.

Study on substrate lateral radiation of electrically pumped organic light-emitting diodes
ZHAO Bian-li, WANG Jing, LI Wen-wen, ZHANG Jing, SUN Ning, WANG Deng-ke, JIANG Nan
 doi: 10.37188/CO.2023-0190
Abstract(15) FullText HTML(10) PDF 4177KB(1)

There is a significant narrowing of the lateral radiation spectrum of the substrate of organic light-emitting diodes as compared to the forward radiation spectrum. Studying the factors that affect the lateral radiation spectrum narrowing of the device and further reducing the spectral linewidth can provide a foundation for the study of the electrically pumped organic light-emitting diode laser radiation. This paper studies the full width at half maximum, peak wavelength, and polarization characteristics of lateral radiation spectrum in organic light-emitting diode substrate, with the thickness changes of hole transport layer NPB. The lateral radiation spectra of organic light-emitting diode with Ag film evaporated on both sides of the substrate edge are compared with those of organic light-emitting diode without Ag film. The full width at half maximum of the lateral radiation spectrum with Ag film is narrower. When the NPB thickness is 130 nm, the full width at half maximum of the lateral radiation spectrum in the device substrate reaches its narrowest, which is 14 nm. This shows that the optical resonator will affect the light propagating laterally in an organic light-emitting diode substrate when mirrors are provided on both edge sides of the substrate. The results indicate new approaches to narrowing the radiation spectrum and amplifying the light of organic light-emitting diodes.

 doi: 10.37188/CO.2024-0018
Abstract(29) PDF 976KB(2)
脉搏蕴含人体丰富的血流信息,检测脉搏并推导出人体心血管系统健康状态正成为研究的热点。本文利用热注射法合成得到尺寸为3 nm的PbS量子点,在金叉指电极表面通过旋涂的方法构筑PbS量子点光电探测器。基于已制备的PbS量子点光电探测器研制了数据可视化的脉搏检测系统。运用光电容积脉搏波描记法,我们对同一测试者不同运动状态以及不同测试者同一运动状态进行测量,经过电路处理将测得数据显示在电子显示屏上。结果表明,探测器在15.2 μW/ cm^2光强度照射下,其响应度(R)和探测率(D*)在-3 V偏压下分别为0.3275 A/W和1.3332×10^12 Jones。将其用于测量脉搏电路中,系统能够有效接收并测得人体脉搏信号,表明基于PbS量子点光电探测器的脉搏检测系统在灵敏度、稳定性以及可靠性均满足应用要求。
The influence factors and optimization of modulation transfer spectroscopy for laser frequency discrimination with a cesium atomic vapor cell
Wang Yue-wei, LU Fei-fei, HOU Xiao-kai, Wang Jun-min
 doi: 10.37188/CO.2023-0191
Abstract(35) FullText HTML(19) PDF 14044KB(0)

Modulation transfer spectroscopy based on nonlinear near-degenerate four-wave mixing process can fundamentally eliminate the Doppler background of spectral lines, and has the advantages of high sensitivity and high resolution. Its dispersive linear pattern has good frequency detection characteristics.A weak probe light and a strong pump light modulated by frequency are transmitted in the atomic (molecular) chamber, and the frequency components of the modulated pump light include the center frequency of the pump light and the positive and negative first-order sidebands generated by modulation. Third-order nonlinear effects of atomic (molecular) samples can produce near-degenerate four-wave mixing, frequency modulation of the pump light can be transferred to the unmodulated probe light, and this modulation transfer only occurs when the sub-Doppler resonance conditions are met. In this experiment, we use an electro-optical potential phase modulator to modulate the pump light to obtain radio frequency modulation transfer spectroscopy (MTS), and study the optimization problem of the zero-crossing slope of the center of the dispersive signal of the MTS spectrum. By changing the modulation frequency of the pump light, the spot size of the pump light and the pump light, and the parameter dependence between the zero-crossing slope of the MTS spectral signal and the two, the optimal MTS spectral signal is obtained when the pump light modulation frequency is −3.6 MHz (about 0.69 times the natural linewidth). Finally, using the optimal MTS spectrum, the DL Pro @ 852 nm laser frequency is locked to the cesium atom D2 line (F = 4) - (F = 5') cycle transition, and the laser frequency fluctuation is about 170 kHz in the 60 minute sampling time, which is significantly improved compared with the frequency fluctuation of the laser −11 MHz during free running.

Polarization sensitive luminescence properties of europium ions in ZnO microrods matrix
YU Chao, CHU Xue-ying, JIANG Li, LI Jin-hua
 doi: 10.37188/CO.2023-0236
Abstract(30) FullText HTML(15) PDF 3844KB(1)

Focusing on the influence of the matrix lattice anisotropy on the polarization luminescence of rare earth ions, ZnO microrods and europium doped ZnO microrods were prepared using a hydrothermal method. Comparative studies have found that the length-to-diameter ratio of doped samples increased, and the morphology of the microrod changed from dumbbell like to straight rod. Analysis of the optical properties shows that the bound exciton luminescence at 385 nm makes the UV luminescence of ZnO microrods appear to be asymmetrical, and a weak visible region luminescence is observed at 550nm. After europium ions doping, the luminescence in the visible region is obviously enhanced. For Eu3+ doped ZnO microrods, Eu3+ ion characteristic luminescence peaks with narrow half width can be observed under 532 nm excitation. When the polarization direction of the incident excitation light was adjusted, the emission of Eu3+ ions changed periodically with the angle of the polarized light. The polarization degree increases with the increase of doping concentration. These results show that the luminescence of the europium ions in ZnO microrods matrix lattice is sensitive to the polarization of excited light. Doped ZnO microrods can integrate the ultraviolet absorption properties of low-dimensional ZnO materials with the excellent visible luminescence properties of rare earth ions, which makes them have important application value in polarization detection and other fields.

Photonic-integrated interferometric array field-of-view splicing subaperture optical path design
HAN Yao-hui, WANG Kun, ZHU You-qiang, LIU Xin-yue
 doi: 10.37188/CO.2024-0030
Abstract(25) FullText HTML(17) PDF 5250KB(3)

The photonic integrated interferometric imaging system generally adds single-mode fiber arrays at the focal plane of the subaperture, and completes the large-field-of-view splicing imaging by receiving beams with different field-of-view angles, but the direct use of fiber arrays leads to the discontinuity of the imaging field-of-view, the focal length of the subaperture becomes longer, and the thickness is increased substantially. To address the above problems, this paper proposes a combination of microlens arrays and fiber optic arrays to subdivide the subaperture image plane to achieve a seamless splicing of the field of view, and through the combination of the telephoto objective lens and the three-lens spatial compression plate significantly reduces the overall thickness of the subaperture array. The design results show that by adding 65*65 microlens array in front of the fiber array to focus the beam twice to achieve the system field of view seamless splicing, the field of view is expanded 65 times, the full field of view is 0.0489 °, the efficiency of spatial optical coupling in the center of each fiber in the single-mode fiber array is not less than 40% when the visible light is incident, and after adding the spatial compression plate to compress the free-space light path, the overall thickness of the system achieves one order of magnitude compression. The system in the realization of photonic integrated interference imaging system large field of view seamless splicing imaging at the same time, for the solution of the problem of ultra-long focal length lens thickness is too large to provide a new way of thinking.

Improved droplet edge detection model based on RCF algorithm
WANG Hui, CAO Zhao-liang, WANG Jun
 doi: 10.37188/CO.2024-0019
Abstract(38) FullText HTML(20) PDF 2331KB(2)

Accurate droplet edge extraction is crucial for measuring water contact angle. To address issues like poor noise robustness, incomplete edge extraction, and low precision in conventional methods, this paper proposes an improved model for droplet edge detection based on RCF. Firstly, a feature fusion module is introduced in the deep feature extraction stage to enhance model robustness and reduce overfitting risks. Secondly, a multi-receptive field module replaces the contact layer after RCF to extract more semantic information and enrich edge details. Thirdly, an efficient channel attention mechanism is introduced before each layer of the model to enhance focus on important features in the image. Lastly, MaxBlurPool down sampling technique is designed and incorporated to reduce computation and parameter requirements, while improving translation invariance. Experimental results on a self-made droplet dataset demonstrate that the proposed model achieves an ODS value of 0.816, an OIS value of 0.829, and a detection accuracy of up to 90.17%, which is an improvement of 1.85 percentage points compared to the original model. It accurately detects droplet edge features.

Structure and cathodoluminescence properties in Dy3+ and Tb3+ doped AlN films
LUO Xuan, MENG He-chen, WANG Xiao-dan, CHEN Zi-hang, ZENG Xiong-hui, GAO Xiao-dong, ZHENG Shu-nan, MAO Hong-min
 doi: 10.37188/CO.2023-0219
Abstract(22) FullText HTML(13) PDF 4822KB(3)

For the first time, Tb3+ and Dy3+ co-doped AlN films were prepared using ion implantation, and their crystal structure and cathodoluminescence properties were investigated. Raman scattering and X-ray diffraction indicate that ion implantation has caused increased compressive stress within the internal lattice. Continuous implantation led to the recombination of some point defects, resulting in a partial release of internal compressive stress. Cathodoluminescence spectra demonstrated that with high-dose Tb3+ implantation, the emission intensity of Tb3+ and Dy3+ exhibited different trends with varying Dy3+ dosage. We propose the existence of an energy transfer mechanism from Tb3+ ions 5D47F6 to Dy3+ ions 6H15/24F9/2 in AlN films. Finally, we observe that varying the dose ratio of Dy3+ ions to Tb3+ ions shifted the emission color between yellow-green and orange-yellow, with color temperatures ranging from 4042 to 5119 K. Adjusting the dose ratio of Dy3+ to Tb3+ enables effective control of chromaticity coordinates and color temperatures.

Laser-assisted Water Jet Machining of High Quality Micro-trap Structures on Stainless Steel Surfaces
Li Liu, 鹏 姚, Dongkai Chu, Xiangyue Xu, Shuoshuo Qu, Chuanzhen Huang
 doi: 10.37188/CO.EN.2024-0004
Abstract(21) PDF 616KB(0)
The study systematically analyzes the impact of various parameters such as laser repetition frequency, pulse duration, average power, water jet pressure, repeat times, nozzle offset, focal position, offset distance between grooves, and processing speed on the surface morphology of stainless steel. The findings reveal that micro-groove depth increases with higher laser power but decreases with increasing jet pressure and processing speed. Interestingly, repeat times have minimal effect on depth. On the other hand, micro-groove width increases with higher laser power and repeat times but decreases with processing speed. By optimizing these parameters, the researchers achieved high-quality pound sign-shaped trap structures with consistent dimensions. We tested the secondary electron emission coefficient of the "well" structure. The coefficient is reduced by 0.5 at most compared to before processing, effectively suppressing secondary electron emission.
 doi: 10.37188/CO.2024-0034
Abstract(33) PDF 1597KB(5)
 doi: 10.37188/CO.2024-0022
Abstract(24) PDF 1280KB(3)
 doi: 10.37188/CO.2024-0021
Abstract(30) PDF 1699KB(4)
 doi: 10.37188/CO.2024-0017
Abstract(21) PDF 557KB(3)
 doi: 10.37188/CO.2024-0016
Abstract(36) PDF 899KB(5)
窄线宽激光器是光谱学和精密计量学等实验的基本组成部分。由于半导体激光器对外部光学反馈十分敏感,所以可以利用光反馈的高带宽抑制半导体激光器的相位噪声,进而压窄线宽。于是我们采用光纤布拉格光栅作为反馈元件,搭建了长外腔反馈回路。为了降低了外界环境的温度起伏和气流扰动的影响,我们对反馈光路的光纤控温,使得1小时内最大温度起伏从0.039 ℃降低到0.003 ℃,并且温度起伏的方差降低了两个数量级。此外我们也测试了反馈带宽对激光线宽的影响,尽管我们实验所用光纤布拉格光栅的带宽远大于自由运转的激光线宽,但我们仍然观察到激光线宽被压窄,且光纤光栅的带宽越小,激光线宽越窄。对于此现象,我们认为在反馈回路中应该存在一种负反馈机制,可以将激光线宽稳定到反馈光谱的某个斜率处,所以光纤光栅的反馈带宽越窄,反馈光谱的斜率越大,反馈越灵敏。另外我们通过在0~1 mW范围内改变光纤光栅的反馈功率,观察到在反射功率0.8 mW时,光反馈将激光线宽从自由运转的100.5 kHz压窄到最窄11.5 kHz,在反射功率1 mW时,0.2 kHz~2 MHz范围内的相位噪声得到了大概22 dB的抑制。
 doi: 10.37188/CO.2024-0003
Abstract(31) PDF 2449KB(4)
 doi: 10.37188/CO.2023-0240
Abstract(26) PDF 219KB(2)
为了实现大靶面、大变倍比显微成像并解决同轴柯勒照明高集成度设计的问题,本文提出了一种基于同轴柯勒照明的大变倍比紧凑型显微镜光学系统的设计方法。首先,对望远镜和显微镜连续变倍光学系统的成像原理进行了分析,并对正组补偿式变倍显微镜光学系统的设计原理进行了理论分析。然后,我们提出把前固定组分解为准直组和汇聚组并在两镜组间设计分光镜,并通过共用透镜组实现同轴柯勒照明系统的紧凑型设计。最后,对大靶面连续变倍显微镜系统和与之匹配的同轴柯勒照明光学系统进行了设计,设计结果表明显微成像光学系统的变倍比为10×,工作距离为60 mm,物方最高分辨率为1.75 µm,同轴照明均匀性为94.3%。该系统具有成像质量好、畸变小、变倍曲线平滑、体积小巧等特点,从而验证了该设计方法的可行性。
双有源区结构4.7 μm中波红外量子级联激光器
 doi: 10.37188/CO.2023-0239
Abstract(25) PDF 271KB(3)
本文报道了基于双有源区的4.7μm中波红外量子级联激光器,脊宽9.5μm,可实现室温连续基横模工作。通过在单有源区中心插入0.8 μm InP间隔层,将原有的单有源区转变成双有源区结构,可显著降低器件有源区的峰值温度,同时抑制高阶横模的产生。在288 K温度下,腔长5 mm双有源区结构的器件,其阈值电流密度为1.14 kA/cm2,连续输出功率为0.71 W,快轴发散角为27.3°,慢轴发散角为18.1°。同常规单有源区结构的器件相比,采用双有源区结构的器件,其最大光输出功率未出现退化,同时器件慢轴方向由多模变化为基横模,光束质量得到了显著改善。本工作为改善高功率中波量子级联激光器的慢轴光束质量提供了另一种解决思路,促进了中波高功率量子级联激光器的产业化进程。
 doi: 10.37188/CO.2023-0238
Abstract(20) PDF 1477KB(1)
同心阵列系统具有小型化与大视场的优势,通过探测器的拼接可实现更大视场高分成像。为了进一步实现大视场系统结构的小型化与轻量化,本文采用伽利略型同心阵列系统结构形式,设计了一款工作在可见光波段,全视场大小为65°,焦距为19 mm,F数为4.7,总长为44.3 mm的同心阵列系统。系统的调制传递函数曲线在特征频率208lp/mm处调制传递函数大于0.3,全视场弥散斑均方根半径均小于探测器像元尺寸2.4m,成像质量接近衍射极限。由于同心阵列系统结构的特殊性,其中继系统排布紧密,各中继系统间的串扰杂散光严重影响成像质量,本文采用内置消杂光光阑的方法抑制串扰杂散光,对光学系统的杂散光进行了仿真分析,分析结果表明,在加入消杂光光阑后,杂光系数均降低至1×10-6以下,验证了串扰杂光抑制方法的有效性。为同心阵列系统的设计与分析提供了参考依据。
 doi: 10.37188/CO.2023-0234
Abstract(27) PDF 1587KB(9)
为提高地基多普勒非对称空间外差(DASH)干涉仪在恶劣温度下的探测精度,对系统进行了光机热集成分析。首先,依据干涉仪的工作原理和相位算法建立了相位与温度的关联依据。其次,设计了光机热分析模型和热变形数据获取模型,采用温度负载仿真分析给出了干涉模块和成像光学系统在不同温度下的变形数据,拟合得出热变形所导致的相位误差。最后,基于各部件热变形造成的风速误差,给出合理的温控方案。结果表明,干涉模块占据主因,必须确保温度控制在20±0.05℃内,并针对温度敏感部件进行温度控制,此时该部件造成的风速误差为3.8 m/s。成像光学系统放大倍数的热漂移、成像光学系统和探测器相对位置的热漂移占据次因,应将其控制在20±2℃以内,此时该部件造成的风速误差为3.05m/s,综上可以将干涉模块、成像光学系统、成像光学系统与探测器相对位置三者共同造成的风速测量误差控制在6.85 m/s内。本文的分析方案和温控措施可以为DASH干涉仪工程应用提供理论依据。
 doi: 10.37188/CO.2023-0226
Abstract(21) PDF 1221KB(0)
 doi: 10.37188/CO.2023-0224
Abstract(18) PDF 683KB(1)
研究了一种基于微机电系统(MEMS)技术的用于高压测量的硅-玻光纤法布里-珀罗(FP)压力传感器,以硅材料作为敏感元件,将电感耦合等离子体(ICP)干法刻蚀后的单晶硅膜片和高硼硅玻璃阳极键合构成FP腔。传感头使用MEMS技术批量制造,结构稳定、抗过载能力强、在高压环境下不容易失效。实验结果表明,该传感器能够实现30 MPa的高压压力测量,灵敏度为46.94 nm/MPa,线性拟合度为0.99897,测量结果具有较好的一致性和可靠性,所设计的压力传感器在高压检测方面有很强的应用前景。
Research on the detection of surface and internal defects in cold rolled steel
CHEN Ming-yu, XIE Yue-chen, LV Xiong-tao, GUO Jian-rong, JIA Guo-jun, XU Zhi-peng, WANG Shi-ling, XIANG Zhen, LIU Dong
 doi: 10.37188/CO.2023-0189
Abstract(27) FullText HTML(19) PDF 5436KB(3)

This paper focuses on the comprehensive detection of defects in cold-rolled steel through examination for surface and internal defects. Regarding surface defect detection, a bilateral line light illumination scheme is proposed and compared with line light illumination. As for internal defect detection, the applicability of various metal internal inspection technologies such as X-ray, ultrasound, and infrared thermography is analyzed from the perspectives of detection resolution and defect edge characteristics. The results show that bilateral line light illumination not only increases the overall average precision of the YOLOv5 object detection algorithm model to 90.16% (an increase of 15.46% compared to the line light illumination) but also improves model classification and training efficiency. X-ray and ultrasound inspection technologies can detect blind holes with a diameter of 0.25 mm, while infrared thermography can detect blind holes with a diameter of 1 mm. In evaluating defect edge characteristics, X-ray inspection technology exhibits a minimum blind hole edge grayscale difference of 145, ultrasound of 89, and infrared thermography of 30. This study addresses the need for improved detection of surface defects in cold rolled steel and provides new research insights for the detection of internal defects.

Coronary artery angiography image vessel segmentation method based on Feature Pyramid Network
GUO Hao-hu, GAO Ruo-qian, GE Ming-feng, DONG Wen-fei, LIU Yan, ZHAO Xu-feng
 doi: 10.37188/CO.2023-0186
Abstract(37) FullText HTML(8) PDF 4842KB(2)

To address issues such as uneven illumination in coronary angiography images, low contrast between vascular structures and background regions, and the complexity of coronary vascular topology, this paper establishes a coronary angiography vascular segmentation annotation dataset. Additionally, it proposes a coronary angiography image vascular segmentation model based on the feature map pyramid. This model, built upon the U-Net architecture, underwent improvements and optimizations. First, the first convolutional layer in the U-Net encoding part was replaced with a 7×7 convolutional layer to increase the receptive field of each layer. Modified ConvNeXt blocks were added to the encoding and decoding layers to enhance the network's ability to extract deeper-level features. Second, a Group Attention (GA) mechanism module was designed and incorporated at the U-Net skip connection to strengthen the features extracted from the encoding part, addressing semantic gaps between the encoder and decoder. Finally, a Pyramid Feature Concatenation (PFC) module was designed at the U-Net decoder, which fused features from different scales. SE attention mechanisms were added to each layer of the PFC to filter out effective information from the feature maps. The loss function of the network is weighted based on the outputs of the Pyramid Feature Concatenation (PFC) module at each layer, serving to supervise the feature extraction process across different layers of the network. The test results of this model on the test set are as follows: The Dice coefficient is 0.8843 and the Jaccard coefficient is 0.7926. Experimental results indicate that this model is highly robust in coronary vascular segmentation, more effectively suppressing noise under low contrast and achieving better segmentation results for coronary vessels when compared to other methods.

Research on visible polarized reflection of target material surface based on improved Blinn masking function
LIU Cheng-lin, ZHAN Jun-tong, ZHANG Su, WANG Chao, FU Qiang, LI Ying-chao, DUAN Jin, JIANG Hui-lin
 doi: 10.37188/CO.2023-0217
Abstract(15) FullText HTML(8) PDF 9917KB(2)

This paper aims to study the visible light polarization reflection characteristics of typical terrain target materials. To achieve this, an improved Blinn type shadow masking function for traditional "V" surface structural defects is introduced. Additionally, the effects of mirror reflection, diffuse reflection, and volume scattering are comprehensively considered. A six-parameter two-dimensional reflection distribution function model for typical terrain target materials is established. Testing of polarization characteristics is conducted on target samples of different materials (polypropylene plastic sheet, 99 alumina ceramic sheet, iron sheet, green painted aluminum sheet) in the visible light 600 nm wavelength band. A genetic algorithm for parameter inversion is used. The experimental and simulation results show that compared with the traditional "V" shielding model, the polypropylene plastic plate model has the highest accuracy improvement and a 70.61% increase in RMSE percentage in the impact of observation angles on the polarization characteristics of the target material surface at an incidence angle of 50°, relative azimuth angle of 180°, and 0° to 60°. Compared with the two reference models, the DoLP model shows a significant improvement in accuracy at an incidence angle of 50°, observation angle of 50°, and relative azimuth angle of 90° to 270°. The model accuracy has improved by at least 24.73 percentage points. The minimum root mean square error of linear polarization is only 1.29%. For the material in this article, the polarization characteristics depend on the value of its complex refractive index. When the incident angle is determined, the observation angle is between 0° and 60°, and the relative azimuth angle is between 0° and 360°. The larger the n/k ratio, the higher the peak of the linear polarization degree. In the visible light band, the wavelength has little effect on the degree of linear polarization.

Design of a fast multidimensional imaging guidance optical system based on array optics
SHI Hao-dong, LU Qi, ZHAO Yi-wu, WANG Jia-yu, ZHAO Xiao, LI Ying-chao, FU Qiang
 doi: 10.37188/CO.2023-0206
Abstract(41) FullText HTML(15) PDF 6324KB(7)

To address the bottleneck that makes the conventional polarization spectral imaging method difficult to apply to the ballistic platform, a fast multi-dimensional imaging guidance optical scheme based on array optics is proposed. The correlation model between channel resolution and telescopic magnification is constructed. The precise matching and efficient utilization of the parameters of the microlens array, spectral filter array, and micro-nano-polarization array detector are realized. Based on the conventional guidance head and commercial polarization detector, a multi-dimensional imaging guidance optical system including spherical is designed. The system adopts a 4×4 optical field segmentation layout, forming 16 spectral channels through the visible light band with a spectral resolution of 16 nm. A polarization spectral data cube in four polarization directions, such as 0°, 45°, 90°, and 135° is acquired efficiently under the conditions of a single optical path and a single detector. The system has an effective focal length of 150 mm and a structure length of 145 mm. Simulation results show that the full-field modulation transfer function of the system is close to the diffraction limit at the Nyquist frequency for 16 channels. The imaging quality meets the requirements of bullet-loaded target multi-dimensional detection and identification.

Terahertz mixer noise figure measurement
TAO Xing-yu, LIU Wen-jie, SUN Yue-hui, QIN Fei-fei, SONG Qing-e, ZHAO Ze-yu, LIU Li-juan, CHEN Tian-xiang, WANG Yun-cai
 doi: 10.37188/CO.2023-0193
Abstract(28) FullText HTML(20) PDF 4441KB(4)

Noise figure (NF) is an important parameter in evaluating the performance of transmitting a signal from a high-frequency electronic device. As the operating frequency increases, the NF of high-frequency electronic devices usually increases, and the excess noise ratio (ENR) of existing noise sources cannot meet the associated measurement requirements. Therefore, this paper aims to achieve the required measurement capabilities regarding the NF of high-frequency electronic devices.


Based on incoherent optical mixing technology, three incoherent optical beams are combined into a unitraveling carrier photodiode (UTC-PD). A tunable terahertz (THz) photonics noise source with a high ENR in the 220-325 GHz frequency range is developed. The ENR can be tuned up to 45 dB. Based on the Y-factor method, the THz photonics noise source is applied to measure a THz mixer with large NF and negative conversion gain.


The measured NF of the THz mixer ranges from 16 to 32 dB, the conversion gain is about -13 dB, and the uncertainty is 0.43 dB.


The tunable THz photonics noise source with high ENR achieves the NF measurement capabilities required by different THz electronic devices. It will play an important role in the measurement of NF of THz electronic devices and in guiding further optimization.

Application of dual-wavelength nanosecond laser cleaning technology on stone artifacts
LI Chen-yu, HU Wen-zhe, ZHANG Xue-yan, LIU Han-wen, LIU Xiao-long, QU Liang, ZHU Meng, DUAN Hong-ying
 doi: 10.37188/CO.2024-0002
Abstract(32) FullText HTML(21) PDF 4442KB(1)

Traditional cleaning methods can not clean small pollution particles on the surface of cultural relics. It can easily cause irreversible damage to the surface of cultural relics. In order to improve the ability to clean pollutants, laser cleaning technology is gradually applied to clean different types of cultural relics. This paper develop a nanosecond laser cleaning system to clean the fragments of stone artifacts in the Palace Museum. The object of the cleanout is black crust pollutants. To avoid the yellowing effect, a dual wavelength combination of 1064 nm near-infrared and 355 nm ultraviolet was used for laser cleaning of simulated marble samples. When the energy density range of these two wavelengths is 3∶2, the system of the real-time observation microstructure photos shows good cleaning effect. This ratio 3∶2 is applied for the sample of marble fragments. The micro-Raman is utilized to evaluate the cleaning effect. The above experimental results confirm the advantages of laser cleaning and also provide the reference of laser cleaning parameters and evaluation methods for laser cleaning of surface pollutants on stone cultural relics. At the same time, it also provides reference for the laser cleaning technology to clean the surface of other stone cultural relics.

Wavefront reconstruction for extended targets under strong atmospheric turbulence
MAO Hao-di, LI Yuan-yang, GUO Jin
 doi: 10.37188/CO.2023-0213
Abstract(34) FullText HTML(14) PDF 9867KB(6)

In order to solve the problem of wavefront detection without ideal point beacon in adaptive optical system under strong turbulent environment, this paper proposes a method to detect the optical field information of extended beacons by using a Plenoptic sensor. The optical field imaging principle, wavefront phase reconstruction algorithm and error influence rule of extended beacons are studied. The imaging process of the extended beacon on the optical field sensor is simplified by using the equivalence method, and the optical field images are rearranged in a specific way. The wavefront reconstruction of 0° field of view is realized by image cross-correlation method and Zernike mode method. Simulation studies were carried out on error influencing factors such as different input aberration coefficients, the number of single-row microlens elements and noise. The results show that: When the input aberration is less than 6.5λ, the wavefront reconstruction accuracy is about 0.08λ. For the image detector with image resolution of 1080×1080 and pixel size of 5.5 μm, the wavefront reconstruction accuracy is the highest when the number of single row microlens units is between 40 and 50, and the system noise hardly affects the accuracy. Finally, an extended beacon wavefront detection system is built to reconstruct the four aberration wavefronts of 0° field of view by detecting the extended beacon. The wavefront reconstruction accuracy of the experimental system is about 0.04λ, which basically meets the wavefront detection requirements of the adaptive optical system.

Research progress of hydroxy-plane laser induced fluorescence detection based on ultraviolet laser
ZHANG Zhong-lin, YANG An-long, WANG Jiang, CHENG Guang-hua
 doi: 10.37188/CO.2024-0013
Abstract(57) FullText HTML(47) PDF 7391KB(7)

Hydroxyl (OH) is a widely existing product in the combustion reaction process. In the combustion diagnosis technology, the two-dimensional spatial distribution based on hydroxyl is commonly used to characterize the structure of the flame front, while hydroxyl is an important parameter to characterize features such as the flame temperature, flame surface density, and heat release rate. The effective detection of hydroxyl in combustion flame is an important support for exploring the evolution of combustion dynamics and revealing the mechanism of random flame events. Planar laser-induced fluorescence (PLIF), as an optical measurement method, has the advantages of high spatial and temporal resolution, nonintrusive nature, and selection of components, and has successfully observed the structure of various combustion flames, such as Bunsen burner flame, turbulent flame, swirl flame and supersonic flame, which provides an important reference for the establishment of combustion models. This paper starts with the basic principle of PLIF detection, reviews the development history and research status of PLIF technology in the field of combustion diagnosis, introduces the PLIF ultraviolet light source technology based on dye laser, optical parametric oscillation and Ti:sapphire tripling-frequency, and discusses the characteristics of different technical routes. Finally, the development of UV laser technology for OH-PLIF is prospected.

Research on the detection method of ship wake weak signal based on synchronous accumulation method
ZONG Si-guang, DUAN Zi-ke, ZHANG Xin, YU Yang, WANG Bai-xiong
 doi: 10.3788/IRLA2022
Abstract(59) FullText HTML(33) PDF 4625KB(5)

In order to adapt to the complex dynamic changing wake bubble field environment, the detection signal-to-noise ratio and detection rate of ship wake weak signal are improved, and the detection range is expanded.


In this paper, a detection method of ship wake weak signals based on synchronous accumulation method is proposed. By taking advantage of the repeatability of periodic signals and the randomness of noise, cumulative normalization is performed on successive periodic signals, which can effectively improve the detection signal-to-noise ratio and reduce the interference of random signals on detection performance. In order to evaluate the detection performance of the algorithm under multi-parameter coupling, a multi-time scale detection capability evaluation model for ship wake weak signals is established.


By conducting a large number of simulated ship wake detection experiments in indoor large pools and outdoor typical lakes, it is verified that the algorithm is suitable for the detection of sparse and discrete tiny far-field wake bubbles to large-scale near-field bubbles under high turbulence disturbance, thus realizing the full-time ship wake tracking and detection and effectively improving the underwater weapon strike capability.


It can provide support for ship wake laser detection and identification engineering practice.

Laser phase noise suppression method for a CO- OFDM-OQAM communication system with real-imaginary-alternate pilots
ZHAO Hang-yu, WANG Dao-bin, ZHANG Shuo, HUANG Quan-sheng, WEN Kun, LI Guang-fu, YUAN Li-hua
 doi: 10.37188/CO.2023-0230
Abstract(45) FullText HTML(25) PDF 5027KB(5)

In this paper, a phase noise suppression algorithm based on real-imaginary-alternate pilots was proposed for a coherent optical orthogonal frequency division multiplexing communication system with offset quadrature amplitude modulation (CO-OFDM-OQAM). The algorithm uses the properties of laser phase noise and the symmetry law of the intrinsic imaginary interference (IMI) to design real-imaginary-alternate pilots. In combination with a linear fitting, it is able to accurately estimate the common phase error (CPE) for CO-OFDM-OQAM. As the compensation was performed in the frequency domain, the computational complexity was significantly reduced compared to the time-domain phase noise suppression algorithms. We built a numerical simulation platform for a polarization multiplexed CO-OFDM-OQAM system with an effective bit rate of 65 GBits/s. Through it, the suppression effect of the proposed method on phase noise was examined. The transmission performance of the system with different laser linewidths and number of subcarriers was investigated. The results obtained confirm that the linewidths required to reach the FEC limit for BER are equal to 801.1, 349, and 138.4 KHz for a fixed OSNR of 25 dB and a total number of subcarriers of 256, 512, and 1024, respectively. For the system using a 16-QAM modulation format with a number of subcarriers of 256 or 512, it compensates well for the laser phase noise without affect the power peak-to-average ratio.

Preparation and Sensing Characteristics of Long-Period Fiber Gratings Based on Periodic Microchannels
Cai Sun, Yuan-Jun Li, He-Er Yang, Xue-Peng Pan, Shan-Ren Liu, Bo Wang, Meng-Meng Gao, Qi Guo, Yong-Sen Yu
 doi: 10.37188/CO.EN.2024-0005
Abstract(48) PDF 743KB(6)
Long period fiber gratings have the advantages of small size, corrosion resistance, anti-electromagnetic interference and high sensitivity, making them widely used in biomedical, power industry and aerospace. In this paper, a long period fiber grating sensor based on periodic microchannels is proposed. Firstly, a series of linear structures are etched in the cladding of a single-mode fiber by femtosecond laser micromachining. Then the laser-modified region is selectively eroded by selective chemical etching to obtain the periodic microchannel structure. Finally, the channels are filled with polydimethylsiloxane (PDMS) to improve the spectral quality. The temperature sensitivity is -55.19 pm/°C, the strain sensitivity is -3.19 pm/με, the maximum refractive index sensitivity is 540.28 nm/RIU and the bending sensitivity is 2.65 dB/m-1. And all of them show good linear response. The sensor has good application prospects in the field of precision measurement and sensing.
Effects of sinusoidal mid-spatial frequency surface errors on optical transfer function
CHEN Jian-jun, WANG Lin-lin, HUO Li-min, KUANG Cui-fang, MAO Lei, ZHENG Chi, YIN Lu
 doi: 10.37188/CO.2023-0229
Abstract(54) FullText HTML(45) PDF 4711KB(4)

Mid-spatial frequency surface errors (MSFSE) can cause small angle scattering in optical systems, affecting system performance. In order to determine a reasonable tolerance for MSFSE in optical design and processing, a quantitative study is conducted on the impact of MSFSE on optical transfer function (MTF) of optical systems. Under diffraction-limited conditions, we derive an expression for the influence of MSFSE on the MTF of optical systems and analyze it. Then, we verify the theoretical derivation results through optical design software simulation.


Assuming that the optical system has a sinusoidal MSFSE on the pupil, we perform Fourier transform on the pupil function and square it to obtain the point spread function (PSF), and then perform Fourier transform on the PSF to obtain the optical transfer function (OTF) of the optical system. By taking the mode of OTF, the expression of MTF under the influence of MSFSE can be obtained. By comparing this expression of MTF with the MTF of an optical system without MSFSE under diffraction-limited conditions, the quantitative impact of MSFSE on the MTF of the optical system can be obtained.


Theoretical calculation results indicate that sinusoidal MSFSE can lead to different losses of MTF at different spatial frequencies, and the changes in MTF losses are periodic. The maximum loss ratios of MTF in optical systems caused by sinusoidal MSFSE with peak to valley (PV) of 0.030 μm, 0.095 μm, 0.159 μm and 0.223 μm are 0.89%, 8.80%, 23.48% and 43.31%, respectively. The loss of MTF will increase nonlinearly with the increase of PV of MSFSE. The theoretical calculation results are consistent with the software simulation results.


The research results can provide a theoretical basis for technical personnel in optical design and processing to determine the tolerance of MSFSE of optical elements in imaging systems.

Research on the influence of sampling on three-dimensional surface shape measurement
闹生 乔, 雪 尚
 doi: 10.37188/CO.EN.2024-0003
Abstract(56) PDF 557KB(0)
In order to accurately measure the three-dimensional surface shape of object, the influence of sampling on it was studied. Firstly, on the basis of deriving spectra expressions through Fourier transform, the generation of CCD pixels was analyzed and its expression was given. Then, basing on the discrete expression of deformation fringes obtained after sampling, its Fourier spectrum expression was derived, resulting in an infinitely repeated "spectra island" in the frequency domain. Finally, on the basis of using a low-pass filter to remove high-order harmonic components and retaining only one fundamental frequency component, the signal strength is reconstructed by inverse Fourier transform. A method of reducing the sampling interval, i.e. reducing the number of sampling points per fringe, was proposed to increase the ratio between the sampling frequency and the fundamental frequency of the grating, so as to more accurately reconstruct the object surface shape under the condition of
Lipids segmentation method based on magnification endoscopy with narrow-band imaging
治晟 武, 鸿博 邹, 文武 朱, 伟明 齐, 立强 王, 波 袁, 青 杨, 晓蓉 徐, 蕙蕙 严
 doi: 10.37188/CO.EN.2023-0024
Abstract(49) PDF 2696KB(1)
Magnification endoscopy with narrow-band imaging (ME-NBI) has been widely used for cancer diagnosis. However, there is a white opaque substance (WOS) whose main component is lipids, making some microstructures invisible. In such lesions, the morphological structure of lipids becomes another marker of tumor grade. In this paper, a lipids segmentation method is proposed. Firstly, the lipid image enhancement algorithm and the specular reflection correction algorithm are introduced. Then, in the framework of active contour model, we propose a segmentation method, which extracts local information from modified hue value, global information from intensity value, adaptively obtains weight factor to segment the lipid region based on the initial contour. The effectiveness of our method is verified by phantom experiment, which shows that the pixel accuracy, sensitivity, and Dice coefficient of our method are all higher than 90%. The proposed method can well reflect the shape of lipids to provide
Composite fast nonsingular terminal sliding mode control of fast steering mirror
LI Zhi-bin, LI Liang, ZHANG Jian-qiang
 doi: 10.37188/CO.2023-0203
Abstract(102) FullText HTML(50) PDF 9740KB(14)

To further enhance the control performance of the precision tracking system for laser communication, this paper studies the control method of the fast steering mirror (FSM) driven by voice coil motor. Aiming at the problems of strong cross coupling characteristics and external disturbances in the FSM, a composite fast nonsingular terminal sliding mode control strategy integrating feedforward decoupling compensation and fixed-time extended state observer is proposed. Firstly, the coupling transfer function matrix model of the FSM with double inputs and double outputs is established by using system identification method, and the feedforward decoupling compensator is designed to compensate for the coupling components and achieve motion decoupling between the X-axis and Y-axis. Secondly, the fixed-time extended state observer is designed for each decoupled single-axis model, to achieve fixed-time estimation of angular velocity and external disturbances simultaneously. Then, the fast nonsingular terminal sliding mode surface is constructed, and the exponential power function is adopted to replace the sign function in control law design, so as to improve the convergence speed of the system and suppress the chattering of sliding mode, the stability of the proposed control system and the finite-time convergence of tracking error are proved based on Lyapunov stability analysis method. Finally, the effectiveness of the proposed composite control strategy is verified by comparative experiments. The experimental results show that under the 100 Hz strong disturbances, the FSM tracking 60 Hz and 120 Hz circular trajectories, the average absolute values of its trajectory tracking error are 0.0036° and 0.0131° respectively, indicating that the system can maintain good tracking performance. The proposed composite control strategy is validated to be effective in meeting the high-precision and strong anti-disturbance requirements of the FSM for laser communication.

Terahertz band-stop filter with H-type structure
CHEN Xiang-xue, FU Zi-qin, WANG Feng-chao, CHEN Jin, YANG Jing
 doi: 10.37188/CO.2023-0179
Abstract(96) FullText HTML(52) PDF 3966KB(11)

In this paper, a metamaterial terahertz band-stop filter is designed based on a symmetrical H-type structure. The continuous metal arm of this H-type structure can flow current, which can provide an effective reference for expanding the application of metamaterial filters in the field of electronics. Using electromagnetic simulation software CST Microwave Studio 2021, the filtering characteristics of the filter were studied, and The geometric parameters of the filter are determined by changing the arm length, period length and double H distance. The results show that the structure can realize the function of polarization selection. Under the condition of y polarization, the filter has no obvious resonance peak in the range of 0.2−2.3 THz, but the transmittance ranges from −15 dB to −3 dB. Under the X-polarization condition, a stopband of 0.15 THz FWHM bandwidth can be obtained at the center frequency of 1.34 THz, and the transmission parameter is about −30 dB. In order to verify the simulation results, the sample of metamaterial filter was prepared by micromachining technology, and the sample was tested by transmissed-terahertz time-domain spectroscopy system. The test results were in good agreement with the simulation results.

Vortex phase-shifting digital holography for micro-optical element surface topography
XUE Yi meng, LIU Bing cai, PAN Yong qiang, FANG Xin meng, TIAN Ai ling, ZHANG Rui xuan
 doi: 10.37188/CO.2023-0180
Abstract(122) FullText HTML(47) PDF 5987KB(24)

Non-destructive, non-contact phase-shifting digital holography has distinct advantages in identifying micro-optical components. Because traditional phase-shifting digital holography requires fine control and cumbersome calibration of the phase shifter, its optical path is susceptible to mechanical vibration interference, which reduces the quality of the holographically reproduced image. This paper proposes a vortex phase-shifting digital holography for the micro-optical element surface measurement method with the help of the special phase distribution of vortex light. The method utilizes a helical phase plate to modulate the vortex phase and introduce a high-precision phase shift. Based on the constructed vortex phase-shifting digital holographic microscopy experimental setup, the actual phase shifts between phase-shift interferograms were determined using the interferometric polarity method, the relationship between the rotation angle of the helical phase plate and the phase shift was calibrated, and the feasibility of the vortex phase shift was experimentally verified. Repeated measurement experiments were carried out on the micro-lens arrays, and the measurement results were compared with those of the ZYGO white light interferometer. The results indicate that a single micro-lens's average longitudinal sagittal height is 12.897 μm with an average relative error of 0.155%. The proposed method enables highly precise measurement of the surface topography of micro-optical elements. It offers the advantages of easy operation, high stability, and high accuracy.

Measurement of methane concentration with wide dynamic range using heterodyne phase-sensitive dispersion spectroscopy
ZHOU Chen, MA Liu-hao, WANG Yu
 doi: 10.37188/CO.2023-0177
Abstract(139) FullText HTML(66) PDF 4644KB(27)

This paper describes the development of dual-sideband beat-suppressed heterodyne phase-sensitive dispersive spectroscopy (HPSDS) for sensitive detection of trace gases across a wide dynamic range, explores the operational characteristics of the electro-optic modulator, and explores bias voltage control methods under sideband suppression mode. The dispersion phase spectral profiles and the corresponding signal-to-noise ratios in both suppression and non-suppression modes were compared before a comprehensive evaluation of the detection performance.


An HPSDS-based detection system was developed based on a near-infrared distributed feedback laser and an electro-optic modulator (EOM). The suppression of the dual-sideband beat was achieved by exploring and analyzing the optimal operational range of the EOM, leading to the optimization of dispersion phase signals with increased amplitude and high signal-to-noise ratio. The dispersion phase signals under typical high-frequency (1.2 GHz) intensity modulation were recorded for different standard methane/nitrogen mixtures. The relationship between the peak-to-peak values of the dispersion phase signals and the varied gas concentrations was then summarized. Meanwhile, wavelength modulation spectroscopy (WMS) experiments were conducted; subsequently, the HPSDS and WMS techniques’ performances were compared in terms of linearity, detection dynamic range, and immunity to optical power fluctuations; finally, the HPSDS-based system's performance was validated under a wide dynamic range and rapid time response was verified by measuring different concentrations of standard gases.


Experimental results indicate that the HPSDS technique exhibits high linearity (R2 = 0.9999), a wide dynamic range (38.5 ppm to 40%), and remarkable immunity to optical power fluctuations.


The dual-sideband-beat-suppression-HPSDS-based methane sensor developed in this study shows great potential for uses involving wide dynamic range detection and on-site practical trace gas detection.

Research progress of space laser communication networking technology
LIU Zhi, JIANG Qing-fang, LIU Shu-tong, TIAN Shao-qian, LIU Xian-zhu, YU Jia-xin, ZHAO Jian-tong, YAO Haifeng, DONG Ke-yan
 doi: 10.37188/CO.2023-0140
Abstract(115) FullText HTML(256) PDF 9778KB(72)

Laser communication utilizes light waves as the transmission medium. It offers many advantages, including high data rates, expansive bandwidth, compactness, robust interference resistance, and superior confidentiality. It has the critical capability to enable high-speed transmission and secure operation of space information networks. Prominent research institutions have committed to studying a series of challenges that need to be solved in the process of networking laser communication technology, including point-to-multipoint simultaneous laser communication, all-optical switching and forwarding of multi-channel signals within nodes, node dynamic random access, and network topology design. Numerous demonstration and verification experiments have been conducted, with a subset of these research results finding practical applications. Based on the analysis and discussion of space laser communication networking technology, this paper summarizes the development of laser communication networking technology both domestically and internationally, focusing on the application of laser communication networking technology in the fields of satellite constellations, satellite relays, and aviation networks; furthermore, it presents a review of pertinent domestic research methodologies, experimental validations, and technical solutions; finally, it predicts the development trend of laser communication networking technology and applications.

Polarization spectral image fusion method for hybrid backgrounds of ground objects
LI Ying-chao, ZHAO Zhe-hao, WANG Qi, LIU Jia-nan, SHI Hao-dong, FU Qiang, SUN Hong-yu
 doi: 10.37188/CO.2023-0185
Abstract(75) FullText HTML(33) PDF 8706KB(12)

To address the issues of blurred edge details and poor contrast in multi-scale transform fused images obtained using remote sensing detection methods for mixed background features, an image fusion approach that combines the sparse representation of non-downsampled contour wavelet transform and a guided filter was utilised to enhance the quality and visual appearance of the fused images. This method involved several steps: Firstly, a multi-scale and multi-directional decomposition was performed on both spectral and polarimetric images using non-downsampled contour wavelet transform to isolate the feature information in each subband; secondly, the low-frequency subbands were fused using a sparse representation approach to minimize the loss of contrast in the fused image; additionally, the high-frequency subbands were fused through a bootstrap filter to enhance the detail information and the contours of the image; finally, the low-frequency and high-frequency fusion coefficients were inverted using non-downsampled contour wavelet inversion to generate the final fused image. Analysis indicates that this method has increased the contrast of the fused image by up to 54.5% relative to the original spectral image and by 15.4% compared to the polarimetric image. This has resulted in a fused image in which it is easier to distinguish objects in shadows within a mixed background. This method was used to fuse spectral and polarimetric images captured by a polarimetric spectral imager at different wavelengths, which resulted in true-colour reproduction. These true-colour restored images demonstrate that this fusion method retains environmental information within the mixed background while distinguishing the object from the background, effectively improving the image quality of polarization spectral remote sensing detection imaging. This approach enhances the integrity and authenticity of image information in polarization spectral remote sensing detection imaging, thereby expanding its application scope in remote sensing detection of complex environments and image recognition.

Reconstruction of snapshot multispectral camera images based on an attention residual network
YAN Gang-qi, LIANG Zong-lin, SONG Yan-song, DONG Ke-yan, ZHANG Bo, LIU Tian-ci, ZHANG LEI, WANG Yan-bo
 doi: 10.37188/CO.2023-0196
Abstract(77) FullText HTML(44) PDF 8459KB(11)

With the rapid advancement of spectral imaging technology, the use of multispectral filter array (MSFA) to collect the spatial and spectral information of multispectral images has become a research hotspot. The uses of the original data are limited because of its low sampling rate and strong spectral inter-correlation for reconstruction. Therefore, this paper proposes a multi-branch attention residual network model for spatial-spectral association based on an 8-band 4 × 4 MSFA with all-pass bands. First, the multi-branch model was used to learn the image features after interpolation in each band; second, the feature information of the eight bands and the all-pass band were united by the spatial channel attention model designed in this paper, and the application of multi-layer convolution and the convolutional attention module and the use of residual compensation effectively compensated the color difference of each band and enriched the edge texture-related feature information; finally, the preliminary interpolated full-pass band and the rest of the band feature information were used in feature learning by residual dense blocks without batch normalization on the spatial and spectral correlation of multispectral images to match the spectral information of each band. Experimental results show that the peak signal-to-noise ratio, structural similarity, and spectral angular similarity of the test image under the D65 light source outperform the state-of-the-art deep learning method by 3.46%, 0.27%, and 6%, respectively; in conclusion, this method not only reduces artifacts but also obtains more texture details.

Phase gradient estimation using Bayesian neural network
ZHANG Kang-yang, NI Zi-hao, DONG Bo, BAI Yu-lei
 doi: 10.37188/CO.2023-0168
Abstract(100) FullText HTML(36) PDF 7531KB(9)

Strain reconstruction is a vital component in the characterization of mechanical properties using phase-contrast optical coherence tomography (PC-OCT). It requires an accurate calculation for gradient distributions on the wrapped phase map. In order to address the challenge of low signal-to-noise ratio (SNR) in phase gradient calculation under severe noise interference, a Bayesian-neural-network-based phase gradient calculation is presented.


Initially, wrapped phase maps with varying levels of speckle noise and their corresponding ideal phase gradient distributions are generated through a computer simulation. These wrapped phase maps and phase gradient distributions serve as the training datasets. Subsequently, the network learns the “end-to-end” relationship between the wrapped phase maps and phase gradient distributions in a noisy environment by utilizing a Bayesian inference theory. Finally, the Bayesian neural network (BNN), after being trained, accurately predicts the high-quality distribution of phase gradients by inputting the measured wrapped phase-difference maps into the network. Additionally, the statistical process introduced by BNN allows for the utilization of model uncertainty in the quantitative assessment of the network predictions’ reliability.


Computer simulation and three-point bending mechanical loading experiment compare the performance of the BNN and the popular vector method. The results indicate that the BNN can enhance the SNR of estimated phase gradients by 8% in the presence of low noise levels. Importantly, the BNN successfully recovers the phase gradients that the vector method is unable to calculate due to the unresolved phase fringes in the presence of strong noise. Moreover, the BNN model uncertainty can be used to quantitatively analyze the prediction errors.


It is expected that the contribution of this work can offer effective strain estimation for PC-OCT, enabling the internal mechanical property characterization to become high-quality and high-reliability.

Tandem pumped Q-switched mode-locked laser operation of Tm:CYA laser
SUN Tangzheng, LI Yunfei, TAN Jingrong, DU Xiaojuan, DING Jiayu, REN Shuting, XU Hao, WANG Chong, YANG Jinfang, ZHANG Mingxia, ZHU Yongle, DONG Zhong, LING Weijun
 doi: 10.37188/CO.2023-0162
Abstract(115) FullText HTML(42) PDF 2637KB(12)

Passively Q-switched mode-locked operation was realized for the first time by inserting a semiconductor saturable absorption mirror (SESAM) mode-locking element into a Tm:CaYALO4(Tm:CYA) laser using in-band pumping technology. The laser cavity adopted an X-type four-mirror cavity structure, and the pump source was an Er:Y3Al5O12(Er:YAG) solid-state laser with a central wavelength of 1650 nm. Output coupling mirrors with transmittances of 0.5%, 1.5%, 3%, and 5% were used to study the laser’s continuous wave (CW) output and mode-locking output characteristics. The experimental results show that the laser has the best output characteristics when an output coupling mirror with a transmittance of 5% is used. The maximum power of 894 mW and the maximum slope efficiency of 16% were obtained when the laser operated in the CW regime. After the CW power was optimized to the highest, the SESAM mode-locked element was added to the optical path. When the absorbed pump power became greater than 1.86 W, the laser operation entered an unstable Q-switched state; when the absorbed pump power increased to 5.7 W, a stable passively Q-switched mode-locked operation was achieved; when the absorbed pump power reached 6.99 W, a mode-locked pulse laser with a maximum output power of 399 mW was obtained by using a 5% output mirror. At that time, the repetition frequency under the Q-switched envelope was 98.11 MHz, the pulse width was 619.4 ps, and the corresponding maximum single pulse energy was 4.07 nJ. The mode-locked pulse modulation depth in a Q-switched envelope was observed to be close to 100%. The experimental results show that same-band pumping technology can be used in lasers to generate Q-switched mode-locked pulses, which provides a new pumping method for generating ultrashort pulse lasers.

A study of active polarization imaging method under strong light background
SHI Hao-dong, XU Jia-wei, ZHANG Jian, WU Hong-bo, WANG Chao, LIU Zhuang, ZHAN Jun-tong, LI Ying-chao, FU Qiang
 doi: 10.37188/CO.2023-0151
Abstract(148) FullText HTML(82) PDF 5740KB(30)

This study proposes an active polarization imaging approach that utilizes laser illumination to tackle the issue of low target detection contrast in strong light backgrounds, which is a challenge in conventional photoelectric detection. The study examines the coupling relationship between the polarization characteristics of three typical target materials and the scattering angle of a laser beam. This is achieved by constructing a laser incident bidirectional reflection distribution model, a laser incident polarization bidirectional reflection distribution model, and a target surface polarization model of laser illumination. Backlight observation experiments are conducted in a controlled darkroom to verify the impact of the scattering angle of the laser beam on the polarization characteristics of the target. The experimental results show an 86.11% increase in target contrast for active polarization imaging under strong light background compared to traditional passive intensity imaging. Additionally, different target materials exhibit differing visible polarization characteristics under varying beam dispersion angles, with metallic materials is higher than that of non-metallic materials. This result aligns with theoretical analysis and support the advantages of active polarization imaging. The outdoor solar backlight observation experiment verifies the applicability of the research method in high-intensity light and long-distance settings. This study can lay a theoretical foundation for improving accurate target perception under a strong light background.

Design of large aperture terahertz wave imaging optical system
CAO Yi-qing, SHEN Zhi-juan
 doi: 10.37188/CO.2023-0175
Abstract(83) FullText HTML(57) PDF 2929KB(12)

The Terahertz wave possesses characteristics of high penetration, low energy, and fingerprint spectrum, etc., making it widely used in the detection field. Therefore, developing a Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, we refer to the structure of Tessar objective lens, which consists four lenses. The balance equations of aberration for the system were established through the application of the aberration theory of the paraxial optical system. Subsequently, we provide a solution function and method of the initial structure parameters of the system. Then, we combine it with optical design software to further correct the aberration of the system. Finally, we design a Terahertz wave detection optical imaging system with a large aperture. The optical system consists of four coaxial refractive lenses with a total focal length of 70 mm, an F-number of 1.4, and a full field of view angle of 8°. The value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view is less than the airy disk radius. Finally, the paper analyzes and discusses the various tolerance types of the system. The results indicate that the Terahertz wave detection optical imaging system, designed in this paper, has a large aperture, a simple, compact form, a lightweight structure, excellent imaging performance and simple processing, which meets the design requirements, and it has important applications in the field of high-resolution detection and other fields within the Terahertz wave band.

An MTF calculation model under the influence of ghost images
XIAO Peng-yi, LIU Ming-xin, YAN Lei, HU Ming-yu, ZHANG Xin
 doi: 10.37188/CO.2023-0121
Abstract(105) FullText HTML(55) PDF 4772KB(14)

Ghost images, as a type of stray light, are caused by residual reflected light between the optical surfaces. These images can degrade image clarity, annihilation targets, and severely affect the performance of optical systems. To investigate the impact of ghost images on optical system performance, we developed a Modulation Transfer Function (MTF) calculation model under the influence of ghost images generated by secondary reflection. This paper first introduces the method of analyzing and describing using the paraxial approximation. Then, starting from the definition of the MTF, and considering the influence of ghost image irradiance on the modulation of the image plane, a calculation model for calculating the MTF under the influence of ghost images is constructed. After performing calculations and comparing them to simulation results, it was found that the maximum mean square error was less than 0.049373, which verifies the accuracy of the model. Furthermore, a detailed analysis was conducted, examining cases that exhibited larger errors and clarifying the range in which this calculation method can be applied The research results indicate that the paraxial approximation method is both accurate and reliable when calculating the MTF under the influence of ghost images is accurate, and is applicable in most cases. This study serves as a valuable exploration in the ghost image analysis of optical systems.

An improved point cloud registration method based on the point-by-point forward method
LI Mao-yue, XU Sheng-bo, MENG Ling-qiang, LIU Zhi-cheng
 doi: 10.37188/CO.2023-0166
Abstract(135) FullText HTML(71) PDF 4847KB(20)

To improve both the efficiency and accuracy of point cloud registration, this study proposed an improved method based on point-by-point advance feature point extraction. Firstly, the point-by-point advance method extracts point cloud feature points rapidly, and greatly reduces the number of point clouds, while retaining the characteristics of the point cloud model. The KN-4PCS algorithm, using normal vector constraints, conducts a preliminary registration of the source and target point cloud. Finally, the fine registration is achieved with the two-way Kd-tree optimized LM-ICP algorithm. In the open point cloud data registration experiment of Stanford University, the average error is reduced by about 70.2% compared with the SAC-IA+ICP algorithm, and the registration time is reduced by about 86.2% and 81.9%, respectively. The algorithm maintains high accuracy and low time consumption even with varying degrees of Gaussian noise. In the point cloud registration experiment of indoor objects, the average registration error was measured to be 0.0742 mm with an average algorithm time of 0.572 s. The comparison and analysis of Stanford open data and real indoor scene object point cloud data shows that this method can effectively improve the efficiency, accuracy, and robustness of point cloud registration. Furthermore, this study establishes a strong foundation for indoor target recognition and pose estimation through the point cloud.

Methods for processing renal tissue samples for Single-Slice Dual-Mode optical correlation imaging
GAO Ge, GUO Xiao-guang, WU Jun-nan, CHEN Hai-long, SHI Bing, HUANG Zhen-li
 doi: 10.37188/CO.2023-0105
Abstract(100) FullText HTML(59) PDF 2106KB(27)

Bright-field imaging can provide cellular and histological morphological information, while fluorescence imaging can provide expression information of key proteins. Dual-modal correlation imaging based on both techniques is currently a common method for examining tissue samples in medical and scientific research. In clinical examination, however, correlation imaging between adjacent tissue slices is often used for observation. In such cases, both the tissue structure and the cellular level may be altered more or less, which is unfavorable when the sample volume is insufficient, the number of cells on the slices is limited, or precise point-to-point morphological information is required. Therefore, the development of single-slice dual-modal optical correlation imaging techniques which provides both tissue morphology and the distribution and expression of multiple target proteins on a single slice, can help to more accurately describe tumors and their microenvironment. This technique is particularly important in renal pathological testing where sample size is small. Renal pathology requires the use of bright-field imaging to obtain pathomorphological information of tissues and cells after hematoxylin-eosin staining, while the use of fluorescence imaging to obtain the distribution and expression of multiple target proteins is a mandatory molecular test for renal pathology screening. This paper focuses on the tissue sample processing methods that allow the coexistence of hematoxylin-eosin staining and immunofluorescence staining on the same renal slice. Improvements and comparative evaluations of the staining, de-colorizing and re-staining processes, as well as innovative fusion techniques for single-slice dual-modal imaging.

Optimization of structural parameters and fabrication of small blazed angle monocrystalline silicon gratings
XU Hao-Yu, JIANG Yan-Xiu, CHEN Xing-Shuo, WANG Rui-Peng, ZHANG Jing, Bayanheshig
 doi: 10.37188/CO.2023-0056
Abstract(193) FullText HTML(36) PDF 6667KB(52)

In order to meet the requirements of the national synchrotron radiation source, the anisotropic wet-etching technology of small blazed angle monocrystalline silicon grating is studied, and the blazed grating suitable for the medium wave soft X-ray band is prepared. Based on the rigorously coupled wave theory, the structural parameters and process tolerance of the small blazed angle grating are designed. In the crystal alignment process, the crystal orientation of the silicon wafer is determined by ring-preetching, and then the grating mask is aligned with the crystal direction of monocrystalline silicon <111> based on the frequency doubling adjustment method. At the same time, the effect of the photoresist ashing technique and the active agent on the groove quality of the grating is investigated, and the scintillating gratings close to the ideal sawtooth groove shape are successfully prepared by the monocrystalline silicon anisotropic wet etching process. The experimental results show that the blazed angle of the prepared grating is 1°, the linear density is 1200 gr/mm, and the root mean square roughness of the blazed surface is less than 0.5nm. This method can be applied to the fabrication of the medium wave soft X-ray band blazed grating, which can greatly reduce the difficulty and cost of fabrication while achieving high diffraction efficiency.

Original Article
Study and analysis of self-absorption-free laser-induced breakdown spectroscopy with high-repetition rate acousto-optic gating
CHEN Fei, WANG Shu-qing, CHENG Nian-kai, ZHANG Wan-fei, ZHANG Yan, LIANG Jia-hui, ZHANG Lei, WANG Gang, MA Xiao-fei, LIU Zhen-rong, LUO Xue-bin, YE Ze-fu, ZHU Zhu-jun, YIN Wang-bao, XIAO Lian-tuan, JIA Suo-tang
2024, 17(2): 253-262.   doi: 10.37188/CO.2023-0147
Abstract(315) FullText HTML(93) PDF 4083KB(150)

To eliminate the self-absorption effect in laser-induced breakdown spectroscopy (LIBS) and improve the accuracy of elemental quantitative analysis, the device of self-absorption free laser-induced breakdown spectroscopy (SAF-LIBS) technology needs to be miniaturized to meet the requirement of convenient elemental analysis in industry. This paper presents a novel quantitative analysis technique, the high repetition rate acousto-optic gated SAF-LIBS method. To enhance integral spectral intensity, a high repetition rate laser is used to produce quasi-continuous plasmas. In addition, an AOM (acousto-optic modulator) serves as an optical gating switch, enabling the use of a compact charge-coupled device (CCD) spectrometer and AOM instead of the intensified charge coupled device (ICCD) and medium step grating spectrometer in conventional large-scale SAF-LIBS devices. The results in a self-absorption-free system that is less bulky and less expensive. After optimizing the system parameters, the quantitative analysis and prediction of the Al element in the sample was achieved. Experimental results show that plasma characteristics are impacted by the laser repetition rate, which affects the intensity of spectral signal. The doublet intensity of Al I 394.4 nm and Al I 396.15 nm is enhanced and then diminished at a laser repetition rate ranging from 1 kHz to 50 kHz, with the optimal repetition rate identified as being 10 kHz. The doublet line intensity ratios of Al decrease with delay time under different fiber collection angles. The highest signal-to-noise ratio is achieved at an angle of 45°, while the optimal optically thin time tot is 426 ns at a certain integration time. Al is quantitatively analyzed and predicted at a laser repetition rate of 10 kHz, fiber collection angle of 45°, and delay time of 400 ns. The experimental results show that the calibration curve linearity of R2 is 0.982 and an average absolute prediction error of aluminum is reduced from 0.8% of single LIBS to 0.18%, which is equivalent to that of traditional SAF-LIBS. Additionally, the high repetition rate acousto-optic gating SAF-LIBS not only effectively eliminates continuous background radiation and broadens spectral lines in optically thick plasma, but also offers the advantages of miniaturization, low cost, convenience, and reliability. Therefore, this study plays a significant role in advancing SAF-LIBS technology from laboratory testing to industrial applications.

Tunable narrow-band perfect absorber based on metal-dielectric-metal
WANG Xiao-kun, LI Zhou, LIANG Guo-long
2024, 17(2): 263-270.   doi: 10.37188/CO.2023-0125
Abstract(218) FullText HTML(79) PDF 4026KB(80)

To achieve perfect narrowband absorber, we proposed a simple three-layer thin film (MDM) structure and developed a theoretical model. A comprehensive investigation was conducted on this structure through a combination of simulations and theoretical calculations. First, we executed theoretical calculations on the structure using both finite-difference time-domain algorithm (FDTD) and transfer matrix algorithm. The effects of several structural parameters on the absorption spectrum were analyzed in this study. We analyzed and discussed the physical mechanism of narrow band perfect absorber structure caused by the structure. Finally, we successfully used magnetron sputtering as a fabrication method to produce three-layer samples. The experimental results were consistent with the theoretical simulation. Our proposed structure for a narrowband perfect absorber can achieve a maximum narrow bandwidth of approximately 21 nm and a maximum absorption of 99.51%. We establish a strong basis for related applications by achieving perfect narrowband absorption.

Modeling and correction of measurement errors based on depth cameras
WEI Rui-li, WANG Ming-jun, ZHOU Yi-ming, YI Fang
2024, 17(2): 271-277.   doi: 10.37188/CO.2023-0047
Abstract(228) FullText HTML(155) PDF 3134KB(91)

Time of Flight (ToF) depth camera is one of the important means to obtain three-dimensional point cloud data, but ToF depth camera is limited by its own hardware and external environment, and its measurement data has certain errors. Aiming at the unsystematic error of ToF depth camera, this paper experimentally verifies that the color, distance, and relative motion of the measured target affect the data obtained by the depth camera, and the error effects are different. A new measurement error model is proposed to correct the error caused by color and distance. For the error caused by relative motion, a three-dimensional motion blur function is established to recover it. Through the numerical analysis of the established calibration model, the residual error of distance and color is less than 4 mm, and the error caused by relative motion is less than 0.7 mm. The work done in this paper improves the quality of the measurement data of the ToF depth camera, and provides more accurate data support for 3D point cloud reconstruction and other work.

Stereo matching algorithm based on multi-feature SAD-Census transformation
WU Fu-pei, HUANG Geng-nan, LIU Yu-hao, YE Wei-lin, LI Sheng-ping
2024, 17(2): 278-290.   doi: 10.37188/CO.2023-0082
Abstract(229) FullText HTML(91) PDF 4628KB(92)

The high mismatching rate of the parallax discontinuity region and the repeated texture region has been a major issue affecting the measurement accuracy of binocular stereo matching. For these reasons, we propose a stereo matching algorithm based on multi-feature fusion. Firstly, the weight of neighboring pixels is given using Gaussian weighting method, which optimizes the calculation accuracy of the Sum of Absolute Differences (SAD) algorithm. Based on the Census transformation, the binary chain code technique has been enhanced to fuse the average gray value of neighborhood pixels with the average gray value of gradient image, and then the judgment basis of the left and right image corresponding points is established, and the coding length is optimized. Secondly, an aggregation technique has been developed that combines the cross method and the improved guide filter to redistribute disparity values with the aim of minimizing false matching rate. Finally, the initial disparity is obtained by the Winner Take All (WTA) algorithm, and the final disparity results are obtained by the left-right consistency detection method, sub-pixel method, and then a stereo matching algorithm based on the multi-feature SAD Census transform is established. The experimental results show that in the testing of the Middlebury dataset, the average mismatch rates of the proposed algorithm for non-occluded regions and all regions are 2.67% and 5.69%, the average error of the 200−900 mm distance is less than 2%, and the maximum error of the actual 3D data measurement is 1.5%. Experimental results verify the effectiveness of the proposed algorithm.

A seawater salinity sensor based on dual peaks resonance long period fiber grating
DU Chao, ZHAO Shuang, SONG Hua-ke, WANG Qiu-yu, JIA Bin, ZHANG Li, CUI Li-qin, ZHAO Qiang, DENG Xiao
2024, 17(2): 291-299.   doi: 10.37188/CO.2023-0101
Abstract(222) FullText HTML(86) PDF 4883KB(88)

To develop a highly sensitive seawater salinity sensor, a long period fiber grating (LPFG) was successfully fabricated using CO2 laser technology to function in close proximity to the dispersion turning point (DTP). An LPFG operating near DTP was fabricated in an 80 μm single mode fiber using CO2 laser micromachining technology. This successful endeavor demonstrates the feasibility of developing LPFG with shorter grating period using CO2 laser micromaching technology. LPFGs with varying periods were fabricated by adjusting the preparation period of CO2 laser to ensure that the cladding mode LP1,9 was operating near DTP, resulting in higher refractive index sensitivity of LPFG. The average sensitivity of 0.279 nm/‰ can be achieved in the seawater with salinity ranging from 5.001‰ to 39.996‰, especially with the dual peaks resonance LPFG at a period of 115.4 μm, thanks to the dual peaks resonance effect. The dual peaks resonance LPFG seawater salinity sensor exhibits high sensitivity and a large attenuation loss, suggesting potential application in seawater salinity monitoring.

Propagation properties of one-dimensional array vortex beams in a marine atmosphere
HOU Zheng-cheng, ZHANG Ming-ming, BAI Sheng-chuang, LI Shu-zhen, LIU Jun, HU You-you
2024, 17(2): 300-311.   doi: 10.37188/CO.2023-0094
Abstract(212) FullText HTML(116) PDF 6416KB(101)

Compared to a single vortex beam, vortex array beams can increase the information transmission capacity. Therefore, studying the propagation properties of vortex array beams is significant for their optical communication applications. In this paper, we select the helical Ince-Gaussian (HIGn,n) modes of order n and simulate the marine atmosphere turbulence using the power spectrum of the refractive index fluctuations in the marine atmosphere. The changes in intensity, phase, scintillation index and spot centroid wander of a one-dimensional array vortex beam in marine atmospheric turbulence have been investigated systematically by using the phase screen method. We find that (1) an increase in either the turbulence intensity or atmospheric turbulence inner scale enhances both the scintillation index and spot centroid wander standard deviation for HIGn,n modes; (2) the scintillation index of HIGn,n mode with odd n decreases with increasing mode order, and is higher than that of HIGn,n mode for even n; (3) the HIGn,n mode with order n>1 has better stability than the LG0,1 mode; and (4) the higher the mode order, the smaller the standard deviation of spot centroid wander of HIGn,n mode. In addition, we perform comparative study on the propagation performance of the linear array vortex beams (LAVBs) and HIG beams. Our study indicates that although LAVBs have better propagation performance than HIG beams, the unique structures of HIG beams can be applied to various application scenarios. Finally, the effects of both the ellipticity parameter and elliptic ring number on the propagation of the HIG modes are explored and analyzed. The results show that increasing either the ellipticity parameter or elliptic ring number is beneficial to improving the anti-turbulence ability of the HIG modes. These results offer significant guidance for the offshore vortex beams application.

An improved phase generated carrier demodulation algorithm of fiber optic fabry-perot sensor
ZHOU Zhen-rui, ZHANG Guo-qiang, QIU Zong-jia, GUO Shao-peng, LI Qun, SHAO Jian, WU Peng, LU Yun-cai
2024, 17(2): 312-323.   doi: 10.37188/CO.2023-0108
Abstract(163) FullText HTML(82) PDF 4284KB(60)

To address the issue of non-linear distortion in the Phase Generated Carrier-Antitangent demodulation (PGC-Atan) algorithm, we have developed an extrinsic Fabry-Perot Interferometer (EFPI) sensor demodulation system based on an improved PGC-Atan algorithm. The theoretical analysis focuses on the affect of nonlinear factors on sine and cosine signals used in arctangent operation of the PGC-Atan algorithm. Such factors include deviations from optimal values of the phase modulation depth (C), companion amplitude modulation, and carrier phase delay. As a solution, we propose an improved PGC-Atan algorithm based on a correction coefficient (PGC-CC-Atan) suitable for external modulation or the case of low companion amplitude modulation scenarios. The PGC-CC-Atan algorithm generates a coefficient relating to C and carrier phase delay while excluding nonlinear parameters in the arctangent operation. Furthermore, an improved PGC-Atan algorithm that utilizes an elliptic fitting algorithm (PGC-EF-Atan) is proposed for internal modulation. The ellipse fitting technique is employed to fit the eclipse using the least squares method based on a matrix block decomposition. The pair of signals that are influenced by nonlinear factors are corrected and transformed into orthogonal signals utilizing three parameters of the ellipse. Finally, the correctness of the two improved algorithms is verified through simulations and experiments. The PGC demodulation system comprises a high dv/di VCSEL laser and a conventional cavity length F-P sensor. By comparing the demodulation performance of the PGC-Atan algorithm with that of the two improved algorithms, their effectiveness in suppressing nonlinear distortion is verified. Experimental results indicate that the two improved algorithms exhibit effective demodulation in the presence of nonlinear factors within a specific range of C values. The signal-to-noise and distortion ratio (SINAD) of demodulation result obtained from PGC-EF-Atan algorithm surpasses that of the PGC-CC-Atan algorithm by 11.602 dB, while the Total Harmonic Distortion (THD) is reduced by 10.951%. Between the two improved algorithms, the PGC-EF-Atan algorithm possesses superior demodulation linearity, accuracy, and nonlinear distortion suppression performance.

Design and fabrication of liquid crystal wavefront corrector based on mask lithography
DU Ying, CHEN Mei-rui, LIU Yu-tong, CAO Zong-xin, MAO Hong-min, LI Xiao-ping, SUN Hui-juan, CAO Zhao-liang
2024, 17(2): 324-333.   doi: 10.37188/CO.2023-0137
Abstract(173) FullText HTML(78) PDF 5922KB(59)

Liquid crystal wavefront correctors (LCWFCs) exhibit high development cost and customization difficulties due to being fabricated based on the process technology of liquid crystal displays. To achieve specialized and low-cost development of LCWFCs, a liquid crystal wavefront corrector is fabricated by using the mask lithography method. Firstly, a 91-pixel passive liquid crystal driving electrode is designed and prepared based on the mask lithography technology and then, packaged as a liquid crystal optical correction unit. A circuit board for driver connection is designed and prepared to connect the optical correction unit and the driving circuit board. Next, the response characteristics of the LCWFC are tested, and the results show that the phase modulation is 5.5 λ, and the response time is 224 ms. Finally, the spherical waves are obtained and the static tilt aberrations are corrected based on Zygo interferometer. The results show that the LCWFC can generate positive and negative defocused wavefronts. Further, after correction of the horizontal tilt aberration, the coefficient of the first term of the Zernike polynomials is decreased from 1.18 to 0.16. Therefore, the aberration is corrected with the amplitude of 86%. This work may provide new ideas for the development of LCWFCs, and then expanding their application fields and scenarios.

Development of high-precision beam splitter for inter-satellite communication system
WANG Zhen-yu, FU Xiu-hua, LIN Zhao-wen, HUANG Jian-shan, WEI Yu-jun, WU Gui-qing, PAN Yong-gang, DONG Suo-tao, WANG Ben
2024, 17(2): 334-341.   doi: 10.37188/CO.2023-0100
Abstract(260) FullText HTML(83) PDF 3211KB(95)

With the rapid development of inter-satellite communication systems, the requirements for data transmission accuracy are constantly increasing. As the core component, the spectral characteristics and surface shape accuracy of the beam splitter directly affect the transmission accuracy of the whole system. According to the interference theory of thin film, Ta2O5 and SiO2 were selected as the high and low refractive index film materials for the design of the film system, and electron beam evaporation was used to prepare a high-precision beam splitter on a quartz substrate. At the same time, a surface shape correction model was established based on the principle of film stress compensation to control the surface shape. Through the detection of a spectral analyzer, it can be seen that the transmittance of beam splitter is greater than 98% at 1563 nm and the reflectance is greater than 99% at 1540 nm within the incidence range of 21.5° to 23.5°. The surface shape was measured by laser interferometer, it can be seen that the reflective surface shape accuracy RMS is corrected from λ/10 to λ/90 (λ=632.8 nm), and the transmissive optical surface shape accuracy RMS is λ/90.

Multi-channel laser beam combining and closed-loop correction technology in visible light band
XU Xin-hang, LI Gao-sheng, XIE Bing, HAN Xu-dong
2024, 17(2): 342-353.   doi: 10.37188/CO.2023-0077
Abstract(198) FullText HTML(90) PDF 4028KB(107)

To achieve periodic closed-loop correction of multiple lasers with different wavelengths in the visible wavelength band, a laser beam combining system is designed. This system involves independent monitoring and adjusting of beam pointing and position deviation. First, according to the application requirements of the system, the design indexes of the beam combining system and the overall beam combining scheme are proposed. Then, based on the overall beam combining scheme, we establish the beam control model for the beam combining system. Through numerical simulation experiments, we obtain the solution method for beam control of the beam combining system. The closed-loop beam combining system realizes independent monitoring of the unit beam’s pointing and position deviation through the respective beam pointing and position monitoring device. The monitoring results are then used to calculate the control quantity of the beam adjusting device. The independent and efficient adjustment of beam pointing and position deviation is achieved using a two-dimensional swing mirror and a one-dimensional platform, respectively. Finally, a closed-loop beam combining simulation experimental system with beam monitoring and adjustment device is built using two laser beams of different wavelengths. The periodic closed-loop beam combining system is verified to have an effective beam combing effect. The experimental results demonstrate that over an extended operational period, both lasers achieve precise beam combining with the reference optical path. Furthermore, the beam combining pointing accuracy is better than ±7 μrad, and the positioning accuracy is better than ±0.84 mm. The laser beam combining system developed in this study boast high beam combining accuracy, a fast correction speed, and excellent augmentability for multiple laser beams. Besides, it can accomplish periodic closed-loop beam combining of laser beams, ensuring long-term working stability of the combined laser.

Design of optical field of vision imaging for defect detection of paper and transparent film
JIANG Shi-fei, ZHANG Zhao-guo, WANG Fa-an, XIE Kai-ting, WANG Cheng-lin, LI Zhi
2024, 17(2): 354-365.   doi: 10.37188/CO.2023-0134
Abstract(175) FullText HTML(96) PDF 6755KB(51)

To achieve synchronous detection of defects in the paper and transparent film layers of packaging boxes, we studied the synchronous imaging of the paper and film defect. Firstly, we established models for a standard sphere integral light field, an ellipsoidal integral light field, and an arc integral light field. We then simulated three different light fields using COMSOL Multiphysics 5.6 and compared their ray angle uniformity and irradiation uniformity. The parameters of ellipsoidal area integral light field are optimized by orthogonal simulation. Secondly, the packaging box was imaged using the ellipsoidal integral light field, the bright and dark field forward lighting. Physical detection and machine vision were used to detect five common defects in the packaging box, including oil stains, pressure marks, openings, bubble wrinkles, and breakages, to verify the effectiveness of defect imaging. The results show that the images can clearly present defect characteristics in the paper base and transparent film layers under ellipsoidal integral light field. The physical detection rates for oil stains, pressure marks, openings, bubble wrinkles, and breakages were 96.2%, 92.5%, 100%, 95%, and 92%, respectively. Anomaly detection rates were 98.6%, 97.5%, 100%, 100%, 98.4%, respectively. Detection rates of defects were 97.6%, 96%, 100%, 97%, and 96%, respectively. This study indicates that the consistent optical path angle and irradiation intensity result in a uniform ellipsoidal integral light field. Consequently, transparent film imaging of the packaging box shows clear defect characteristics that satisfy the standards for industrial detection application.

An XY defocus aberration correction method for high-energy lasers
FENG Ya-fei, WEI Cheng-fu, REN Xiao-ming, GUO Jian-zeng, WANG Jie
2024, 17(2): 366-373.   doi: 10.37188/CO.2023-0142
Abstract(174) FullText HTML(66) PDF 4640KB(67)

A method for correcting XY defocus aberrations, based on Hartmann-Shack wavefront sensor and two-dimensional beam-shaping light path, was presented due to the large percentage of defocus and 0° astigmatism aberrations with large PV values in high-energy laser beam. The first step is to derive an expression for XY defocus aberrations by linearly combining the defocus and 0° astigmatism terms of Zernike polynomials. The coefficients directly characterize the wavefront peak-to-valley (PV) values of X and Y defocus. At the same time, compensation for XY defocus wavefronts of the laser beam can be achieved by fine-tuning the mirror spacing in the two-dimensional shaping optics of the high-energy laser. Therefore, the Hartmann wavefront sensor is used to extract the coefficients of XY defocus aberrations from the laser beam. The computer dynamically adjusts the mirror spacing in the two-dimensional shaping optics based on these coefficient values to correct XY defocus aberrations and improve the beam quality of the output laser beam. The results of the experiment showcase a significant decrease in PV value of XY defocus aberrations from 5.2 μm and 1.1 μm to less than 0.5 μm, as well as a decrease in β factor from 3.1 to 1.8, resulting in substantial improvement in beam quality.

Design of terahertz wave imaging optical system with large aperture
CAO Yi-qing, SHEN Zhi-juan
2024, 17(2): 374-381.   doi: 10.37188/CO.2023-0129
Abstract(146) FullText HTML(68) PDF 2901KB(66)

The Terahertz wave has some characteristics of high penetration, low energy and fingerprint spectrum, etc., and is widely used in the detection field. Therefore, design of Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, referring to the structure of Tessar objective lens consisting of four lenses, we apply the aberration theory of paraxial optical system to establish the balance equations of aberration of the system, and give solve function and method of the initial structure parameters of the system. Then, by combining with optical design software to further correct the aberration of the system. Finally, a Terahertz wave detection optical imaging system with large aperture is designed. The optical system is composed of four coaxial refractive lenses. Its total focal length is 70 mm, F-number is 1.4, full field of view angle is 8°. The value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view is less than the Airy disk radius. At last, we analyze and discuss the various tolerance types of the system. The design results show that the Terahertz wave detection optical imaging system designed in this paper has a large aperture, a simple and compact form, a light-weight structure, excellent imaging performance and simple processing, etc., which meets the design requirements, and it has important applications in the field of high-resolution detection and other fields within the Terahertz wave band.

Design of three-band co-aperture optical system based on single sensor
ZHANG Kun, LI Jing-chen, SUN Si, CHEN Qing-rong, YANG Fan
2024, 17(2): 382-389.   doi: 10.37188/CO.2023-0098
Abstract(177) FullText HTML(69) PDF 4581KB(66)

The existing multi-band imaging system has the problems of large volume, high power consumption, and difficulty in integrating design. To address these challenges, we proposed a three-band co-aperture imaging optical system based on single sensor. First, a 1×2 multi-band lens array in the aperture stop of the optical system is designed. This array effectively captures both the visible and short-wave infrared bands simultaneously in a single image plane. In addition, the imaging position deviation of the center wavelength of both bands are controlled within one pixel, resulting in dual-band fusion imaging. To address the issue of different diffraction limits in multi-band imaging, we propose to use the joint optimization method to simultaneously control the off-axis offset and aperture size of the split channel lens array. On the above basis, we suggest utilizing a dual electric diaphragm to control the switching speed of the three imaging channels. Finally, a three-band co-aperture optical system based on single sensor with a focal length of 30 mm and operating bands ranging from 480 to 900 nm, from 900 to 1700 nm, and from 480 to 1700 nm is designed. The system exhibits multiple advantages, such as excellent imaging quality, a compact structure, no moving optical elements, and a rapid switching speed of the imaging band, as indicated by the design and analysis results.

A benchmark construction method for large aperture circular segmented optical systems
AN Qi-chang, WU Xiao-xia, LIU Xin-yue, WANG Xun, LI Hong-wen
2024, 17(2): 390-397.   doi: 10.37188/CO.2023-0149
Abstract(191) FullText HTML(67) PDF 5060KB(57)

To realize integration detection and construct stability maintaining benchmark for large apertures of segmented telescopes, we propose a benchmark construction method. In this study, we use local pupil projection to perform pupil alignment mapping. In addition, we construct a system confocal spatial benchmark using a microlens array. On the basis of annular whole-body control mode, a joint analysis method of confocal and curvature radius enables joint adjustment of the curvature radius and system alignment. Finally, the stripe envelope formed by white light interference is used for coarse common phases detection, and the channel spectral method is used to obtain precise connection between coarse and fine common phases. Additionally, the spatial confocal reference positioning exhibits an accuracy of less than 125 μm, and the common phase reference has a coverage range better than 0.5 μm within a 20-μm-range. Furthermore, the uncertainty of the spectral reference is less than 5%. We have effectively improved the accuracy of optical system in-situ measurement by achieving hierarchical and multimodal suppression of disturbances from different spatiotemporal features. We have shortened the length of the traceability chain and increased the efficiency and accuracy of detection by utilizing the new method of common reference in-situ measurement.

Three-dimensional surface shape reconstruction of fiber bragg gratings in a ring arrangement
WANG Yan, XU Hao-yu, WANG Jun-liang, ZHU Wei, JIANG Chao
2024, 17(2): 398-408.   doi: 10.37188/CO.2023-0088
Abstract(170) FullText HTML(84) PDF 6282KB(53)

To improve the accuracy of palm surface reconstruction in flexible robot grasp sensing, we conduct a COMSOL simulation to select a ring arrangement comprising of 7 fiber Bragg grating (FBG) flexible sensors packaged with polydimethylsiloxane (PDMS) on a 436 mm×436 mm×2 mm polypropylene plate. Assuming that the center and two corner ends of the plate were subjected to stress, respectively, we collected sensor data using a fiber grating demodulation instrument during the experiment. The data was continuously interpolated using cubic spline interpolation. Several planes Y intersected with the fitting ring which created a three-dimensional surface. We calculated the point function to obtain the point set and achieve a fitting visual display of the spatial surface. When the center of the end of the surface is under stress, the plate experienced a minimum relative error of 0.549% in end displacement, with a maximum relative error of 8.300%, the minimum absolute error of 0.051 cm, and a maximum absolute error of 1.255 cm. When both corners at the end of the plate are under stress, for the end displacement of the plate reconstruction, the minimum relative error is 2.546%, and a maximum relative error is 14.289%, the minimum absolute error is 0.005 cm, and the maximum absolute error is 0.729 cm. These experimental results provide a foundation to implement palm grip sensing in flexible robots.

Scanning measurement method of small size parts without marks
MO Cai-li, WANG Li-zhong, REN Mao-dong, ZHAO Jian-bo, WANG Sen, ZHOU Hao-jun
2024, 17(2): 409-422.   doi: 10.37188/CO.2023-0103
Abstract(160) FullText HTML(86) PDF 3947KB(73)

Small-size parts have a small surface area and complex structure. The traditional mark splicing method needs to manually paste marks on the surface of parts, resulting in missing the measurement data of the surface and becoming holes. The feature splicing method requires the surface of parts to have easily distinguishable geometric or distance features, which are not suitable for rotating parts containing repetitive features. We propose a scanning measurement method without marks based on mechanical splicing, which does not need to paste marks or depend on the surface features of parts. Firstly, the camera calibration method based on photogrammetry is used to reconstruct the high-precision three-dimensional coordinates of the target on the calibration board. By tracking the position of the coded target, the rotation matrix corresponding to different angles of the turntable is established, and the direction vector of the rotation axis and the fixed point coordinates on the axis are solved. Then the synchronous calibration of the rotation axis and the camera is completed. Secondly, based on the accurate calibration of poses of two rotation axes, the rotation mosaic matrix is constructed by using the turntable angle to realize the rough registration of multi-view point clouds. Finally, based on the Normal Iterative Closest Point (NICP) algorithm, the fine registration of the point clouds is completed. Experimental results show that the angle error between the two rotation axes calibrated by the target tracking method is 0.023° lower than that of the traditional standard ball fitting method. After calibration, the average size error of the standard ball is less than 0.012 mm. In the automatic measurement of small-size parts, the point cloud splicing effect of the mechanical splicing method after fine registration is similar to that of the mark splicing method, and the splicing stability is higher. The mechanical splicing method is suitable for the 3D topography measurement of small-size parts where the marks cannot be pasted.

An autofocus algorithm for fusing global and local information in ferrographic images
LIU Xin-liang, ZHANG Long-quan, LENG Sheng, WANG Jing-qiu, WANG Xiao-lei
2024, 17(2): 423-434.   doi: 10.37188/CO.2023-0124
Abstract(149) FullText HTML(89) PDF 4210KB(44)

To address the issues of large error and slow speed of manual focusing in ferrographic image acquisition, we propose an autofocus method for fusing global and local information in ferrographic images. This method includes two stages. In the first stage, the global autofocus stage, the feature vectors of the whole image is extracted by Convolutional Neural Networks (CNN) , and the features extracted in the focus process is fused by the Gate Recurrent Unit (GRU) to predict global defocusing distance, which serves as coarse focusing. In the local autofocus stage, the feature vector of the wear particle is extracted and the current features is fused with those extracted in the previous focusing process by GRU. The current defocusing distance is predicted by the resulting fused data based on the information of the thickest particle, which facilitates fine focusing. Moreover, we propose a determination method for autofocus direction using Laplacian gradient function to improve autofocus accuracy. Experimental results indicate an autofocus error of 2.51 μm on the test set and a focusing accuracy of 80.1% with a microscope depth of field of 2.0 μm. The average autofocus time is 0.771 s. The automatic ferrographic image acquisition system exhibits excellent performance and offers a practical approach for its implementation.

A denoising method combining bitonic filtering and sine-cosine transform for shearography fringe pattern
WU Rong, LU Yang, OUYANG Ai-guo
2024, 17(2): 435-443.   doi: 10.37188/CO.2023-0072
Abstract(265) FullText HTML(118) PDF 3319KB(147)

Shearography is a non-contact, full-field, and high-precision optical deformation measurement technology. There is a lot of random noise in the acquired speckle fringe pattern caused by environmental factors, which affects the measurement accuracy. The traditional denoising methods easily cause the fringe information to be lost or even damaged while filtering out the noise. To solve this problem, we propose an image denoising method by combining sine and cosine transform and bitonic filtering. In this method, the phase fringe image is firstly obtained by sine and cosine transform. Secondly, the two images are denoised by the bitonic filtering method respectively. Finally, the filtered two images are merged into the final phase fringe image. Experimental results show that for the filtered phase pattern, the speckle suppression index is 0.999 and the average retention index is 2.995, which prove that the proposed method can improve the quality of the phase pattern better than the traditional denoising method, and can preserve the details and edge information of the phase fringes to a large extent.

A photoacoustic tomography image reconstruction method based on forward imaging model
CHENG Li-jun, SUN Zheng, SUN Mei-chen, HOU Ying-sa
2024, 17(2): 444-455.   doi: 10.37188/CO.2023-0114
Abstract(215) FullText HTML(103) PDF 6463KB(67)

Aiming at the issue of degraded image quality in photoacoustic tomography (PAT) caused by the inhomogeneous light fluence distribution, complex optical and acoustic properties of biological tissues, and non-ideal properties of ultrasonic detectors, we propose a comprehensive forward imaging model. The model takes into account variables such as the inhomogeneous light fluence, unsteady speed of sound, spatial and electrical impulse responses of ultrasonic transducers, limited-view scanning, and sparse sampling. The inverse problem of the imaging model is solved by alternate optimization, and images representing optical absorption and speed of sound (SoS) distributions are reconstructed simultaneously. The results indicate that the structural similarity of the reconstructed images of the proposed method can be enhanced by about 83%, 56%, and 22%, in comparison with back projection, time-reversal, and short-lag spatial coherence techniques, respectively. Additionally, the peak signal-to-noise ratio can be improved by approximately 80%, 68% and 58%, respectively. This method considerably enhances the image quality of non-ideal imaging scenarios when compared to traditional techniques.

All-optical logic gate based on nonlinear effects of two-dimensional photonic crystals
WU Rong, YANG Jian-ye, ZHANG Hao-chen
2024, 17(2): 456-467.   doi: 10.37188/CO.EN-2023-0021
Abstract(167) FullText HTML(92) PDF 6004KB(52)

All-optical XOR, NOT and two-input AND logic gates are designed based on the nonlinear effect and linear interference effect of photonic crystals. The complex logic expressions are divided by inversion theorem, and all-optical NOR gate and four-input AND gate logic devices are designed by cascade combination. In this paper, the Finite-Difference Time-Domain (FDTD) method is used for simulation, and the coupling characteristics of nonlinear annular cavities are analyzed. Then, the above logic devices are designed under the condition that the signal wavelength is 1.47 μm, and more input devices can be designed by expanding the input. The influence of signal power on the logic function of the four-input AND logic devices is analyzed. The results show that when the power of the signal light source is between 1.1 W/μm2 and 3.4 W/μm2, the logical contrast ratio of the output is greater than 10 dB. The response time of the designed device is only 1.6 ps, the occupied area is small, and the device is easy to expand and integrate. It has great application prospect in optical processing systems and integrated optical paths.

A red-emitting copolymer phosphors based on bimetallic Eu-Ir complex for Near-UV chip-based LEDs
WANG Zi-hao, YANG Ya-min, ZHANG Ai-qin, JIA Hu-sheng, XU Bing-she, JIA Jing
2024, 17(2): 468-480.   doi: 10.37188/CO.EN-2023-0023
Abstract(146) FullText HTML(55) PDF 4442KB(61)

In this paper, a new Eu-Ir bimetallic complex Eu(FIrPic)2(Phen)UA is synthesized using the Ir complex FIrPic as ligands for Eu ions and red-emitting phosphorescent copolymer PM-Eu-Ir is successfully prepared via radical polymerization for commercial near UV chip-based LEDs. The Eu3+ ions were found to be effectively sensitizable by adding Ir-complex with enhanced ultra-violet light absorption at around 400 nm without affecting the fluorescence emission characteristic of the Eu3+ ions. The proposed copolymer PM-Eu-Ir exhibits the strongest emission peak at 612 nm with the CIE coordinates (0.461, 0.254) under 365 nm ultra-violet light excitation, which matches well with the 365 nm near-UV chip. The micro-morphology of the red copolymer phosphor PM-Eu-Ir is a typical multilayer spatial network structure; as well as having appreciable red emission and the corresponding fluorescence lifetime of 634.54 μs, it also has excellent thermal stability in a wide range of 25~250 °C. The LEDs fabricated by the copolymer PM-Eu-Ir display red light emission with a 149800 cd/m2 luminance. The results support the potential utilization of prepared copolymer phosphor as a red component in the fabrication of near UV chip-based white LEDs.

Controllable inversion and focusing behaviors of Swallowtail-Gaussian beams in fractional Schrödinger equations
HUANG Hong-wei, CHENG Ke, YANG Ceng-hao, YAO Na
2024, 17(2): 481-492.   doi: 10.37188/CO.EN-2023-0018
Abstract(171) FullText HTML(78) PDF 8459KB(70)

By transferring a one-dimensional swallowtail catastrophe to an optical field, the evolution dynamics of the Swallowtail-Gaussian (SG) beams in fractional Schrödinger equations (FSE) with different potentials, which include the linear, parabolic, and Gaussian potential and non-potential cases, were investigated using the split-step Fourier method. In a non-potential case, the SG beams split into two sub-beams, and their splitting trajectories along straight lines can be curved with a larger Lévy index in FSE. In a linear potential case, periodic inversion and focusing behaviors are found, and a larger Lévy index can strengthen their peak intensities at focusing points and curve trajectories. However, the period distance of inversion and focusing is only affected by linear potentials rather than the Lévy index. In a parabolic potential case, the beams evolve from chaos interference into an apparent period in inversion and focusing of main and side lobes with a larger Lévy index, where the inversion and focusing position are combined and determined by parabolic potential and the Lévy index. In a Gaussian potential case, the evolution dynamics are evidently constrained within potential barriers. In a narrow barrier, the periodic inversion and focusing display chaotic behavior because of the interference of both the reflected main and side lobes. In contrast, the periodic evolution in a wider barrier becomes more prominent owing to the attenuation of the side lobes. The study of the SG beam in FSE offers the possibility of optical modulators and switches through the utilization of the higher-order swallowtail catastrophe wave fields.

Incident angle-tuned filter based on 1D resonant waveguide grating in full conical mounting
FAN Li-na, SHA Jin-qiao, CAO Zhao-liang
2024, 17(2): 493-500.   doi: 10.37188/CO.EN-2023-0030
Abstract(187) FullText HTML(57) PDF 2697KB(72)

This paper proposes and demonstrates a tunable filter using full conical mounting. The designed 1D resonant waveguide grating presents a tunable single reflection peak. The peak reflectance can theoretically reach 100%. The resonant wavelength can be tuned from 642.5 nm to 484.6 nm by changing the incident angle. The resonance between the 1st-order diffracted wave and fundamental transverse electric (TE) guided mode generates the reflection peak. This feature was achieved by optimizing the grating thickness to support the TE guided mode and suppress the transverse magnetic (TM) guided mode. The same concept can be applied to tunable filters with high dynamic range by increasing the thickness and period of grating in equal proportion.

On-machine detection technology and application progress of high dynamic range fringe structured light
LIU Ze-long, LI Mao-yue, LU Xin-yuan, ZHANG Ming-lei
2024, 17(1): 1-18.   doi: 10.37188/CO.2023-0068
Abstract(489) FullText HTML(145) PDF 6064KB(280)

Fringe structured light technology is a non-contact measurement method, which has developed rapidly in recent years and provides a new solution for on-machine detection in mechanical processing. However, the accuracy of structured light for on-machine detection is compromised by the convoluted lighting in machining environments and metal parts’ high reflectivity, leading to inaccurate measurements. Applying high dynamic range (HDR) technology to structured light detection can reduce the effect of high reflectivity, achieving the measurement of metal parts in complex scenes. This paper introduces the measurement principle of structured light and summarizes the challenges of on-machine detection for HDR structured light. Subsequently, this paper provides a comprehensive review of HDR structured light technology. In the context of on-machine detection of mechanical processing, the HDR technology based on hardware equipment and the HDR technology based on stripe algorithm are discussed and analyzed, respectively. Following this, different technologies are summarized according to the requirements of on-machine detection. The advantages and disadvantages of various methods are presented, and the applicability of on-machine detection is compared. Finally, the potential applications are analyzed, and the technological prospects will be proposed in combination with the research hotspots of advanced manufacturing technology and precision measurement in recent years.

Research progress on the related physical mechanism of laser-induced breakdown spectroscopy
LIU Rui-bin, YIN Yun-song
2024, 17(1): 19-37.   doi: 10.37188/CO.2023-0019
Abstract(389) FullText HTML(103) PDF 1508KB(228)

Laser Induced Breakdown Spectroscopy (LIBS) is a new method for qualitative and quantitative analysis of the constituents of a material using plasma spectra produced by the interaction of a strong pulsed laser with the material. In the process of pulsed laser-induced plasma, different laser parameters (energy, pulse width, wavelength), environmental conditions during the detection process and the properties of the material itself have different degrees of influence on the physical mechanism of laser-induced plasma, which in turn affects the results of LIBS quantitative analysis. We review the physical mechanisms of LIBS technology in the current state, including the basic principles of LIBS, the differences in laser parameters, and the physical mechanisms involved in the differences in environmental and material properties. It provides a basis for a deeper understanding of laser-matter interactions and for improving the detection capabilities of LIBS.

Key technology analysis and research progress of high-power narrow linewidth fiber laser based on the multi-longitudinal-mode oscillator seed source
SUN Shi-hao, ZHENG Ye, YU Miao, LI Si-yuan, CAO Yi, WANG Jun-long, WANG Xue-feng
2024, 17(1): 38-51.   doi: 10.37188/CO.2023-0074
Abstract(252) FullText HTML(88) PDF 8949KB(200)

Narrow linewidth fiber lasers, based on the multi-longitudinal-mode oscillator seed source, have obvious advantages in engineering applications and space-limited loading platforms. Additionally, they are considered ideal sub-modules for high-power spectral combinations. The time domain of this type of seed is unstable due to the self-pulse effect, causing significant spectral broadening and stimulated Raman scattering effects during the amplification process, which limits their further improvement in output power and affects the purity of laser spectra. In this paper, we introduce four commonly used narrow linewidth seeds. The mechanism and suppression methods of the self-pulse effect in multi-longitudinal mode oscillator seeds are analyzed. Critical technologies essential for the optimization and relevant progress of the multi-longitudinal-mode oscillator seed source and amplifier stages are discussed in detail. A future development outlook is also presented. This paper serves as a useful reference for the design of narrow linewidth fiber lasers based on the multi-longitudinal-mode oscillator seed source.

Development and prospects of enhanced absorption spectroscopy
REN Yi-jie, YAN Chang-xiang, XU Jia-wei
2023, 16(6): 1273-1292.   doi: 10.37188/CO.2022-0246
Abstract(1053) FullText HTML(458) PDF 4881KB(425)

Optical path absorption spectroscopy is an important branch of absorption spectroscopy. In recent years, there has been a proliferation of optical path absorption spectroscopy techniques based on different light source technologies, absorption cavity technologies, and detection methods. As the demands on detection sensitivity and absorption optical path length increased, optical path absorption spectroscopy techniques based on the principle of enhanced absorption emerged, including integrated cavity spectroscopy (ICOS), cavity-enhanced absorption spectroscopy (CEAS) and cavity ring-down spectroscopy (CRDS). Enhanced absorption spectroscopy is advantageous for its high spectral resolution, high sensitivity, fast response time, and portability, but it presently lacks a unified concept and clear classification criteria. This paper compares the development history of absorption spectroscopy techniques and clarifies the concept of their multi-optical path. Based on whether resonant absorption occurs in the absorption cavity, the concept of absorption spectroscopy techniques based on resonance is proposed, and the current research status of resonant absorption spectroscopy techniques is analyzed and summarized, and the applications of this technique in various fields are outlined. Finally, the future development of key technologies in resonance absorption spectroscopy is envisioned.

Advances in optical fiber tweezer technology based on hetero-core fiber
LI Hong, ZHU Ying-xin, ZHOU Ya-ni, WANG Hai-bo, DONG Ming-li, ZHU Lian-qing
2023, 16(6): 1293-1304.   doi: 10.37188/CO.2023-0016
Abstract(463) FullText HTML(230) PDF 6097KB(214)

Optical fiber tweezers are widely used in biochemical analysis, life sciences, and other fields due to their simple structure, flexible operation, and compact size. The hetero-core structure of the optical fiber probe possesses inherent advantages in near-field evanescent wave optical trapping force, core beam coupling transmission, and cross-synergistic application of microfluidic technology, which can realize the functions of cell and subcellular particle collection and transportation, and can significantly improve the three-dimensional particle trapping capability as well as dynamic manipulation level. In this paper, the structural characteristics and application technology research progress of optical fiber tweezers based on different core structures are reviewed. This paper sorts and compares key technologies, including probe preparation, laser source, and coupling mode, in hetero-core optical fiber tweezers systems. It also summarizes and provides a perspective on the role and development of hetero-core fibers with different structures in optical fiber tweezers.

A review of the effect of GaN-Based Micro-LED sidewall on external quantum efficiency and sidewall treatment techniques
KUANG Hai, HUANG Zhen, XIONG Zhi-hua, LIU Li
2023, 16(6): 1305-1317.   doi: 10.37188/CO.2023-0091
Abstract(455) FullText HTML(79) PDF 4670KB(174)

Micro-LEDs offers the benefits of high brightness, high response frequency, and low power consumption, making them an attractive candidate for future display technologies and Visible Light Communication (VLC) systems. Nonetheless, their low External Quantum Efficiency (EQE) currently impedes their scaled mass production and further applications. In order to break through the bottleneck of low EQE, we conducted an analysis of Micro-LED external quantum efficiency’s contributing factors. The influencing factors for EQE are analyzed. It is concluded that the carrier loss and non-radiative recombination caused by sidewall defects are the main reasons for the decrease in EQE. In addition, we summarized the impact of sidewall defects on carrier transport and composites, and we also reviewed the commonly used sidewall treatment technology and repair methods, and pointed out that the existing sidewall treatment methods are helpful but insufficient for improving EQE, and the mechanism of carrier interaction with sidewall defects is not very clear. It is suggested to carry out a thorough and systematic study on the types and distribution of sidewall defects, the mechanism of carrier and sidewall defects, and the defect repair mode in the sidewall treatment process. Finally, future development trends are projected. This paper offers design ideas and theoretical foundations to enhance the external quantum efficiency and accelerate the process of commercialization and mass production of Micro-LEDs.

Recent advances in metasurfaces for polarization imaging
ZHOU Jun-zhuo, HAO Jia, YU Xiao-chang, ZHOU Jian, DENG Chen-wei, YU Yi-ting
2023, 16(5): 973-995.   doi: 10.37188/CO.2022-0234
Abstract(1791) FullText HTML(763) PDF 6268KB(967)

Polarization imaging, a novel photoelectric detection technology, can simultaneously acquire the contour information and polarization features of a scene. For specific application scenarios, polarization imaging has the excellent ability to distinguish different objects and highlight their outlines. Therefore, polarization imaging has been widely applied in the fields of object detection, underwater imaging, life science, environmental monitoring, 3D imaging, etc. Polarization splitting or the filtering device is the core element in a polarization imaging system. The traditional counterpart suffers from a bulky size, poor optical performance, and being sensitive to external disturbances, and can hardly meet the requirements of a highly integrated, highly functional, and highly stable polarization imaging system. A metasurface is a two-dimensional planar photonic device whose comprising units are arranged quasi-periodically at subwavelength intervals, and can finely regulate the amplitude and phase of the light field in different polarization directions. Polarization devices based on metasurface are featured with compactness, lightweight and multi-degree freedom, offering an original solution to ultracompact polarization imaging systems. Targeted at the field of polarization imaging, this paper illustrates the functional theory, developmental process and future tendency of related metasurfaces. We discuss the challenges and prospect on the future of imaging applications and systematic integrations with metasurfaces.

Review of the cavity-design of high-energy thin-disk laser multi-pass amplifiers
CHEN Yi, SUN Jun-jie, YU Jing-hua, YAO Zhi-huan, ZHANG Yi-wen, YU De-yang, HE Yang, ZHANG Kuo, PAN Qi-kun, CHEN Fei
2023, 16(5): 996-1009.   doi: 10.37188/CO.2023-0009
Abstract(620) FullText HTML(346) PDF 6648KB(326)

In order to clarify the cavity design methods of thin-disk multi-pass amplifiers, we summarize the different types of thin-disk multi-pass amplifiers and concludes that there are four fundamental design concepts: (1) 4f relay imaging, (2) resonant cavity design/optical Fourier transform, (3) near-collimated beam transmission, and (4) others. Each amplifier design method is described and the current status of its research is listed in as much detail as possible. By comparing the four types of disk multi-pass amplifiers, it is found that the varying methods have distinct advantages and disadvantages. 4f relay imaging requires a vacuum environment to avoid gas ionization at the focal point, making the mechanics and adjustment more difficult; the resonant cavity design/optical Fourier transform concept multi-pass amplifier has a small spot at the mirrors, making it more suitable for lower energy multi-pass amplifiers; the near collimated beam transmission method has great development potential because it does not require a vacuum environment, but accurately controlling the surface shape of the thin-disk is difficult while the laser is operating. Therefore, from the perspective of laser design, it is necessary to continue to optimize the design of the thin-disk multi-pass amplifier to realize the diversification of application scenarios and the sustainable expansion of output energy.

Research progress of miniature head-mounted single photon fluorescence microscopic imaging technique
FU Qiang, ZHANG Zhi-miao, ZHAO Shang-nan, LIU Yang, DONG Yang
2023, 16(5): 1010-1021.   doi: 10.37188/CO.2023-0007
Abstract(531) FullText HTML(199) PDF 8052KB(233)

Miniature head-mounted single-photon fluorescence microscopy is a breakthrough approach for neuroscience research that has emerged in recent years. It can image the neural activity of freely moving vivo animals in real time, providing an unprecedented way to access neural signals and rapidly enhancing the understanding of how the brain works. Driven by the needs of brain science research, there have been many types of miniature head-mounted single-photon fluorescence microscopes, such as high-resolution imaging, wireless recording, 3D imaging, two-region imaging and two-color imaging. In order to have a more comprehensive understanding of this new optical neuroimaging technology, we classify its technologies according to the imaging field of view, introduce the characteristics of different types of micro-head-mounted single-photon fluorescence microscopes reported so far, and focus on the optical system scheme and optical performance parameters used. The advantages and disadvantages of different schemes are analyzed and compared and the future direction of development is described to provide reference for the practical application of brain science researchers.

Recent progress of non-line-of-sight imaging reconstruction algorithms in typical imaging modalities
ZHAO Lu-da, DONG Xiao, XU Shi-long, HU Yi-hua, ZHANG Xin-yuan, ZHONG Yi-cheng
2023, 16(3): 479-499.   doi: 10.37188/CO.2022-0186
Abstract(1313) FullText HTML(493) PDF 11662KB(545)

Non-line-of-sight (NLoS) imaging is a promising technique developed in recent years, which can reconstruct hidden scenes by analyzing the information in the intermediate surface, and "see around the corner", and has strong application value in many fields. In this paper, we review the reconstruction algorithm for NLoS imaging tasks. Firstly, considering the crossover and non-independent phenomena existing in the NLoS imaging classification, we use the different features of physical imaging models and algorithm models to reclassify them. Secondly, according to the proposed classification criteria, we respectively review the traditional and deep learning-based NLoS imaging reconstruction algorithms, summarize the state-of-the-art algorithms, and derive the implement principle. We also compare the results of deep learning-based and traditional NLoS imaging reconstruction algorithms for reconstruction tasks. Finally, the current challenges and the future development of NLoS imaging are summarized. Different types of NLoS imaging reconstruction algorithms are comprehensively analyzed in this review, which provides important support for the further development of NLoS imaging reconstruction algorithms.

Research progress of gas detection based on laser-induced thermoelastic spectroscopy
LOU Cun-guang, DAI Jia-liang, LI Rui-kai, LIU Xiu-ling, YAO Jian-quan
2023, 16(2): 229-242.   doi: 10.37188/CO.2022-0137
Abstract(922) FullText HTML(491) PDF 7682KB(563)

Laser-Induced Thermo-Elastic Spectroscopy (LITES) is a new developed gas detection technology based on the thermoelastic effect of Quartz Tuning Forks (QTF). The QTF has the advantages of low cost, small volume, high sensitivity and wide spectral response range, and the LITES is becoming a vital method for trace gas detection. In this paper, the basic principle of gas concentration measuring based on LITES is firstly analyzed. Secondly, from the perspective of various technical methods, this paper introduces the methods for improving the sensitivity of QTF detectors, and reviews the research progress of LITES system in recent years. The performance of these systems is evaluated by the signal amplitude, Signal-to-Noise Ratio (SNR), minimum detection limit, and Normalized Noise Equivalent Absorption (NNEA) coefficient. Finally, the practical application of LITES in the field of gas detection technology is briefly reviewed, and the methods for further improving its sensitivity are summarized and prospected.

Research progress of temperature, humidity and pressure detection technology using raman lidar
LIU Dong, YAO Qing-rui, ZHANG Si-nuo, GAO Jia-xin, WANG Nan-chao, WU Jiang, LIU Chong
2023, 16(2): 243-257.   doi: 10.37188/CO.2022-0145
Abstract(1148) FullText HTML(564) PDF 4220KB(565)

Atmospheric temperature, humidity and pressure are deemed important atmospheric parameters. Quickly and accurately understanding the temperature, humidity and pressure information of the atmosphere and their changing trends is of great significance to research on meteorology, climatology, and artificial weather research. Raman lidar can obtain various atmospheric environment-related parameters by separating Raman scattering signal inversion, which can achieve high accuracy detection of atmospheric parameter profile information. Raman lidar has unique advantages and potential in atmospheric temperature, humidity and pressure detection. With an introduction to the principle and inverse analysis algorithm of Raman lidar for atmospheric temperature, humidity and pressure detection, this paper also highlights the advantages and disadvantages along with related advances of spectral devices such as filters, etalons and gratings commonly used in Raman lidar. The detection techniques involved in Raman lidar are also included. Finally, typical applications of meteorological parameter measurements by Raman lidar are shown.

Research progress on high-resolution imaging system for optical remote sensing in aerospace
SU Yun, GE Jing-jing, WANG Ye-chao, WANG Le-ran, WANG Yu, ZHENG Zi-xi, SHAO Xiao-peng
2023, 16(2): 258-282.   doi: 10.37188/CO.2022-0085
Abstract(1713) FullText HTML(693) PDF 10445KB(747)

With the continuous development of optical imaging technology and the growing demand for remote sensing applications, cross-scale high-resolution optical technology has been widely used in the field of remote sensing. In order to obtain more detailed information on the target, domestic and foreign researchers have carried out relevant research in different technical directions. In this paper, through the technical classification of remote sensing imaging, we introduce a representative aerospace optical remote sensing high-resolution imaging system. It focuses on monomer structure, block expandable imaging, optical interference synthesis aperture imaging, diffraction main mirror imaging, optical synthetic aperture and other technologies. It provides a new idea for the development of high-resolution optical remote sensing loads on the ground.

Application of laser in the medical field
GU Yong-gang, NIU Jian, YANG Jian, XU Hong-xing
2023, 16(2): 283-295.   doi: 10.37188/CO.2023-0017
Abstract(1363) FullText HTML(635) PDF 3656KB(523)

With the rapid development of laser technology, the application of laser in the medical field has gained growing attention. Due to its advantages of non-contact, high precision, low damage, portability and operational flexibility, laser treatment significantly enriches the clinical treatment toolkit. Moreover, it has substituted traditional methods for certain diseases and improved the overall medical treatment capability. Currently, laser treatment has gained increasing market share and has a great potential for even more widespread applications. Here, we introduce the laser treatment technique and the requirements of medical laser systems, expound the current status of the applications of laser treatment in clinical departments in a comprehensive manner, and give suggestions regarding to the problems in the laser treatment field in China.

Bound states in continuum in periodic optical systems
YAO Jian-quan, LI Ji-tao, ZHANG Ya-ting, LI Jie, YUE Zhen, XU Hang, YANG Fan
2023, 16(1): 1-23.   doi: 10.37188/CO.2022-0189
Abstract(3159) FullText HTML(751) PDF 7237KB(1191)

Periodic optical systems, such as photonic crystals and optical metamaterials, can localize high-density electromagnetic field energy at subwavelength scales and obtain extremely small mode volumes, so they have great application potential in the field of light manipulation. In recent years, a strong interaction between light and matter in periodic optical systems has been discovered, which is called Bound States in Continuum (BIC). Optics BICs are special electromagnetic eigenstates whose frequencies lie in the radiation continuum but are completely localized, and have shown interesting physics and rich application scenarios. This paper systematically reviews the classification and theory of BICs in periodic optical systems, and summarizes their basic physical properties and the latest application development. BICs in periodic optical systems are injecting new impetus into the fields of integrated optics, information optics, bio-optics, topological optics, and nonlinear optics.

Recent progress on synthesis and optical characterization of two-dimensional Bi2O2Se
XIE Bing, AN Xu-hong, ZHAO Wei-wei, NI Zhen-hua
2023, 16(1): 24-43.   doi: 10.37188/CO.2022-0071
Abstract(1150) FullText HTML(537) PDF 12124KB(600)

Two-dimensional (2D) Bi2O2Se has attracted broad attention in the field of electronic and optoelectronic applications in the UV-Vis-NIR region due to its unique crystal structure, energy band, high carrier mobility, and excellent stability. In this paper, we review the recent research progress in the material synthesis and optical characterization of Bi2O2Se. Firstly, the synthetic method and growth mechanism of 2D Bi2O2Se are introduced, including Chemical Vapor Deposition (CVD), wet chemical process, Molecular Beam Epitaxy (MBE) and Pulsed Laser Deposition (PLD), etc. Via steady-state spectrum study, the properties change of 2D Bi2O2Se with thickness change can be studied, such as the band gap. The defect type, temperature coefficient and thermal conductivity of 2D Bi2O2Se material can be further studied by focusing on the crystal vibration mode. Transient spectrum techniques can benefit the study of relaxation process and carriers transport properties in 2D Bi2O2Se materials. Finally, we summarize the existing challenges and application prospects for the promising Bi2O2Se field.

Panoramic endoscopic imaging technology and it’s applications
HUO Jia-yi, LI Mian-hao, WANG Zi-chuan, YUAN Bo, YANG Qing, WANG Li-qiang
2023, 16(1): 44-60.   doi: 10.37188/CO.2022-0074
Abstract(1199) FullText HTML(656) PDF 5785KB(698)

Panoramic endoscopic imaging technology can effectively reduce the observation blind area of internal organs. It has many advantages, such as shortening the operation time, reducing the risk of intraoperative bleeding, improving the prognosis and shortening the postoperative recovery time. It has important application value in minimally invasive surgery and preoperative examination. It is a research hotspot in recent years. This paper combs the panoramic endoscopic imaging technology from two aspects: principle and product applications. Firstly, various panoramic endoscopic imaging technologies based on two-dimensional and three-dimensional imaging are reviewed, their implementation methods are described, and their key indexes and performances are analyzed. Secondly, the capsule endoscope, panoramic enteroscope and other different types of products derived from panoramic endoscopic imaging technology are compared and analyzed, and the development trend and application prospect of panoramic endoscopic imaging technology are prospected.

Research progress of monolithic integration master-oscillation power-amplifiers
TAN Man-qing, YOU Dao-ming, GUO Wen-tao, LIU Wei-hua
2023, 16(1): 61-75.   doi: 10.37188/CO.2022-0022
Abstract(860) FullText HTML(409) PDF 6306KB(539)

Besides its advantages in volume, power and beam quality, a monolithic integration Master-Oscillation Power-amplifier (MOPA) can also realize a narrower linewidth and dynamic single-mode by integrating Bragg grating. Its application value is high in the fields of frequency doubling, pumping, optical communication and sensing, which makes it a popular research topic in recent years. This paper firstly went over the mainstream structure and characteristics of monolithic integrated MOPA, including a tapered amplifier, ridge amplifier, Bragg grating and three-section MOPA. Based on their working principles and performance characteristics, we introduce the main research directions and the latest development trends in combination with their problems. Aiming at the problem of beam quality degradation at high power in monolithic integrated MOPA, the optimal design of epitaxial layer structure, facet optical film and electrode aspects are then summarized for monolithic integrated MOPAs. After that, we sort out the research progress of MOPAs with different performance characteristics for various application requirements including high power, narrow linewidth, high beam quality and high brightness. Finally, we prospect the development trend of monolithic integrated MOPA.

Design, preparation and application of orthogonal excitation-emission upconversion nanomaterials
JIA Heng, FENG Xiao-rui, LI Da-guang, QIN Wei-ping, YANG Long, HE Wei-yan, MA Hui-yan, TENG Ying-yue
2023, 16(1): 76-93.   doi: 10.37188/CO.2022-0134
Abstract(1524) FullText HTML(684) PDF 6214KB(571)

Rare earth-doped upconversion luminescence nanomaterials have received considerable attention from researchers due to their great potential for applications in many fields such as information security, biomedicine, optical fiber communication, digital displays, and energy. The recently-developed upconversion luminescence nanoparticles with orthogonal excitation-emission properties have attracted especially strong research interest because their distinct luminescence outputs can be dynamically modulated by switching the excitation conditions. The orthogonal luminescence properties further endow such nanocrystals with a set of new features and functionalities, which largely expands their potential applications. This review summarizes the progress in the development of orthogonal upconversion luminescence of rare earth ions, and provides a systematic discussion on design principles and construction strategies of orthogonal excitation-emission systems based on core-shell structures, as well as introduces their recent advances in various fields of applications including data storage, security anti-counterfeiting, digital displays, sensing, bioimaging and therapy. Furthermore, the prospective opportunities and challenges in the future research of orthogonal luminescence systems are also provided.

Resolution, super-resolution and spatial bandwidth product expansion——some thoughts from the perspective of computational optical imaging
ZUO Chao, CHEN Qian
2022, 15(6): 1105-1166.   doi: 10.37188/CO.2022-0105
Abstract(3610) FullText HTML(892) PDF 19381KB(1775)

Conventional optical imaging is essentially a process of recording and reproducing the intensity signal of a scene in the spatial dimension with direct uniform sampling. In this process, the resolution and information content of imaging are inevitably constrained by several physical limitations such as optical diffraction limit, detector sampling, and spatial bandwidth product of the imaging system. How to break these physical limitations and obtain higher resolution and broader image field of view has been an eternal topic in this field. In this paper, we introduce the basic theories and technologies associated with the resolution, super-resolution, and spatial bandwidth product expansion, as well as some examples in the field of computational optical imaging. By placing these specific cases into the higher dimensional framework of "computational optical imaging", this paper reveals that most of them can be understood as a "spatial bandwidth regulation" scheme, i.e., a process of exploiting the available degrees of freedom of the imaging system to optimally encode, decode, and transmit information within the constraints of the limited spatial bandwidth of the imaging system, or figuratively speaking - "dancing with shackles". This is essentially a legal trade-off and choice between "gain" and "loss" under physical constraints. The conclusions of this paper are expected to provide valuable insights into the design and exploration of new imaging mechanisms and methods for various complex practical imaging applications.

Supervisor: Chinese Academy of Sciences

Sponsors: the Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP), CAS

Editor-in-Chief: Wang Jiaqi, Academician

ISSN 2097-1842

CN 22-1431/O4



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