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Research progress of optical tweezers with hetero-core fiber
LI Hong, ZHU Ying-xin, ZHOU Ya-ni, WANG Hai-bo, DONG Ming-li, ZHU Lianq-ing
 doi: 10.37188/CO.2023-0016
Abstract(17) FullText HTML(18) PDF 5688KB(5)

Optical fiber tweezers have a simple structure, operate flexibly and are small in size, and are widely used in biochemical analysis, life science and other fields. The optical fiber probe with hetero-core structure has natural advantages in near-field evanescent wave optical trapping, core beam coupling transmission, and cross-synergistic applications of microfluidic technology. It can realize cell and subcellular particle collection and transportation and can significantly improve the three-dimensional capture ability and dynamic manipulation level of particles. In this paper, the structural characteristics and application technology research progress of fiber optical tweezers with different core structures are reviewed. Their key technologies such as probe preparation, laser source and coupling mode are listed and compared. The role and development of hetero-core fibers with different structures in fiber optical tweezers are summarized and predicted.

Isolation of single wavelength laser communication terminals
GAO Wei-rao, DONG Ke-yan, JIANG Lun
 doi: 10.37188/CO.2022-0253
Abstract(18) FullText HTML(10) PDF 6472KB(11)

For data communication between single wavelength laser communication terminals, good isolation between signal transmission and reception is the key to establish duplex bidirectional laser communication.In this paper, aiming at the transmission and reception scheme of a single laser wavelength laser communication terminal and the overall communication performance of the laser communication terminal, the influence of the surface roughness and contamination level of key components on the isolation performance of the laser communication terminal is analyzed.The model parameters are derived from Harvey model and ABg model, and the designed scheme is analyzed using TracePro software.When the surface roughness or contamination level of λ/2 wave plate, λ/4 wave plate and optical antenna structure in the signal transmission channel increases,the backscattering caused by the elements will reduce the isolation performance in the signal transmission channel.At the same time, the measurement result of laser communication terminal isolation is 77.86dB, which is basically consistent with the software simulation result of 78.35dB. This result can be applied in laser communication system communication.

Real-time measurement for boresight vibration of dual line scan cameras
ZHAI Guo-fang, YU Qing-sheng, WANG Yun-long, GAO Wei-jun
 doi: 10.37188/CO.2022-0175
Abstract(23) FullText HTML(19) PDF 3056KB(9)

In order to realize the real-time measurement of the boresight vibration of the dual line array surveying and mapping camera, a measurement model of the optical axis of the aerospace line array surveying and mapping camera is established. First, by setting up laser transceivers at both ends of the focal plane of the camera, through the central prism correlation, the angle parameter change measurement model between the two cameras is constructed. And proposes an optical axis measurement method for multi-line array cameras based on the dual-vector attitude determination principle. The calculation expression is given; the algorithm error is analyzed, and verified by simulation. In addition, the residuals of two algorithms are simulated, and the results show that the simplified algorithm is only in good agreement with the dual vector algorithm in a small measurement range, but when the detection range is expanded to 2 second, the algorithm in this article can be used to obtain 0.1 arc-second results. Finally, it was tested and verified in a thermal vacuum environment. It was verified that the calibration accuracy of the internal and external parameters of the camera using this algorithm reached 0.1 arc-second. The results showed that the angle parameters of the two cameras exhibited the periodicity of the orbit, which provided good conditions for the subsequent development of stereo surveying and mapping tasks.

Integrated nitride optoelectronic chip for motion detection and visible light communication
FENG Xiao-xiao, HAN Ming-yu, CHEN Mei-peng, FANG Qian, WANG Yong-jin, LI Xin
 doi: 10.37188/CO.2023-0028
Abstract(41) FullText HTML(21) PDF 3712KB(10)

The motion of objects is everywhere in nature. With the development of smart vehicle and 6G mobile communications, the demand for highly integrated integrated sensing and communication (ISAC) devices withcommunication and motion sensing is increasing. Based on the coexistence of luminescence and detection characteristics of GaN multiple quantum wells, an optoelectronic chip based on GaN on sapphire substrate is proposed in this paper. This chip has sensitive motion detection function and visible light communication function.The transmitter of the chip emits visible light in blue band to the moving target object. The visible light signal modulated by the motion of the target object is reflected back to the receiver of the chip to stimulate the changing photocurrent. By analyzing the changing photocurrent, the motion of the target object rotating at different speeds can be detected. The change period of the photocurrent curve is consistent with the rotation period of the target object. This paper also studies the visible light communication performance of the optoelectronic chip. The optoelectronic chip can be used as a visible light communication transceiver terminal, can also process and transmit the motion detection signals collected by the chip. The optoelectronic chip based on GaN multi-quantum wells provides a promising way in the field of low-cost, low-power, highly integrated optical motion sensing applications. It is a highly integrated ISAC terminal device with significant value.

Research progress of miniature head-mounted single photon fluorescence microscopic imaging technique
FU Qiang, ZHANG Zhi-miao, ZHAO Shang-nan, LIU Yang, DONG Yang
 doi: 10.37188/CO.2023-0007
Abstract(19) FullText HTML(13) PDF 8253KB(19)

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, this paper will 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.

立发 胡, Lv Jiang, 启立 胡, 星宇 徐, 杨 黄, 吴晶晶 吴, 琳 俞
 doi: 10.37188/CO.EN.2023-0001
Abstract(14) PDF 1074KB(4)
Fiber bragg grating accelerometer based on flexure hinge and bearing
SONG Ying, ZHANG Hao-ran, LI Jian-zhi, SHEN Bo-hao, LIU Zhan-jian
 doi: 10.37188/CO.2022-0252
Abstract(62) FullText HTML(18) PDF 5186KB(29)

This paper develops a fiber Bragg grating accelerometer based on bearing and flexure hinge for the measurement of medium-high frequency vibration signals. The mathematical model between its natural frequency and sensitivity and structural parameters is derived based on the mechanical model. Moreover, the structural design is optimized based on the theoretical analysis results, then the sensor was fabricated. Ultimately, its dynamic characteristics are validated using finite element simulation and vibration experiment. The results show that both its operating frequency range and acceleration sensitivity are 10−1200 Hz and 17.25 pm/g. In addition, this proposed sensor has some extinguished advantages such as an error of less than 0.3 g, a good linearity of greater than 0.99, a repeatability error of 2.33%, and free of temperature.

Design of optical power splitter with adjustable split ratio
XIE Feng, ZHU Shuo-long, ZHANG Zhen-rong
 doi: 10.37188/CO.2023-0038
Abstract(57) FullText HTML(31) PDF 5025KB(36)

In order to solve some problems of the traditional analytical theory design scheme, such as high computational complexity, limited analytical solution, and time-consuming, based on the design of traditional optical device, a scheme for designing an optical power splitter with adjustable split ratio according to the reverse design method is proposed. In a compact region of 1.92 μm×1.92 μm, Ge2Sb2Se4Te1(GSST) is introduced to change the refractive index distribution of the device. The direct binary search algorithm is utilized to search the optimal state distribution of GSST in crystalline and amorphous states. And a T-shaped optical power splitter with adjustable split ratio is designed and implemented for the same device structure. The initial structure, split ratio, phase change material region state distribution, manufacturing tolerance, and light field distribution of the device are simulated and analyzed. The result shows the minimum relative errors of the designed optical power splitters with three splitting ratios of 1∶1, 1.5∶1 and 2∶1 between wavelengths 1530 nm and 1560 nm are 0.004%, 0.14% and 0.22%, respectively. The maximum fluctuations of the transmission curve in the manufacturing tolerance range are 0.95 dB, 1.21 dB and 1.18 dB, respectively. The splitter has a compact structure and has great potential for applications in optical communication and information processing.

Multi-scale attention fusion for image super-resolution reconstruction
CHEN Chun-yi, WU Xin-yi, HU Xiao-juan, YU Hai-yang
 doi: 10.37188/CO.2023-0020
Abstract(88) FullText HTML(39) PDF 6106KB(40)

The resolution of optical imaging is limited by diffraction limit, system detector size and many other factors. In order to obtain images with richer details and clearer textures, a multi-scale feature attention fusion residual network was proposed. First, shallow features of the image were extracted using a layer of convolution, and then the multi-scale features are extracted by a cascade of multi-scale feature extraction units. The local channel attention module is introduced in the multi-scale feature extraction unit to adaptively correct the weights of feature channels and improve the attention to high frequency information. The shallow features and the output of each multi-scale feature extraction unit were used as hierarchical features for global feature fusion reconstruction. Finally, the high resolution image was reconstructed by introducing shallow features and multi-level image features using the residual branch. The algorithm uses Charbonnier loss to make the training more stable and converge faster. Comparative experiments on the international benchmark datasets show that the model outperforms most state-of-the-art methods on objective metrics. Especially on the Set5 data set, the PSNR index of the 4× reconstruction result is increased by 0.39dB, and the SSIM index is increased to 0.8992, and the subjective visual effect of the algorithm is better.

Design and achievement of device for ammonia gas detection with high-precision based on laser spectroscopy
YANG Tian-yue, GONG ting, GUO Gu-qing, SUN Xiao-cong, TIAN Ya-li, QIU Xuan-bing, HE Qiu-sheng, GAO Xiao-ming, LI Chuan-liang
 doi: 10.37188/CO.2023-0023
Abstract(39) FullText HTML(17) PDF 938KB(28)

Ammonia emission will cause harm to the environment and human health. It is particularly important to monitor the ammonia concentration with high precision. Off-axis integrating cavity output spectroscopy (OA-ICOS), which has the advantages of high sensitivity and high response speed, is used in this paper and has been designed to a high-precision ammonia detection device. The gas absorption cell is composed of two high reflection mirrors with a reflectivity of 99.99%, and the base length of the optical resonator is 30 cm. Finally, the optical path of nearly 3000 m was realized. The distributed feedback laser (DFB) with a central wavelength of 1528 nm which is tuned to 6548.611 cm−1 and 6548.798 cm−1. The concentration of NH3 is changed from 10 ppm to 50 ppm and is detected under the atmospheric pressure of 140 torr at room temperature. The measurement results show that the linear fit R2 between NH3 concentration and signal amplitude can reach 0.99979. The Allan variance is used to analyze the experimental data, and the minimum detection limit of the system can reach 7 ppb at 103 s. The experimental results show that the detection device has good stability and high sensitivity, meets the demand for high-precision detection of ammonia gas, and also provides technical experience for domestic independent research and development of high-precision detection equipment for trace gases.

Lightweight YOLOv5s vehicle infrared image target detection
LIU Yan-lei, LI Meng-zhe, WANG Xuan-xuan
 doi: 10.37188/CO.2022-0254
Abstract(71) FullText HTML(42) PDF 7069KB(35)

Vehicle infrared image target detection is an important way of road environment perception for autonomous driving. However, existing vehicle infrared image target detection algorithms have defects, such as low memory utilization, complex calculation and low detection accuracy. In order to solve the above problems, an improved YOLOv5s lightweight target detection algorithm is proposed. Firstly, the C3Ghost and Ghost modules are introduced into the YOLOv5s detection network to reduce network complexity. Secondly, the αIoU loss function is introduced to improve the positioning accuracy of the target and training efficiency. Then, the subsampling rate of the network structure is reduced, and the KMeans clustering algorithm is used to optimize the prior anchor size to improve the detection ability of small targets. Finally, coordinate attention and spatial depth convolution modules are introduced into the Backbone and Neck respectively to further optimize the model and improve the feature extraction ability of the model. The experimental results show that compared with the original algorithm YOLOv5s, the improved algorithm can compress the model size by 78.1%, reduce the number of params and Giga Floating-point Operations Per Second by 84.5% and 40.5% respectively, and improve the mean average precision and detection speed by 4.2% and 10.9% respectively.

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
 doi: 10.37188/CO.2023-0009
Abstract(80) FullText HTML(35) PDF 6400KB(41)

In order to clarify the cavity design methods of thin-disk multi-pass amplifiers, this paper summarizes 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 multipass 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 increase its breadth of applications and realize the sustainable expansion of output energy.

Effect of slit height on the spectral resolution of a monochromator and its verification
ZHANG Jing, ZHANG Bo, LIU Kai, WANG Kai-yang, FENG Shu-long, LI Wen-hao, YAO Xue-feng
 doi: 10.37188/CO.2023-0004
Abstract(36) FullText HTML(34) PDF 5729KB(27)

: Monochromators are widely used in spectral calibration, material analysis and other aspects and research of high spectral resolution monochromator systems is of great significance as a result. Based on the vector grating equation, the influence of the height of the incident slit on the spectral line diffraction of a spectrometer is investigated, and the analytical expressions for diffraction 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 diffraction 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 nm−900 nm was designed, and a prototype was built to verify the influence of the slit height on spectral line diffraction, and to explore the influence of slit height on spectral resolution.


: 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.


: The slit height will affect the spectral resolution of a grating monochromator, and the experimental results can provide a reference for better use of monochromators.

Multispectral demosaicing method based on an improved guided filter
QI Hai-chao, SONG Yan-song, ZHANG Bo, LIANG Zong-lin, YAN Gang-qi, XUE Jia-yin, ZHANG Yi-qun, REN Bin
 doi: 10.37188/CO.2022-0231
Abstract(31) FullText HTML(9) PDF 1920KB(28)

In order to better preserve high-frequency information in demosaicing multispectral images, this paper proposes a new demosaicing method for multispectral images based on an improved guided filter. This method first models the strong correlation between adjacent pixels based on the autoregressive model, gradually estimates the model parameters at each pixel, obtains the optimal estimation value by minimizing the estimation error in the local window, interpolates the sampling dense band G, and generates high-quality guide images. The windowed intrinsic variation coefficient is then introduced into the penalty factor to obtain a weighted guide filter with edge sensing ability and to reconstruct the remaining sparse sampling bands. Finally, the CAVE dataset and the TokyoTech dataset are used for simulation. The experimental results show that compared with the five mainstream band multispectral image demosaicing methods, the peak signal-to-noise ratio and structure similarity of the reconstructed image in the CAVE dataset and the TokyoTech dataset are improved by 3.40%, 2.02%, 1.34% and 0.30%; and 6.11%, 5.95%, 2.28% and 1.42%, respectively. The local structure and color information of the original image are also better preserved, and the edge artifacts and noise are reduced.

Design of focusing solar simulator based on freeform surface
WEI Xiu-dong, LI Bai-lin, ZHAO Yu-hang, TANG Jian-fang, ZHANG Ji, HUANG Yong-huan, XU Ying-chao
 doi: 10.37188/CO.2022-0207
Abstract(37) FullText HTML(23) PDF 12867KB(33)

The concentrating solar simulator can obtain high-power convergence of solar radiation spots, which has important applications in the fields of solar thermal power generation and thermochemical research. To obtain uniform solar radiation spots, a free-form condenser design method based on non-imaging optics is proposed, and its design principle and specific method are described. A freeform condenser is designed in comparison to a non-coaxial ellipsoidal condenser with the same containment angle, and the correctness of its method of design 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 freeform condenser can produce a spot with an average irradiance of 274.4 kW/m2 in the target and a diameter of 60mm. 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%.

Development and prospects of enhanced absorption spectroscopy
REN Yi-jie, YAN Chang-xiang, XU Jia-wei
 doi: 10.37188/CO.2022-0246
Abstract(70) FullText HTML(49) PDF 4774KB(33)

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.

Research on the polarization mode of underwater waves based on atmospheric multiple scattering
GU Jing-qiao, LI Gao-jie, HU Peng-wei, QIAN Jian-qiang
 doi: 10.37188/CO.2022-0223
Abstract(27) FullText HTML(30) PDF 8845KB(26)

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 resulting underwater polarization distribution pattern 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’s degree and 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 and 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.

Infrared small target detection via L1−2 spatial-temporal total variation regularization
ZHAO Deming, SUN Yang, LIN Zaiping, XIONG Wei
 doi: 10.37188/CO.2022-0229
Abstract(30) FullText HTML(22) PDF 4348KB(30)

To solve the frequent problem of false alarms caused by complex background clutters in infrared small-target detection, a novel detection method based on \begin{document}${L_{1 - 2}}$\end{document} spatial-temporal total variation regularization is proposed. First, the input infrared image sequence is transformed into a spatial-temporal infrared patch-tensor (STIPT) structure. This step can associate the spatial and temporal information by using the high dimensional data structures in the tensor domain. Then, weighted Schatten p-norm and \begin{document}${L_{1 - 2}}$\end{document} spatial-temporal total variation regularization are incorporated to recover the low-rank background component to preserve the strong edges and corners, which can improve the accuracy of sparse target component recovery. Finally, the STIPT structure can be transformed into an infrared image sequence by the inverse operator, and an adaptive threshold segmentation is used to obtain the real target. The method is verified using a contrast test that incorporates five methods, and the experimental results show that the false alarm rate by this method decreases to 71.4%, 71.7%, 68.5%, 74.3% and 20.47% compared with the Maxemeidan, Tophat, LIRDNet, DNANet and WSNMSTIPT algorithms. The time cost also decreased to 42.4%, 82.9% and 28.7% of that of the Maxemeidan, DNANet and WSNMSTIPT. The extensive experimental results demonstrate the superiority of this method in detection performance, which can greatly improve the accuracy and efficiency of target detection with complex background clutters.

A target location method for aerial images based on fast iteration over DEM elevation
LI Zi-hao, KUANG Hai-peng, ZHANG Hong, ZHUANG Chu-heng
 doi: 10.37188/CO.2022-0215
Abstract(29) FullText HTML(18) PDF 6615KB(25)

In the positioning process of aerial cameras with large inclination angles, the influence of height error in the earth ellipsoid model can be effectively solved with the help of a digital elevation model. This is very important for obtaining accurate ground coordinates, especially elevation. Firstly, the orientation of the line-of-sight angle of geographical coordinates in the geographic coordinate system is solved by transforming homogeneous coordinates according to the position and attitude information of the carrier aircraft and the frame angle information of the aerial camera, and then the longitude and latitude of the target point are determined by a digital elevation model. To overcome the tedious nature of calculating target elevation and the non-convergence in the imaging process, a fast iterative method is proposed to iterate over the target elevation’s value. The difference between the light elevation of the visual axis and the ground elevation is calculated by halving the target elevation. The median elevation difference is calculated iteratively until it is less than a certain threshold. Finally, Monte Carlo analysis was used to analyze the error terms in the whole imaging process. When the convergence threshold is 1/10 DEM in grid accuracy, the iteration efficiency increases by 50% and the convergence speed is greatly improved. Through the calculation of the digital elevation model, when the flight height is 15,409 meters and the camera frame’s angle is greater than 74°, a mountainous area’s target circular error probability is less than 200 m which meets the real engineering needs.

The Measurement and Suppression of Forward Stray Light for Spaceborne Gravitational Wave Detection
LENG Rong-kuan, WANG Shang, WANG Zhi, CHEN Zhi-wei, FANG Chao
 doi: 10.37188/CO.2022-0251
Abstract(81) FullText HTML(48) PDF 6226KB(40)

In gravitational wave interferometric detection, the problem of stray light has received long-term attention. In the spaceborne gravitational wave detection program, the laser light emitted by the local interferometer produces backward coherent stray light when passing the telescope while the radiation from space that is incident to the spacecraft produces forward incoherent stray light. Forward incoherent stray light has received less attention at this point, but it is a necessary factor of gravitational-wave telescope design. Therefore, this paper studies stray light produced by space gravitational wave telescopes in orbit. First, the annual solar angle is calculated according to the orbital data of the three-star satellite formation of the Taiji Project, and the solar radiation around the 1064 nm band is evaluated. The baffle shadowing function is derived, which satisfies the requirement for the baffle design. The telescope is then modeled optically and mechanically and scatter measurements are conducted for critical optical components. Finally, the stray light reaching the pupil of the telescope is determined based on the energy of the incident sunlight. The results show that when the angle between the incident light and the optical axis is 60°, the stray radiation at the exit pupil is 4.27×10−13 W, and the corresponding point source transmittance is 8.7×10−9 which meets the requirement for space gravitational waves to detect extremely low levels of stray light.

Research on the influencing factors of angle measurement accuracy of an interferometer star tracker
RUAN Yu-xiang, DONG Lei
 doi: 10.37188/CO.2022-0232
Abstract(27) FullText HTML(15) PDF 3706KB(32)

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 form 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 Mohr 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 Mohr 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.

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
 doi: 10.37188/CO.2023-0006
Abstract(61) FullText HTML(35) PDF 7703KB(43)

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. The existing typical space gravitational wave telescope structure has high secondary mirror sensitivity, which is difficult to meet the manufacturing and adjustment tolerance requirements 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 400mm, a magnification of 80 times, a scientific field of view of ± 8μrad, 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 tolerance 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.

Method for Simultaneous Measurement of Waveguide Propagation Loss and Bending Loss
作文 范, 连希 贾, 赵一 李, 敬杰 周, 庆宇 丛, 宪峰 曾
 doi: 10.37188/CO.EN.2022-0027
Abstract(43) PDF 570KB(36)
The propagation loss of waveguide is a key indicator to evaluate the performance of an integrated optical platform. The commonly used cut-back method to measure the propagation requires the introduction of the Spiral test structure. In order to remove the effect of bending loss, the bending radius is usually designed to be large enough, taking up a lot of foot print. In this paper, we suggested a method to measure the propagation loss and bending loss of waveguide simultaneously with cut-back structure. The bending loss can be exponentially fitted with the bending radius according to simulation, which can be further simplified as linear fitting between the natural logarithm of the bending loss and the bending radius. A genetic algorithm was used to fit the insertion loss curve of the cutback structure and calculate the propagation loss and bending loss. With this method, we measured a cut-back structure of lithium niobate waveguide and got the propagation loss of 0.558dB/cm and bending
Super resolution reconstruction for colorectal endoscopic images based on residual network
ZHENG Yue-kun, GE Ming-feng, CHANG Zhi-min, DONG Wen-fei
 doi: 10.37188/CO.2022-0247
Abstract(64) FullText HTML(62) PDF 7390KB(46)

In this paper, an image super-resolution reconstruction algorithm SMRAN based on residual attention network is proposed to solve the problems of low resolution, less texture information and blurred details of colorectal endoscopic images. Images in the colorectal polyp endoscope image dataset PolypsSet are selected as raw data for experiments. A convolutional network is built to extract the shallow features of the low-resolution image and a Res-Sobel block is designed to enhance the edge features of the image. The multi-scale feature fusion block MEB is designed by introducing convolution kernels of different sizes to adaptively extract image features of different scales to obtain effective image information. The Res-Sobel block and multi-scale feature fusion module block MEB are connected through the residual attention network. Finally, the high-resolution image is reconstructed by the sub-pixel convolution layer. When the amplification factor is ×4, the performance of the proposed algorithm on the test set are as follows: the peak signal-to-noise ratio PSNR is 34.25dB and the structural similarity SSIM is 0.8675. Comparing with the traditional bicubic interpolation algorithm and commonly used deep learning algorithms such as SRCNN and RCAN, the proposed algorithm SMRAN shows better super-resolution reconstruction results on colorectal endoscopic images.

Multi-channel phase measurement system for the space laser interferometry
ZHANG Qiang-tao, LIU He-shan, LUO Zi-ren
 doi: 10.37188/CO.2022-0258
Abstract(60) FullText HTML(43) PDF 7515KB(43)

In the space gravitational wave detection Taiji mission, a heterodyne laser interferometer is used to detect gravitational wave signals in the middle and low frequency bands. In the Taiji mission, the laser interferometry system is composed of multi-channel interferometers, which involves the phase acquisition and readout of multiple sets of the interference signals. Therefore, the multi-channel phase measurement system is one of the key core technologies of the space laser interferometry. In this paper, a multi-channel phase measurement system is proposed, designed and tested based on the requirements of the Taiji mission and its ground-based laser interferometry experiments. First, the hardware and software design of the multi-channel phase measurement system is given, including hardware architecture design, phase measurement algorithm based on digital phase-locked loop and its implementation on FPGA, software architecture design, etc. Second, a time-domain functional tests of the multi-channel phasemeter are performed, which includes the phase accuracy and linearity. The results show that the dynamic and static phase linearity and accuracy of the multi-channel phase measurement system under different working conditions are good. Finally, the frequency domain noise tests of different channels, different frequencies and different amplitudes are carried out on the multi-channel phasemeter. The results show that the phase noise level of the multi-channel phase meter designed in this paper is better than \begin{document}$ 2{\text{π}} \mu rad/\sqrt{H\textit{z}} $\end{document} in the frequency band of 0.1 mHz−1 Hz. There is good consistency between different channels, and the phase noise introduced by channel differences or ADC chip differences is negligible in the target frequency band; for any interference signal with a frequency between 5−25 MHz, the phasemeter can be in the target frequency band meet the requirements within. Therefore, the multi-channel phase measurement system meets the requirements of space gravitational wave detection and ground-based interference experiments. At the same time, the research results of this paper also provide an experimental basis for expanding the phase measurement system with more channels in the future.

The connection between the preparation process of the graphene/silicon hetero-junction photodetector and its voltage-current characteristics
YANG Ya-xian, ZHANG Guo-qing
 doi: 10.37188/CO.2022-0259
Abstract(69) FullText HTML(40) PDF 4161KB(48)

Wet transfering two-dimension (2D) material to semiconductor substrate is a common method to prepare hetero-junction photodetector. In the process of wet transfer preparation of hetero-junction, different preparation details have significant effects on the properties of the hetero-junction formed by 2D materials and semiconductors. In this paper, a series of identical Gr/Si hetero-junction devices were prepared by wet transfer method, the relationship between its preparation technology and the voltage-current characteristics was studied in detail. The experimental results show that the gradient drying process can significantly reduce the dark current of the Gr/Si hetero-junction photodetector, the optimal drying temperature peak is 170 °C, and the leakage current basically no longer changes above 170 °C. The surface impurities and residual water in the inter-layer of Gr/Si van der Waals hetero-junction has a significant effect on the leakage current of the hetero-junction. The selective etching and annealing process of Gr/Si van der Waals hetero-junction can also reduce the leakage current greatly . Therefore, suitable drying process, selective etching process and annealing process are necessary in the preparation of Gr/Si hetero-junction photodetector. These results can give reference for the fabrication of two-dimensional material hetero-junction devices by wet transfer method.

 doi: 10.37188/CO.2022-0243
Abstract(63) PDF 1027KB(36)
利用半导体性单壁碳纳米管(SWCNT)的高吸收系数、优异的光电特性和高载流子迁移率等特点,本文构筑了基于半导体性SWCNT (sc-SWCNT)/富勒烯(C60)异质结的透明全碳宽光谱的场效应晶体管型光电探测器。该器件的大部分结构均由碳基材料组成,全碳异质结作为导电沟道材料,金属性SWCNT作为源漏电极,氧化石墨烯(GO)作为介质层,在可见光波段透光率均高于80%。电学测试结果表明,该光电探测器表现出了较强的栅控能力,实现了从405-1064 nm的可见光-近红外宽光谱响应,在5 mW/cm<sup>2</sup>的940 nm激光照射下,该器件光电响应率可以达到18.55 A/W,比探测率达到5.35×10<sup>11</sup> Jones,同时,表现出了优异的循环稳定性。
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
 doi: 10.37188/CO.EN-2023-0005
Abstract(51) FullText HTML(63) PDF 3676KB(45)

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 within two 45˚-cut birefringent crystals, forming two orthogonally polarized beams with spatial separation inside and allowing the system to pump the laser at the waist of the cavity mode for more efficient pumping. 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.

Ground principle verification of clock noise transfer for Taiji program
JIANG Qiang, DONG Peng, LIU He-shan, LUO Zi-ren
 doi: 10.37188/CO.2023-0012
Abstract(113) FullText HTML(48) PDF 7740KB(64)

The Taiji Project is a space gravitational wave detection mission proposed by the Chinese Academy of Sciences, which uses the method of 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 dissynchronization of the clock between satellites, Taiji Project intends to use the sideband multiplication transfer scheme to measure and eliminate the inter-satellite clock noise. This paper discusses the requirements, principles, and methods of inter-satellite clock noise transmission of the Taiji project, and designs experiments for principle verification. By building an electronics experiment, 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 Taiji project. 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 Taiji pathfinder and lays an experimental and theoretical foundation for the design of clock noise transmission scheme and parameter of future Taiji Project.

Microfluidic-microscopic image deformation correction method for planktonic algal cells
HU Xiang, YIN Gao-Fang, ZHAO Nan-jing, HE Qian-Feng, LIANG Tian-Hong, HUANG Peng, Xu Min, JIA Ren-Qing
 doi: 10.37188/CO.2022-0244
Abstract(72) FullText HTML(39) PDF 2527KB(58)

Flow cytomicrographic analysis is an important development in the automatic identification of planktonic algae in the water column, where the deformation of microscopic images under rapid injection conditions affects the accuracy of automatic identification of planktonic algae. Based on a microfluidic-microscopic imaging system for planktonic algae, the effect of flow rate on the deformation of microscopic images was investigated by analysing the deformation of algal cells and image clarity at different injection flow rates.Based on the principle of deformation caused by a rolling shutter photographing a moving object, a method of image deformation correction with unidirectional offset pixels is proposed and analysed in comparison with images acquired under static conditions of algal cells.The experimental results showed that the average values of aspect ratio and sharpness of L. oocystis cell images under static conditions were 1.16 and 116.53 respectively; during the dynamic injection process, the deformation (aspect ratio) of cell images gradually increased and the sharpness decreased as the flow rate increased; the average values of aspect ratio before and after correction were 1.35 and 1.26 respectively at 95 µL/min injection flow rate, and the dispersion of deformation decreased from 0.33 before correction to 0.1. The mean value of aspect ratio before and after correction was 1.35 and 1.26 respectively at 95 µL flow rate.The results provide a method for improving the accuracy of automatic identification of planktonic algal cells in the water column.

The Poynting vectors, spin and orbital angular momentums of uniformly polarized cosh-Pearcey-Gauss beams in the far zone
LIAO Sai, CHENG Ke, HUANG Hong-wei, YANG Cenghao, LIANG Meng-ting, SUN Wang-xuan
 doi: 10.37188/CO.EN.2022-0022
Abstract(75) FullText HTML(59) PDF 10531KB(84)

We propose cosh-Pearcey-Gauss beams with uniform polarization, which are mainly modulated by a hyperbolic cosine function (n, Ω) and the angles related to uniform polarization (α, δ). Based on angular spectrum representation and the stationary phase method, the Poynting vector, spin and orbital angular momentum in the far zone are studied. The results show that a larger n or Ω in the hyperbolic cosine function can partition the longitudinal Poynting vectors, SAMs and OAMs into more multi-lobed parabolic structures. Different polarizations described by (α, δ) can distinguish their Poynting vectors and angular momentums between the TE and TM terms, though this does not affect the patterns of the whole beam. Furthermore, the weight of the left and right sides of longitudinal Poynting vectors, SAMs and OAMs in TE and TM terms can be modulated by left-handed or right-handed elliptical polarization, respectively. The results in this paper may be useful for information storage and polarization imaging.

Tunable long-wave infrared optical parametric oscillator based on temperature-adjustable ZnGeP2
TIAN Jun-tao, LI Hui, ZHAO Li-li, LI Zhi-yong, WANG Hai, LIU Song-yang, XU Wen-ning, BAI Jin-zhou, TAN Rong-qing
 doi: 10.37188/CO.2022-0217
Abstract(86) FullText HTML(51) PDF 4182KB(79)

In order to realize tunable longwave infrared laser, this paper designs a ZGP temperature tuned longwave infrared optical parametric oscillator. Using a Ho:YAG laser with the center wavelength of 2097 nm to pump ZGP crystals with different phase matching angles, the laser with a segment continuously tunable range of 7.53−8.77 μm is realized in the temperature range of 15−30°C, with a total tuning range of 1.24 μm. The output power of ZGP - OPO is greater than 1.503 W over the entire tuning range. The output power is 1.503 W at the idler wavelength of 8.77 μm, and the corresponding slope efficiency and optical conversion efficiency are 12.19% and 6.53%, respectively. The experimental results show that temperature tuning of ZGP is an effective technical method to obtain continuously tunable long-wave infrared laser. The research of this experiment has potential application value in the field of engineering of tunable long-wave laser.

Ultrafast laser nested Machining method for angle-multiplexed optically encrypted metasurface
ZHANG Xiao-bin, HAN Wei-na
 doi: 10.37188/CO.2022-0228
Abstract(93) FullText HTML(56) PDF 6895KB(69)

Optical encryption materials for pattern information have been widely used in anti-counterfeiting, information encryption and storage, and structural color metasurface based on anisotropic functional reuse has been developed. The optical encrypted metasurface based on one-dimensional grating diffraction requires the processing of mask or unit structure one by one, resulting in low limiting efficiency. The structure uniformity of traditional ablated LIPSS is poor, which affects the device performance. Based on the above problems, an optical metasurface machining method based on the modified structure of picosecond laser direct writing phase change material Ge2Sb2Te5 is proposed. Firstly, the dispersion performance of the prepared GST modified gratings was characterized, and combined with the polarization dependence of the modified gratings, the angle-multiplexed information encryption metasurface was designed, and the metasurface prepared by the proposed method was further demonstrated. It realizes the performance of encryption under natural light, selective decryption reading and dynamic display under strong light. Compared with the traditional processing method, the proposed method can generate a series of grating structures in the form of simultaneous printing in a direct writing process, which improves the processing efficiency. At the same time, the grating structure obtained by processing is uniform and consistent, which improves the color rendering effect. The modified grating with 16° difference in orientation Angle realizes the selective information reading without crosstalk, and the obtained structure color is uniform and bright. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting, information encryption storage and wearable flexible display devices. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting information encryption storage and wearable flexible display devices.

Development of a doppler asymmetric spatial heterodyne interferometer for ground-based wind field detection at 557.7 nm band
欢 刘, 伦 江, 菲 张, 芸 付, 延嵩 宋, 峰 佟
 doi: 10.37188/CO.EN.2022-0018
Abstract(55) PDF 228KB(69)
A ground-based Doppler Asymmetric Spatial Heterodyne (DASH) interferometer with high signal-to-noise ratio (SNR) and large etendue(AΩ) with thermal compensation was developed to detect wind field information in the middle atmosphere. The detailed parameters and index of the DASH interferometer were developed for the 557.7 nm oxygen airglow spectral line. The system was designed with an expanded field of view (FOV) and thermal compensation. The half-FOV angle reached 2.815°, the etendue was 0.09525cm2sr, and the system SNR was approximately 113.75. Through the thermal compensation design, the final optical path difference with temperature variation(dΔd0/dT) was only 2.224×10-7mm/℃. The optical system was designed and optimized according to the corresponding parameters. Image-side telecentric and bilateral telecentric optical system structures were used in the entrance optics and exit optics, respectively. And parameters such as telecentricity and distortion met the detection requiremen
Laser Doppler velocimetry based on dual polarization structure
TAO Shan-jing, ZHEN Sheng-lai, FANG Jian, CHEN Xin, LU Tao, YU BenLi
 doi: 10.37188/CO.2022-0211
Abstract(80) FullText HTML(30) PDF 4924KB(74)

In order to eliminate the uncertainty caused by the inclination of the beam, a dual polarization laser Doppler velocimetry system is established in this paper. The system uses a dual beam dual probe structure to detect the motion information of the object. Firstly, the included angle of the two beams is accurately obtained through the rotation experiment. For any beam inclination, the dual probe device is used to collect the scattered beam from the moving object surface, and the Doppler frequency shift of the two interference signals is obtained by combining the dual polarization optical path structure. Then, the refined framing algorithm is innovated to demodulate the two interference signals in real time, and the real speed of the object is obtained by synthesizing the two speed components. The experimental results show that the average error between the measured value and the theoretical value can reach 1% ~ 5% when the speed is within the range of 10 mm/min ~ 1500 mm/min. In the process of non-stationary motion, the RMSE average of V-T image corrected by thinning and framing algorithm is 1.19mm/min. The structure of the system meets the requirements of stability and reliability, high accuracy and strong anti-interference ability in speed measurement.

Fano resonances design of metamaterials based on deep learning
Yang Zhi-hu, Fu Jia-hui, Zhang Yu-ping, Zhang Hui-yun
 doi: 10.37188/CO.2022-0208
Abstract(146) FullText HTML(123) PDF 4559KB(101)

In this paper, a metamaterial Fano resonance design method based on deep learning is proposed to obtain high-quality factor (high-Q) resonances with desired characteristics, such as linewidth, amplitude, and spectral position.The deep neural network is used to establish the mapping between the structural parameters and the transmission spectrum curve, and the forward network is used to predict the transmission spectrum.The inverse network achieves the on-demand design of high Q resonance. The low mean square error ( MSE ) is achieved in the design process, and the mean square error of the training set is 0.007.The results indicate that compared with the traditional design process, using deep learning to guide the design can achieve faster, more accurate, and more convenient purposes.The design of Fano resonance can also be extended to the automatic inverse design of other types of metamaterials, significantly improving the feasibility of more complex metamaterial designs.

Double-slot ultra-compact polarization beam splitter based asymmetric hybrid plasmonic structure
WANG Fang, LIU Hua, MA Tao, MA Shou-dao, LIU Yu-fang
 doi: 10.37188/CO.EN.2022-0028
Abstract(137) FullText HTML(93) PDF 4908KB(114)

To improve the extinction ratio of a polarization beam splitter, we propose a dual-slot ultra-compact polarization splitter (PBS) consisting of a hybrid plasma horizontal slot waveguide (HSW) and a silicon nitride hybrid vertical slot waveguide (VSW). The coating material is silicon dioxide, which can prevent the oxidation of the mixed plasma and also facilitate integration with other devices. The mode characteristics of the HSW and VSW are simulated by using the finite element method (FEM). At suitable HSW and VSW widths, the TE polarization modes in HSW and VSW are phase-matched, while the TM polarization modes are phase mismatched. Therefore, the TE mode in an HSW waveguide is strongly coupled with a VSW waveguide by adopting a dual-slot, while the TM mode directly passes through the HSW waveguide. The results show that PBS achieves an extinction ratio (ER) of 35.1 dB and an insertion loss (IL) of 0.34 dB for the TE mode at 1.55 μm. For the TM mode, PBS reached 40.9 dB for ER and 2.65 dB for IL. The proposed PBS is designed for the 100 nm bandwidth, high ER, and low IL, which can be suitable for photonic integrated circuits (PICs).

 doi: 10.37188/CO.2022-0226
Abstract(137) PDF 651KB(74)
为了实现双面抛光晶圆总厚度变化(TTV)和变形程度中弯曲度(Bow)和翘曲度(Warp)的测量,提出了一种干涉测量的方法。采用两个带有标准镜的菲索式相移干涉仪对晶圆正反面同时进行测量,将测量所得晶圆正反面形貌与未放置晶圆时两个干涉仪的空腔形貌进行组合运算,可得到不受标准镜误差影响的双面抛光晶圆的表面相关参数。在组合运算中,由于两个标准镜未精确对准会产生映射误差,影响相关参数的测量结果。针对这一问题,在晶圆测量之前,将三点定位装置固定在两个标准镜之间,基于三点定圆定理不断调整两个标准镜的位置,可使映射误差极小,进而减小映射误差对测量结果的影响。实验结果表明,50 mm晶圆横向和纵向的映射误差分别为21.592μm和37.480μm,TTV、Bow和Warp分别为0.198μm、-0.326μm和1.423μm。为了进一步验证调整方法的有效性,采用单个干涉仪对晶圆进行翻转测量,由测量结果可知晶圆的TTV、Bow和Warp分别为0.208μm、-0.326μm和1.415μm。所提干涉法在调整好两个标准镜的位置后,可以方便快速的用于大批量大尺寸晶圆的测量,提高了晶圆的检测效率,同时具有较高的测量精度。
Decoherence of temporal quantum correlation in electrically controllable quantum-dots molecules
XIE Jia-ling, YAN Kai, TAN Jia, CAO Zhao-liang, HAO Xiang
 doi: 10.37188/CO.EN-2022-0025
Abstract(120) FullText HTML(118) PDF 472KB(111)

The decoherence of temporal quantum correlation is explored in a voltage-controlled quantum dots molecule in a cavity. The temporal correlation in the hybrid system is studied by Leggett-Garg inequalities. The inequality violations can be interpreted as the existence of temporal quantum correlation during dynamical evolution. The temporal quantum correlation is enhanced by its electron tunnel’s strength and cavity frequency detuning. It is found that there is no temporal correlation in the regions where the values of spatial quantum correlation are zero and the maximal violations occur in conditions with high values of quantum coherence. In contrast, spatial coherence can persist at times when no violation is detected. The open quantum system approach is used to investigate the environmental effects on inequality violations. The temporal correlation is suppressed by the spontaneous decay of the quantum dots and cavity leakage. These results are serviceable in processing quantum information in hybrid quantum systems.

High quality factor dual wavelength Fano resonance based on continuous bound states
WANG Lin, DONG Fan-long
 doi: 10.37188/CO.2022-0166
Abstract(121) FullText HTML(73) PDF 6310KB(98)

In order to improve the quality value (Q) to enhance the coupling between light and matter. In this paper, a dielectric metamaterial with simple structure, low fabrication requirements was proposed. It can excite symmetric protected bound states in the continuum (BICS). The dielectric metamaterial has a planar nanopore plate composed of tetrameric pores. By changing the position of the nanopores, the symmetrical protection BIC can be transformed into the symmetrical protection quasi BIC(QBIC), and then two high Q value Fano resonances can be induced. Through simulation calculation, the Fano resonance Q value can reach 1e6 when Δ=3 nm. Then, the far-field radiation of QBIC and Fano resonance is decomposed into the contributions of different multipole components. Based on the scattering power and electric field vector distribution, it can be found that the dielectric metamaterials λ1 Fano resonance with high Q value is mainly due to magnetic quadrupole and toroidal dipole, while λ2 Fano resonance has high Q value is mainly due to the toroidal dipole. Finally, the influence of nanopore side length and nanopore filling material on the two Fano resonances is analyzed and calculated. The research in this paper can provide theoretical guidance for the future research and preparation of high Q value optical response devices.

Coplanar excitation of terahertz spoof surface plasmon and high-Q sensing
YAN De-xian, CHENG Gang, LI Er-ping, LI Xiang-jun, ZHANG Xue-ru, WU Yi-lin
 doi: 10.37188/CO.2022-0204
Abstract(112) FullText HTML(67) PDF 2261KB(163)

In this paper, the coplanar excitation of terahertz Spoof Surface Plasmon (SSP) realized by using a single-layer grating meta-surface coupling method is proposed, which overcomes the disadvantages such as the inconvenience of reflection measurement when applying the medium couplers. The periodic grating and terahertz SSP composite structure are simultaneously constructed on the monolayer metal structure. When the terahertz waves are incident vertically, the wavevector of grating structures and the wavevector of SSPs are matched, and the SSP mode can be excited. The high Q value resonant peaks can be generated in the transmission spectrum, and its factor Q can reach 1923. The effects of the structural parameters on the grating-coupled meta-surface transmission spectrum and dispersion characteristics are also analyzed. In addition, based on the high Q resonant peak in the transmission spectrum of the designed structure, the high sensing sensitivity is about 67 GHz/RIU at the resonant center frequency of 0.22 THz. The structure proposed in this paper, which realizes terahertz SSP excitation and high Q sensing by treating a single-layer meta-surface structure, exhibits great application potential in many practical applications.

Repeated zoom accuracy index of an electrowetting lens and its optimization method
HUANG Peng, YANG Xiao-ying, CHEN Bin, SONG Yue
 doi: 10.37188/CO.2022-0209
Abstract(89) FullText HTML(50) PDF 6739KB(86)

In order to improve the stability of an electrowetting liquid lens’s zoom, based on the research of glass lenses, a statistical data-based index of liquid lens zoom stability and liquid lens repeated zoom accuracy is proposed. An experimental method is presented to optimize the structural parameters and materials of the liquid lens. Firstly, the main factors affecting the accuracy of a liquid lens’s repeat zoom were obtained through preliminary experimental research, including the polar solution volume, taper and non-polar solution viscosity. Secondly, taking the accuracy of the liquid lens’s repeat zoom and zoom range as evaluation indicators, it was found that the relationship between the accuracy of the liquid lens’s repeat zoom and the voltage is not monotonic, and that it rises first and then falls. On this basis, through the range analysis and comprehensive balance method, the primary and secondary factors and the optimal combination of parameters is obtained. After that, orthogonal experiments were used to optimize the design parameters. Finally, the effectiveness of this method was verified by experiments. The experimental results show that the repeat zoom accuracy of the optimized liquid lens is 0.2 m−1, and the zoom range is −15.2−5.85 m−1 over the voltage range of 0 to 230 V. It basically meets the requirements of stable and reliable liquid lens zoom, high precision, and large zoom range.

Recent advances in metasurfaces for polarization imaging
ZHOU Jun-zhuo, HAO Jia, YU Xiao-chang, ZHOU Jian, DENG Chen-wei, YU Yi-ting
 doi: 10.37188/CO.2022-0234
Abstract(460) FullText HTML(283) PDF 10063KB(285)

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.

Research on an adaptive optics system suitable for near-ground imaging
WANG Hai-ming, QUAN Jia-ning, GE Bao-zhen
 doi: 10.37188/CO.2022-0230
Abstract(87) FullText HTML(44) PDF 5940KB(92)

In order to overcome the adverse effects of near-ground turbulence on the imaging quality of the optical systems at imaging distances of tens to hundreds of meters, an optical imaging system based on a long focal length telescopic objective lens and an integrated adaptive module is designed. With a system center height of 1.9 m and the imaging distance of 50~200 m, the outdoor imaging experiment of a resolution plate is carried out. The experimental results show that the influence of turbulence on imaging quality is obvious at medium and long distances of 50~200 m near the ground. The experimental system can effectively overcome the influence of turbulence at different distances and improve the consistency of image resolution and clarity. As the imaging distance increases, the influence of turbulence increases, and the system’s correction ability and the imaging quality decrease. The imaging resolution of the system can reach 0.5 mm at an imaging distance of 100 m. Cracks on the surface of a concrete model are observed and corrected at a distance of 200 m. The experimental results show that the system can suppress the influence of turbulence and improve the clarity of the image, which verifies the practical application ability of the system.

Passive athermalization design of a cooled infrared optical system
LI Kang, ZHOU Feng, WANG Baohua, GONG Hui
 doi: 10.37188/CO.2022-0205
Abstract(91) FullText HTML(51) PDF 5829KB(96)

Under conditions with large temperature differences in an infrared optical system, its imaging quality will deteriorate due to severe temperature changes. Large field-of-view medium-wave infrared cameras for airborne forest fire monitoring work in drastically changing environments. The system also has high requirements for stray radiation. In order to ensure that the optical system performs stably and with good imaging quality in the large field-of-view and the required large temperature range, a cooled medium-wave infrared optical system is designed based on athermalization and the comprehensive evaluation method of stray radiation based on noise equivalent temperature difference. The optical system consists of 6 lenses and 1 filter whose working wavelength is 3.7~4.8 μm; its F-number, focal length, and field of view are 2.5, 62.5 mm and 14.36°×10.87°, respectively. The pixel resolution of the medium-wave uncooled detector is 640×512. By using a combination of silicon and germanium materials and reasonably distributing the optical power, achromatic aberration and athermalization designs are realized. Through cold reflection optimization and cold aperture matching, stray radiation noise in the system is well-suppressed. By a bit of aspheric optimization, higher-order aberrations are corrected based on the requirements. The results show that the imaging quality of the optical system is stable and good in the temperature range of −55~+70 °C.

Study on the cophasing error of the Golay3 sparse aperture imaging system
QIAN Jun-hong, ZHANG Rong-zhu
 doi: 10.37188/CO.2022-0203
Abstract(117) FullText HTML(59) PDF 5665KB(96)

Multiple sub-aperture interference imaging enables the images formed by the sparse aperture imaging system to have a higher resolution after the cophasing error is corrected. In this paper, the MTF and surface target imaging of the system are analyzed with a Golay3 sparse aperture imaging system as the research object when there are different piston and tilt errors among the sub-apertures. A Golay3 sparse aperture imaging system was developed to carry out an imaging experiment with the USAF1951 resolving power test target as the area target. Three-aperture synthetic imaging is achieved by adjusting the position of the plane mirror in the light beam deflection and the adjustment module to correct the piston and tilt errors of the sub-apertures. The results of a theoretical analysis are then verified. According to calculations, the developed system’s angular resolution of 1.38 urad is close to the equivalent single-aperture imaging system’s theoretical resolution of 1.18 urad. The developed Golay3 sparse aperture imaging system can correct the cophasing errors and improve the imaging resolution.

Static interferometric high-temperature temperature field imaging and detection method
ZHANG Rui, TANG Wei-ping, WANG Zhi-bin, XU Cheng-yu, XUE Peng, LI Meng-wei
 doi: 10.37188/CO.2022-0168
Abstract(108) FullText HTML(57) PDF 3489KB(84)

In order to realize the non-contact high-precision measurement of high-temperature temperature fields such as the tail flame, combustion and explosion of aerospace engines, a static interferometric high-temperature temperature field imaging and detection method is studied. Firstly, a static interference high-temperature temperature field detection system is designed. Using a theoretical analysis of the measurement principle of high-temperature temperature fields, the relationship between the optical path difference and the temperature at the lowest point of high-temperature interference signal intensity is studied; Secondly, according to the response band of the visible light area array detector and the common temperature range, a static interferometric Savart prism is designed, and temperature field imaging is realized by using it for one-dimensional scanning; Finally, the optical system is designed and the corresponding relationship between the minimum optical path difference of the interference and the temperature is obtained by fitting. From this, the linear fitting formula is obtained. Simulations are conducted to verify the interference signal image where the temperature field after passing through the system reaches the area detector. The static interferometric high-temperature temperature field detection method can achieve the high-precision detection of 1000 K−3000 K temperatures. In the linear region, the temperature measurement resolution is 1.4 K and the temperature measurement relative error is better than 0.8%. This research lays the foundation for high-precision high-temperature temperature field imaging in the military and civilian fields.

Theoretical design and preparation of high performance mwir notch filter
SHANG Peng, CHEN Bei-xi, SUN Peng, LIU Hua-song, BAI Jin-lin, JI Yi-qin, CAO Bo, MA Yuan-fei, LIN Quan
 doi: 10.37188/CO.2022-0193
Abstract(28) FullText HTML(33) PDF 5346KB(141)

In order to effectively suppress the interference of CO2 radiation from 4.3 μm attachment on 3 μm−5 μm MWiR target signal, based on the Needle random intercalation optimization algorithm, an accurate inversion correction model for the growth error of multi-layer ultra-thick Ge/Al2O3 films under quartz crystal monitoring is established by the electron beam evaporation method, thus realizing the design, the accurate inversion and the accurate preparation of MWiR notch filter; in order to solve the problem that the surface profile of the MWiR notch filter changes greatly, the preset substrate surface method is used to realize the low surface profile regulation of MWiR notch filter. The results show that the high refractive index Ge film has good deposition stability with the increase of coating time, while the deposition scale factor of low refractive index Al2O3 thin film changes up to 11.9% in a regular gradual trend. For the prepared MWiR notch filter, the average cut-off transmittance is <0.3% at 4.2 μm−4.5 μm, and the average transmittances are >95% at 3.5 μm−4.05 μm and 4.7 μm−5.0 μm. The surface profile of the substrate after coating can be effectively controlled in a small range. The film has good adaptability to complex environment, and has successfully passed the environmental test of firmness, high temperature, low temperature and damp heat specified in GJB 2485-95.

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(76) FullText HTML(46) PDF 4148KB(111)

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.

High precision structural light scanning viewpoint planning for aircraft blade morphology
LI Mao-yue, CAI Dong-chen, ZHAO Wei-xiang, XIAO Gui-feng
 doi: 10.37188/CO.2022-0221
Abstract(98) FullText HTML(42) PDF 6500KB(109)

The machining quality and detection accuracy of aero-engine blades have a very important influence on the service life of blades. Aiming at the problem of improving the accuracy of blade detection, a high-precision scanning viewpoint planning method based on structured light was proposed in this paper. Firstly, the coarse model data were obtained by coarse scanning under the overall size of the blade, and the field of view was determined according to the camera resolution and acquisition accuracy. Secondly, the improved Angle Criterion algorithm was used to extract the boundary, and the boundary segmentation points were determined according to the boundary coordinates and the range of visual field. The coarse model was sliced by the section line method of surface, and the internal segmentation points were determined according to the slice results, so as to complete the uniform segmentation of point clouds. Then, a directed bounding box was established for the segmented point cloud data to obtain the coordinates of the center point, and the normal vector was statistically analyzed to determine the orientation of the main normal, so as to generate the viewpoint coordinates of high-precision scanning. Finally, the surface morphology of the blade was tested and verified. The experimental results show that the average standard deviation of the proposed method is reduced by 0.0054mm and the collected viewpoint is reduced by 1/3 compared with the viewpoint acquisition result of the supervoxel segmentation, which has a good application prospect in machining inspection of thin-walled blades.

Microwave photonic RF frequency multiplying phase shifter with tunable multiplication factor and a full 360-deg tunable range
YAN Ying, MA Jian-xin
 doi: 10.37188/CO.EN.2022-0019
Abstract(173) FullText HTML(150) PDF 5775KB(147)

A filterless microwave photonic phase shifter (MPPS) with a tunable frequency multiplication factor (FMF) and a full 360-deg tunable range is theoretically analyzed and verified by simulation. In the scheme, two parallel Mach-Zehnder modulators (MZM), cascaded with two dual-parallel integrated Mach-Zehnder modulators (DPMZM) by a 2×2 optical coupler (OC), are used to generate the ±1st- to 4th-order sidebands adjustably, and a phase modulator (PM) is used to phase shift one of the two lightwaves. After photodetection, the 2nd- to 8th- order harmonics with a continuously tunable phase shift from 0 to 360-deg can be generated by adjusting the RF driving signal and the DC bias voltage of the DPMZM, and the DC voltage of the PM. Simulation results demonstrate that both 360-deg continuously tunable phase shift and frequency multiplication can be implemented. Large Optical Sideband Suppression Ratio (OSSR) and Electrical Spurious Suppression Ratio (ESSR) of around 20 dB can be obtained. The phase shifter wavelength insensitive performance has been also evaluated by simulation.

Laser intensity distribution measurement method based on tomographic imaging
WANG Qian, CAI Wei-wei, TAO Bo
Abstract(306) FullText HTML(274) PDF 9813KB(173)
In order to accurately measure the laser intensity distribution, this paper proposes a method based on tomographic imaging. Firstly, numerical studies were performed to validate the correctness of the imaging model and convergence of the reconstruction algorithm. Reconstruction errors were less than or equal to 7.02% with different laser intensity distribution phantoms employed and less than 8.5% with the addition of different random noise levels under 10%. Additionally, a demonstration experiment was performed with the employment of a customized fiber bundle to realize the measurement from seven views. Seven views are distributed along a semi-circle plane which is perpendicular to the propagation direction of the laser beam. The distance from the laser beam to each view is nearly 160 mm and the angle coverage range of the seven views is about 150°. Laser-induced fluorescence obtained after the laser passed through a rhodamine-ethanol solution was collected by the tomographic imaging system. Then, the laser intensity distribution was obtained through absorption-corrected three-dimensional (3D) reconstruction. The correlation of the projection and re-projection of the one view was used to quantitatively access the accuracy after the other six views were adopted in the reconstruction. The results show the feasibility of the method with a correlation coefficient of 0.9802. It can be predicted that the 3D laser intensity measurement scheme proposed in this work has a broad prospect in the field of laser applications.
Ground electronics verification of inter-satellites laser ranging in the taiji program
DENG Ru-jie, ZHANG Yi-bin, LIU He-shan, LUO Zi-ren
 doi: 10.37188/CO.2022-0041
Abstract(539) FullText HTML(273) PDF 7219KB(246)
In the Taiji program, laser interferometry is utilized to detect the tiny displacement produced by the gravitational wave signals. Due to the large-scale unequal arm, the laser frequency noise is the largest noise budget in the space interferometer system. To reduce the influence of laser frequency noise, a technology called the Time Delay Interferometry (TDI) is utilized to deal with it. The TDI is a kind of data post-processing method, which forms the new data stream by the method of the time delay to initial data. But the premise of TDI needs to obtain accurate absolute arm length between satellites. Thus, for that requirement, we discuss the ranging system scheme and implement a ground electronics verification experiment. The ranging system is based on Direct Sequence Spread Spectrum (DS/SS) modulation, and it mainly includes three parts, which are the signal structure, a Delay Locked Loop (DLL), and a data processing algorithm. In DS/SS modulation, types of pseudo-random code can make a difference to the quality of correlation and the ranging accuracy. Therefore, to design the optimal pseudo-random code, we compare the correlation and flexibility in choosing lengths of the m sequence, gold sequence, and Weil code. Weil code that has a shift-cutoff combination with the best autocorrelation is chosen as the ranging code. The ground electronics verification experiment is set up for simulating the physical process of signal transmission and verifying system performance. The main device of the experiment is a FPGA card based on the K7 chip from Xilinx, which is used to simulate the function of communication and ranging between satellites. Meanwhile, we change the length of the Radio Frequency (RF) coaxial cable to correspond to different ranges. The experimental process can be summarized as follows. Firstly, 16-bit data at 24.4 kbps and 1024-bit Weil code at 1.5625 Mbps are modulated with Binary Phase Shift Keying (BPSK) in the 50 MHz sampling frequency. Then the signal is transmitted through RF coaxial cables of 10 to 60 m in length. In receiving end, the signal is consolidated by DLL and the ranging information is collected. To measure the range accurately, we use a centroid method to optimize the collected data. The results show that the ranging accuracy is better than 1.6 m within 60 m. In conclusion, this experiment proves the principle of the scheme and its feasibility, laying a technical foundation for optical system verification in the future.
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(321) FullText HTML(131) PDF 11662KB(229)

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.

Original Article
Research progress of grating projection on machine 3D topography inspection technology
LV Hong-yu, LI Mao-yue, CAI Dong-chen, ZHAO Wei-xiang
2023, 16(3): 500-513.   doi: 10.37188/CO.2022-0083
Abstract(158) FullText HTML(105) PDF 6376KB(239)

Vision-based measurement has good application prospects and far-reaching development significance for advanced manufacturing fields such as aerospace, the military industry and electronic chips. Among them, on-machine 3D vision detection technology based on structured light is one of the hotspots and challenges in the field of precision machining. Based on the on-machine 3D measurement process of structured light, we discuss and summarize the key technologies, including its technical requirements, methods and principles involved, related research status and existing problems in the measurement calibration, phase optimization solution, on-machine 3D point cloud processing and reconstruction of different feature surfaces. Finally, according to the actual needs of relevant technologies in the future, prospects are made with regard to processing field calibration, dynamic real-time 3D reconstruction, sub-micron and nano measurement, and measurement processing integrated data transmission technology, with the corresponding research ideas put forward.

A vanadium dioxide-assisted switchable multifunctional metamaterial structure
YAN De-xian, CHEN Xin-yi, FENG Qin-yin, LU Zi-jun, ZHANG He, LI Xiang-jun, LI Ji-ning
2023, 16(3): 514-522.   doi: 10.37188/CO.2022-0195
Abstract(178) FullText HTML(91) PDF 4835KB(171)

In this paper, a multifunctional metamaterial device based on the phase transition properties of vanadium dioxide (VO2) is proposed. The metamaterial structure consists of a top layer combined with VO2-filled Split Ring Resonator (SRR) and a metal cross, a polyimide (PI) dielectric layer, and a metal substrate. When the VO2 is in the insulating state, the cross-polarization conversion function can be realized, and its Polarization Conversion Rate (PCR) is greater than 90% in the range of 0.48-0.87 THz. When the VO2 is in the metallic state, the device can realize dual-frequency absorption and be applied in high-sensitivity sensing functions. The absorption rates are higher than 88% at the frequencies of 1.64 THz and 2.15 THz. By changing the refractive index of the sample material, the sensing sensitivities at the two related frequencies are about 25.6 GHz/RIU and 159 GHz/RIU, and the Q-factors are 71.34 and 23.12, respectively. The proposed metamaterial multifunctional device exhibits the advantages of a simple structure, a switchable function, and high-efficiency polarization conversion, and provides potential application value in future terahertz communication, imaging and other fields.

Graphene quantum dots fluorescence enhancement and pH response characteristics
ZHANG Bei-long, LI Jin-hua, LU Dong-xiao, ZHANG Ke-xin, WANG Xiao-jun, MA Li
2023, 16(3): 523-534.   doi: 10.37188/CO.2023-0053
Abstract(34) FullText HTML(17) PDF 7495KB(39)

In this paper, the effect of the cross-linking agent 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) on the optical properties of graphene quantum dots (GQDs) and the reasons are investigated in detail. GQDs were prepared by a hydrothermal method and reacted with EDC to obtain GQDs/EDC composites. The spectral properties of GQDs and GQDs/EDC were investigated. The effect of pH on the fluorescence of GQDs/EDC and its mechanism were investigated using PBS solution and artificial gastric juice samples. The experimental results show that EDC passives the surface defects of GQDs, making the fluorescence of GQDs increase rapidly in <1 min time and remain stable up to 20 min. Under different EDC contents the fluorescence intensity of GQDs/EDC is significantly enhanced by about 264 times compared to GQDs alone. The pH response experiments shows that GQDs/EDC had a linear response pattern of fluorescence and absorption intensity in the pH range of 1.75−4.01 and 4.01−9.28. Biocompatibility showed that the cell viability of human breast cancer cells was greater than 80% at sample concentrations of 25−300 µg/mL and remained at 74% even at high concentrations of 500 µg/mL; Finally, the detection of artificial gastric pH has high accuracy with relative standard deviation RSD ≤1.10%. The EDC-mediated fluorescence enhancement makes GQDs more advantageous in the fields of detection, sensing and imaging. Besides, the sensitive pH response characteristics of GQDs/EDC provide a good prospect for pH detection applications.

Assembling and test method for main focus survey telescope based on curvature sensing
AN Qi-chang, WU Xiao-xia, LI Hong-wen, CAI Yu-qi
2023, 16(3): 535-541.   doi: 10.37188/CO.2023-0010
Abstract(43) FullText HTML(19) PDF 4984KB(37)

The integrated detection of the main focus telescope is realized by sensing the curvature wavefront of the telescope. First of all, the curvature sensing process of the main focus telescope and the basic principle of dynamic stability transfer in multiple links are analyzed using Fourier optics theory. Secondly, the error analysis of static correction and dynamic surface shape measurement in the integrated detection of the main focus telescope is carried out. After that, the degree of freedom locking in the adjustment process is analyzed. Finally, the principle of the integrated detection process is realized through experiments. The obtained wavefront detection residual is better than 0.08λ( λ=633 nm). The spatial resolution is 10/m−1, and the temporal resolution is 0.2 Hz. This method can effectively improve the imaging quality of main focus telescope with the large-aperture large-field, and reduce the demand for the stability of the external environment in the integrated detection process by using the non-interference and high robustness characteristics of the curvature sensor, so as to provide assistance for the more detailed time-domain astronomical observation in the future.

Thermal control design and flight test of a satellite-borne cryogenic optical system
LIU Qing-zhi, YI Hua, JIANG Hai, LIU Yin-nian
2023, 16(3): 542-549.   doi: 10.37188/CO.2022-0200
Abstract(100) FullText HTML(50) PDF 3245KB(107)

In order to reduce influence of background infrared radiation, the temperature of the whole optical system should be below −20 °C for satellite-borne long-wave infrared imagers working in orbit. On the base of the weak heat conduction structure, a Ω type flexible sunshield made of MLI was developed and a cryogenic optical system was achieved through direct radiation cooling. Cage-like three-dimensional heat conduction straps made of copper were developed and an isothermal design for the body tube was realized. The cryogenic optical system applied to space remote sensing was used for the first time in China when it was tested in orbit with SJ-9B satellite. The results showed the temperature of the whole optical system could be maintained at −35 °C~−20 °C all the time, and the temperature difference in the body tube was no more than 4 °C. All flight test data met the temperature requirement of the long-wave infrared imager. This thermal control method is simple and effective, which can provide a reference for the thermal design of similar satellite-borne infrared optical systems.

Effect of atmospheric turbulence on the tracking accuracy of high-resolution remote sensing satellites
CAO Zong-xin, CAO Nan, YANG Yan-yan, DING Zhi-ya, MAO Hong-min, PENG Jian-tao, FAN Li-na, LU Huan-jun, SUN Hui-juan, HU Li-fa, CAO Zhao-liang
2023, 16(3): 550-558.   doi: 10.37188/CO.2022-0196
Abstract(179) FullText HTML(65) PDF 5850KB(176)

We focuse on the effects of camera aperture, atmospheric turbulence intensity and satellite orbit height on the tracking and positioning accuracy of high-resolution remote sensing satellites. Firstly, we establish a turbulence model and turbulence simulation method based on Kolmogorov turbulence theory for observation of the Earth. Then, the influence of camera aperture, satellite orbit height and atmospheric coherence length on the positioning accuracy of the satellite is simulated and analyzed, and then a universal formula is deduced to calculate the tilt aberration of turbulence wavefront. Finally, based on this universal formula, a theoretical formula for calculating jitter is derived for Earth observation. This work can provide a theoretical basis of the influence of atmospheric turbulence for the design, analysis and evaluation of high-resolution remote sensing satellites.

Synchronization transmission technology of semiconductor lasers with transverse effect
ZHAO Li-na, WEI Qing-tao
2023, 16(3): 559-566.   doi: 10.37188/CO.2022-0031
Abstract(266) FullText HTML(165) PDF 4597KB(187)

In this paper, a dynamic equation of a semiconductor laser with transverse effect is given by modifying the dynamic model, and the influence of the transverse effect on its output characteristics is analyzed. On this basis, the synchronization transmission technology of a semiconductor laser’s output signal with transverse effect is further studied. The results show that the output of the semiconductor laser presents a new spatiotemporal chaotic state after considering the transverse effect, and is very sensitive to the initial value. At the same time, whether the synchronization transmission of single-channel or multi-channel signals is carried out by a semiconductor laser, its transmission performance is very stable. The synchronization technology is very simple and easy to apply in practice.

Short pulse laser drive technology in a distance-selective imaging system
WANG Chong, YANG Jia-hao, ZHU Bing-li, HAN Jiang-hao, DANG Wen-bin
2023, 16(3): 567-577.   doi: 10.37188/CO.2022-0142
Abstract(157) FullText HTML(68) PDF 6287KB(215)

In a distance-selected imaging system based on single-photon detection, a short-pulse laser is emitted and synchronization control between the transmitter and receiver is performed, and the detector operates in photon counting mode and integrates in time to complete the imaging. In order to obtain a short pulse laser that meets the system requirements while reducing the system’s size and cost, we propose to apply two types of narrow pulse generation circuits based on RF bipolar transistor and Step Recovery Diode (SRD) to single photon distance selective imaging systems. We introduce the principle and design method of both types and verify the system through simulation, physical fabrication and testing. The characteristics of the pulse generator and factors affecting its pulse width and amplitude are analyzed. The physical test results show that the transistor-based method can generate a narrow pulse with a rise time of 903.5 ps, a fall time of 946.1 ps, a pulse width of 824 ps, and an amplitude of 2.46 V; the SRD-based method can generate a narrow pulse with a rise time of 456.8 ps, a fall time of 458.3 ps, a pulse width of 1.5 ns, and an amplitude of 2.38 V; and the repetition frequency of both can reach 50 MHz. Both design methods can be used with external current-driven laser diodes to achieve excellent short pulse laser output.

Design of reflector assembly and adhesive layer under airborne wide temperature conditions
ZHANG Jia-qi, GUO Yi-bo, ZHANG You-jian, ZHANG Zhi-hua
2023, 16(3): 578-586.   doi: 10.37188/CO.2022-0194
Abstract(185) FullText HTML(61) PDF 8618KB(158)

Airborne ambient temperature varies widely and airborne vibration can be strong. Because there is a difference in the thermal expansion coefficients of an Invar inlay and mirror material, a mirror’s higher coating temperature means that the traditional bonding process will lead to bonding failure and the surface precision of the mirror cannot meet system requirements. Therefore, this paper proposes a new method of bonding the mirror after processing and coating, and designs some important parameters for the adhesive layer. RTV is used as the main binder for the mirror and the inlay, and the effect of RTV curing on the structure is alleviated by favorable elasticity. The thickness of RTV is 1.1 mm, its width is 7.2 mm and the thickness of the epoxy adhesive is 0.022 mm. The simulation results show that the RMS of the mirror shape is 25.91 nm and the first-order frequency of the mirror group mode is 242 Hz when the gravity is 1 g and temperature change are −40 °C (the initial temperature is 20 °C). The final surface detection RMS is 15.8 nm and the resonance frequency is 213 Hz. The experimental results show that the design, structure and bonding layer can meet the wide temperature range and vibration requirements.

Development and algorithm research of optical alignment system for a high precision flip chip bonder
HAN Bing, MA Hong-tao, XU Hong-gang, YAN Ying, JU De-han, ZHAO Chun-yu
2023, 16(3): 587-595.   doi: 10.37188/CO.2022-0101
Abstract(159) FullText HTML(90) PDF 4972KB(216)

Aiming at the urgent demand of high-precision optical alignment systems for a domestic infrared focal plane flip chip bonder, an optical alignment system was designed and verified, and the parallel adjustment, optical alignment and coordinate system error compensation algorithms applied to the system were researched. Firstly, this paper analysed the optical alignment process of a flip chip bonder, then introduced the parallelism adjustment and optical alignment algorithm, and proposed a more reasonable error compensation algorithm according to the test process of the optical alignment system. Finally, based on the above calculation algorithm, the optical alignment system was designed including three parts: a collimation system, a microscopic imaging system and a laser ranging system. The functions of parallel coarse adjustment, feature point recognition and parallel fine adjustment were realized. The experimental results show that the collimation system has a good collimation effect, the microscopic imaging system has high resolution and good imaging quality, and the ranging accuracy of the laser ranging system is 0.084 μm. The designed high-precision optical alignment system solves the urgent need of a domestic infrared focal plane flip chip bonder for high-precision optical alignment systems. It has been applied in a certain types of flip chip bonders, and has very important social significance for improving the independent research and development and production capacity of domestic high-end large-scale integrated circuits.

Sea-sky-line detection method based on polarization difference images
SU De-zhi, LIU Liang, WANG Kun, WU Shi-yong, LIU Ling-shun, MING Rui-long, GONG Jian
2023, 16(3): 596-606.   doi: 10.37188/CO.2022-0181
Abstract(157) FullText HTML(64) PDF 7462KB(181)

Aiming at the problem of sea-sky-line detection in low-contrast infrared images being difficult and easily affected by interference factors such as clouds, strip waves and sea clutter, we propose a method of using polarization difference images for sea-sky-line detection. Firstly, Polarization Difference Imaging (PDI) is used to enhance the local contrast of the sea surface area and the Signal-to-Noise Ratio (SNR) of the sea-sky-line. A large-scale local contrast accumulation method of the polarization difference images is then used to determine the sea-sky-line area. Finally, the accurate detection of a small-scale sea-sky-line is completed by combining the gradient significance and polynomial fitting in the sea-sky-line area. Overall, the methodology integrates multi-dimensional information such as the Degree of Linear Polarization (DOLP) and the Angle of Polarization (AOP) for sea-sky-line detection, and combines large-scale and small-scale detection, which can effectively overcome interference of factors such as clouds, strip waves and sea clutter. The experimental results show that the accuracy of this algorithm for sea-sky-line detection is 98.5%, and the average time consumed is 16 ms. The experimental results indicate that the proposed algorithm can realize fast and accurate sea-sky-line detection so it has wide applicability in different scenes.

Lightweight infrared detection of ammonia leakage using shuffle and self-attention
ZHANG Yin-hui, ZHUANG Hong, HE Zi-fen, YANG Hong-kuan, HUANG Ying
2023, 16(3): 607-619.   doi: 10.37188/CO.2022-0127
Abstract(143) FullText HTML(81) PDF 4865KB(214)

Ammonia gas is an important basic industrial raw material, and realizing its non-contact detection is of great significance for the timely detection of ammonia gas leaks to avoid major safety incidents. Aiming at the shortcoming of conventional ammonia leak detection devices that can only respond when ammonia diffuses to a certain range and makes contact with a sensor, a Shuffling Self-Attention Network (SSANet) model is proposed to realize the infrared non-contact detection of ammonia leaks. Due to the high noise and low contrast of ammonia leakage images obtained by infrared cameras, an infrared detection dataset of ammonia leakage was established through non-local mean denoising and contrast-limited adaptive histogram equalization preprocessing. On the basis of YOLOv5s, the SSANet model uses the K-means algorithm to cluster and analyze the candidate frame suitable for the infrared detection of ammonia gas leakage to preset the model’s parameters. Using the lightweight ShuffleNetv2 network, the depth of 3×3 in the Shuffle Block can be adjusted. The separate convolution kernel is replaced with a 5×5 depth, and the feature extraction network is reconstructed with an SK5 Block containing a new convolution module, which makes the model size, calculation and parameters non-intensive while improving the detection accuracy. The Transformer module is used instead of its original version. The C3 module in the network bottleneck module is replaced by Transformer module to realize the bottom-up fusion of multi-head attention in the leake area, and further improves the detection accuracy. The experimental results show that the size and parameter requirements of the SSANet model are reduced by 76.40% and 78.30%, respectively, to 3.40 M and 1.53 M compared with the basic model of YOLOv5s; the average detection speed of a single image is increased by 1.10% to 3.20 ms; and the average detection accuracy is increased by 3.50% , reaching 96.30%. We provide an effective detection algorithm for the development of a non-contact detection device for ammonia leakage to ensure the safe production and stable operation of ammonia-related enterprises.

A flux measurement for high-magnification convergent radiation spots
WEI Xiu-dong, ZHAO Yu-hang, ZHANG Ya-nan, XU Ying-chao
2023, 16(3): 620-626.   doi: 10.37188/CO.2022-0139
Abstract(185) FullText HTML(93) PDF 4109KB(194)

A new method for measuring the flux distribution of a high-magnification convergent radiation spot is proposed. A radiation flux sensor is used to measure the flux density at different positions of the spot, and the calibration curve of the grayscale and flux density at different positions of the spot is fitted by a polynomial, and finally the flux distribution of the radiation spot is obtained and its principle is also elaborated. In order to verify the accuracy and feasibility of the measurement method, a high-magnification convergent radiation spot flux distribution measurement experiment is carried out, and the results are compared with the direct measurement results from the radiant flux sensor. The results show that the measurement results of the proposed method are consistent with the direct measurement results, and the average deviation is less than 0.54%. Through analysis, the measurement uncertainty of this measurement method is 4.35%, and the measurement accuracy is higher than the traditional measurement method. The experimental results indicate that the proposed method can meet the needs of practical applications.

An improved algorithm for monocular camera edge spectrum based ranging by defocused images
JIE Deng-fei, WANG Hao, LV Hui-fang, TIAN Bo-tao, ZHANG Zhan-xiang
2023, 16(3): 627-636.   doi: 10.37188/CO.2022-0171
Abstract(163) FullText HTML(54) PDF 3959KB(152)

In order to achieve accurate target ranging of weak or non surface texture features using a monocular camera, an improved defocused image ranging algorithm based on preserving edge spectral information is presented. By comparing two classical defocal ranging theories with Fourier transform and Laplace transform as the foundational principals of calculation, a corresponding definition evaluation function is constructed. We select the method based on the spectrum definition function with better sensitivity, and select the calculation range of the frequency domain by retaining the information on the target edge. To verify the feasibility of the algorithm, 6 sets of different duck egg samples are used to obtain scattered focus images of different apertures and distances, and the improved algorithm was used to solve the distance of the duck eggs from the camera lens. The experimental results show that the improved algorithm based on the edge spectrum preservation has a good ranging effect with a correlation coefficient of 0.986 and Root Mean Square Error (RMSE) of 11.39 mm. It is found that the range ability can be effectively improved after the image rotation processing of the duck egg image taken at an oblique angle, with the RMSE is reduced from 11.39 mm to 8.76 mm, the average relative error is reduced from 2.85% to 2.28% and the correlation coefficient reaches 0.99. The proposed algorithm fundamentally meets the requirements of stability and high accuracy in ranging targets with weak or non surface texture features.

White light interferometry micro measurement algorithm based on principal component analysis
CHEN Hao-bo, ZHANG Li-wei, SUN Wen-qing, CHEN Bao-hua, CAO Zhao-liang, WU Quan-ying
2023, 16(3): 637-644.   doi: 10.37188/CO.2022-0172
Abstract(199) FullText HTML(142) PDF 9492KB(242)

A white light interferometry micro measurement algorithm based on principal component analysis is proposed to solve the problem of the phase solution in white light interferometry and realize the height measurement of micro morphology. The white light microscopic interference system is used to collect multiple interferograms and reconstruct them into vector form. From a set of interferograms, the background illumination can be estimated by a temporal average, eliminating background light components. Then, the eigenvalues and eigenvectors representing the original data are obtained by a matrix operation. Finally, the phase distribution is calculated by the arctangent function. Experimental results indicate that the measurement result of a standard step height of 956.05 nm by the proposed method is about 953.66 nm and the solution is approximately consistent with the iterative algorithm. In comparison to the iterative algorithm, the processing speed of the proposed method is 2 orders of magnitude faster. The interference fringes with surface roughness of 0.025 μm is analyzed, the mean of the surface roughness calculated by the proposed method is 24.83 nm, and the sample’s standard deviation is 0.3831 nm. The proposed method improves the deficiency of monochromatic interferometry and has the advantages of high speed, low computational requirements and high accuracy.

Lane detection based on dual attention mechanism
REN Feng-lei, ZHOU Hai-bo, YANG Lu, HE Xin
2023, 16(3): 645-653.   doi: 10.37188/CO.2022-0033
Abstract(526) FullText HTML(304) PDF 6660KB(214)

In order to improve the performance of lane detection algorithms under complex scenes like obstacles, we proposed a multi-lane detection method based on dual attention mechanism. Firstly, we designed a lane segmentation network based on a spatial and channel attention mechanism. With this, we obtained a binary image which shows lane pixels and the background region. Then, we introduced HNet which can output a perspective transformation matrix and transform the image to a bird’s eye view. Next, we did curve fitting and transformed the result back to the original image. Finally, we defined the region between the two-lane lines near the middle of the image as the ego lane. Our algorithm achieves a 96.63% accuracy with real-time performance of 134 FPS on the Tusimple dataset. In addition, it obtains 77.32% of precision on the CULane dataset. The experiments show that our proposed lane detection algorithm can detect multi-lane lines under different scenarios including obstacles. Our proposed algorithm shows more excellent performance compared with the other traditional lane line detection algorithms.

Aligning method for point cloud prism boundaries of cultural relics based on normal vector and faceted index features
YANG Peng-cheng, YANG Zhao, MENG Jie, XIAO Yuan, CUI Jia-bao
2023, 16(3): 654-662.   doi: 10.37188/CO.2022-0156
Abstract(149) FullText HTML(95) PDF 5751KB(172)

Three-dimensional reconstruction is a common method for cultural relics information conservation, mainly through point cloud alignment technology to reorganize the spatial point cloud information of cultural relics, and its alignment accuracy has an important impact on cultural relics recovery. To address the problems of low accuracy and poor robustness in the alignment of complex point cloud texture features on the surface of cultural relics, this paper proposes a local point cloud alignment method based on normal vector angle and faceted index features. Firstly, the normal vector angle and covariance matrix thresholds are set according to the point cloud planar characteristics, and the point cloud feature points satisfying both features are extracted; secondly, the point cloud local feature point set is extracted by the K-nearest neighbor search methhod, and the two sets of point cloud center-of-mass positions are overlapped by rigid transformation for coarse alignment; finally, the nearest points are iterated based on ICP for fine alignment. By comparing with the traditional ICP, the point cloud alignment error of the proposed method reduces by 3% and the matching time reduces by 50%, which effectively improves the accuracy and efficiency of alignment and enhances the robustness of point cloud alignment.

3D reconstruction method based on a rotating 2D laser scanner and multi-sensor
ZHANG Xin-rong, WANG Xin, WANG Yao, XIANG Gao-feng
2023, 16(3): 663-672.   doi: 10.37188/CO.2022-0159
Abstract(155) FullText HTML(99) PDF 5297KB(178)

3D reconstruction technology is one of the most popular research directions in machine vision, and has been widely used in the fields of unmanned driving and digital processing and production. Traditional 3D reconstruction methods include depth cameras and multi-line laser scanners, but the point clouds obtained by depth cameras have incomplete and inaccurate information, and the high cost of multi-line laser scanners hinders their application and research. To solve these problems, a three-dimensional reconstruction method based on a rotating two-dimensional laser scanner was proposed. First, a stepper motor was used to rotate a 2D laser scanner to obtain 3D point cloud data. Then, the position of the laser scanner was calibrated by multi-sensor fusion, and the point cloud data was matched by transforming the coordinate system. Finally, the collected point cloud data were filtered and simplified. The experimental results show that compared with depth camera/IMU data fusion, the reconstruction method’s average error of the proposed method is reduced by 0.93 mm, and it is 4.24 mm, the accuracy has reached the millimeter level, and the error rate is also controlled within 2%. The cost of the whole set of equipment is also greatly reduced compared to the multi-line laser scanner. It basically meets the requirements of high precision and low cost and retaining the shape characteristics of the object.

Design and simulation of the dummy thoracic finite element model based on mashine vision
LIU Shuang, CHEN Li-xin, ZHANG Jun-dong, SHA Lu-ming, YU Zheng-lei, XU Tao, ZHANG Qi
2023, 16(3): 673-681.   doi: 10.37188/CO.2023-0005
Abstract(45) FullText HTML(27) PDF 5675KB(34)

This paper focuses on the field of automobile passive safety in my country. By scanning the Hybrid III 50th automobile crash dummy, a finite element simulation model of the dummy chest is constructed. The genetic algorithm is used to optimize the parameters. After optimization, all the indicators of the calibration test meet the requirements of the regulations. The simulation results are consistent with the experimental test results, and the error is less than 5%. Then we put the finite element dummy model containing the chest model into the vehicle system for frontal collision simulation analysis. The results show that the score of chest injury is 80%, and the error of the simulation results is less than 10% compared with the test results. The model has a good degree of simulation and can be used for the study of vehicle crash safety performance.

Phase-extracting method of optical frequency scanning interference signals based on the CEEMD-HT algorithm
YANG Ke-yuan, DENG Zhong-wen, CHEN Wen-jun, YAO Xin, SUN Hai-feng, SHEN Li-rong
2023, 16(3): 682-700.   doi: 10.37188/CO.2022-0173
Abstract(137) FullText HTML(39) PDF 4568KB(150)

Aiming at the problem that the optical frequency scanning nonlinearity affects the phase extracting accuracy of the optical Frequency Scanning Interferometry (FSI) signal, and thus reduces the FSI ranging accuracy, a phase-extracting method based on the Complementary Ensemble Empirical Mode Decomposition and Hilbert Transform (CEEMD-HT) algorithm is proposed in this paper. Based on theoretical derivation and simulation analysis of the CEEMD-HT algorithm, the effectiveness of the algorithm in solving the phase of the non-stationary interference signal in scanning-frequency is verified by simulation. Further simulation experiments were implemented by using the real output optical frequency obtained with FSI ranging system as the simulation conditions. The simulation results showed that the CEEMD-HT algorithm significantly improved the phase extracting accuracy of the interference signal and the FSI ranging accuracy. Finally, the proposed interference signal phase-extracting method was verified via the experiment of the FSI ranging system. The results showed that the ranging repeatability of the measurement system based on the CEEMD-HT algorithm was 2.79 μm in the free space measurement range of 2 m. Compared with EMD-HT and direct measurement methods, the ranging repeatability was improved by 5.19 times and 8.28 times, respectively.

Bandwidth-tunable terahertz metamaterial half-wave plate component
LV Ting-ting, FU Tian-shu, LIU Dong-ming, SHI Jin-hui
2023, 16(3): 701-714.   doi: 10.37188/CO.2022-0198
Abstract(112) FullText HTML(108) PDF 2692KB(175)

We propose a “leaf-type” hybrid metamaterial to realize bandwidth-tunable half-wave plate based on vanadium dioxide (VO2) phase transition. The hybrid metamaterial is regarded as a hollow “leaf-type” metallic structure and act as a dual-band half-wave plate when VO2 film is in the insulating phase. Within 1.01−1.17 THz and 1.47−1.95 THz, it can accomplish y- to x-polarization conversion with a polarization conversion rate over 0.9 and an average relative bandwidth of 26%. The metamaterial becomes a solid core “leaf-type” metallic structure when VO2 is in the metallic phase. Within 1.13−2.80 THz, it can act as a broadband half-wave plate with a relative bandwidth of 85%. The working principle of the bandwidth-tunable half-wave plate is explained by the instantaneous surface current distribution and electric field theory in detail. The proposed “leaf-type” hybrid metamaterial half-wave plate has potential application prospects in THz imaging, sensing and polarization detection.

Fabric image retrieval algorithm based on fractal coding and Zernike moment under the wavelet transform
ZHANG Qin, CAO Yi-qing
2023, 16(3): 715-725.   doi: 10.37188/CO.EN-2022-0021
Abstract(38) FullText HTML(46) PDF 6790KB(34)

A fabric image retrieval algorithm based on fractal coding and Zernike moments under a wavelet transform is proposed, which can quickly and accurately retrieve images from a database that are similar to fabric images submitted for retrieval. Firstly, the low-frequency component is obtained by a wavelet transform, and the transformed low-frequency sub-image is fractally encoded to obtain its coding parameters. Then, the Zernike moment of the low-frequency sub-image is calculated. The fractal coding parameters and Zernike moment under a wavelet transform are combined as the fabric image retrieval characteristic. The algorithm overcomes the problems of low retrieval accuracy and the high time consumption of direct feature extraction under a single feature. Compared with the Basic Fractal Image Compression (BFIC) algorithm, the joint orthogonal fractal parameters with the improved Hu invariant moment and Variable bandwidth Kernel density estimation of Fractal parameters (HVKF) algorithm and the Sparse Fractal Image Compression (SFIC) algorithm, the proposed algorithm ensures the quality and lower encoding time of the reconstructed image. The experiments show that the average precision and average recall of fabric image retrieval are higher than those of existing methods.

Phase measurement with dual-frequency grating in a nonlinear system
QIAO Nao-sheng, SHANG Xue
2023, 16(3): 726-732.   doi: 10.37188/CO.EN.2022-0013
Abstract(208) FullText HTML(164) PDF 2673KB(218)

To gain better phase measurement results in nonlinear measurement systems, a phase measurement method that uses dual-frequency grating after reducing the nonlinear effect is proposed. Firstly, the nonlinear effect of the phase measurement system is discussed, the basic reason for the existence of high-order spectra components in the frequency domain is analyzed, and the basic method used to reduce the nonlinear effect and separate fundamental frequency information is given. Then, on the basis of reducing the nonlinear effect’s influence on the system, the basic principle of phase measurement for the fringe image of a measured object using the dual-frequency grating method is analyzed. To verify the correctness and effectiveness of the proposed phase measurement method, a computer simulation and a practical experiments were implemented with good results. In the simulation, the error value of this method was 27.97% for the method with nonlinear influence, and 52.51% for that with almost no nonlinear influence. In the experiment, the effect of phase recovery produces the best results. This shows that the proposed phase measurement method is effective with a small error.

SSFM-global-error-local-energy method for improving computational efficiency of passively mode-locked fiber laser
YAN Run-bin, HE Xiao-ying, ZHANG Chuan, ZHANG Yin-dong, RAO Lan
2023, 16(3): 733-742.   doi: 10.37188/CO.EN.2022-0016
Abstract(136) FullText HTML(77) PDF 4593KB(146)

We propose a method for improving the computational efficiency of passively mode-locked fiber laser, which is composed by Symmetric Split-step Fourier Method (SSFM) and the Global-Error-Local-Energy (GELE) method for solving propagating equations. Our proposed method relies on the limitation of local energy increment related with global error within a certain value to control the selection of step size. This method has advantage of an automatic step adjustment mechanism. To achieve the same order of computation accuracy, the computational time of our method is 255 s, while SSFM with small constant step size method needs to calculate 3855 s. The computational time of our proposed method is one or two orders of magnitude less than that of the SSFM, which indicates our method can enhance the computational efficiency by a factor up to 10. It could be expanded with high-order algorithms, such as the fourth-order Runge-Kutta in the interaction picture (RK4IP), Adams, predictor–corrector, etc. for improving the accuracy.

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(321) FullText HTML(131) PDF 11662KB(229)

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(481) FullText HTML(180) PDF 7682KB(386)

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(488) FullText HTML(251) PDF 4220KB(325)

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(603) FullText HTML(307) PDF 10445KB(456)

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(276) FullText HTML(138) PDF 3656KB(183)

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(1165) FullText HTML(316) PDF 7237KB(590)

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(485) FullText HTML(279) PDF 12124KB(402)

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(514) FullText HTML(277) PDF 5785KB(468)

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(480) FullText HTML(218) PDF 6306KB(401)

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(832) FullText HTML(407) PDF 6214KB(396)

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(1307) FullText HTML(319) PDF 19381KB(916)

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(446) FullText HTML(292) PDF 7155KB(382)

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(689) FullText HTML(492) PDF 7127KB(485)

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(679) FullText HTML(394) PDF 10167KB(457)

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.

Recent progress on the reconstruction algorithms of structured illumination microscopy
ZHOU Bo, WANG Kun-hao, CHEN Liang-yi
2022, 15(6): 1211-1227.   doi: 10.37188/CO.EN.2022-0011
Abstract(291) FullText HTML(278) PDF 6600KB(382)

As an early component of modern Super-Resolution (SR) imaging technology, Structured Illumination Microscopy (SIM) has been developed for nearly twenty years. With up to ~60 nm wavelengths and 564 Hz frame rates, it has recently achieved an optimal combination of spatiotemporal resolution in live cells. Despite these advantages, SIM also suffers disadvantages, some of which originated from the intrinsic reconstruction process. Here we review recent technical advances in SIM, including SR reconstruction, performance evaluation, and its integration with other technologies to provide a practical guide for biologists.

Advances in organic fluorescent probes for super-resolution imaging of cellular lipid droplets
ZHOU Ri, WANG Chen-guang, LU Ge-yu
2022, 15(6): 1228-1242.   doi: 10.37188/CO.2022-0077
Abstract(479) FullText HTML(296) PDF 9403KB(315)

Lipid droplets are a kind of spherical organelle in eukaryotic cells and are relevant to many cellular physiological processes. Fluorescence imaging techniques are one of the most powerful tools to visualize and study lipid droplets. However, conventional wide-field microscopy and confocal microscopy can only provide a resolution of about 250 nm due to the limitation of optical diffraction. This resolution is quite insufficient for visualizing the small lipid droplets, especially the nascent ones (size of about 30~60 nm). Emerging super-resolution microscopes that can break the diffraction limit (such as stimulated emission depletion microscopy, structured illumination microscopy and photoactivated localization microscopy) have gradually attracted much interest in recent years. To obtain high-resolution fluorescence images of lipid droplets, the advanced fluorescent probes which meet the special requirements of the corresponding super-resolution microscopes are highly essential. This review paper will briefly introduce the working principles of various super-resolution microscopes, discuss the special requirements on the photophysical properties of fluorescent probes, and systematically summarize the research progress of super-resolution imaging of lipid droplets by employing these fluorescent probes. Meanwhile, this review will compare the advantages and shortcomings of different super-resolution techniques for lipid droplets imaging, and prospect their future possible trends.

Advances in multi-dimensional single molecule imaging
LI Meng-fan, CHEN Jian-wei, SHI Wei, FU Shuang, LI Yun-ze, LUO Ting-dan, CHEN Jun-fan, LI Yi-ming
2022, 15(6): 1243-1257.   doi: 10.37188/CO.2022-0088
Abstract(326) FullText HTML(292) PDF 8194KB(333)

Single-molecule imaging is widely used for the reconstruction of three-dimensional subcellular structures. The point spread function is an important window to analyze the information of a single molecule. Besides 3D coordinates, it also contains abundant additional information. In this paper, we reviewed the recent progress of multi-dimensional single-molecule imaging, including spatial location, fluorescence wavelength, dipole orientation, interference phase, etc. We also briefly introduced the latest methods for molecule localization and proposed the further directions for its research.

Multi-target panoramic digital pathology: from principle to application
ZHANG Xin-hua, LI Cai-wei, ZHANG Yu, HUANG Sheng-nan, SHI Han, WU Jun-nan, REN Shi-jie, LIU Ke-han, GAO Tong-lu, SHI Bing
2022, 15(6): 1258-1274.   doi: 10.37188/CO.2022-0091
Abstract(786) FullText HTML(409) PDF 6335KB(384)

Digital pathology has brought new opportunities for remote pathological consultation and joint consultation owing to its convenient storage, management, browsing and transmission. However, because of the limited field of view of a microscope, panoramic imaging cannot be achieved while ensuring a high resolution. The proposal of panoramic digital pathology makes up for this defect and achieves panoramic imaging while ensuring high resolution. However, a single slice can only detect a single target, and disease diagnosis needs to observe the expression of multi-target at the same time. In recent years, multi-target panoramic digital pathology technology has developed rapidly. It has attracted much attention because of its great application potential in drug research and development, clinical research and basic research. Owing to its large field of view, wide range of colors and high flux, the system can detect the expression of various biomarkers on a whole tissue section in situ in a short time to identify the phenotype, abundance, state, and relationship of each cell. Firstly, this paper reviews the development process of digital pathology, panoramic digital pathology and multi-target panoramic digital pathology, as well as the update and iteration of technology in the development process, and illustrates the importance of developing multi-target panoramic digital pathology. Then, the multi-target panoramic digital pathology is described in detail from three perspectives: biological sample preparation, multi-color imaging system and image processing. Next, the applications of multi-target panoramic digital pathology in biomedical fields, such as tumor microenvironments and tumor molecular typing are described. Finally, the advantages, challenges and future development of multi-target panoramic digital pathology are summarized.

Recent development of cryo-correlated light and electron microscopy
LU Jing, LI Wei-xing, XU Xiao-jun, JI Wei
2022, 15(6): 1275-1286.   doi: 10.37188/CO.2022-0095
Abstract(278) FullText HTML(118) PDF 5916KB(240)

Cryo-electron tomography (cryo-ET) has become a cutting-edge technology in life sciences for the investigation of protein complexes directly in their natural state. In cryo-ET, the sample’s thickness must be less than 300 nm and the target molecule must be within the lamella, which is prepared by cryo-Focus Iron Beam (FIB) milling. In order to precisely navigate molecules and to improve the efficiency of sample preparation, cryo-Correlative Light and Electron Microscopy (cryo-CLEM) has been introduced to perform in-situ imaging on the frozen samples. The cryo-CLEM combines the localization advantages of fluorescence imaging with the resolution advantages of electron microscopy. By registering images of light and electrons, frozen samples can be thinned by FIB milling, so the efficiency of cryo-ET sample preparation can be improved. In this paper, we review the latest progress and applications of cryo-CLEM technologies, with a particular focus on super-resolution cryo-CLEM imaging and integrated cryo-CLEM. The advantages and limitations of various methodologies, as well as their application scope, are discussed. A discussion on cryo-CLEM's limitations and potential directions for its future development are also presented.

Trans-scale optical endoscopy imaging technology
WANG Zi-chuan, ZHANG Wei, GUO Fei, JIA Zhi-qiang, WANG Li-qiang, DONG Wen-fei, YANG Qing
2022, 15(6): 1287-1301.   doi: 10.37188/CO.2022-0078
Abstract(605) FullText HTML(353) PDF 8063KB(417)

Due to the advantages of high resolution, multi-scale, multi-dimension, low radiation and easy to integrate, optical imaging technology plays an important role in biomedical field. In the field of endoscopy, how to obtain, process and visualize the endoscopic image information is the core of the problem what optical imaging technology need to solve. The obtaining of trans-scale endoscopic image of patients in the medical clinical is more advantageous to the surgeon for the diagnosis of patients and can improve in accuracy of the operation. The review starts with the application of trans-scale optical imaging technology in the field of endoscopy, focusing on the different optical systems to obtain trans-scale images in clinical endoscopy, including trans-scale optical zoom system, multi-channel imaging system, fiber-scanning imaging system, and expounds its progress and future trends.

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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