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A non-null interferometryfor concave aspheric surface
ZHANG Xu, LI Shi-jie, LIU Bing-cai, TIAN Ai-ling, LIANG Hai-feng, CAI Chang-long
 doi: 10.37188/CO.2023-0042
Abstract(48) FullText HTML(21) PDF 7432KB(38)

In order to realize the rapid, high-precision, and universal testing of concave aspheres, a non-null interferometry is proposed in this paper, which takes the asphere as a sphere and measures it directly with an interferometer. Combined with the corresponding data processing methods, the test results of the aspheric are obtained. Firstly, the detection theory of this method is introduced, the calculation and removal models of retrace error and adjustment error are established, and the data processing method of shape error is studied. Secondly, taking two concave aspherical surfaces with different parameters as an example, the retrace error and adjustment error are simulated, which verified the effectiveness of the method. Finally, a non-null interferometric experimental setup of concave aspheric surface is performed, and its shape error is successfully obtained. By comparing the results with autocollimation method and LUPHOScan method, it is found that the surface distribution and evaluation indicators of the results are highly consistent, which verifies the correctness of this method. This method provides an effective measurement method for concave aspheric surface with high precision, universality, and convenience.

Detector temperature control system for ultraviolet spectrometer
JIANG Xue, HOU Han, MA Qing-jun, LIN Guan-yu
 doi: 10.37188/CO.2023-0133
Abstract(27) FullText HTML(12) PDF 2627KB(9)

A temperature control system that employs an incremental PID algorithm based on FPGA technology has been developed to decrease detector noise and dark current while ensure the CMOS detector of the spectrometer obtain more accorate spectrum curve. Considering the current temperature and the control parameters, the appropriate control quantity is calculated to ensure the detector realize the target temperature. Controlling the temperature change rate of the detector is realized through front stage control, effectively solving the problem of overshooting. By adding the anti-integral saturation algorithm and the transition link of the target value, the function of the temperature change rate of the detector is controllable, and the problem of overshoot is solved. Multiple environmental tests conducted on the entire machine indicate that the system can control the temperature of the detector to reach any desired temperature within a specified temperature difference range of 40 °C at room temperature. The sensor temperature has a margin of error of ±0.1 °C. Compared to the conventional analog PID control method, the proposed method offers significant advantages of high sensitivity and strong stability. At a temperature of −10 °C, the noise of the detector is substantially reduced.

Non-uniform illumination correction algorithm for cytoendoscopy images based on illumination model
ZOU Hong-bo, ZHANG Biao, WANG Zi-chuan, CHEN Ke, WANG Li-qiang, YUAN Bo
 doi: 10.37188/CO.2023-0059
Abstract(63) FullText HTML(19) PDF 5292KB(38)

Cytoendoscopy requires continuous amplification with a maximum magnification rate of about 500 times. Due to optical fiber illumination and stray light, the image has non-uniform illumination that changes with the magnification rate, which affects the observation and judgement of lesions by doctors. Therefore, we propose an image non-uniform illumination correction algorithm based on the illumination model of cytoendoscopy. According to the principle that image information is composed of illumination and reflection components, the algorithm obtains the illumination component of the image through a convolutional neural network, and realizes non-uniform illumination correction based on the two-dimensional Gamma function. Experiments show that the average gradient of the illumination channel and the discrete entropy of the image are 0.22 and 7.89, respectively, after the non-uniform illumination correction by the proposed method, which is superior to the traditional methods such as adaptive histogram equalization, homophobic filtering, single-scale Retinex and the WSI-FCN algorithm based on deep learning.

Design of all-optical logic gate based on two-dimensional photonic crystal
WU Rong, ZHANG Hao-chen, YANG Jian-ye
 doi: 10.37188/CO.EN-2023-0014
Abstract(24) FullText HTML(10) PDF 4869KB(22)

In this paper, an XNOR gate and NAND gate structure, utilizing a two-dimensional photonic crystal with a line defect and linear interference effect alongside waveguide coupling, has been designed. The band structure of the photonic crystal has been analyzed using the plane wave expansion method. The finite-difference time-domain method and the linear interference effect are used to simulate the stable electric field diagram and the normalized power of the XNOR gate and NAND gates on the Rsoft platform. The simulation results demonstrate that the XNOR gate that was designed possessed a contrast of 29.5 dB, a response time of 0.073 ps, and a data transmission rate of 13.7 Tbit/s. On the other hand, the designed NAND gate has a contrast of up to 24.15 dB, a response time of 0.08 ps, and a data transmission rate of 12.5 Tbit/s. With these parameters, the designed structure showcases a high contrast, short response time, and fast data transmission rate.

Stimulated brillouin scattering in double-clad thulium-doped fiber amplifier
LIU Qing-min, SUN Hui-jie, HOU Shang-lin, LEI Jing-li, WU Gang, YAN Zu-yong
 doi: 10.37188/CO.EN-2023-0011
Abstract(20) FullText HTML(9) PDF 5323KB(21)

A theoretical analysis was conducted on the effect of stimulated Brillouin scattering on the laser output performance in a 2 µm thulium-doped fiber amplifier. The study examined the optical mode distribution, effective refractive index, effective mode field area, and normalized frequency of the double-clad thulium-doped fiber at 793 nm pump wavelength and 1.9−2.1 µm laser waveband. The stimulated Brillouin scattering characteristics, including the Brillouin frequency shift and the Brillouin gain spectrum, in the double-clad thulium-doped fiber were numerically simulated in the laser waveband of 1.9−2.1 µm. The influence of stimulated Brillouin scattering on the laser output performance of thulium-doped fiber amplifiers was investigated using the theoretical model of stimulated Brillouin scattering in gain fibers. In the DTDF-10/130 double-clad thulium-doped fiber, a 100W continuous wave with a wavelength of 793 nm is used as a pump to amplify a continuous signal wave that has a wavelength of 2 µm and carries a power of 0.01 W. The maximum output powers of the signal wave are 25.27 W, 31.08 W and 34.06 W for pump power filling factors are 0.01, 0.02 and 0.03, respectively. The corresponding optimal lengths for the double-clad fiber lengths are 2.66 m, 2.02 m and 1.75 m. Additionally, the stimulated Brillouin scattering generates a Stokes optical power of 1.68 W, 1.39 W and 1.14 W, respectively. It is evident from the results that the double-clad fiber with large pump power filling factor in the thulium-doped fiber amplifier can effectively reduce the fiber length, thus to minimizing the influence of stimulated Brillouin scattering on the output power of the signal laser. The numerical model can optimize the fiber length of the fiber amplifier, which is of great significance to improve experimental efficiency and reduce experimental costs.

All-solid-state acousto-optic mode-locked laser operating at 660 nm
WANG Yu-ning, ZHENG Quan, SU Xin, BAI Zhong-shu, ZHANG Xiu-qi, LIU Chao-zhi, LIU Wei
 doi: 10.37188/CO.EN-2023-0013
Abstract(50) FullText HTML(25) PDF 5512KB(47)

Red lasers with a picosecond pulse width are widely used in various fields such as industrial, medical, scientific research and information industries due to their narrow pulse width and high peak power. This paper presents an all-solid-state laser, operating at 660 nm with picosecond pulse width, narrow band, and high conversion efficiency, which is demonstrated by the Acousto-Optic Mode-Locked (AOML) method. By carefully optimizing the cavity and implementing external frequency doubling with two LiB3O5 (LBO) crystals along with various techniques, we have successfully developed a mode-locked red laser source with a maximum output power of 8.6 W. The laser operates in a pulsed side-pumped regime and consists of a number of mode-locked pulses with a frequency of 100 MHz and a pulse width of 887 ps. The optical-to-optical conversion efficiency from 1319 nm to 660 nm can reach up to 41%.

Design and experiment of high resolution detection imaging system for ultra-thin and ultra-short object-image distance
LI Yan-wei, WU Yan-xiong, CHEN Tai-xi, WEI Hao-dong, XIE Xin-wang, DONG Lei-gang, LI Jun-chi, LI Jian-jie
 doi: 10.37188/CO.2023-0099
Abstract(35) FullText HTML(16) PDF 11857KB(32)

In order to shorten the axial and radial dimensions of the 12-inch wafer detection imaging system, a solution combining the small Angle prism refraction path and the ultra-short object-image distance lens is proposed. A small Angle prism with better shape accuracy than 1/12λ (λ=632.8 nm) is designed to convert the optical path and realize the horizontal arrangement between the lighting system and the imaging lens. The radial size is only 80 mm, which greatly reduces the radial size of the whole system without affecting the imaging quality. At the same time, a small angle of 12° bright field lighting is realized. A symmetrical hybrid optical system with magnification of 0.264 is designed. A pure spherical system is used to obtain a large imaging field of view. The image height is 81.92 mm, and the object image distance is only 392.5 mm, which greatly reduces the axial size of the whole system. The design results show that the average optical transfer function of the whole imaging system is better than 0.4@100l p/mm, the relative distortion is better than 0.03%, and the uniformity of the image surface illuminance is better than 50%. The actual test results show that the actual imaging resolution is better than 18.88 μm, which reaches the ultimate resolution of the system. The uniformity of illumination of image surface is 43.3%, which meets the development requirement of uniformity better than 40%. The research results show that the ultra-thin and ultra-short object-image distance imaging system is reasonable and effective, which solves the problem of space size compression of the 12-inch wafer detection imaging system and reduces the development cost. It provides a reference for the development of the imaging system for detecting large objects in short distance.

All-optical logic gate based on nonlinear effects of two-dimensional photonic crystals
Rong Wu, 建业 杨, Hao-chen Zhang
 doi: 10.37188/CO.EN.2023-0021
Abstract(5) PDF 1548KB(0)
Analysis of key technologies and 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
 doi: 10.37188/CO.2023-0074
Abstract(38) FullText HTML(9) PDF 7981KB(35)

Narrow linewidth fiber lasers, which are based on an oscillator seed source with multiple longitudinal-mode, offer substantial advantages for engineering applications and space-limited platform payloads. 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. These effects limit the further improvement in output power and affect the purity of laser spectra. This paper introduces four commonly used narrow linewidth seeds. The mechanism and suppression methods of the self-pulse effect in multi-longitudinal mode oscillator seeds were 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.

Research progress on the related physical mechanism of laser-induced breakdown spectroscopy
LIU Rui-bin, YIN Yun-song
 doi: 10.37188/CO.2023-0019
Abstract(64) FullText HTML(7) PDF 1501KB(33)

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.

Optical Design and Spectral Optimization of Philips Prism 3CMOS Camera
CHEN Su-hao, LÜ Bo, LIU Wei-qi
 doi: 10.37188/CO.2023-0155
Abstract(15) FullText HTML(3) PDF 5024KB(6)

In response to the demand for high imaging quality and high chromaticity in color digital cameras, this paper investigates the optical system design and camera spectral optimization methods of 3CMOS cameras based on Philips prisms. By modeling the optical path of the Philips prism, the structural parameters of the prism were optimized, reducing the volume of the system 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 optical system designed in this article has good imaging quality, and the optimized camera spectrum achieves good color performance and uniformity.

Design of a Highly Sensitive Photoelectric Detection Circuit for TDLAS Gas Laser Telemetry
PEI Zi-yi, HU Peng-bing, PAN Sun-qiang, QI Hai-yang, LIU Su-mei, LIU Dong
 doi: 10.37188/CO.2023-0107
Abstract(12) FullText HTML(2) PDF 2327KB(5)

To address weak gas laser telemetry optical signals and strong interference from environmental factors, a Highly Sensitive Photoelectric Detection Circuit (HSPDC) for TDLAS laser telemetry has been designed and investigated using wavelength modulation technology. In addition, Furthermore, a noise suppression method for TDLAS signals based on this technology was determined. The photodiode ideal model is utilized to analyze the linear response characteristics of the photodetector circuit and determine the essential photodiode parameters. Based on the cascade amplification principle, the HSPDC is designed, simulated, and tested, achieving a lower limit of optical power detection of 0.11 nW, a signal attenuation of 0.79 dB (f=10 kHz). The cutoff frequency is one order of magnitude higher than the existing 108 V/A cross-impedance amplification circuit. Therefore, HSPDC is applicable for high-speed modulation of weak optical signals. The laser telemetry system exhibits excellent detection performance at a modulation frequency of 3 kHz, with a detection sensitivity of 88.66 mV/ppm, a detection limit of less than 0.565 ppm, and a linear fit R2 of 0.9996. The study demonstrates that the HSPDC photoelectric detection circuit offers the advantages of fast response, high detection sensitivity and accuracy, rendering it ideal for gas laser telemetry applications.

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(17) FullText HTML(8) PDF 7480KB(6)

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 all-weather continuous measurement, wide-band and hyperspectral detection, 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 was used to optimize the optical structure, and the optimization results showed that the spectrometer operated in the range of 250-952 nm wavelengths, of which the UV-visible channel operated in the wavelength range of 250-675 nm, the spectral resolution was better than 1 nm, the MTFs were 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 were 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, and this hyperspectral imaging spectrometer system can realize occultation detection of trace gases . It can be seen that the hyperspectral imaging spectrometer system can realize the occultation detection of trace gases.

A red-emitting copolymer phosphors based on bimetallic Eu-Ir complex for Near-UV chip-based LEDs
Zihao Wang, Yamin Yang, 爱琴 张, 并社 许, Jing Jia
 doi: 10.37188/CO.EN.2023-0023
Abstract(15) PDF 1395KB(2)
In this work, a new Eu-Ir bimetallic complex Eu(FIrPic)2(Phen)UA is synthesized using the iridium complex FIrPic as ligands for europium 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 could be effectively sensitized by the addition of Ir-complex with the enhancement of ultra-violet light absorption at around 400 nm, without affecting the characteristic fluorescence emission 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, besides 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 ℃.
Design of large aperture terahertz wave imaging optical system
CAO Yi-qing, SHEN Zhi-juan
 doi: 10.37188/CO.2023-0175
Abstract(20) FullText HTML(5) PDF 2929KB(2)

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(18) FullText HTML(8) PDF 4772KB(7)

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 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
 doi: 10.37188/CO.2023-0124
Abstract(17) FullText HTML(10) PDF 7318KB(3)

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, Convolutional Neural Networks (CNN) extract the feature vectors of the whole image, and the Gate Recurrent Unit (GRU) fuses the features extracted in the focus process to predict the global defocusing distance, which serves as coarse focusing. In the local autofocus stage, the system exacted the feature vector of the wear particle and employs the GRU to fuse the current features with those extracted in the previous focusing process. The resulting fused data predicts the current defocusing distance 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.

Design and fabrication of liquid crystal wavefront corrector based on mask lithography
DU Ying, CHEN MeiRui, LIU YuTong, CAO ZongXin, MAO HongMin, LI XiaoPing, SUN HuiJuan, CAO ZhaoLiang
 doi: 10.37188/CO.2023-0137
Abstract(16) FullText HTML(11) PDF 7526KB(3)

Liquid crystal wavefront correctors (LCWFCs) have the high development cost and customization difficulty as they are usually fabricated based on the process technology of liquid crystal displays. In the paper, to achieve specialized and low-cost development of LCWFCs, it is fabricated with the mask lithography method. Firstly, a 91 pixels passive liquid crystal driving electrode was designed and prepared based on mask lithography technology and then, packaged as a liquid crystal optical correction unit. Then, a driver connection circuit board was designed and prepared to connect the optical correction unit and the driving circuit board. Next, the response characteristics of the LCWFC were tested, and the results show that the phase modulation is 5.5λ, and the response time is 224 ms. Finally, the spherical waves are generated 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.

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(25) FullText HTML(16) PDF 4847KB(4)

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.

An XY defocus aberration correction method for high-energy lasers
FENG Ya-fei, WEI Cheng-fu, REN Xiao-ming, GUO Jian-zeng, WANG Jie
 doi: 10.37188/CO.2023-0142
Abstract(17) FullText HTML(3) PDF 4520KB(5)

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, this study utilizes the Hartmann wavefront sensor 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 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.

A point cloud classification downsampling and registration method for artifacts 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(18) FullText HTML(7) PDF 4831KB(4)

3D reconstruction is crucial for digitizing artifacts, and the accuracy of 3D point cloud registration is a significant metric for evaluating the reconstruction quality. In practice, artifact point cloud data includes numerous details, and using conventional downsampling methods may result in the loss of such details, thereby affecting registration accuracy. This paper proposes a method for downsampling and registering artifacts point clouds based on curvature features. First, 3D point clouds data of artifacts 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. We downsample different point sets based on their feature attributes, with varying weights assigned to retain the shape features and details of the point cloud as much as possible. Finally, point cloud registration is achieved through the use of a rigid transformation model. Compared to the traditional global downsampling ICP method, the downsampling processing before point cloud registration reduces the point cloud data 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 artifacts point cloud data.

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
 doi: 10.37188/CO.2023-0108
Abstract(24) FullText HTML(14) PDF 4333KB(8)

To address the issue of non-linear distortion in the Phase Generated Carrier (PGC) demodulation algorithm, we have developed an extrinsic Fabry-Perot Interferometer (EFPI) sensor demodulation system that is based on an improved PGC-Atan algorithm. The theoretical analysis focuses on the nonlinear factors affecting 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 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.

Omnidirectional spatial monocular vision indoor localization measurement based on a two-degree-of-freedom rotary table
WU Jun, WANG Hao-shuang, SHAN Teng-fei, GUO Run-xia, ZHANG Xiao-yu, CHEN Jiu-sheng
 doi: 10.37188/CO.2023-0106
Abstract(17) FullText HTML(12) PDF 3649KB(3)

To address the problem of limited field of view measurement in traditional monocular vision measurement systems, this paper proposes an omnidirectional spatial monocular vision measurement method based on a two-degree-of-freedom rotary table. First, calibrate the rotating axis parameters of the double-degree-of-freedom rotary table. Then, take pictures of the checkerboard calibration plate fixed with the two-degree-of-freedom rotary table using an auxiliary camera. Extract the position coordinates of the checkerboard corner points and convert them to the same camera coordinate system. The direction vector of the initial position axis parameter was obtained through PCA (principal component analysis) plane fitting, and the position parameter in the rotation axis parameter in the initial position was determined using the method of spatial least squares circle fitting. The camera data acquired at various angles is transformed into coordinate system one using the rotary table rotation angle and the Rodrigues formula. This enables measurement of the target in the horizontal and vertical omnidirectional space. Finally, verification of the measurement accuracy of the proposed method was conducted using a high-precision laser rangefinder. Additionally, experiments comparing the omnidirectional spatial measurement ability of the method with the binocular vision measurement system and wMPS measurement system were 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.

Three-dimensional surface shape reconstruction of fiber bragg gratings in a ring arrangement
WANG Yan, XU Haoyu, WANG Jun-liang, ZHU Wei, JIANG Chao
 doi: 10.37188/CO.2023-0088
Abstract(13) FullText HTML(11) PDF 6516KB(2)

To improve the accuracy of palm surface reconstruction in flexible robot grasp sensing, this study conducts 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. The plate experienced a minimum relative error of 0.549% in end displacement, with a maximum relative error of 8.300%. the center of the surface’s end yielded a 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, a minimum relative error of 2.546%, and a maximum relative error of 14.289% arise in plate reconstruction end displacement. 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.

Design of a single sensor based three-band co-aperture optical system
ZHANG Kun, LI Jing-chen, SUN Si, CHEN Qing-rong, YANG Fan
 doi: 10.37188/CO.2023-0098
Abstract(12) FullText HTML(4) PDF 3288KB(4)

The existing multi-band imaging system poses issues of large volume, high power consumption, and difficulty in integrating design. To address these challenges, we proposed a solution in the form of a design methodology for a single sensor based three-band co-aperture imaging optical system. 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 to 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. In addition, we suggest utilizing a dual electric diaphragm to control the switching speed of the three imaging channels. Finally, a single sensor based three-band co-aperture optical system 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 photoacoustic tomography image reconstruction method based on forward imaging model
CHENG Li-jun, SUN Zheng, SUN Mei-chen, HOU Ying-sa
 doi: 10.37188/CO.2023-0114
Abstract(25) FullText HTML(14) PDF 9835KB(3)

The aim of this study is to address the issue of degraded image quality in photoacoustic tomography (PAT) caused by the inhomogeneous light fluence, complex optical and acoustic properties of biological tissues, and non-ideal properties of ultrasonic detectors. This paper proposes a model-based method for reconstructing PAT images. A comprehensive forward imaging model is proposed to describe the physical process of imaging in non-ideal scenarios. The model takes into account variables such as the heterogeneity of 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 SoS distributions are reconstructed simultaneously. The study outcomes indicate that utilizing this method for image reconstruction enhances the structural similarity of the reconstructed images 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.

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
 doi: 10.37188/CO.2023-0101
Abstract(20) FullText HTML(7) PDF 5114KB(4)

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. LPFGs with varying periods were fabricated using a 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 peak resonance LPFG at a period of 115.4 μm, thanks to the dual peak 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.

HongWei Huang, Ke Cheng, YANG Ceng-hao, YAO Na
 doi: 10.37188/CO.EN.2023-0018
Abstract(15) PDF 1153KB(1)
By transferring one-dimensional swallowtail catastrophe to optical field, the evolution dynamics of the swallowtail-Gaussian (SG) beams in fractional Schrödinger equation (FSE) with different potentials, where include the linear, parabolic and Gaussian potential and non-potential cases, are investigated by using the split-step Fourier method.
Optical simulation design of SMD beads for wide beam and high uniformity display
WEI Wei, CHEN Zhi-zhong, KUO Hao-chung, JIA Chuan-yu, FANG Fang, ZOU Jun, FANG Qian, WU You, SUN Ming-hao, LI Qian, KUANG Yu-han, YIN Qi-kai, ZHANG Guo-yi
 doi: 10.37188/CO.EN-2023-0017
Abstract(27) FullText HTML(53) PDF 2829KB(9)

This study analyses the optical requirements of wide beam and high uniformity light beads, which are currently used in displays. Packaging micro light-emitting diode (LED) chips with a novel non-Lambertian distribution has facilitated the production of micro-LED chip light beads that are wide in beam and high in uniformity. The light output efficiency and beam angle of fixed beads were simulated using brackets made of copper, titanium, aluminium and silver, as well as materials that were completely reflecting and absorbing. The simulations were conducted at various fixture angles, packaging heights, sapphire thicknesses, and patterned sapphire substrate sizes. By adjusting the chip and packaging parameters, we can obtain one, two, or three light beams with SMD lamp beads characteristics that provide wide angles, high uniformity, and far-field light distribution. These characteristics can meet the current display requirements for LED and LCD.

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(43) FullText HTML(18) PDF 361KB(22)

In order to improve the visible light band (0.3 μm~0.9 μm) A simplified method for high-temperature calibration in the visible light band has been proposed to improve the efficiency of high-temperature calibration. First of all, a high-temperature calibration model of visible light band with exposure time variable is proposed. Through a large number of experimental data, it is found that the gray value of each channel of RGB camera not only changes linearly with the increase of exposure time, but also changes linearly with the increase of Black-body radiation brightness. Then, the specific form of high-temperature calibration model of visible light band is determined. Then, in order to solve the unknowns in the simplified high-temperature calibration model of visible light band, image data under two exposure times are collected under two Black-body radiation brightness, and then the image data is processed to obtain the high-temperature calibration curve of RGB camera under any exposure time. Finally, a comparison is made between the simplified visible light band high-temperature calibration method proposed in this article and 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 and the calibrated value is 3.38%, the maximum relative error between the calculated value of the G channel and the calibrated value is 2.56%, and the maximum relative error between the calculated value of the B channel and the calibrated value is −1.14%. Moreover, the relative error between the calculated value of each channel and the calibrated value does not exceed 3.50%. The mathematical model proposed in this article can effectively simplify the traditional high-temperature calibration method, thereby greatly shortening the high-temperature calibration time and improving the calibration efficiency of high-temperature calibration.

Propagation properties of one-dimensional vortex array beams in a marine atmosphere
HOU Zheng-cheng, ZHANG Ming-ming, BAI Sheng-chuang, LI Shu-zhen, LIU Jun, HU You-you
 doi: 10.37188/CO.2023-0094
Abstract(42) FullText HTML(24) PDF 4944KB(30)

Compared with a single vortex beam, vortex array beams can expand the transmission capacity of information, and the study of their propagation properties is of great significance for their optical communication applications. In this paper, we select the helical Ince-Gaussian (HIGn,n) modes of order n and use the power spectrum of the refractive index fluctuations in the marine atmosphere to simulate the turbulence of the marine atmosphere. The changes of 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) when either the turbulence intensity or atmospheric turbulence inner scale is increased, both the scintillation index and spot centroid wander standard deviation of HIGn,n modes are enhanced; (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 with 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 have also comparatively studied the propagation performance of the linear array vortex beams (LAVBs) and HIG beams, and found that even though LAVBs have better propagation performance than HIG beams, the unique structures of HIG beams can be applied to different application scenarios. Finally, the effects of ellipticity parameter and elliptic ring number on the propagation of the HIG modes are explored and analyzed. The results show that increasing the ellipticity parameter or elliptic ring number is beneficial to improving the anti-turbulence ability of the HIG modes. The research results obtained in this paper are of guiding significance for the offshore application of vortex beams.

Scanning measurement method of small size parts without marks
MO Cai-li, WANG Li-zhong, ZHAO Jian-bo, WANG Sen, ZHOU Hao-jun, REN Mao-dong
 doi: 10.37188/CO.2023-0103
Abstract(33) FullText HTML(19) PDF 9253KB(27)

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. First, the camera calibration method based on photogrammetry is used to reconstruct the high precision 3D coordinates of the target on the calibration board. By tracking the position of the encoded 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. Second, 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.

Design of cooled lwir large ratio zoom optical system
TANG Han, XIA Li-kun, LIU Lian, LIU Yun, LIU Xuan, LIU Yu, ZHANG Run-qi, ZHOU Chun-fen, YANG Kai-yu
 doi: 10.37188/CO.2023-0052
Abstract(33) FullText HTML(13) PDF 6135KB(18)

With the improvement of the spatial resolution and area array specifications of the cooled LWIR focal plane detector, the application range of the cooled LWIR thermal imager is becoming wider and wider, and the corresponding optical system needs to be improved to meet the needs of different fields. Compared with the MWIR optical zoom system, the LWIR optical zoom system has fewer available materials and is difficult to athermalize in high and low temperature environments. In this paper, the multi-field optical zoom system is realized by using mechanical compensation zoom technology, and the active compensation athermalization technology is used to make the system image clear from −40 °C to +65 °C, to realize the design of the four-field LWIR optical system with four lenses. The focal lengths of the four fields of view are 25 mm, 109 mm, 275 mm and 400mm, the zoom ratio is 15, the envelope of the optical system is 280 mm(L)×200 mm(W), and the total weight of the optical components is 618 g. The optical system has SWaP-C characteristics such as light weight, high performance, and low cost, and will be widely used in security fields such as auxiliary navigation, search, and tracking.

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
 doi: 10.37188/CO.2023-0100
Abstract(45) FullText HTML(15) PDF 4306KB(23)

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. In this paper, based on 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, 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, 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.

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(26) FullText HTML(17) PDF 2106KB(21)

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.

NIR-II fluorescence confocal imaging based on indirect wavefront shaping
TAN Tian, SHI Tian-yue, WU Chang-feng, PENG Hong-shang
 doi: 10.37188/CO.2023-0070
Abstract(32) FullText HTML(12) PDF 4814KB(27)

Optical aberrations caused by the scattering of biological tissues limit the imaging performance of optical systems. We have explored a fluorescence confocal imaging technique that utilizes wavefront shaping indirectly, operating in the near-infrared II range. First, we synthesized a highly efficient fluorescent probe in the near-infrared II range, where reducing the scattering of biological tissue can enable high-contrast biopsy imaging. Second, the study investigate the adaptive optical method, utilizing indirect wavefront measurement. The indirect wavefront shaping technology was applied to the laser scanning confocal system, enabling the measurement and compensation of optical aberrations caused by biological tissues, and obtaining imaging of biological tissues with a high signal-to-noise ratio. Finally, an indirect wavefront shaping-based near-infrared II fluorescence confocal imaging system was deployed and relavant experiments were conducted. The experimental outcomes reveal that the system effectively compensates for the aberrations induced by air plates, scattering media and mouse skull, and increases the final signal intensity to 1.47, 1.95 and 2.85 times, respectively. As a result, the final imaging quality is significantly enhanced.

Effect of atmospheric turbulence on imaging quality of high-resolution remote sensing satellites
MAO Hong-min, DING Zhi-ya, YANG Yan-yan, JIANG Su-qi, PENG Jian-tao, CAO Nan, HU Li-fa, CAO Zhao-liang
 doi: 10.37188/CO.2023-0083
Abstract(35) FullText HTML(23) PDF 4763KB(32)

Remote sensing satellites play an crucial role in both national defense and civil exploration. However, the imaging quality of high-resolution remote sensing satellites is significantly affected by atmospheric turbulence. This paper focuses on the impact of camera aperture, satellite orbit altitude and atmospheric turbulence intensity on the imaging quality of space cameras during remote sensing satellite Earth detection. Firstly, the turbulence wavefront simulation method based on the spherical wave model and Kolmogorov turbulence theory is analyzed. Subsequently, the disturbed wavefront, impacted by the camera aperture, satellite orbit height and atmospheric turbulence intensity, is analyzed, and a universal formula is derived. In addition, an equation for imaging resolution, taking into account aperture, satellite orbit height and atmospheric coherence length, is developed. Finally, this study examines the effect of atmospheric turbulence on the modulation transfer function (MTF). The analysis focuses on the relative error of MTF concerning camera aperture, satellite orbit height and atmospheric coherence length, with reference to an MTF value of 0.15. This study provides a theoretical basis for designing, analyzing, and assessing high-resolution remote sensing satellites.

On-machine verification technology and application progress of high dynamic range fringe structured light
LIU Ze-long, LI Mao-yue, LU Xin-yuan, ZHANG Ming-lei
 doi: 10.37188/CO.2023-0068
Abstract(63) FullText HTML(13) PDF 7626KB(53)

With the development of industrial manufacturing towards intelligence, precision and integration, on-machine verification of the machining process can provide timely feedback on measurement results, compensate and correct processing parameters, thereby aiding in enhancing machining accuracy and efficiency. Fringe structured light technology is a non-contact measurement method, which has developed rapidly in recent years. It has the characteristics of simple measurement principle, low costs, high measurement accuracy and easy integration, which provides a new solution for on-machine verification. However, the accuracy of structural for on-machine verification 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 structural light detection enables the measurement of metal parts in complex scenes and reduces the effect of high reflectivity. This paper introduces the measurement principle of structured light and summarizes the challenges of on-machine verification for HDR structured light. Subsequently, this paper provides a comprehensive review of HDR structured light technology. Based on the context of on-machine verification, the HDR technology using hardware equipment and the stripe algorithm are discussed and analyzed, respectively. Following this, different technologies are summarized according to the requirements of on-machine verification. The advantages and disadvantages of various methods are presented, and the applicability of on-machine verification 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.

Mixed lighting based on the linear dimming of three-primary-color LEDs
HUANG Tao, XIA Zhen-ping, PENG Zi-xiong, LIU Yu-jie, LI Chao-chao, GU Min-ming
 doi: 10.37188/CO.2023-0084
Abstract(39) FullText HTML(10) PDF 3810KB(27)

In order to provide high-quality, intelligent, and healthy lighting sources, a linear dimming hybrid lighting system is constructed using three-primary-color LED light sources. An optimization method for dimming and color mixing is proposed. The light chromaticity and light intensity of the mixed light source are set by color temperature and brightness level, which makes the mixed lighting effect more in line with the demand of "human-centric lighting". In the intelligent optimization of the system, the color temperature is converted into CIE \begin{document}$ {u}'{v}' $\end{document} chromaticity coordinates, and the luminance is converted into brightness to make the optimization calculations more accurate. The system adopts the linear dimming method, effectively preventing the health and safety risks caused by light source flicker, and effectively solves the problem of large linear dimming chromaticity drift with an optimization algorithm. Experiments demonstate that the chromatic stability of the mixed light in the hybrid lighting system is maintained within the first step of the CIE \begin{document}${u}'{v}' $\end{document} chromaticity diagram between a color temperature range of 2000 K to 8000 K. Moreover, the system exhibits imperceptible color deviation over the entire range of light intensity adjustments at the corresponding color temperature. This finding also indicate that linear dimming hold a superior edge over pulse-width dimming method in keeping the optical chromaticity stable. Theoretical exploration and experimental results demonstrate that the mixed lighting system is straightforword and practical, with significant practical value.

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(34) FullText HTML(6) PDF 6667KB(27)

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.

Structured light depth and phase estimation with light self-limited attention for a hybrid network
ZHU Xin-jun, ZHAO Hao-miao, WANG Hong-yi, SONG Li-mei, SUN Rui-qun
 doi: 10.37188/CO.2023-0066
Abstract(58) FullText HTML(13) PDF 5480KB(38)

Phase retrieval and depth estimation are vital to three-dimensional measurement using structured light. Currently, conventional methods used for structured light analysis have limited efficiency and produce unreliable results. To enhance the reconstruction effect of structured light, this paper proposes a hybrid network for structured light phase and depth estimation based on Light Self-Limited Attention (LSLA). Specifically, a CNN-Transformer hybrid module is constructed and integrated into a U-shaped structure to harness the complementary benefits of CNN and Transformer. The network is assessed comparatively with other networks in tasks related to structured light phase estimation and depth estimation. The outcome of the experimental indicates that the suggested network achieves finer detail processing in phase and depth estimation compared to other networks. Specifically, in structured light phase anddepth estimation, its accuracy improves by 31% and 26%, respectively. Therefore, the proposed network improves the accuracy of deep neural networks in the aforementioned areas.

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
 doi: 10.37188/CO.2023-0082
Abstract(35) FullText HTML(15) PDF 6453KB(28)

The high mismatch 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, this paper proposes a stereo matching algorithm that utilize 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 error. 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 the average error matching rate of the proposed algorithm is 4.18%, 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%, all using the test of the Middlebury dataset. The experimental results verify the effectiveness of the proposed algorithm.

Multi-channel laser beam combining and closed-loop correction technology in visible light band
XU Xin-hang, LI Gao-sheng, HAN Xu-dong
 doi: 10.37188/CO.2023-0077
Abstract(31) FullText HTML(14) PDF 4003KB(30)

To achieve periodic closed-loop correction of multiple visible wavelength lasers, a laser beam combining system is being 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 enables 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 was built using tow laser beams of different wavelengths. The periodic closed-loop beam combining system was 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 ±7μrad, 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.

Modeling and correction of measurement errors based on depth cameras
WEI Rui-li, WANG Ming-jun, ZHOU Yi-ming, YI Fang
 doi: 10.37188/CO.2023-0047
Abstract(34) PDF 0KB(0)

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. Based on the oscillation error and the fact that each signal can be expressed in the form of a Fourier series, 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 4mm, and the error caused by relative motion is less than 0.7mm. 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.

CCD/EMCCD Photoelectronic Parameter Test System: design and use
吉 沈, Viacheslav V. Zabudsky, Wei-jing Chang, Qi-yue Na, Yun-fei Jian, Oleg V. Rikhalsky, Oleksandr G. Golenkov, Volodymyr P. Reva
 doi: 10.37188/CO.EN.2023-0016
Abstract(66) PDF 621KB(12)
This article describes design and using of the developed equipment that intended for measuring of CCD and EMCCD (electron multiplying charge-coupled device) chips photoelectrical parameters. Test system provides measurements of dark currents, responsivity of output amplifier, efficiency of charge transfer, charge capacity and other parameters testing in automatic and manual mode. The system can be configured for measurements of different format and architecture CCD/EMCCD both on wafer and in package. The developed equipment was used for 576 × 288, 640 × 512, 768 × 576, 1024 × 1024, 1280 × 1024 CCD and EMCCD chip testing and sorting.
A denoising method combining bitonic filtering and sine-cosine transform for shearography fringe pattern
WU Rong, LU Yang, OUYANG Ai-guo
 doi: 10.37188/CO.2023-0072
Abstract(74) FullText HTML(41) PDF 2358KB(73)

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, this paper proposes an image denoising method based on the combination of 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.

Design and optimization of micro LED vehicle light projection optical system
LI Xianglan, LV Jin-guang, ZHENG Kai-feng, CHEN Yu-peng, ZHAO Bai-xuan, ZHAO Ying-ze, QIN Yu-xin, WANG Wei-biao, LIANG Jing-qiu
 doi: 10.37188/CO.2023-0063
Abstract(142) FullText HTML(55) PDF 8045KB(86)

The development of smart cars puts forward higher requirements for intelligent light systems with projection functions. Compared with the vehicle light system using traditional technology, the vehicle light system using Micro LED projection display technology can make the system structure simpler and the light utilization rate higher, which is more conducive to miniaturization, energy saving and integration because of its good self-luminous characteristics. In this paper, we propose a light projection scheme based on Micro LED array, design a 200×150 white Micro LED array with a pixel size of 80 μm×80 μm as the display light source and the field of view angle is 16°×34° object image tilt, and optimize the tilt angle and optical system structure of the object surface. In addition, the reverse distortion processing method and the pixel grayscale modulation method are used to solve the problems of keystone distortion and illumination uniformity of the projected image of the vehicle light, and a projection experimental platform is built to verify the image correction method. The experimental results show that the keystone distortion coefficients of the corrected images in the x and y directions decrease from 0.0932 and 0.3680 to 0.0835 and 0.0373, respectively, and the uniformity of the illumination of the image surface increases from 83.2% to 93.2%. In this paper, the optimization design of the oblique projection vehicle lighting system based on Micro LED and its image correction method are used to realize the projection of the vehicle light with high luminous efficiency and low distortion.

Calculation of orbit heat flow and research on radiation characteristics of space target
ZHENG Hong-ru, MA Yan, ZHANG Shuai, WANG Jian-chao, QU You-yang
 doi: 10.37188/CO.2023-0033
Abstract(118) FullText HTML(74) PDF 4452KB(98)

With the increasingly crowded space resources in low orbit, space situational awareness is an important support for the normal operation of space assets, and optical observation is one of the important means. In this paper, the solar radiation, the earth radiation and the earth albedo radiation received by the space target are simulated by Monte Carlo simulation method, and the simulation program is written based on the unstructured tetrahedral grid, and the calculation results are compared and verified. Furthermore, for the orbit external heat flow received by the sun-synchronous orbit satellite, the grid with solar panels is used to analyze the orbit heat flow received by each surface with or without occlusion. The results show that the average heat flow value of -Y surface decreases by 53.79 W/m2 after considering occlusion in the ground mode. The average surface heat flow value of +Y-Z side panel decreased by 32.05 W/m2. The temperature characteristics of each surface are given based on the properties of surface materials, and the accuracy of the calculation is verified by combining with the on-orbit telemetry data of the solar panel temperature. Finally, the infrared radiation intensity in each direction of the two modes is calculated. The results show that the influence of heat flow on the surface is different under different observation modes. The temperature of the surface varies with time under the earth mode, while the heat flow on the surface is stable under the sun mode. Under the two modes, the temperature of the solar panel is higher, the radiation intensity is larger, and it has obvious infrared characteristics, which is convenient to carry out infrared observation.

Repetition frequency and 228 nm narrow pulse width tunable deep UV laser
WANG Jin-yan, MA Fang, ZHENG Lei, TIAN Dong-he, CHEN Xi, ZHENG Quan
 doi: 10.37188/CO.2023-0058
Abstract(113) FullText HTML(77) PDF 3985KB(81)

Ultraviolet lasers play an important role in the study of ultraviolet resonance Raman spectroscopy. The Raman resonant Raman effect enhance Raman signals and reduces the detection limit of Raman measurement. This paper focuses on the study of an all-solid-state deep-ultraviolet laser with an output wavelength of 228 nm. The laser uses Nd:YVO4 as a gain medium and electro-optic q-switched cavity dumping technique to achieve a fundamental frequency output of 914 nm in pulse widths of several nanoseconds. Then, the second-harmonic generation is achieved by LiB3O5(LBO), and the fourth-harmonic 228 nm UV laser is obtained by beta-barium-borate (BBO). The variation of fundamental and second harmonic laser power at different repetition rates is investigate. The average power of Nd:YVO4 is saturated and decreases with increased repetition rate due to the low gain at 914 nm. The output efficiency of UV laser is optimized by adjusting the focus lens. At the pump power of 30 W, the highest average power of a 228nm UV laser is 84 mW at 10 kHz. The repetition rate of UV laser is continuously adjustable within the range of 5 kHz−25 kHz, and the pulse width is maintained at 2.8 to 2.9 ns which meets the application requirements in the field of UV spectroscopy detection technology.

Design and characteristic analysis of off-axis meta-lens
HU Jin-gao-wa, ZHAO Shang-nan, WANG Ling-jie, YE Hao-kun, ZHANG Jian-ping, ZHANG Xin
 doi: 10.37188/CO.2023-0039
Abstract(166) FullText HTML(55) PDF 7106KB(111)

As a new type of planar optical element, meta-lens can flexibly control the phase, polarization and amplitude of light. They have great potential for device lightweighting and mass manufacturing, and have garnered widespread attention. Off-axis meta-lens, a special type of meta-lens with certain dispersion effect, can be used as a spectral element, providing a unique and feasible way to realize micro instruments. This paper proposes a design method for off-axis meta-lens and analyzes the effects of numerical aperture, off-axis angle, and incident wavelength on the simulation deviation, resolution and focusing efficiency of off-axis meta-lenses, which provides valuable insights for subsequent research and application of off-axis meta-lenses.


Several off-axis meta-lenses with parameters NA=0.408 α=13°, NA=0.18 α=13°, NA=0.408 α=20° were simulated by Lumerical, respectively.


The simulation results indicate that the off-axis angle is directly proportional to the spectral resolution. As the angle increases, t the spectral resolution becomes larger, but the focusing efficiency decreases. A smaller numerical aperture result in a smaller coverage of the phase distribution, leading to a larger deviation between the simulation and theory.


Designers need to reasonably balance parameters such as numerical aperture and off-axis angle according to the requirements to finally achieve the desired effect. The conclusion of this study is an important reference value for theoretical analysis and parameter design of off-axis meta-lens in practical application.

Study on the optimal detection position of brix value of Yongquan honey tangerines based on hyperspectral imaging technology
LI Bin, WAN Xia, LIU Ai-lun, ZOU Ji-ping, LU Ying-jun, YAO Chi, LIU Yan-de
 doi: 10.37188/CO.2023-0057
Abstract(64) FullText HTML(39) PDF 4582KB(70)

The objective of this study is to explore the optimal detection location and the best prediction model of the brix value of Yongquan honey tangerines, which can provide a theoretical basis for the brix measurement and classification of honey tangerines. With the wavelength range of 390.2−981.3 nm hyperspectral imaging system was used to study the best location for detecting the brix of Yongquan honey tangerines, and the spectral information of the calyx, fruit stem, equator and global of Yongquan honey tangerines were combined with their brix values of corresponding parts to establish its prediction model. The original spectra from the different locations were pre-processed by standard normal variance transformation (SNV), multiple scattering correction (MSC), baseline calibration (Baseline) and convolutional smoothing (SG), respectively, and the partial least squares regression (PLSR) and least squares support vector machine (LSSVM) models were established based on the pre-processed spectral data. The best pre-processing methods for different parts of the honey tangerine were found, and the spectral data obtained from these pre-processing methods were analyzed using the competitive adaptive re-weighting algorithm (CARS) and uninformative variable elimination (UVE) to identify characteristic wavelengths. Finally, the PLSR and LSSVM models were established and compared based on the selected spectral data. The results show that the global MSC-CARS-LSSVM model demonstrates the most accurate prediction performance, with a correlation coefficient of Rp=0.955 and an RMSEP value of 0.395. Alternatively, the SNV-PLSR model of the equatorial location of honey tangerines was found to be the next more effective, with a correlation coefficient of Rp=0.936, and an RMSEP value of 0.37. The correlation coefficients of the two prediction models are similar, the equatorial location can be used as the optimal location for measuring the brix of honey tangerines. This study demonstrates that the use of varying segments of the orange impacts the accuracy of prediction models. Identifying the optimal location and prediction model can provide a theoretical basis for classifying oranges for brix testing.

Design of UV small f-number high variable power hyperspectral resolution imaging spectrometer
LIU Yang, LI Bo, LIN Guan-yu, WANG Xiao-xu, LI Han-shuang, GU Guo-chao
 doi: 10.37188/CO.2023-0037
Abstract(87) FullText HTML(39) PDF 5840KB(79)

Conventional imaging spectrometers generally have low variable power, which is not conducive to the extended application of large-field, long-slit, multi-channel optical systems. In space remote sensing, the radiation energy of the ultraviolet band is low, which requires the imaging spectrometer to have a smaller F-number. In order to meet the requirement of detecting small F-number of high variable power and high spectral resolution imaging spectrometer, a high spectral resolution Offner UV imaging spectrometer with high variable power is designed in this paper. An improved Offner structure with light and small size is adopted in the rear beam splitting system of the imaging spectrometer. Based on the requirements of variable power ratio and small F-number of the imaging spectrometer, the initial Offner structure parameters are derived theoretically. A meniscus lens is inserted in front of the image to increase the degree of freedom of optimization of the system and improve the imaging quality of the system. The resulting imaging spectrometer works in the 270~300 nm band with a long slit of 40 mm, a spectral resolution better than 0.6 nm, a spectral sampling of 0.15nm, the system variable power ratio less than 0.22, and an F number less than 2. the system modulation transfer function (MTF) is better than 0.9 at a cutoff frequency of 14 lp/mm, and the root mean square radius (RMS) of each field of view in each band is less than 12 μm. This study provides a design scheme for the UV-band hyperspectral detection imaging spectrometer with small F-number and high variable power.

Effect of electron irradiation on CsPbBr3 perovskite nanocrystal
ZHANG Bo-wen, HAN Dan, XUE Mengyun, CAO Rongxing, LI Hongxia, ZENG Xianghua, XUE Yu-xiong
 doi: 10.37188/CO.2023-0044
Abstract(129) FullText HTML(136) PDF 6967KB(90)

With excellent optical properties and high carrier mobility, perovskite materials have become highly competitive materials in the field of space solar cells. However, space particle irradiation can change the structure and optical properties of materials, leading to a rapid degradation of device performance. In order to investigate the influence of electron irradiation on the structure and optical properties of CsPbBr3 nanocrystals, this paper conducted electron irradiation experiments on CsPbBr3 materials, characterized the microscopic morphology of CsPbBr3 nanocrystals by high-resolution transmission electron microscopy method. Moreover, this paper investigated the change trend of crystal structure by X-ray diffraction analysis and X-ray photoelectron spectroscopy analysis. The results revealed electron irradiation caused the CsPbBr3 nanocrystals to become rough and significantly reduced in size. The nanocrystal became compact and formed nanocluster under high-dose electron irradiation. Furthermore, the optical properties of CsPbBr3 materials were characterized using steady-state UV-Vis absorption spectra and photoluminescence spectra. The analysis of lattice expansion-induced bandgap changes after irradiation was performed using first principles calculations. It is demonstrated that electron irradiation deepened the color of nanocrystals and affected the light transmittance of CsPbBr3 nanocrystalline, thereby enhancing the optical absorption performance of the samples. However, electron irradiation also led to the decomposition of CsPbBr3 nanocrystals, resulting in a significant reduction in luminescence intensity by 53.7%−78.6% after high-dose irradiation. These findings provide valuable data support for the study of spatial radiation damage mechanisms and the application of perovskite nanocrystals.

A Novel Methane and Hydrogen sensor with Surface Plasmon Resonance-Based Photonic Quasi-crystal Fiber
LIU Qiang, ZHAO Jin, SUN Yudan, LIU Wei, WANG Jianxin, LIU Chao, LV Jingwei, WANG Shimiao, JIANG Yu, CHU Paul K
 doi: 10.37188/CO.2022-0025
Abstract(126) FullText HTML(76) PDF 4148KB(175)

A novel photonic quasi-crystal fiber (PQF) sensor based on surface plasmon resonance (SPR) is designed for simultaneous detection of methane and hydrogen. In the sensor, Pd-WO3 and cryptophane E doped polysiloxane films deposited on silver films are the hydrogen and methane sensing materials, respectively. The PQF-SPR sensor is analyzed numerically by the full-vector finite element method and excellent sensing performance is demonstrated. The maximum and average hydrogen sensitivities are 0.8 nm/% and 0.65 nm/% in the concentration range of 0% to 3.5% and the maximum and average methane sensitivities are 10 nm/% and 8.81 nm/% in the range between 0% and 3.5%. The sensor provides the capability of detecting multiple gases and has large potential in device miniaturization and remote monitoring.

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(444) FullText HTML(227) PDF 4881KB(223)

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(174) FullText HTML(114) PDF 6097KB(123)

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(115) FullText HTML(26) PDF 4670KB(75)

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.

Original Article
High repetition frequency 257 nm deep ultraviolet picosecond laser with 5.2 W output power
FAN Hao-ran, CHEN Xi, ZHENG Lei, XIE Wen-xia, JI Xin, ZHENG Quan
2023, 16(6): 1318-1323.   doi: 10.37188/CO.2023-0026
Abstract(101) FullText HTML(76) PDF 3888KB(111)

To improve the detection efficiency of deep ultraviolet laser for semiconductor detection, it is necessary to develop 257 nm deep ultraviolet picosecond laser with high power and high repetition frequency. In this study, a 257 nm deep ultraviolet laser was experimentally investigated based on photonic fiber amplifier and extra-cavity frequency quadrupling. The seed source uses a fiber laser with a central wavelength of 1030 nm and a pulse width of 50 ps, delivering a power output of 20 mW and a repetition frequency of 19.8 MHz. High power 1030 nm fundamental frequency light was obtained through a two-stage ytterbium-doped double cladding (65 μm/275 μm) photonic crystal fiber rod amplification structure, and 257 nm deep ultraviolet laser was generated using double frequency crystal LBO and quadruple frequency crystal BBO. The seed source uses a two-stage photonic crystal fiber amplifier to get a 1030 nm laser with output power of 86 W. After the laser focusing system and frequency doubling, a second harmonic output power of 47.5 W at 515 nm and a fourth harmonic output power of 5.2 W at 257 nm were obtained.The fourth harmonic conversion efficiency was 6.05%. The experimental results show that this structure can obtain high power 257 nm deep ultraviolet laser output, providing a novel approach to improve the detection efficiency of the lasers for semiconductor detection.

The polarization mode of underwater waves based on atmospheric multiple scattering
GU Jing-qiao, LI Gao-jie, HU Peng-wei, QIAN Jian-qiang
2023, 16(6): 1324-1332.   doi: 10.37188/CO.2022-0223
Abstract(157) FullText HTML(141) PDF 6352KB(124)

Underwater polarized light with certain distribution characteristics is formed when sunlight is scattered by the atmosphere and refracted by the surface of the water. The polarization distribution pattern of the underwater polarized light can be used in navigation. In this paper, an air-water model is proposed to calculate the polarization pattern of sky light under varying wave conditions and simulate the underwater polarization distribution pattern under the influence of wave refraction. Distribution images are simulated for underwater polarization degree and polarization angle in conditions with calm water, sinusoidal waves and random waves with different solar altitude angles. The results are verified using underwater experiments. The comparison of the polarization distribution pattern under the waves with that under the calm water show that the proposed model can accurately characterize the characteristics of the polarization distribution pattern under typical wave surfaces, providing a theoretical basis for improving the environmental adaptability of underwater polarization navigation under fluctuating water surface conditions.

Laser backscattering characteristics of ship wake bubble target
ZONG Si-guang, ZHANG Xin, YANG Shao-peng, DUAN Zi-ke, CHEN Bao
2023, 16(6): 1333-1342.   doi: 10.37188/CO.2023-0043
Abstract(97) FullText HTML(36) PDF 4559KB(84)

In order to improve the laser wake guidance distance and the detection signal-to-noise ratio, it is of great theoretical and practical value to study the backscattering characteristics of bubble targets with different distances, bubble sizes, bubble number densities, and bubble layer thicknesses. The laser backscattering characteristics of ship wake bubble targets with different distances, scales, numerical densities, and thicknesses are studied using Monte Carlo simulations and indoor experiments. When the bubble density is 102−108 m−3 and the thickness of the bubble layer is greater than 0.05 m, there is always an echo signal for both large- and small-scale bubbles. When the thickness of the bubble layer is less than 0.05 m, no echo signal is detected. At this situation, the thickness of the bubble layer is the greatest impact factor on the backward scattering of bubbles. When the bubble number density is 109 m−3 and the thickness of the bubble layer is below 0.05 m, the pulse width of the large-scale bubble echo signal widens. The number density and scale characteristics of the bubbles have the greatest impact on the backscattering of bubbles. A laser backscattering measurement system at the scale of typical underwater bubbles is built to verify the influence of different ship wake bubble characteristics on the laser backscattering detection system, which can provide support for the ship wake laser detection project.

Multimodal feature fusion based on heterogeneous optical neural networks
ZHENG Yi-zhen, DAI Jian, ZHANG Tian, XU Kun
2023, 16(6): 1343-1355.   doi: 10.37188/CO.2023-0036
Abstract(127) FullText HTML(69) PDF 7292KB(107)

Current study on photonic neural networks mainly focuses on improving the performance of single-modal networks, while study on multimodal information processing is lacking. Compared with single-modal networks, multimodal learning utilizes complementary information between modalities. Therefore, multimodal learning can make the representation learned by the model more complete. In this paper, we propose a method that combines photonic neural networks and multimodal fusion techniques. First, a heterogeneous photonic neural network is constructed by combining a photonic convolutional neural network and a photonic artificial neural network, and multimodal data are processed by the heterogeneous photonic neural network. Second, the fusion performance is enhanced by introducing attention mechanism in the fusion stage. Ultimately, the accuracy of task classification is improved. In the MNIST dataset of handwritten digits classification task, the classification accuracy of the heterogeneous photonic neural network fused by the splicing method is 95.75%; the heterogeneous photonic neural network fused by introducing the attention mechanism is classified with an accuracy of 98.31%, which is better than many current advanced single-modal photonic neural networks. Compared with the electronic heterogeneous neural network, the training speed of the model is improved by 1.7 times; compared with the single-modality photonic neural network model, the heterogeneous photonic neural network can make the representation learned by the model more complete, thus effectively improving the classification accuracy of MNIST dataset of handwritten digits.

Design of focusing solar simulator based on free-form surface
WEI Xiu-dong, LI Bai-lin, ZHAO Yu-hang, TANG Jian-fang, ZHANG Ji, HUANG Yong-huan, XU Ying-chao
2023, 16(6): 1356-1364.   doi: 10.37188/CO.2022-0207
Abstract(182) FullText HTML(105) PDF 12865KB(133)

The concentrating solar simulator can obtain solar radiation spots with high-power convergence, which has important applications in the fields of solar thermal power generation and thermochemical research. To obtain uniform solar radiation spots, a free-form surface condenser design method based on non-imaging optics is proposed, and its design principle and specific method are described. The designed free-form condenser is compared with a non-coaxial ellipsoidal condenser with the same containment angle, and the correctness of its design method is verified by simulation analysis. The simulation results show that when a xenon lamp with a rated power of 6 kW is used as the light source, the single-lamp solar simulator composed of a free-form condenser can produce a spot with an average irradiance of 274.4 kW/m2 in the target region with a diameter of 60 mm. The spot’s unevenness decreases from 18.28% to 5.69% compared with that of a non-coaxial ellipsoidal solar simulator. The seven-lamp solar simulator can produce a spot with an average irradiance of 1.65 MW/m2, with a spot unevenness that decreases from 13.19% to 5.49%.

Design of an optical system for generating ring-shaped laser beam
CHEN Bao-hua, WU Quan-ying, TANG Yun-hai, FAN Jun-liu, CHEN Xiao-yi, YU Hao-mo, SUN Yi
2023, 16(6): 1365-1375.   doi: 10.37188/CO.2023-0045
Abstract(159) FullText HTML(96) PDF 6086KB(110)

We present a method for designing a transmissive-reflective combined optical system to generate a focused ring-shaped laser beam. The design aims to achieve a freely adjustable radius for the focused ring-shaped laser beam and ensure uniform beam intensity even after defocusing. Based on the principle of equal energy splitting, the transmissive system establishes mapping functions for the input and output light projection height. It optimizes the lens parameters to shape the incident Gaussian light into a flat-topped circular shape, thus achieving uniformity of beam intensity. On the other hand, the reflective system uses the adjustable diameter range of the focal plane ring-shaped light and working distance parameters. By applying the principle of geometric ray tracing, it calculates the parameters of the conical reflecting mirror, parabolic cylindrical mirror, and dynamic mirror, then the flat-topped circular light is transformed into a ring-shaped light. The experimental results show that when the half-apex angle of the dynamic mirror is 16°, the designed system can achieve a freely adjustable radius for the focused ring-shaped laser beam from 15 mm to 30 mm with a size error not more than 0.05 mm, and the intensity uniformity after defocusing reaches 84%. The design method can achieve both uniformity of intensity and freedom of size adjustment without replacing the system lens. It has good operability and yields higher precision and efficiency in the processing of ring-shaped light.

Design of catadioptric anamorphic optical system
WU Qing, SHI Guang-wei, ZHANG Jian-ping, ZHAO Shang-nan, ZHANG Xin
2023, 16(6): 1376-1383.   doi: 10.37188/CO.2023-0035
Abstract(154) FullText HTML(77) PDF 4530KB(106)

The anamorphic optical system has a two-plane symmetry, with different focal lengths in the two symmetry planes. This system can obtain a wider field of view when using sensors with conventional size. We propose a method for designing catadioptric anamorphic optical systems based on their first-order aberration characteristics. A catadioptric anamorphic optical system is designed by using a biconic surface, with a focal length of 500 mm in the XOZ plane and 1000 mm in the YOZ plane. The system’s F-number is 10, and the full field angle is 1°×1°. The mean value of the full field of view MTF of the system is higher than 0.3 at 80 lp/mm. The overall structure of the system is compact, and the imaging quality is excellent.

Design of optical system for low-sensitivity space gravitational wave telescope
YU Miao, LI Jian-cong, LIN Hong-an, HUANG Yao-zhang, LUO Jia-xiong, WU Yan-xiong, WANG Zhi
2023, 16(6): 1384-1393.   doi: 10.37188/CO.2023-0006
Abstract(194) FullText HTML(95) PDF 5499KB(140)

The Taiji program is a key task for China's space gravitational wave detection, and as an important part of space gravitational wave detection, the telescope's performance will directly affect the accuracy of gravitational wave detection. For the existing typical space gravitational wave telescope structures, due to the high sensitivity of secondary mirror, it is difficult to meet the requirements for manufacturing and adjustment tolerance of larger aperture space gravitational wave telescopes, especially the tolerance requirements for in-orbit stability. In order to solve the above problems, firstly, a new optical system structure of space gravitational wave telescope with intermediate image plane set between three and four mirrors is proposed to reduce the sensitivity of the secondary mirror. Combined with the theoretical method of Gaussian optics, the initial parameters of the structure of the new telescope are theoretically analyzed and calculated. Secondly, through the optimization design, a telescope optical system with a pupil diameter of 400 mm, a magnification of 80 times, a field of view of ± 8 μrad, and a wavefront error RMS value of better than 0.0063λ was obtained. Finally, the sensitivity evaluation tolerance allocation table of the telescope system is established, and the tolerances of the existing telescope structure and the new telescope structure are compared and analyzed. Compared with the existing telescope structure, the sensitivity of the new telescope structure is reduced by 30.4%. The results show that the new telescope structure has the advantage of low sensitivity, which provides an optimal scheme for the design of space gravitational wave telescopes.

Ground-based principle verification of clock noise transfer for the Taiji program
JIANG Qiang, DONG Peng, LIU He-shan, LUO Zi-ren
2023, 16(6): 1394-1403.   doi: 10.37188/CO.2023-0012
Abstract(238) FullText HTML(119) PDF 6390KB(155)

The Taiji program is a space gravitational wave detection mission proposed by the Chinese Academy of Sciences, which uses laser differential interference to detect pm-level displacement fluctuations caused by gravitational waves between satellites. In order to eliminate the phase measurement error caused by the desynchronization of the clocks in satellites, the Taiji program intends to use the sideband multiplication transfer scheme to measure and eliminate inter-satellite clock noise. We discuss the requirements, principles, and methods of inter-satellite clock noise transmission of the Taiji program, and design experiments for the principle verification. By building an electronics experiment system, the limit value of the clock noise of the two systems was tested, the relevant parameters of the experiment were determined, and the principle of the sideband multiplication transfer scheme was verified by further optical experiments. The experimental results show that the clock noise cancellation scheme and related parameters proposed in this paper are reasonable and feasible, and are suitable for the needs of the Taiji program. Moreover, in the 0.05 Hz−1 Hz frequency band, the suppression effect of inter-satellite clock noise is better than 2π×10−5 rad/Hz1/2, which meets the noise requirements of the Taiji pathfinder and lays an experimental and theoretical foundation for the design of a clock noise transmission scheme and parameters of the Taiji program in the future.

Thermal design of ground weak force measurement system for inertial sensors
REN Li-min, CHEN Li-heng, MENG Xu, WANG Zhi
2023, 16(6): 1404-1413.   doi: 10.37188/CO.2023-0022
Abstract(70) FullText HTML(55) PDF 4490KB(65)

In order to meet the ultra-high temperature stability requirements of the ground weak force measurement system for inertial sensor, the thermal design of the whole system is carried out. Firstly, the structure of ground weak force measurement system of inertial sensor, heat transfer path of sensitive structure and internal heat source are introduced. Secondly, according to the index requirements of the thermal control of the system, a high-precision thermal control method combining the three-stage thermal control structure and Proportional Integral Differential (PID) control algorithm is proposed to reduce the influence of temperature noise on the detection sensitivity of the inertial sensor. Then, UG/NX software is used to establish the finite element model and carry out the thermal analysis calculation under different working conditions, and the temperature change value of the measurement system in the time domain after equilibrium is (1.2−1.6) ×10−5 K. Finally, the temperature distribution of the measurement system in the time domain is described in the frequency domain, and the temperature stability results of sensitive structure of the inertial sensor are obtained. The analysis results show that under the current thermal control measures, the temperature stability of the sensitive structure of the inertial sensor is better than 10−4 K/Hz1/2, meeting the requirements of thermal control indicators, and the thermal design scheme is reasonable and feasible.

Narcissus suppression of medium-wave infrared imaging system
BU He-yang, YU Lin-yao, TIAN Hao-nan, WANG Jian
2023, 16(6): 1414-1423.   doi: 10.37188/CO.2023-0008
Abstract(102) FullText HTML(78) PDF 7506KB(95)

Narcissus refers to the phenomenon in an infrared system where a cooled imaging sensor can “see” its own reflected image by the reflection of the frontal optical surfaces. Control of narcissus is one of the important requirements in the design of the infrared imaging system. A cooled medium-wave infrared imaging system with Cassegrain reflection structure is designed and analyzed to obtain the optical surfaces with serious narcissus. In addition, the narcissus is reduced by Zemax, and the optimization of the system transfer function MTF is taken into account while the narcissus is controlled. The optimized medium-wave infrared imaging system is compared with the imaging system without narcissus suppression through NARCISSUS macro (narcissus analysis macro), Tracepro modeling software and actual imaging, and it was found that the narcissus induced equivalent temperature difference (NITD) of the detector image surface decrease from 1.0484 K to 0.1576 K. The energy and size of the narcissus spot did not show marked change during the focusing of the system. The optimized optical structure can effectively control the narcissus of the system.

Infrared radiation characteristics of space target based on ground-based detector
ZHENG Hong-ru, MA Yan, ZHANG Shuai, CHEN Ya-tao
2023, 16(6): 1424-1432.   doi: 10.37188/CO.2023-0032
Abstract(116) FullText HTML(44) PDF 7114KB(83)

Constructing the radiation characteristics of space targets is of great significance for the development of space situational awareness technology. In this study, we aim to investigate the infrared radiation characteristics of space targets by developing a simulation program based on the finite element method and unstructured tetrahedral mesh. Through vector coordinate transformation, we calculate the orbit external heat flux received by each surface of the target. By combining the surface material properties and Bidirectional Reflection Distribution Function (BRDF), the temperature and infrared radiation characteristics of each target surface were simulated. Furthermore, we analyze the spectral radiation intensity of the target in the ascending and descending orbital arcs under ground-based detection conditions, taking into account the effects of atmospheric attenuation and background radiation. The results show that, for a three-axis stabilized synchronous orbit satellite with solar panels fixed in the flight direction, the temperature variation range of each surface in the sunlight area and the shadow area is small. The detection effect of the long-wave band of 8~14 μm is better than that of the medium-wave band of 3~5 μm, and the maximum radiation intensity is about 770 W/sr. Ground-based infrared spectrum detection is more affected by the atmosphere, and the detection band must be optimally selected.

Influencing factors of angle measurement accuracy of an interferometer star tracker
RUAN Yu-xiang, DONG Lei
2023, 16(6): 1433-1441.   doi: 10.37188/CO.2022-0232
Abstract(120) FullText HTML(80) PDF 3787KB(126)

In order to improve the traditional attitude measurement accuracy of star sensors, interference angle measuring technology can be combined with a traditional star sensor. Based on the centroid positioning technology of traditional star sensors, the light intensity information of star image points is subdivided to break through the accuracy limitation of centroid positioning and obtain a highly precise interferometric star sensor with a large field of view. In this paper, the factors that restrict the angle measurement accuracy of interferometer sensors are deeply studied with particular interest given to the influence of interference fringe segmentation error on angle measurement accuracy. Through research and analysis, we conclude that the asymmetry error is not the main factor affecting the angle measurement accuracy of interferometric sensors. When the mismatch error between the Moire fringe period and the overall optical dimension of the optical wedge array is less than 1%, the single-factor angle measurement error is less than 0.01". For non-orthogonal error between Moire fringe orientation and an optical wedge’s array arrangement direction, the accuracy error of single-factor angle measurement is sure to be less than 0.01" when the fringe rotation angle is less than 0.1°. Therefore, the above two main errors should be suppressed in the production and assembly so that the measurement accuracy of the interferometer sensor is closer to the high-precision theoretical value.

Effect of slit height on the spectral resolution of a monochromator
ZHANG Jing, ZHANG Bo, LIU Kai, WANG Kai-yang, FENG Shu-long, LI Wen-hao, YAO Xue-feng
2023, 16(6): 1442-1449.   doi: 10.37188/CO.2023-0004
Abstract(248) FullText HTML(130) PDF 5537KB(152)

Monochromators are widely used in spectral calibration, material analysis and other aspects, so research of high spectral resolution monochromator systems is of great significance. Based on the vector grating equation, the influence of the height of the incident slit on the spectral line bending of a spectrometer is investigated, and the analytical expressions of the spectral line bending at the same wavelength and the slit height are given. An optimization scheme of the spectral resolution of the monochromator based on the suppression of spectral line bending by the slit height is proposed. According to the performance index requirements of a highly sensitive and ultra-fast time response detector, a three-grating monochromator optical system with a spectral resolution of 0.1 nm and a band range of 185−900 nm was designed, and a prototype was built to verify the influence of the slit height on spectral line bending, and to explore the influence of slit height on spectral resolution on the above basis. The experimental results show that the spectral resolution can be improved from 0.32 nm to 0.1 nm by optimizing the slit height when the slit width is fixed.

All-aluminum high-resolution camera with lightweight and compact size
SUN Jing-xu, XIE Hong-bo, LI Shu-xian, XIE Xin-wang, WANG Shuo, ZHOU Feng
2023, 16(6): 1450-1462.   doi: 10.37188/CO.2023-0062
Abstract(56) FullText HTML(17) PDF 6550KB(45)

In order to meet the urgent need of developing lightweight and compact space cameras quickly, effectively, and rapidly, a detailed comparative analysis is conducted, including optical system forms and imaging systems. The optical system form of RC+ compensation group is determined, and the imaging system of small F#+micropixel is adopted. Compared with the detailed parameters of the DOVE camera, a lightweight all-aluminum high-resolution camera with a resolution of 3.48 m at an orbital altitude of 500 km is designed. The overall design results of the camera, its optical and optomechanical structures, imaging electronics, and thermal control are described in detail. The optical design results of the RC+ compensation group of F5.6 are obtained. Using RSA-6061 microcrystalline aluminum alloy as the structural material of the mirror, coupled with an integrated high-rigidity hard aluminum alloy structure, the static (gravity and temperature deformation) simulation analysis results meet the optical design tolerance requirements. The dynamic simulation analysis results show that the first order mode is 302.92 Hz, which has a sufficiently high dynamic stiffness and safety redundancy. The imaging electronics using a 3.2 μm large area array 9 K×7 K detector is designed for low noise miniaturization. Thermal control is provided by the satellite platform at a temperature level of 20 °C± 4 °C for the camera. Integration test results show that: (1) The RMS wave aberration of the central field of view is λ/15.6, and the wavefront aberration of the five fields of view is better than λ/12.3, which ensure high-quality imaging near the diffraction limit of the camera. The measured optical transfer function at Nyquist frequency is 0.217; (2) The maximum sinusoidal vibration of the camera in three directions is amplified 1.17 times, and the first-order mode of the camera is 295 Hz, with a deviation of 2.61% from the simulation result. The structural stiffness is high and the mechanical stability is good. Under vacuum environment of 10−4 Pa and three different temperatures of 16 °C, 20 °C and 24 °C, the image is clear and can distinguish the corresponding resolution plate image at Nyquist frequency; (3) The image of 2 km outfield target is good, as well as clear and distinct grayscale image with sharp shadow boundaries. The all-aluminum high-resolution camera is achieved 3.48 m resolution at a track height of 500 km,width of 15 km×15 km and a total weight of 2 kg. The structural rigidity and strength test results meet the requirements of space launch scenarios, and these can provide theoretical guidance and engineering reference for the design of lightweight and higher-resolution space cameras.

Compact voice coil deformable mirror with high wavefront fitting precision
HU Li-fa, JIANG Lv, HU Qi-li, XU Xing-yu, HUANG Yang, WU Jing-jing, YU Lin
2023, 16(6): 1463-1474.   doi: 10.37188/CO.EN-2023-0001
Abstract(93) FullText HTML(41) PDF 4985KB(83)

To meet the requirements of wavefront distortion correction for miniaturized adaptive optics systems, a Deformable Mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice coil actuator were optimized by electromagnetic theory and the finite element method. The DM was optimized with respect to thermal deformation, resonance frequency, coupling coefficient and other parameters. Finally, wavefront fitting and residual calculation were completed according to the influence function. The optimized 69-element Voice Coil Deformable Mirror (VCDM) has a large phase stroke, good thermal stability, and a large first resonance of 2220 Hz. The RMS of the fitting residuals of the VCDM for the first 35 Zernike modes with a PV value of 1 μm are all below 30 nm. For complex random aberrations, the compact VCDM can reduce the wavefront RMS to less than 10%. Compared with a traditional VCDMs, the results of our compact VCDM indicate that it has a higher wavefront fitting precision. The compact VCDM with high performance and low cost has good potential applications in human retinal or airborne imaging systems.

Polarization-multiplexing of a laser based on a bulk Yb:CALGO crystal
JIN Hao-shu, LIU Hui, XU Si-yuan, LU Bao-le, BAI Jin-tao
2023, 16(6): 1475-1481.   doi: 10.37188/CO.EN-2023-0005
Abstract(157) FullText HTML(155) PDF 3589KB(140)

The polarization-multiplexing of a laser based on a medium with a large gain bandwidth and a high thermal conductivity can benefit dual-frequency and dual-comb lasers’ spectral bandwidth and power. This paper presents a demonstration of the polarization-multiplexing of a laser based on a bulk Yb:CALGO crystal. The polarization multiplexing is realized by sandwiching the gain crystal with two birefringent crystals which are cut at 45˚ to their optical axis. This sandwich-configuration creates inside the cavity two orthogonally polarized beams which are spatially separated only in the sandwich-configuration part but collinear in other part. Meanwhile, a single pump beam is also split into two beams automatically, matching the two cavity modes. This configuration also allows the gain crystal to be located in at the waist of cavity modes, which benefits the pumping efficiency. The laser outputs watt-level power with a slope efficiency exceeding 30%. A dual-frequency operation with terahertz frequency separation is realized by inserting an etalon into the cavity.

A sliding-mode control of a Dual-PMSMs synchronization driving method
SONG Xiao-li, ZHANG Chi, GUO Ya-wei
2023, 16(6): 1482-1492.   doi: 10.37188/CO.EN-2022-0026
Abstract(82) FullText HTML(34) PDF 3933KB(84)

Speed synchronization performance and anti-interference are important factors that affect the synchronous operation dynamic response and steady-state accuracy of dual Permanent Magnet Synchronous Motors’ (Dual-PMSMs). By introducing cross-coupling control as the framework, an integral sliding mode speed tracking controller based on an improved bi-power reaching method is proposed to reduce the speed error between two motors. A load torque observer is designed to bring the observed value into the Sliding Mode Control (SMC) reaching method that enhances the anti-disturbance performance of the system. Meanwhile, a synchronous controller is designed using a Fuzzy-Proportional-Integral-Derivative (FPID) control to improve the synchronization of the Dual-PMSMs. The results show that compared with the traditional PI algorithm as the target speed is 800 r/min, the proposed control method can decrease the two motors’ speed synchronization error from 25 r/min to 12 r/min under a no-load startup and reduce the speed synchronization error from 7 r/min to 2.2 r/min with sudden load torque, improving the synchronization and disturbance rejection.

The influence of the number of coupling regions on the output of the ding-shaped microring resonator
WU Rong, ZHANG Hao-chen
2023, 16(6): 1493-1500.   doi: 10.37188/CO.EN-2023-0009
Abstract(56) FullText HTML(31) PDF 4304KB(73)

In order to explore the influence of the number of coupling regions on the output of the ding-shaped microring resonator, the physical model of the ding-shaped microring resonator is established and studied by using the transfer matrix method. On this basis, the influence of the number of different coupling regions on the output of the ding-shaped microring resonator is analyzed. The experimental results show that with the increase of the number of coupling regions, the number of resonance peaks increases in the range of 1.54~1.56 μm working wavelength, the full width at half maximum (FWHM) decreases, the quality factor Q increases, the energy storage performance of the device is better, and the filter function on a specific wavelength can be realized. It can be concluded that the number of coupling regions has a great influence on the performance of the ding-shaped microring resonator. The number of coupling regions is selected according to the actual needs in the design.

Orbital-angular-momentum spectra in coherent optical vortex beam arrays with hybrid states of polarization
YANG Ceng-hao, CHENG Ke, HUANG Hong-wei, LIAO Sai, LIANG Meng-ting, SHU Ling-yun
2023, 16(6): 1501-1511.   doi: 10.37188/CO.EN-2023-0010
Abstract(134) FullText HTML(67) PDF 5056KB(106)

Orbital-Angular-Momentum (OAM) is one of the most important parameters in high-capacity optical communication or super-resolution imaging. Based on the Huygens-Fresnel principle and the theory of coherent combination, we propose hybridly polarized vortex beam arrays in coherent combinations of radial off-axis Gaussian beamlets with vortex and polarization Topological Charges (TC). The effect of vortex, polarization and addition TC and the number of beamlets on OAM spectra of the proposed beam arrays at input and output plane are both stressed. The results show the number of beamlet and hybrid polarization present joint effect on maximal weight of OAM-modes. An increase of maximal weight value at OAM-mode is accompanied by the growing number of the beamlet, while the hybrid polarization can not significantly increase the maximum weight of OAM spectra. As the number of beamlets increases, hybrid polarization can't significantly improve the maximal weight value in OAM spectra. Furthermore, the maximal mode equals the total TC at central Optical Vortex (OV) and it is irrelevant to the number of beamlets. Whereas for other modes for non-zero weight, their locations are jointly determined by vortex, polarization and addition TCs and the number of beamlets. This work may provide potential applications in the OAM-based communication and polarization imaging technologies.

InGaAs/AlGaAs quantum well intermixing induced by Si impurities under multi-variable conditions
LIU Cui-cui, LIN Nan, MA Xiao-yu, ZHANG Yue-ming, LIU Su-ping
2023, 16(6): 1512-1523.   doi: 10.37188/CO.2022-0257
Abstract(53) FullText HTML(31) PDF 4320KB(43)

Catastrophic Optical Mirror Damage (COMD) on the cavity surface is the key factor limiting the threshold output power of high-power quantum well semiconductor laser diodes. To improve the output power of the laser diode, the band gap width of the active material in the cavity surface of the semiconductor laser diode can be adjusted by the quantum well intermixing technology to form a non-absorbing window transparent to the output laser. Based on the primary epitaxial wafers of InGaAs/AlGaAs high power quantum well semiconductor laser diode, using the single crystal Si dielectric layer grown by Metal Oxide Chemical Vapor Deposition (MOCVD) as the diffusion source, the research on Si impurity induced quantum well intermixing was carried out by using the Rapid Thermal Annealing (RTA) process. The effects of growth characteristics of Si dielectric layer, the temperature and time of RTA on the intermixing process were investigated. The experimental results show that the epitaxial 50 nm Si dielectric layer at 650 °C combined with 875 °C/90 s RTA treatment can obtain about 57 nm wavelength blue shift while maintaining the photoluminescence spectrum shape and the primary epitaxial wafers. It is found that the diffusion of Si impurities into the waveguide layer on the primary epitaxial wafer is the key to the remarkable effect of quantum well intermixing by the energy spectrum measurement technique.

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(444) FullText HTML(227) PDF 4881KB(223)

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(174) FullText HTML(114) PDF 6097KB(123)

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(115) FullText HTML(26) PDF 4670KB(75)

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(1141) FullText HTML(590) PDF 6268KB(693)

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(380) FullText HTML(214) PDF 6648KB(235)

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(324) FullText HTML(98) PDF 8052KB(195)

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(898) FullText HTML(344) PDF 11662KB(496)

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(708) FullText HTML(363) PDF 7682KB(529)

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(782) FullText HTML(400) PDF 4220KB(486)

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(1154) FullText HTML(497) PDF 10445KB(638)

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(564) FullText HTML(320) PDF 3656KB(343)

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(2067) FullText HTML(539) PDF 7237KB(912)

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(804) FullText HTML(433) PDF 12124KB(542)

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(907) FullText HTML(500) PDF 5785KB(642)

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(656) FullText HTML(320) PDF 6306KB(505)

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(1239) FullText HTML(577) PDF 6214KB(534)

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(2263) FullText HTML(581) PDF 19381KB(1311)

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.

In-vivo across-scales two-photon microscopic imaging technique
CHEN Shuai, REN Lin, ZHOU Zhen-qiao, LI Min, JIA Hong-bo
2022, 15(6): 1167-1181.   doi: 10.37188/CO.2022-0086
Abstract(764) FullText HTML(483) PDF 7155KB(501)

Two-photon microscopy’s ability to maintain good spatial resolution in thick biological tissues has led to its application in in-vivo brain imaging studies soon after its conception. As neural networks have cross-scale multidimensional spatio-temporal properties, two-photon microscopy has developed rapidly and significantly in recent years to meet the demand for in-vivo cross-scale imaging of the brain. This paper firstly introduces the working principle of two-photon microscopy, then reviews the progress of two-photon microscopy from five perspectives: imaging field of view, imaging flux, imaging depth, resolution, miniaturization, and analyzes the difficulties and future challenges of cross-scale two-photon in-vivo microscopic imaging technology.

Multi-channel multiplexing digital holographic imaging for high throughput
HUANG Zheng-zhong, CAO Liang-cai
2022, 15(6): 1182-1193.   doi: 10.37188/CO.2022-0070
Abstract(1077) FullText HTML(711) PDF 7127KB(624)

Optical imaging has become the dominant method for characterizing information in biological systems. The rapid, non-destructive and comprehensive characterization of biological samples in recent years has placed high demands on the resolvable volume of imaging systems. Digital holography records an entire complex wavefront including both the amplitude and phase of the light field by interference imaging. Due to fast, non-destructive, and 3D imaging abilities, digital holography has been used in numerous applications such as digital pathology, label-free observation and real-time monitoring of in vitro cells. First, this paper introduces the main ways to achieve high-throughput imaging, and analyzes the advantages of digital holography and the evolution of spatial bandwidth. Secondly, a theoretical framework for high-throughput multi-channel multiplexing digital holography based on the Hilbert transform is presented. Then, an extended field of view digital holographic microscope is introduced based on this theoretical framework. Experimental results indicate that the system achieves 8 times the space-bandwidth product higher than that of conventional off-axis holographic microscopes without sacrificing spatial and temporal resolution. This high-throughput digital holographic multiplexing technology can make full use of the redundant spatial bandwidth of single intensity image, which verifies the feasibility of high-throughput multi-channel multiplexing digital holography.

Large field-of-view optical microscopic imaging technology
WANG Yi-qiang, LIN Fang-rui, HU Rui, LIU Li-wei, QU Jun-le
2022, 15(6): 1194-1210.   doi: 10.37188/CO.2022-0098
Abstract(1041) FullText HTML(512) PDF 10167KB(617)

With the characteristics of real-time, high-resolution and non-invasive, optical microscopy can scale from cells, tissues to whole living organisms, which has greatly expanded our understanding to the nature of life. However, due to the limited Space-Bandwidth Product (SBP), it is hard for a conventional optical microscope to achieve a large field of view with a high resolution. This makes it very difficult for microscopic imaging in large field of view biological imaging applications, such as imaging of neural circuits between the synapse of the brain neural networks. Recently, large field-of-view imaging technology has received increasing attention and experienced rapid development. The SBP has been improved ten times or even a hundred times as compared to a traditional optical microscope and the field-of-view has been expanded without sacrificing resolution, which, in turn, has resolved some major problems in biomedical research. This review introduces the progress, characteristics and corresponding biological applications of several typical trans-scale optical imaging techniques in recent years, and gives an outlook on their future development.

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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