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Resolution, super-resolution and spatial bandwidth product expansion——some thoughts from the perspective of computational optical imaging
ZUO Chao, CHEN Qian
 doi: 10.37188/CO.2022-0105
Abstract(80) FullText HTML(30) PDF 18927KB(129)
Abstract:

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.

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
 doi: 10.37188/CO.2022-0085
Abstract(135) FullText HTML(104) PDF 12279KB(150)
Abstract:

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.

Panoramic endoscopic imaging technology and it’s applications
HUO Jia-yi, LI Mian-hao, WANG Zi-chuan, YUAN Bo, YANG Qing, WANG Li-qiang
 doi: 10.37188/CO.2022-0074
Abstract(134) FullText HTML(83) PDF 8055KB(160)
Abstract:

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.

In-vivo across-scales two-photon microscopic imaging technique
CHEN Shuai, REN Lin, ZHOU Zhen-qiao, LI Min, JIA Hong-bo
 doi: 10.37188/CO.2022-0086
Abstract(161) FullText HTML(110) PDF 7253KB(151)
Abstract:

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.

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
 doi: 10.37188/CO.2022-0088
Abstract(116) FullText HTML(104) PDF 8357KB(126)
Abstract:

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.

Terahertz imaging quality improved by light field processing
XIN Tao, PENG Shuo, DONG Li-quan, ZHANG Shao-hui, ZHANG Cun-lin
 doi: 10.37188/CO.EN.2022-0005
Abstract(138) FullText HTML(106) PDF 4064KB(48)
Abstract:

Terahertz (THz) technology becomes increasingly important nowadays, especially in testing-and security-related fields. Extending the field of view and increasing the imaging quality are both vital challenges for THz imaging. To address these problems, we build a THz light field imaging system based on a single-camera scanning configuration, that utilizes the 4D information of the spatial and angular distribution of THz waves. Based on the 4D plenoptic function and the parameterization method with two parallel planes, the intensity consistency of THz propagation is used for refocusing calculation, then a series of refocused images can be obtained by integrating original light field image corresponding to different imaging distances and views. Compared with the Original THz imaging, the field of view and the imaging quality of the THz light field imaging are effectively improved. In our experiment, the field of view was enlarged by a factor of 1.84 and the resolution increased from 1.3 mm to 0.7 mm. Furthermore, information on some obscured targets could also be retrieved by defocusing the obstructions. This method could improve the imaging quality of THz imaging as well as expand its functions, which inspires a new for THz nondestructive testing (NDT) and security inspection.

Recent development of cryo-correlated light and electron microscopy
LU Jing, LI Wei-xing, XU Xiao-jun, JI Wei
 doi: 10.37188/CO.2022-0095
Abstract(48) FullText HTML(21) PDF 5916KB(46)
Abstract:

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) which light microscopy and electron microscopy are performed on in-situ frozen samples has been introduced. 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. 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.

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
 doi: 10.37188/CO.2022-0091
Abstract(253) FullText HTML(91) PDF 6338KB(170)
Abstract:

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 the 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.

Classification model based on fusion of multi-scale feature and channel feature for benign and malignant brain tumors
JIANG Lin-qi, NING Chun-yu, YU Hai-tao
 doi: 10.37188/CO.2022-0067
Abstract(57) FullText HTML(61) PDF 4141KB(104)
Abstract:

Aiming at the problems of complex and inaccurate classification of benign and malignant brain tumors, a classification model was proposed based on the fusion of multi-scale and channel features. The model used ResNeXt as the backbone network. First, the multi-scale feature extraction module based on dilated convolution was used to replace the first convolution layer, which can make full use of dilation rates to obtain the image information from different receptive fields, and combine the global features with significant subtle ones. Second, the channel attention mechanism module was added in the network to fuse the feature channel information in order to increase the attention to the tumor, and reduce the attention to redundant information. Finally, the combination optimization strategy, the MultiStepLR strategy of the learning rate, the label smoothing strategy and the transfer learning strategy on medical images were adopted to improve the learning and generalization abilities of the model. The experiments were carried out on BraTS2017 Dataset and BraTS2019 Dataset, and the classification accuracy were 98.11 % and 98.72 %, respectively. Compared with other advanced methods and classical models, the proposed classification model can effectively reduce the complexity of the classification process and improve the detection accuracy of benign and malignant brain tumors.

Wide-field-of-view and high-resolution HiLo optical sectioning microscopy system
LANG Song, ZHANG Yan-wei, ZHENG Han-qing, XU Lin-yu, WANG Lu-han, GONG Yan
 doi: 10.37188/CO.2022-0087
Abstract(133) FullText HTML(79) PDF 6181KB(157)
Abstract:

The fields of modern biology and biomedicine urgently need wide-field-of-view (FOV), high-resolution microscopic technology and instruments for trans-scale observation of biological samples to meet the requirement of major scientific for research. Limited by the spatial bandwidth product, traditional commercial microscopes cannot meet this demand. Besides, the existing high spatial bandwidth product microscopy systems have problems such as bulky volume and high implementation costs. In this paper, based on the HiLo optical sectioning technology and the self-designed wide-field-of-view and high-resolution objective, a wide-field-of-view and high-resolution HiLo optical sectioning microscopy system was developed. The FOV and imaging resolution of this system were tested. Brightfield imaging experiments were carried out on mouse brain slices by this system and the results were compared with that of OLYMPUS commercial microscope. At the same time, wide-field fluorescence imaging comparison experiments were carried out on wheat seed fluorescent slices. The experiment results show that the FOV of this system reaches 4.8 mm×3.6 mm (the diagonal FOV is 6.0 mm), the lateral resolution reaches 0.74 μm, and the axial resolution reaches 4.16 μm. The comparative experiment proved that this system has the advantages of wide FOV, high resolution and the ability of fast optical sectioning imaging simultaneously. This system can carry out rapid 3D imaging of large-volume biological samples, which will provide strong technical support for researches such as embryonic development, brain imaging, and digital pathology diagnosis.

Multi-channel multiplexing digital holographic imaging for high throughput
HUANG Zheng-zhong, CAO Liang-cai
 doi: 10.37188/CO.2022-0070
Abstract(268) FullText HTML(223) PDF 8141KB(226)
Abstract:

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.

Image photoplethysmography for mental stress detection
RAO Zhi, LI Bing-lin, SUI Ya-ru, JI Xiao-qiang, LI Ming-ye
 doi: 10.37188/CO.2022-0180
Abstract(8) FullText HTML(5) PDF 4718KB(31)
Abstract:

To achieve non-contact daily mental stress detection, this paper proposes a image photoplethysmography to detect mental stress. First, a video of the subject's face is recorded by the cell phone camera. Then, the proposed Dynamic Region of Interest (ROI) extraction method based on Face Mesh is used to obtain the weak skin color changes caused by heart rate fluctuations. Next, the Fast Independent Component Analysis (FastICA) algorithm, wavelet transform and narrowband bandpass filtering are combined to extract the signal and heart rate variability information based on image photoplethysmography. Then, stress-induced experiments are conducted on 30 subjects to screen 14 features for mental stress detection by comparing the differences in heart rate variability parameters between normal and stressful states, and to explore the relationship between short-term mental stress and daily mental stress due to stress induction. Finally, an additional 67 subjects are tested for daily mental stress, and a triple classifier for mental stress detection is built using the machine learning algorithm. The experimental results show that the accuracy of the three classifications of mental stress can reach 95.2%. Given that this method does not require long-term measurements and can accurately detect human mental stress levels using only a smartphone, and that the measurement method is simple, and easy to administer, and does not affect the normal psychological and mental state of the subject, it can be used as a valid tool in psychological research.

Recent progress on the reconstruction algorithms of structured illumination microscopy
ZHOU Bo, WANG Kun-hao, CHEN Liang-yi
 doi: 10.37188/CO.EN.2022-0011
Abstract(58) FullText HTML(107) PDF 6599KB(125)
Abstract:

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.

Large field-of-view optical microscopic imaging technology
WANG Yi-qiang, LIN Fang-rui, HU Rui, LIU Li-wei, QU Jun-le
 doi: 10.37188/CO.2022-0098
Abstract(237) FullText HTML(195) PDF 10670KB(188)
Abstract:

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.

Double-ring-modulated light sheet fluorescence microscopic technique for multi-scale high-resolution 3D imaging
WANG Peng, ZHOU Yao, ZHAO Yu-xuan, FEI Peng
 doi: 10.37188/CO.2022-0093
Abstract(117) FullText HTML(95) PDF 10727KB(131)
Abstract:

In this paper, we propose a non-diffraction Light Sheet Fluorescence Microscopy (LSFM) technique, which readily enables multi-scale 3D fluorescence imaging of diverse biological samples with size ranging from microns to centimeters. To solve the problem of heavy sidelobes in conventional non-diffraction Bessel LSFM, we invent a double-ring-modulated approach which can generate non-diffraction light sheets with ~0.4 to ~5 µm tunable thickness and the ratio of the sidelobe was reduced to less than 30%. Then we built a multi-scale LSFM system based on this novel approach. The system showed versatile multi-scale imaging abilities, such as dual-color 3D dynamic imaging of single live cell, 3D super-resolution imaging of expansion cells and high-throughput 3D mapping of entire meso-scale organs. Therefore, we demonstrate that this multi-scale imaging modality can substantially improve the efficiency of LSFM for advancing various biomedical studies, such as cell biology, tissue pathology, and neuroscience.

Multi-color virtual fluorescence emission difference microscopy
HUANG Yu-ran, ZHANG Zhi-min, DONG Wan-jie, XU Liang, HAN Yu-bing, HAO Xiang, KUANG Cui-fang, LIU Xu
 doi: 10.37188/CO.2022-0080
Abstract(142) FullText HTML(80) PDF 6301KB(66)
Abstract:

Fluorescence emission difference microscopy is a super-resolution imaging technique with strong universality of fluorescent dyes and low phototoxicity. However, due to the limitation of its principle, traditional fluorescence emission difference microscopy has a high system complexity, low stability and limited imaging speed. In order to improve these defects, we design and build a set of multi-color virtual fluorescence difference microscopy system, and it’s imaging method and parameter are analyzed. On the basis of the existing principle of multi-color virtual fluorescence emission difference microscopy, the influence of the signal-to-noise ratio and background is further considered, and a virtual fluorescence emission difference microscopy imaging model that can be verified experimentally is established. The experiments show that the system and method have the characteristics of simple structure, strong background denoising ability, strong universality of fluorescent dyes, and low phototoxicity. Its imaging resolution is 1.9 times higher than that of confocal system, and its imaging speed is doubled compared to the traditional fluorescence emission difference microscopy system. It has obtained good imaging results at three wavelengths, and has been experimentally verified in biological cell imaging.

Trans-scale optical endoscopy imaging technology
WANG Zi-chuan, ZHANG Wei, GUO Fei, JIA Zhi-qiang, WANG Li-qiang, DONG Wen-fei, YANG Qing
 doi: 10.37188/CO.2022-0078
Abstract(210) FullText HTML(95) PDF 8090KB(179)
Abstract:

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.

Advances in organic fluorescent probes for super-resolution imaging of cellular lipid droplets
ZHOU Ri, WANG Chen-guang, LU Ge-yu
 doi: 10.37188/CO.2022-0077
Abstract(186) FullText HTML(182) PDF 9403KB(99)
Abstract:

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.

3D reconstruction method based on rotating 2D laser scanner and multi-sensor
ZHANG Xin-rong, WANG Xin, WANG Yao, XIANG Gao-feng
 doi: 10.37188/CO.2022-0159
Abstract(16) FullText HTML(11) PDF 5571KB(10)
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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 the application of this technology and Research. To solve the above problems, a three-dimensional reconstruction method based on a rotating two-dimensional laser scanner was proposed. First, a stepper motor was used to drive a 2D laser scanner to rotate to obtain 3D point cloud data. Then, the position of the laser scanner was calibrated by the method of multi-sensor fusion, and the point cloud data matching was completed by the coordinate system transformation. Finally, the collected point cloud data were filtered and simplified. The experimental results show: Reconstruction method compared with depth camera/IMU data fusion, the average error is reduced by 0.93 mm, the average error 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 reconstruction method of the multi-line laser scanner. It basically meets the requirements of retaining the shape characteristics of the object, high precision and low cost.

A method for aligning 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
 doi: 10.37188/CO.2022-0156
Abstract(13) FullText HTML(6) PDF 4108KB(8)
Abstract:

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 K-nearest neighbor search extracts the point cloud local feature point set, 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, this method reduces the point cloud alignment error by 3% and reduces the matching time by 50%, which effectively improves the accuracy and efficiency of alignment and enhances the robustness of point cloud alignment.

A study of the method for sea-sky-line detection based on polarization difference images
SU De-zhi, LIU Liang, WANG Kun, WU Shi-yong, LIU Ling-shun, MING Rui-long, GONG Jian
 doi: 10.37188/CO.2022-0181
Abstract(9) FullText HTML(6) PDF 1066KB(12)
Abstract:

Aiming at the problem of sea-sky-line detection in low-contrast infrared images being difficult and easily affected by such interference factors as clouds, strip waves and sea clutter, this paper proposes 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 method of large-scale local contrast accumulation of the polarization difference images is then used to determine the sea-sky-line area. Finally, the accurate detection of small-scale sea-sky-line is completed via combining the methods of 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 the 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, and that fast and accurate sea-sky-line detection can be realized through this algorithm, which in turn has wide applicability to different scenes.

太赫兹人工表面等离子体共面激发与高Q传感
 doi: 10.37188/CO.2022-0204
Abstract(4) PDF 396KB(7)
Abstract:
本文提出使用单层光栅超表面结构耦合的方式实现太赫兹人工表面等离子体激元(SSP)共面激发,克服了通过介质耦合器在实际应用时需要反射测量不便等缺点。在单层金属结构上同时构造周期性光栅和太赫兹SSP复合结构,当太赫兹波垂直入射时,实现光栅波矢和SSP波矢相匹配,激发SSP模式,在透射谱中可以产生高Q值谐振峰,其Q因子可以达到1923。分析了结构参数对光栅耦合超表面透射谱以及色散特性的影响。其次,基于该结构透射谱中的高Q谐振峰,进行传感研究,在谐振中心频率为0.22THz时,实现传感灵敏度为67GHz/RIU。本文所提出的光栅耦合超表面结构,仅仅使用单层超表面结构实现了太赫兹SSP模式的激发以及高Q传感,在诸多实际应用领域具有较大的研究潜力。
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
 doi: 10.37188/CO.2022-0189
Abstract(173) FullText HTML(11) PDF 12002KB(80)
Abstract:

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 those 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.

Multiple Fano resonance properties of nanoring-heptamer metal-dielectric structures
LV Jing-wei, WANG De-bao, LIU Chao, LIU Qiang, WANG Jian-xin, YANG Lin, MU Hai-wei, CHU Paul K
 doi: 10.37188/CO.2022-0170
Abstract(27) FullText HTML(23) PDF 6396KB(36)
Abstract:

In order to achieve tunable multiple Fano resonance characteristics and design a refractive index sensor with high sensitivity, a nanoring-heptamer metal-dielectric composite nanoantenna structure is proposed, and the influencing factors and variation rules of its Fano resonance characteristics are studied by using the Finite Element Method (FEM). Researches show that Fano resonance characteristics of the hybrid nano-antenna is sensitive to the changes of the height, incident angle and internal gap. In addition, the electric intensity and the Purcell factor (PF) under the excitation of the electric dipole source can reach 134.74 V/m and 3214 respectively, which greatly enhances the electric intensity near the center of the nanoantenna. The hybrid nanoantenna has high Sensitivity (S) and Figure of Merit (FOM) 1400 nm/RIU−1 and 17 RIU−1, respectively, which can be used as two significant performance index for evaluating the refractive index sensor with high sensitivity. This paper provides a feasible way to realize the tunability of Fano resonance in the composite nanoantenna and a solid theoretical basis for practical applications such as surface-enhanced Raman scattering, quantum emitters, and refractive index sensors.

Analysis of diffraction effect of microlens array on Shack-Hartmann wavefront sensor
Qinyu Zhu, Meirui Chen, Huanjun Lu, Lila Fan, Jiantao Peng, Huijuan Sun, Guoding Xu, Hongmin Mao, Zhaoliang Cao
 doi: 10.37188/CO.2022-0176
Abstract(51) FullText HTML(33) PDF 5884KB(33)
Abstract:

The diffraction effect of microlens array will affect the detection accuracy of Shack-Hartmann wavefront sensor. Based on Huygens-Fresnel diffraction theory, a two-dimensional microlens array diffraction model is established to simulate and analyze the two-dimensional diffraction spot array generated in the focal plane when the ideal parallel light is incident on the microlens array. First the maximum centroid calculation error is determined by calculating the centroid error in the process of diffraction spot shifting by one pixel. Then the wavefront is reconstructed by using the modal method to obtain the wavefront detection error. The simulation results show that the maximum wavefront error caused by diffraction is 0.125 λ at 0.21 and 0.79 pixels offset, that is, when the wavefront deflection is 0.03° and 0.13°. Finally, an experiment is performed to verify the effectiveness of the error calculation method. This work provides a theoretical basis for the design of Hartmann wavefront detector.

Multiple scattering transmission characteristic of polarized light in ellipsoidal fine particles
WANG Peng-cheng, ZHANG Su, SHEN Cheng-biao, ZHAN Jun-tong, DUAN Jin, LI Ying-chao, LIU Zhuang
 doi: 10.37188/CO.2022-0144
Abstract(26) FullText HTML(29) PDF 4059KB(29)
Abstract:
Objetive

To investigate the multiple scattering transmission characteristic of polarized light in ellipsoidal fine particles, the simulation and experiment verification system of black carbon aerosol particles was established.

Method

The polarization transmission characteristic after multiple scattering of the randomly oriented ellipsoidal fine particles are studied by combining T-matrix with Monte Carlo method. The half-material simulation environment testing was established to verify the simulation algorithm, and the ellipsoidal fine particles were prepared by extending ganoderma lucidum spores burning time. The size distribution and optical thickness of the ellipsoidal fine particles were measured by malvern spraytec and light power meter respectively. The simulation result can be proved by combining the experiment with simulation.

Result

: The results show that, with the increasing of the concentration of black carbon ellipsoidal fine particles, the degree of polarization (DOP) of the horizontal, vertical, 45° linearly polarized light and the right circularly polarized light all decrease, and the polarization preservation ability of three kinds of linear polarizations are basically consistent. The polarization preservation ability of circularly polarized light is gradually superior to the linearly polarized light with the increasing of concentration. The gap between the linear and circular polarizations becomes more larger and the maximum value is reached at 3.12 optical thickness. When optical thickness is greater than 3.12, the DOP difference between the circularly and the linearly polarized lights tend to be stable. By calculation, the percent agreement between simulation and experiment is better than 70.84%.

Conclusion

These results can expand the environmental applicable range of polarization detection and provide theoretical support for studying the polarization detection of atmospheric non-spherical particles.

Visible light emission of Ultraviolet polarization sensitive CsPbBr3 Nano-films
JI Yu-jin, CHU Xue-ying, DONG Xu, LI Jin-hua
 doi: 10.37188/CO.2022-0152
Abstract(22) FullText HTML(18) PDF 4280KB(30)
Abstract:

In order to detect polarized ultraviolet light by visible optical elements, CsPbBr3 nanocrystals/metal wire-grid composited films were fabricated. The stability of its fluorescence was improved by depositing Al2O3 passivation layer. The green fluorescence of perovskite nanocrystals film was sensitive to the polarization of ultraviolet exciting light. The crystal structure of the CsPbBr3 nanoparticles was cubic. The average size of the nanoparticles with a cubic morphology was about 39 nm. An obvious green fluorescence at about 530 nm were observed under ultraviolet light excitation. The emission of the CsPbBr3 nanocrystals/metal wire-grid composited film periodically changed with the polarization direction of the excited light. The luminous polarization ratio is about 0.54. The fluorescence was enhanced when Al2O3 was deposited on its surface by atomic layer deposition technology. The polarization ratio of the passivated film can still reach 0.36. The above results show that the stability and polarization of perovskite nanocrystals film can be optimized by passivation and metal wire-grids, respectively. The ultraviolet polarization sensitive nanocrystals composited film exhibits important application value in the fields of ultraviolet polarization detection and liquid crystal display.

Study on Flux measurement method for High Flux Spot
WEI Xiu-dong, ZHAO Yu-hang, ZHANG Ya-nan, XU Ying-chao
 doi: 10.37188/CO.2022-0139
Abstract(45) FullText HTML(22) PDF 4131KB(35)
Abstract:

A new method for measuring the flux distribution of high-magnification convergent radiation spot is proposed. The 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 polynomial, and finally the radiation spot is obtained. In order to verify the accuracy and feasibility of the measurement method, a high-magnification convergent radiation spot flux distribution measurement experiment was carried out, and the direct measurement results of the radiant flux sensor were compared. The results show that the measurement results of the new method are consistent with the direct measurement results, and the average deviation is < 0.54%. Through analysis, the measurement uncertainty of this measurement method is 4.35%, and the measurement accuracy is higher than the traditional measurement. The method has been improved to meet the needs of practical applications.

Phase measurement with dual-frequency grating in nonlinear system
QIAO Nao-sheng, SHANG Xue
 doi: 10.37188/CO.EN.2022-0013
Abstract(37) FullText HTML(29) PDF 618KB(45)
Abstract:

To gain better phase measurement results in the nonlinear measurement system, a phase measurement method which uses dual-frequency grating after reducing nonlinear effect almost 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 to reduce the nonlinear effect and separate the fundamental frequency information is given. Then, on the basis of reducing the nonlinear effect influence for the system, the basic principle of the phase measurement for the fringe image of the measured object using the dual-frequency grating method is analyzed. To verify the correctness and effectiveness for the proposed phase measurement method, computer simulation and practical experiments are implemented, and good results are obtained. In the simulation, the error value of this method is 27.97% of the method with nonlinear influence, and 52.51% of with almost no nonlinear influence. In the experiment, the effect of phase recovery is the best. It shows that the phase measurement by using this method mentioned in this paper has good effect and small error.

Design and fabrication of an optical film for an external cavity diode laser
YOU Dao-ming, TAN Man-qin, GUO Wen-tao, CAO Ying-chun, WANG Zi-jie, YANG Qiu-rui, WAN Li-li, WANG Xin, LIU Hen
 doi: 10.37188/CO.EN.2022-0010
Abstract(44) FullText HTML(41) PDF 6458KB(72)
Abstract:

The optical film is one of the most crucial components of the external cavity diode laser (ECL). However, the widely used optical film that employs the plane wave method (PWM) is not ideal in ECL. The finite-difference time-domain (FDTD) method is used to analyze this problem with the effect facet dimensions and structure taken into account. According to the simulation, PWM's film suffers from poor reflectivity and deviation of the reflection curve, which significantly affects performance. Therefore, the optical film design is optimized and verified by experiments. Magnetron sputtering is used to fabricate the optical film, which is then applied to ECL. The measurement results show that the reflectivity of Anti-Reflection (AR) film is reduced by 30% after optimization, while the reflectivity of High-Relection (HR) film increased by 7% to 96%. The prepared ECL has more than 650 mW of single-mode power with a 3 dB linewidth of less than 90 pm. In this paper, the optical film suitable for ECL is designed and fabricated, and provides a reference for optical films in ECLs and other semiconductor optoelectronic devices.

Research progress of grating projection on machine 3D topography inspection technology
LYU Hong-yu, LI Mao-yue, CAI Dong-chen, ZHAO Wei-xiang
 doi: 10.37188/CO.2022-0083
Abstract(33) FullText HTML(20) PDF 6731KB(61)
Abstract:

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, this paper discusses and summarizes 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, predictions 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.

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
 doi: 10.37188/CO.2022-0172
Abstract(40) FullText HTML(26) PDF 9235KB(69)
Abstract:

in order to save the problem of the phase solution in white light interferometry and realize the height measurement of micro morphology, white light interferometry micro measurement algorithm based on principal component analysis was proposed. 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 matrix operation. Finally, the phase distribution is calculated by arctangent function. Experimental results indicate that the measurement result of standard step height of 956.05 nm by the proposed method is about 953.66 nm, the solution is approximately consistent with the iterative algorithm, in comparison to the iterative algorithm, the average time of the proposed method is 2 orders of magnitude faster. The interference fringes with surface roughness of 0.025 μm were analyzed, the mean of surface roughness calculated by the proposed method was 24.83 nm, and the sample standard deviation is 0.3831 nm. The proposed method improves the deficiency of monochromatic interferometry and has advantages of low computational requirements, fast and high accuracy.

Imaging comparison experiment of an underwater imaging system with a semiconductor white laser, a monochromatic laser and an led white light as the light source
JIANG Zi-qi, LIU Xiao-mei, CAI Fu-hong, ZHANG Dian, CAI Wei-yu, LIU Hua
 doi: 10.37188/CO.EN.2022-0012
Abstract(27) FullText HTML(30) PDF 9191KB(60)
Abstract:

To solve the problems of short illumination distance and narrow spectral range in the current underwater detection technology, an underwater semiconductor white laser imaging system was established. The quality of the images captured by the system under different light sources and different conditions was studied. A white laser with a power of 220 mw and a color temperature of 6469 K synthesized by an RGB semiconductor laser is used as the underwater lighting source, which is respectively compared with three RGB monochromatic lasers and an LED white light source under different conditions. For these images, different algorithms are used to process, analyze and evaluate their quality. The results indicate that when the white laser is used as the underwater light source, the collected image is not only better than that with the LED white light source with respect to information detail and structural integrity, but also better than the monochrome laser in color reproduction of the target and the integrity of the edge feature information. The semiconductor white laser has the advantages of concentrated energy, strong color rendering, and high illuminance, and its light source performance can meet the requirements of underwater low-illumination imaging. With the same imaging system and imaging distance, images with stronger authenticity, better texture and more target feature information can be obtained.

Research progress of gas detection based on thermoelastic spectroscopy
LOU Cun-guang, DAI Jia-liang, LI Rui-kai, LIU Xiu-ling, YAO Jian-quan
 doi: 10.37188/CO.2022-0137
Abstract(82) FullText HTML(23) PDF 8216KB(69)
Abstract:

Laser-induced thermoelastic spectroscopy (LITES) is a new developed gas detection technology that based on the thermoelastic effect of quartz tuning fork (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 measuring gas concentration based on LITES is firstly analyzed. Secondly, from the perspective of various technical methods, this paper introduces the methods for improving the sensitivity of the QTF detector, 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 coefficient (NNEA). Finally, the practical application of LITES in the field of gas detection technology is briefly reviewed, and the methods for further improving the sensitivity are summarized and prospected.

Design of solar concentrated uniform line light source of composite ellipsoid cavity
YANG Yi, ZHANG Xiangxiang, LU Yu, KONG W J
 doi: 10.37188/CO.2022-0138
Abstract(68) FullText HTML(29) PDF 2010KB(77)
Abstract:

Objective: In order to implement a solar direct pumping slab high power laser, a linear uniform high-power density pump source is studied. Method: In this paper, the design method of a high-power density uniform linear light source is proposed by combining the first-order concentrating system with seven confocal ellipsoids to form a composite ellipsoid cavity. Each ellipsoid realizes the equal radiation flux segmentation of the circular first focal spot. The mirror imaging characteristics do not significantly decrease the peak power density. After decomposition, the mirror spot forms a uniform linear light source at the second point of focus. The mathematical model of equal radiation flux is given by coordinate changes, and the rotation and translation parameters of each ellipsoid are solved by the annealing algorithm. Result: The first-order system is composed of a Fresnel lens with a radius of 30 mm, a focal length of 70 mm and with a = 3.4 mm, c = 3.15 mm single ellipsoidal cavity. The second-order composite ellipsoidal cavity concentrating system is attached. The effective length is 12 mm, the peak power density is 1.09 × 106 W/m2, and the uniformity is 95.46 %. Conclusion: Compared with the contribution of each ellipsoid parameter to the uniformity, the uniformity effect is significantly improved when the rotation parameter θ of the middle ellipsoid is 1.4°. The change of the edge ellipsoid parameter Δ has a significant influence on the effective length of the linear light source, and its optimal value is 0.53 mm.

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
 doi: 10.37188/CO.2022-0134
Abstract(370) FullText HTML(199) PDF 8543KB(150)
Abstract:

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.

Design of compound eye optical system with hexagonal band arrangement and common optical path
FAN Chen, LIU Jun, GAO Ming, LV Hong
 doi: 10.37188/CO.2022-0116
Abstract(60) FullText HTML(25) PDF 11493KB(76)
Abstract:

In order to solve the challenges of low space utilization and small aperture size for the sub-eye in bionic compound eye systems, a design method for a large aperture compound eye system with a hexagonal ring arrangement is proposed in this paper. Using the filling factor theory, taking the traditional curved surface circular arrangement as the control group, it is demonstrated that the hexagonal band arrangement model can effectively improve the space utilization of a large-aperture compound eye system. Aiming at the limited target information acquisition of a single-band compound eye system, an infrared dual-band common optical path imaging form was designed, supplemented by a two-color image sensor, which enhanced the multi-dimensional ability of the compound eye system to obtain information. At the same time, a mathematical model of the sub-aperture positioning of the hexagonal band arrangement is established. The bionic compound eye system is composed of 91 sub-apertures with an entrance pupil diameter of 16mm, a focal length of 48mm and a field of view of 9°. The combined total field of view of the sub-apertures is 96°×85°. The focal length of the relay system is 6.14 mm. In a temperature range of −40℃−+60℃, the sub-aperture and the relay systems basically have no influence from thermal differences. The cold reflection effect of the detector can be ignored. The simulation results show that the RMS radius of each sub-channel is smaller than the airy spot and the optical distortion value of each sub-channel is less than 0.1%. The MTF of the edge sub-channel in the MWIR/LWIR band is above 0.5 at 17 lp/mm. The system has a compact structure and strong detection ability, and can be used for multi-target detection and recognition in complex environments.

Study on measurement repeatability of high power laser measuring device based on light pressure
ZHAO Li-qiang, SUN Zhen-shan, YU Dong-yu, YANG Hong, ZHANG Yun-peng, SUN Qing
 doi: 10.37188/CO.2022-0092
Abstract(78) FullText HTML(25) PDF 5050KB(100)
Abstract:

Measurement repeatability is the largest uncertainty component of a light pressure measurement device, which directly affects the accuracy of the measurement results. In order to improve the accuracy of the measurement power in the process of high-power laser measurement, a high-power laser measuring device based on light pressure is built. Quality measurement repeatability and laser power measurement repeatability experiments were carried out, and the results of the two experiments were compared and analyzed. The experimental results show that the measurement repeatability of the light pressure measuring device gradually decreased with the increase of the measured mass and the measured laser power, indicating that the light pressure method has more advantages in measuring high-power lasers. In the laser power measurement repeatability experiment, the influence of eccentric loads and airflow disturbance is avoided, so the laser power measurement repeatability is better than the measurement repeatability calculated according to the equivalent mass. The research results have guiding significance for further improving the measurement accuracy of the light pressure method in the future.

Quantitative analysis of thorium in graphite using femtosecond laser-induced breakdown spectroscopy
LIU Xiao-liang, WANG Lan, PENG Ling-ling, LI Xiao-yan, LIU Yun-hai, ZOU Chun-Yan
 doi: 10.37188/CO.2022-0082
Abstract(54) FullText HTML(51) PDF 3959KB(92)
Abstract:

In order to promote the application of laser-induced breakdown spectroscopy (LIBS) in the nuclear industry, in this paper, a femtosecond LIBS(fs-LIBS) system was used to quantitatively analyze Thorium (Th) in a highly pure graphite matrix. According to the Th concentration in the Thorium-based fuel, a total of 9 homemade Th2O3-graphite mixture samples with Th concentrations that varied from 0.35% to 35.15% were prepared by the standard addition method. The favorable experimental parameters such as the treatment methods for LIBS detection, laser pulse energy and delay times were studied before the quantitative analysis. The results show that the signal intensity of the fs-LIBS spectrum acquired by the scanning with moving method is significantly higher than that without the moving method. For the Th I 396.21 nm line, the Relative standard deviation (RSD) value of multiple measurements for the scanning method was just 5.7%, which was much lower than that of without the moving method (20.4%). The Th spectral lines show obvious saturation due to the self-absorption effect in the higher concentration region, and thus the basic calibration method was no longer applicable. Therefore, an exponential function was used to fit the spectral line intensity and concentration in the whole concentration region, and the concentration saturation thresholdvalues corresponding to the analytical lines Th I 394.42, 396.21, and 766.53 nm were obtained. The basic calibration method has good detection performance when the calibration curves were constructed by using a lower concentration below the saturation threshold. For the peak area and peak intensity of each analytical line, using the internal standard method with the internal standard line (C I 247.85 nm), a good linear relationship can be found between them and the Th concentrations in the whole concentration region, especially for analytical line Th I 766.53 nm with a higher saturation threshold. The internal standard method had good prediction performance for unknown samples with higher concentrations. The above results show that fs-LIBS has the potential to monitor and analyze the thorium concentration in the thorium-based fuel cycle.

Theoretical investigation on super-resolving refractive index measurement with parity detection
WANG Qiang, WANG Qian-qian, WANG Zhen, HAO Li-li
 doi: 10.37188/CO.2022-0119
Abstract(128) FullText HTML(10) PDF 4102KB(53)
Abstract:

The refractive index measurements based on traditional wave optical methods are mainly depended on intensity and wavelength detection strategies. An interferometric spectrometer is generally used as the best wavelength detecting device, this device is used to measure signal intensity by optical power meter, analyze the change of fringe numbers and record the corresponding optical path difference, then calculate the wavelength of signal light. Therefore, its essence is still based on intensity detection. However, the resolution of interference signal with intensity detection is restricted by classical diffraction limit, thus its resolution is difficult to further improve. In order to solve this bottleneck problem, parity detection which could break through the classical resolution limit and realize super-resolving refractive index measurement is proposed in this paper. According to the theory of quantum detection and estimation, the expressions for signals and their corresponding sensitivities of refractive index measurement with parity and intensity detections were derived respectively and their numerical comparison was carried out. At the same time, the influences of loss on resolution and sensitivity of the output signal were investigated. Numerical results show that parity detection has enhanced resolution \begin{document}${\text{2{\text{π}} }} \sqrt {\text{N}}$\end{document} times comparing to intensity detection and realizes super-resolving refractive index measurement, meanwhile its best sensitivity could approach to the refractive index measurement shot noise limit \begin{document}${\lambda \mathord{\left/ {\vphantom {\lambda {\left( {2{\text{π}} l\sqrt N } \right)}}} \right. } {\left( {2{\text{π}} l\sqrt N } \right)}}$\end{document}. Losses could reduce signal's sensitivity and resolution, in addition to the greater losses and lower photon number, the resolution of parity detection is always better than that of intensity detection. Finally, based on the detection itself, the physical essence of the super-resolving refractive index measurement is analyzed.

Spatial pulse position modulation multi-classification detector based on deep learning
WANG Hui-qin, HOU Wen-bin, HUANG Rui, CHEN Dan
 doi: 10.37188/CO.2022-0106
Abstract(32) FullText HTML(41) PDF 2590KB(53)
Abstract:

In order to effectively avoid high computational complexity when using maximum likelihood (ML) detection, a deep learning-based spatial pulse position modulation (SPPM) multi-classification detector is proposed by combining a deep neural network (DNN) and step detection. In the detector, the DNN is used to establish a non-linear relationship between the received signal and the PPM symbols. Thereafter, the subsequent received PPM symbols are detected according to this relationship, so as to avoid the exhaustive search process of PPM symbol detection. The simulation results show that with the proposed detector, the SPPM system approximately achieves optimal bit error performance on the premise of greatly reducing detection complexity. Meanwhile, it overcomes the error platform effect caused by K-means clustering (KMC) step classification detection. When the PPM order is 64, the computational complexity of the proposal is about 95.45% and 33.54% lower than that of ML detectors and linear equalization DNN detectors, respectively.

Research progress of raman lidar temperature and humidity pressure detection technology
LIU Dong, YAO Qing-rui, ZHANG Si-nuo, GAO Jia-xin, WANG Nan-chao, WU Jiang, LIU Chong
 doi: 10.37188/CO.2022-0145
Abstract(73) FullText HTML(28) PDF 5304KB(48)
Abstract:

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.

Study of 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
 doi: 10.37188/CO.2022-0142
Abstract(29) FullText HTML(20) PDF 5287KB(53)
Abstract:

In a distance-selected imaging system based on single-photon detection, a short-pulse laser is emitted and between the transmitter and receiver for synchronization control, and the detector operates in photon counting mode and integrates in time to complete the imaging. In this paper, 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 these two types of narrow pulse generation circuits 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.

Real-time detection of infrared ammonia leakage through lightweighted shuffling self-attention
ZHANG Yin-hui, ZHUANG Hong, HE Zi-fen, YANG Hong-kuan, HUANG Ying
 doi: 10.37188/CO.2022-0127
Abstract(12) FullText HTML(11) PDF 6077KB(52)
Abstract:

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 realizes 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%. This paper provides 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.

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
 doi: 10.37188/CO.2022-0101
Abstract(34) FullText HTML(21) PDF 5011KB(55)
Abstract:
Objective

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.

Method

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.

Results

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 0.084μm.

Conclusion

The designed high-precision optical alignment system solves the urgent need for 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.

Sub region curvature sensing method for survey telescope with larger aperture
AN Qi-chang, WU Xiao-xia, ZHANG Jing-xu, LI Hong-wen, ZHU Jia-kang
 doi: 10.37188/CO.2022-0117
Abstract(70) FullText HTML(38) PDF 4972KB(107)
Abstract:

The large aperture sky survey telescope needs closed-loop error correction based on the feedback of its wavefront sensing system, so as to give it a better confirm to its limit detection ability. In this paper, firstly, the basic theoretical expression of sub region curvature sensing is derived. Then, a joint simulation model is established. The process of sub region curvature sensing is simulated and analyzed by using the combination of optical design software and numerical calculation software. Finally, by setting up a desktop experiment, the cross-comparison of single- and multi-target curvature sensors is carried out to verify the correctness of the algorithm. Compared to the traditional active optical technology, the method proposed in this paper can improve the detection signal-to-noise ratio and sampling speed by expanding the available guide stars. For the standard wavefront, compared with the single guide star curvature sensor, the error is 0.02 operating wavelengths (RMS), and the error is less than 10%, which can effectively improve the correction ability of the active optical system.

Dynamic 3D measurement error compensation technology based on phase-shifting and fringe projection
CAO Zhi-rui
 doi: 10.37188/CO.EN.2022-0004
Abstract(47) FullText HTML(56) PDF 1891KB(91)
Abstract:

In the process of dynamic 3D measurement based on phase-shifting and fringe projection, the ideal correspondence between object points, image points and phases in different fringe images is destroyed. On this condition, the application of traditional phase formulas will produce significant measurement errors. In order to reduce the dynamic 3D measurement error, the basic principle of the error is firstly analyzed, and the errors are equivalent to the phase-shifting errors between different fringe images. Then, a dynamic 3D measurement error compensation method is proposed, and this method combines the advanced iterative algorithm based on least squares and the improved Fourier assisted phase-shifting method to realize the high-precision calculation of random step-size phase-shifting and phase. The actual measurement results of a precision ground aluminum plate show that the dynamic 3D measurement error compensation technology can reduce the mean square errors of dynamic 3D measurement by more than one order of magnitude, and the dynamic 3D measurement accuracy after compensation can be better than 0.15mm.

Research progress of monolithic integration master-oscillation power-amplifiers
TAN Man-qing, YOU Dao-ming, GUO Wen-tao, Wei-hua LIU
 doi: 10.37188/CO.2022-0022
Abstract(194) FullText HTML(109) PDF 6277KB(152)
Abstract:

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 MOPAs’ epitaxial layer, facet optical film and electrode aspects, we then summarized the optimal design of monolithic integrated MOPAs. After that, we sorted 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 prospected the development trend of monolithic integrated MOPA.

Spectral diagnosis of an arc jet actuator
YUAN Ye, TIAN Leichao, GUO Cheng, ZHAO Qing
 doi: 10.37188/CO.2022-0097
Abstract(40) FullText HTML(30) PDF 5307KB(88)
Abstract:

At present, the simulation research of arc actuator is only limited to obtaining the working characteristics of the plasma generated by the actuator, such as potential, pressure, temperature and velocity, while the plasma state is only limited to diagnosing its electron temperature and electron density by spectrum. The two are separated. This paper attempts to unify the two. Therefore, the arc jet plasma actuator designed here adopts the finite element method to solve the nonlinear multi physical equations. The working characteristics of the arc jet plasma actuator are numerically simulated, and the potential, pressure, temperature and velocity distributions inside the actuator are obtained. On this basis, the electron density is calculated, The simulation calculation model of the plasma state (electron temperature and electron density) of the actuator is obtained from the working condition of the actuator. Then the spectral diagnosis of jet plasma is carried out by using the emission spectral diagnosis method, and the electron density of plasma is calculated by using the intensity ratio method of discrete spectral lines. The diagnostic experiment of arc plasma actuator shows that the maximum electron temperature is 10505.8 k and the maximum electron density is 5.75 e + 22 m−3. For the plasma electron temperature and plasma density under different working conditions, the experimental and simulation results increase with the increase of inlet gas flow and discharge current. It shows that our simulation model of plasma state is reasonable and applicable for our miniaturized arc jet actuator with high jet velocity. At the same time, it also shows that our unified consideration is basically successful. Of course, there are still areas worthy of further improvement.

Positioning algorithm for laser spot center based on BP neural network and genetic algorithm
ZHANG Jing-yuan, CHEN Bei-bei, YANG Yong-xing, ZHU Qing-sheng, LI Jin-peng, ZHAO Jin-biao
 doi: 10.37188/CO.2022-0084
Abstract(47) FullText HTML(38) PDF 3779KB(96)
Abstract:

The traditional laser spot center positioning algorithm in a vibrating environment has problems such as long processing time and low accuracy. This paper proposed a laser spot center positioning method based on a genetic algorithm optimized BP neural network. This algorithm uses a BP neural network to predict the spot center position and a genetic algorithm to optimize the neural network. Based on the BP neural network, the spot center position derived by the gray weighted centroid method, centroid method, Gaussian fitting method, and the radius of laser spot obtained by the centroid method are used to predict the actual center position of the spot. Genetic algorithms are used to optimize the weights and thresholds of neural networks to improve prediction accuracy. An experimental platform is established to simulate the vibration environment by applying perturbations to the optical system and the data is collected for neural network training and algorithm verification. The experimental results show that the number of calibration test iterations before and after optimization is 55 and 29, and the average errors are 0.81 pixels and 0.45 pixels, respectively. Under the optimization of the genetic algorithm, the iteration speed and prediction accuracy of the neural network algorithm is improved.

Recent progress on synthesis and optical characterization of two-dimensional Bi2O2Se
XIE Bing, AN Xu-hong, ZHAO Wei-wei, NI Zhen-hua
 doi: 10.37188/CO.2022-0071
Abstract(66) FullText HTML(58) PDF 18910KB(107)
Abstract:

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.

Improving sensitivity by multi-coherence of magnetic surface plasmons
YANG Zongmeng, XING Qian, CHEN Yian, HOU Yumin
 doi: 10.37188/CO.EN.2022-0009
Abstract(82) FullText HTML(70) PDF 4516KB(104)
Abstract:

This paper studies the coherence of magnetic surface plasmons in one-dimensional metallic nano-slit arrays and proposes a double-dip sensing method to improve sensitivity. Different from the conventional way of scanning wavelength at a fixed incident angle, coherence of surface plasmons is investigated by changing the incident angle at a fixed wavelength. Due to the retardation effect, two coherence dips move in opposite directions as the refractive index of the surrounding medium changes. Compared with one dip used for sensing, two oppositely moving dips can efficiently improve the sensitivity. The sensitivity of two dips can reach 141.6°/RIU while the sensitivities of two single dips are 39.2°/RIU and 102.4°/RIU respectively. Besides, the inconsistency between the refractive index of slit medium and upper medium has few influences on the sensing performance, which can lead to wide practical applications.

Temperature control method of CO2 laser operating in airborne wide temperature range
ZHAO Zi-yun, CHEN Fei, ZHANG Kuo, HE Yang
 doi: 10.37188/CO.2022-0089
Abstract(52) FullText HTML(34) PDF 750KB(91)
Abstract:

Airborne lidar is an important means to achieve long-range accurate atmospheric monitoring. The laser wavelength is consistent with the absorption spectrum of most atmospheric pollutants and chemical substances, which makes it an important laser source for airborne lidar. However, it is difficult to design a temperature control system for airborne CO2 laser to work in a wide temperature range of −40 °C−55 °C under the condition of controlling volume and weight. This paper proposes a temperature control method. In the method, the laser characteristic and environment temperature are used as input, thermo electric cooler and forced air cooling are combined to control the laser temperature. According to the structure and heat transfer characteristics of laser, thermo electric cooler and forced air cooling, the finite element model of temperature control method is established, and the temperature control performance of laser is optimized based on the model. In the high temperature environment of 55 °C, the temperature of the laser is controlled at 40 °C, after the temperature control system works for 25 min. In the low temperature environment of −40 °C, the laser temperature is controlled at 25 °C after the temperature control system works for 20 minutes, which meets the normal working requirements of the laser. According to the laser and the established temperature control method, the experimental research on the working ability of the laser in high and low temperature environment is carried out, the temperature data of the laser in the experimental process is collected, and the laser output power is measured under high and low temperature conditions. The experimental results show that the experimental measured temperature data is consistent with the finite element simulation results, the error between them is less than 10%. The laser with proposed temperature control method can work steadily, and the output power of the laser is consistent with that of the laser at room temperature.

A novel methane and hydrogen sensor with surface plasmon resonance-based photonic quasi-crystal fiber
LIU Qiang, ZHAO Jin, SUN Yu-dan, LIU Wei, WANG Jian-xin, LIU Chao, LV Jing-wei, WANG Shi-miao, JIANG Yu, CHU PaulK
 doi: 10.37188/CO.EN.2022-0006
Abstract(83) FullText HTML(50) PDF 4373KB(115)
Abstract:

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.

The Poynting vector and angular momentum density of cosh-Pearcey-Gaussian vortex beams in uniaxial crystals
Mengting Liang, Ke Cheng, Ling-yun Shu, Sai Liao, Cenghao Yang, HongWei Huang
 doi: 10.37188/CO.EN.2022-0007
Abstract(68) PDF 2784KB(116)
Abstract:
We investigate a family of the cosh-Pearcey-Gaussian vortex (CPeGV) beams, obtain the general propagation expressions of a CPeGV beam, and study the longitudinal and transverse Poynting vector and angular momentum density (AMD) when the CPeGV beams propagate in uniaxial crystals. The effects of the cosh modulation parameter, topological charge, and propagation distance on the propagation properties of CPeGV beams are discussed. A larger cosh modulation parameter can lead the energy transfer significantly along the transverse Poynting vector direction. Moreover, we also investigate how the cosh modulation parameter and topological charge influence the propagation properties in the far-field. A larger cosh modulation parameter can lead AMD to present four-lobes structures rather than usual parabolic curves. Our investigation will provide a better understanding of the state of the CPeGV beams propagating in uniaxial crystals and be useful for applications in information transmission.
Flexible fiber grating hydrophone array theoretical and experimental research
ZHU Miao, GU Hong-can, SONG Wen-zhang
 doi: 10.37188/CO.2022-0079
Abstract(60) FullText HTML(44) PDF 7177KB(131)
Abstract:

In order to improve the suitability of the fiber hydrophone towing line array, a flexible fiber grating hydrophone array was proposed.The sound pressure sensitivity of three flexible fiber grating hydrophones was calculated according to the mechanical theoretical model,and the influence factors were compared and analyzed. The 2-element flexible fiber hydrophone sample arrays with diameters of 10 mm,12 mm and 16 mm were developed through finite element simulation for frequency response analysis. The sensitivity was measured by vibration liquid column experiment. The experimental results show that the response is flat within the frequency range of 200−800 Hz, and the average sound pressure sensitivities of hydrophone arrays with different structural parameters are −160.87 dB, −154.59 dB, and −156.73 dB, respectively. The theory and simulation analysis are verified. By further optimizing the material and structure parameters and using weak reflection fiber grating, the integrated flexible hydrophone array with hundreds elements can be constructed according to the design in this paper.

Double doughnut-shaped focal spots with controllable position in axial direction
TIAN Yu-yuan, ZHANG Jia-qi, JIANG Xiao-tong, SUN Mei-yu, SHI Qiang, ZHU Lin-wei
 doi: 10.37188/CO.2022-0036
Abstract(75) FullText HTML(59) PDF 5334KB(143)
Abstract:

In order to generate double doughnut-shaped focal spots in adjustable position along axial direction. Based on a formula of annular radius derived from vector diffraction integral, a vortex phase zone plate was designed to produce the double doughnut-shaped focal spots in axial direction. The focusing properties of the modulated vortex phase zone plate was further investigated in tightly focused system. First, integral formulas of linearly and circularly polarized vortex beams were calculated under high NA focusing condition. Then the intensity distributions of linearly and circularly polarized vortex beams in high NA focusing system were simulated by the integral formulas with various axial shifting distances and topological charges. Finally, the corresponding experimental results of linearly and circularly polarized light were also given, utilizing a spatial light modulator loaded on double doughnut-shaped phase patterns. The double doughnut-shaped focal spots with the topological charge of 1 and axial distances of ±10 μm and ±15 μm were produced when the incident light was linear polarization. As well as the double doughnut-shaped focal spots with axial distances of ±20 μm and topological charge of 1−4 were also produced when the incident light was circular polarization. The simulated and experimental results demonstrated that two doughnut-shape focal spots with controllable axial shifting distance and dark spot size could be produced in the tight focusing region of a high NA objective when it modulated by the vortex phase zone plate. This kind of vortex phase zone plate could be applied in the field of optical micromanipulation, two-beam super-resolution nanolithography, and stimulated-emission-depletion fluorescence microscopy (STED).

Laser intensity distribution measurement method based on tomographic imaging
WANG Qian, CAI Wei-wei, TAO Bo
Abstract(152) FullText HTML(132) PDF 9813KB(32)
Abstract:
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(231) FullText HTML(107) PDF 7219KB(60)
Abstract:
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.
Viewpoint planning of structured light scanning for complex surface parts
REN Ming-yang, WANG Li-zhong, ZHAO Jian-bo, TANG Zheng-zong
 doi: 10.37188/CO.2022-0026
Abstract(180) FullText HTML(100) PDF 6408KB(43)
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In order to realize the efficient and automatic measurement of complex curved surface parts, this paper proposes a view planning method of surface structure light scanning based on an improved grid method, and applies it to the automatic measurement of complex curved surface automobile parts. Firstly, aiming at the problem of serious redundancy and poor scanning integrity of a manual teaching viewpoint, a scanning viewpoint planning algorithm for surface structured light based on an improved grid method is proposed. According to the effective measurement range of a surface structured light scanner, the grid size is determined, and the candidate viewpoint generation strategy is improved. The effective measurement range of candidate viewpoints is obtained by the measurement constraint condition of the scanner, and the optimal viewpoint is determined by the viewpoint quality evaluation function. Secondly, in view of the low efficiency of the algorithm and the low accuracy of feature reconstruction in the process of viewpoint planning, the voxel grid method is used to simplify the model. The complex surface model is segmented by the octree algorithm, and the voxel grid size is determined according to the normal vector consistency error. For the models with different geometric characteristics, the influence of the weight coefficient on the scanning quality is analyzed, and the optimal weight coefficient is given. Finally, the scanning viewpoint planning and measurement experiments of automobile sheet metal parts and reducer shell are carried out. The results show that the viewpoint planning of the automobile sheet metal parts takes 21.93 s, the scanning integrity is 99.124 %, and the scanning accuracy is 0.025 mm. The viewpoint planning of automobile reducer shell takes 158.29 s, its scanning integrity is 93.231 %, and its scanning accuracy is 0.032 mm. This method can quickly complete the viewpoint planning of complex curved surfaces, and the model with planning viewpoint scanning has good integrity and high precision, which can meet the requirements of automatic measurement of complex curved surface parts.
Influence of radiation coupling effect on polarization characteristics of targets
SU De-zhi, LIU Liang, WU Shi-yong, ZHANG Ji-lei, WANG Kun, Ling-shun LIU
 doi: 10.37188/CO.2022-0035
Abstract(190) FullText HTML(112) PDF 3486KB(40)
Abstract:
Infrared polarization imaging technology has the advantages of long detection range and high rate of target recognition. However, the polarization characteristics of targets are easily affected by background radiation in complex environments, which significantly reduces the detection capability of infrared polarization equipment. Based on the polarized Bidirectional Reflectance Distribution Function (pBRDF), this paper establishes a calculation model for the target’s degree of linear polarization (DoLP), comprehensively considering the radiation coupling effect between the target and the background. The variation of the target’s DoLP under two conditions - with and without a strong radiation backplate – is then comparatively studied. Additionally, in order to solve problems of land-based and airborne small-angle detection, simulation research is done to find out how the target’s DoLP is influenced by parameters such as the temperatures and the included angle between the target and the backplate. Research results show that the radiation coupling effect significantly reduces the target’s degree of polarization when the temperatures of the target and the backplate are the same, but it does not change the trend of the target’s degree of polarization, which increases with an increase in temperature. When the temperature of the target and the backplate is 30 °C, 40 °C, and 50 °C, the maximum degree of polarization of the target is 63.7%, 44.9%, and 42.2% of those without a strong radiation backplate, respectively. It can be concluded then that the higher the temperature, the stronger the radiation coupling effect between the target and the backplate, and the greater the reduction of the target’s degree of polarization; and that the strength of the radiation coupling effect is not only related to the temperature, but also to the included angle between the target and the backplate. With the increase of the included angle, the target’s DoLP first increases and then decreases, and the maximum value is obtained when the included angle is about 105°. Therefore, the radiation coupling effect changes the target’s DoLP to a certain extent, thereby affecting the detection ability of the infrared polarization equipment. Finally, through building a long-wave infrared polarization imaging system, the established calculation model of the target’s degree of polarization is verified by experiments, whose results are basically consistent with those of the simulation analysis. Overall, the research results in this paper have certain guiding significance for improving the detection and identification capabilities of land-based and airborne infrared polarization equipment.
Lane detection based on dual attention mechanism
REN Feng-lei, ZHOU Hai-bo, YANG Lu, HE Xin
 doi: 10.37188/CO.2022-0033
Abstract(197) FullText HTML(123) PDF 6652KB(50)
Abstract:
In order to improve the performance of lane detection algorithms under complex scenes like obstacles, we have proposed a multi-lane detection method based on dual attention mechanism in this paper. Firstly, we designed a lane segmentation network based on a spatial and channel attention mechanism. With this, we obtain 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.
Synchronization transmission technology of semiconductor lasers with transverse effect
ZHAO Li-na, WEI Qing-tao
 doi: 10.37188/CO.2022-0031
Abstract(130) FullText HTML(79) PDF 4571KB(34)
Abstract:
In order to account for the transverse effect of semiconductor lasers, the dynamic equation of a semiconductor laser with transverse effect is given by modifying the dynamic model describing it, 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 dependence of 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.
Research on highly sensitive detection of oxygen concentrations based on tunable diode laser absorption spectroscopy
YANG Shu-han, QIAO Shun-da, LIN Dian-yang, MA Yu-fei
 doi: 10.37188/CO.2022-0029
Abstract(236) FullText HTML(83) PDF 4544KB(55)
Abstract:
Tunable diode laser absorption spectroscopy (TDLAS) is a recently laser spectral gas detection technology developed. Compared with common oxygen sensors such as electrochemical devices and ionic conductive ceramics, TDLAS has the advantages of high selectivity and sensitivity, fast response, on-line measurement and strong anti-background spectral interference ability. Oxygen (O2) is an important gas in habitable environments and is greatly significant to industrial production and human life, and the detection of O2 concentration is also widely used in these fields. Based on this, this paper adopts TDLAS technology to carry out high sensitivity measurements of O2 in air. Using a semiconductor laser with an output wavelength of 760 nm as the light source, the oxygen concentration in the environment is 20.56 % by direct absorption spectroscopy, and the minimum detection limit is 283.27×10−6. In the wavelength modulation spectroscopy method, the laser wavelength modulation depth is optimized to obtain a complete second harmonic waveform, which can be used to calibrate the oxygen concentration. The SNR of the system is 380.74, and the minimum detection limit is about 540×10−9. The system realized in this paper has good oxygen detection ability and can be widely used in various fields of oxygen concentration detection.
Trend of action on the display effect based on pepper's ghost images affected by illumination and color temperature from led light sources
LIN Jia-yuan, ZOU Nian-yu, LIANG Jing, HE Xiao-yang, MU Yu-fan, HUANG Xia, HE Qi-peng
 doi: 10.37188/CO.2022-0027
Abstract(121) FullText HTML(92) PDF 3938KB(37)
Abstract:
With the continuous development of digital display technology, display methods have also changed. Pepper's ghost images that adopt modern display methods require the light environment of the exhibition space to ensure the effect and ensure better visual comfort. In order to explore the influence of the lighting environment on the display effect based on Pepper's ghost images, a virtual imaging display space is set up to analyze the factors and trends affecting the imaging effect. A virtual imaging display space is set up in which 12 sets of LED lighting conditions with different illuminances and color temperatures are generated. 25 observers were used to conduct a psychophysical experiment. Conclusion: color temperature has no significant effect on the evaluation of color authenticity, detail expressiveness and stereoscopic expressiveness for Pepper's ghost images; Illumination has no strong effect on the evaluation of the color authenticity of Pepper's ghost images, but has a significant effect on their detail expressiveness and stereoscopic expressiveness. Under the lighting environment where the color temperature is 3500 K and the illumination is 10 lx, the detailed expressiveness and stereoscopic expressiveness of the display effect are relatively high and the visual comfort of 2500 K and 10 lx is better.
Design of a radiometric calibration light source based on a freeform reflector
TIAN Jie-wen, YE Xin, FANG Wei
 doi: 10.37188/CO.2022-0021
Abstract(163) FullText HTML(82) PDF 6259KB(68)
Abstract:
  Objective  In order to reduce the space needed on a satellite, this paper proposes a design method for a free-form reflector for collimating illumination of integrating spherical light sources. By using this method, a square irradiance distribution with small diameter can be achieved.   Method  Firstly, the mathematical model of off-axis reflection lighting of free-form surface is established through the point light source model, then the free-form surface is discretized by Chebyshev points, and the free-form surface model that satisfies the point light source illumination is solved. Finally, the light source characteristics of the integrating sphere are analyzed. The method of free-form surface energy distribution completes the transformation from the point light source illumination model to the integrating sphere illumination model   Result   The analysis shows that when the illumination area is set at 140 mm*140 mm, the irradiance non-uniformity of the target surface is less than 0.02.   Conclusion  This method can meet the requirements of light weight, short light path and simple structure for spaceborne calibration.
Experimental study on CCD damage by Multi-wavelength raman lasers
LIU Jin-sheng, LIU Jin-bo, LI Xiao-wen
 doi: 10.37188/CO.2021-0228
Abstract(131) FullText HTML(57) PDF 4217KB(62)
Abstract:
The damage threshold of an interline transfer CCD irradiated by different wavelength nanosecond Raman lasers was studied and an experiment with 496 nm, 532 nm, 632 nm Raman and multispectral Raman laser-irradiated CCD was carried out. The damage threshold interval of dot damage, line damage and total damage were observed and collected by adjusting the energy of each focused Raman laser. By careful fitting, the damage threshold interval and the damage possibility curve of the CCD at different laser energy densities with each Raman laser were estimated. Results showed that the multispectral Raman laser including a residual pump laser is most effective for damaging the CCD than the monochrome Raman laser, and the 630 nm Raman laser acts better than 574 nm and the 496 nm Raman laser. The microscopic images of the damaged CCD were reviewed, and the electronic characters of the damaged CCD were also tested to understand the damage and blindness mechanism of a Raman laser pulse-irradiated CCD.
Multi-channel optical switching based on scanning mirror instrumentation
XIAO Ze-hua, LI Ming-yu, SU Guo-shuai, He Ze-nan
 doi: 10.37188/CO.2022-0020
Abstract(217) FullText HTML(89) PDF 2019KB(67)
Abstract:
An optical switch based on a scanning mirror was designed in this paper. The optical switch is programmable and controlled by an embedded Linux system that switches between the fiber array channels on the UI of the touch display. Meanwhile, the switching sequence and residence time of the optical switch can be preset. In addition, the optical switch can be self-calibrated to obtain the maximum output power of each channel. The principle of the optical switch is analyzed and the performance of the optical switch is measured experimentally. The experimental results show that the average insertion loss is less than 17 dB for the single mode fiber array, the average crosstalk between adjacent channels is more than 30 dB, and the switching time between the adjacent channel is less than 1.3 mS. The average insertion loss is less than 2.4 dB for the multi-mode fiber array. It has the advantages of low loss, low delay, high precision, good stability, high repeatability, low cross-talk between the adjacent channel, and good man-machine interaction for the application of the WDM test device.
A study on the measurement method of heliostat surface shape error based on photogrammetry
WEI Xiu-dong, ZHANG Fan, XU Ying-chao
 doi: 10.37188/CO.2021-0210
Abstract(89) FullText HTML(32) PDF 4247KB(64)
Abstract:
In the tower solar thermal power plant, the heliostat mirror shape errors have an important impact on the optical efficiency of the heliostat field, so it is necessary to measure the heliostat surface shape error. The heliostat is generally made up of splicing multiple sub-mirrors, the tilt angle error of the sub-mirror is an important part of the heliostat mirror shape errors. This paper proposes a measurement method for the tilt angle errors of the heliostat sub-mirror based on the photogrammetry. That is, under the condition of known the shape size of the heliostat sub-mirror, the spatial position coordinates of the 4 corner points of the heliostat sub-mirror are calculated by using the principle of photographic imaging. Then the normal direction of the sub-mirror is found, and the tilt angle of the sub-mirror is calculated by using the normal line obtained. Finally, the purpose to measure the tilt angle error of the heliostat sub-mirror is achieved. The measurement principle of the method is elaborated, the calculation formula is derived, and relevant verification experiments were carried out using planar mirrors and cameras. By measuring the plane mirror with different tilt angles at different distances, the deviation between the measured tilt angle and the actual tilt angle of the plane mirror is about 0.1°−0.3°, and the experimental results show that the method can accurately measure the tilt angle error of the sub-mirror of heliostat, thus the correctness and feasibility of the method are verified.
Review
Review of optical systems′ desensitization design methods
MENG Qing-yu, QIN Zi-chang, REN Cheng-ming, QI Yun-sheng
2022, 15(5): 863-877.   doi: 10.37188/CO.2022-0096
Abstract(359) FullText HTML(196) PDF 6933KB(247)
Abstract:

The effective realization of desired optical system performances depends not only on the design results of imaging quality, but also on the realizability of various tolerances such as optical manufacturing tolerances, assembly tolerances, and environmental tolerances. An optical system with low error sensitivity relaxes tolerance requirements, which can better resist image quality degradation disturbed by errors. While reducing manufacturing costs, it effectively improves the realizability of an optical system, thereby reducing error sensitivity. It is an important link that should be considered in optical system design. This paper analyzes and summarizes the research status of optical system error sensitivity, summarizes typical optical system desensitization methods, and summarizes the application of these methods in optical system design. Finally, potential future development directions for low error sensitivity design methods for optical systems are provided.

Research progress of single molecule biological detection methods and applications
ZHOU Wen-chao, LI Zheng-hao, WU Jie
2022, 15(5): 878-894.   doi: 10.37188/CO.2022-0129
Abstract(206) FullText HTML(110) PDF 7451KB(182)
Abstract:

Single molecule biological detection technology is an efficient technology to understand the dynamic characteristics of various biomolecules at the single molecule level and explore their structure and function. The advantage of this technology is that it can detect the heterogeneity of free energy on a single molecule, which is beyond the traditional methods. Therefore, researchers use it to solve long-standing problems in complex biological systems, heterogeneous catalysis, biomolecular interactions, enzyme systems and conformational changes. In terms of medical detection, detecting specific information about single molecules or their interactions with biological factors is not only crucial for the early diagnosis and treatment of various diseases such as cancer, but also has great potential for real-time detection and precision medicine. The advantages of high specificity and high precision of single-molecule bioassays are used to real-time detection of single biomolecules in molecular populations, and can be combined with multiple high-throughput analysis for the precise diagnosis of clinical samples. In this paper, the principle of single molecule detection and the application of biosensing are introduced, and the detection methods and related applications are summarized. Finally, the prospect and development direction of this research direction are discussed.

Recent advances in lateral mode control technology of diode lasers
WANG Li-jie, TONG Cun-zhu, WANG Yan-jing, LU Huan-yu, ZHANG Xin, TIAN Si-cong, WANG Li-jun
2022, 15(5): 895-911.   doi: 10.37188/CO.2022-0143
Abstract(256) FullText HTML(105) PDF 4726KB(190)
Abstract:

High power diode lasers are widely used for pumping solid-state lasers and fiber lasers, material processing, laser radars, free-space optical communication, security and defense. However, conventional diode lasers suffer from large far-field divergence angles, poor beam quality and low brightness, which restricts their direct applications. Broad-Area diode Lasers (BALs) can achieve high output power and efficiency. However, their lateral mode is usually influenced by many physical mechanisms, leading to a large number of guided lateral modes at high-power operation. It results in a rapid increase of the far-field width and strongly deteriorated beam quality, limiting the improvement of diode lasers′ brightness. Therefore, the lateral modes should be carefully controlled. In this paper, the factors influencing the diode lasers′ lateral modes are reviewed, and the lateral mode characteristics, optical field distribution and their relations with the device construction are analyzed. Then, the current lateral mode control technologies are described in detail. The beam quality and brightness of the output beam can be enhanced via the suppression of high-order lateral modes and the far-field blooming effect. As a result of advanced lateral mode control, novel high-brightness diode lasers can be developed at the chip level, which is beneficial for developing new diode lasers applications and reducing their system cost.

Review of ultraviolet photodetectors based on micro/nano-structured wide bandgap semiconductor oxide
CHEN Xing, ZHOU Chang, LIU Ke-wei, SHEN De-zhen
2022, 15(5): 912-928.   doi: 10.37188/CO.2022-0132
Abstract(267) FullText HTML(151) PDF 6212KB(147)
Abstract:

Ultraviolet photodetection technology is another dual-use detection technology after infrared detection and laser detection technology, which has broad application prospects. Vacuum photomultiplier tubes and Si-based photodiodes are common commercial UV detectors, but vacuum photomultiplier tubes are susceptible to high temperatures and electromagnetic radiation, and need to work under high pressure while Si-based photodiodes require expensive filters. Wide bandgap semiconductor ultraviolet photodetectors have overcome some of the problems faced by the above two devices, and are becoming the research hotspot. Among them, wide bandgap oxide materials have attracted extensive attention, due to the advantages of easy preparation for high response and high gain devices, and rich micro-structures and nano-structures. In this paper, ultraviolet photodetectors based on micro/nano-structured wide bandgap semiconductor oxide are combed, and some related researches in recent years are reviewed. The oxide materials involved include ZnO, Ga2O3, SnO2 and TiO2, etc. and the device structures involved include metal-semiconductor-metal devices, Schottky junction devices and heterojunction devices, etc.

Review of physical implementation architecture in compressive spectral imaging system
LI Yun-hui
2022, 15(5): 929-945.   doi: 10.37188/CO.2022-0104
Abstract(177) FullText HTML(67) PDF 16648KB(144)
Abstract:

Different from the traditional point-to-point mapping imaging method, computational optical imaging combines the physical regulation of the front-end optical signal with the processing of the back-end digital signal to make the image information acquisition more efficient. This new imaging mechanism is expected to alleviate the contradiction between low manufacturing cost and high performance indicators under the framework of traditional imaging technology, especially in the acquisition of high-dimensional image information. Since the system architecture supported by physical devices is the cornerstone of computational optical imaging, aiming at the sub-technical field of compressive spectral imaging, in this paper, we introduce the existing optical devices that can realize spatial or spectral modulation. Based on this, the architecture of multi-type compressive spectral imaging system is sorted out and summarized, which can be categorized as single-pixel spectral imaging, coded aperture spectral imaging, spatial-spectral dual-coded spectral imaging, microarray spectral imaging and scattering medium spectral imaging, based on the information modulation process. We focus on the information modulation and acquisition principles of various system architectures and their modulation effects on the spatial-spectral data cube, and then analyze and explore the common issues. Finally, the technical challenges faced are given, and the future development trend is discussed.

Research progress of high-speed vertical-cavity surface-emitting laser in CIOMP
TIAN Si-cong, TONG Cun-zhu, WANG Li-jun, BIMBERG Dieter
2022, 15(5): 946-953.   doi: 10.37188/CO.2022-0136
Abstract(213) FullText HTML(93) PDF 7657KB(158)
Abstract:

High-speed vertical-cavity surface-emitting laser (VCSEL) is one of the main light sources for optical communication. Driven by the rapid growth of data traffic, the high-speed VCSEL is developing towards larger bandwidth and higher bit rate. By optimizing the epitaxy design and the growth of VCSELs, the design and the fabrication of VCSELs, and the high-frequency characterization techniques, much remarkable progress of high-speed VCSELs with different wavelengths have been achieved in modulation bandwidth, transmission rate, mode, power consumption in Changchun Institute of Optics, Fine Machanics and Physics (CIOMP). The research progress of high-speed VCSELs includes: high-speed single-mode 940 nm VCSEL with 27.65 GHz modulation bandwidth and 53 Gbit/s transmission rate; 200 Gbit/s optical link based on 850 nm, 880 nm, 910 nm and 940 nm high-speed VCSELs via wavelength division multiplexing; ultra-low power consumption as low as 100 fJ/bit of high-speed VCSEL via optimization of photon lifetime; 1030 nm high-speed VCSEL with 25 GHz modulation bandwidth; 1550 nm high-speed VCSEL with 37 Gbit/s transmission rate. The developed high-speed VCSELs have important application prospects in optical communication.

Survey of non-blind image restoration
YANG Hang
2022, 15(5): 954-972.   doi: 10.37188/CO.2022-0099
Abstract(297) FullText HTML(143) PDF 3076KB(173)
Abstract:

Non-blind image restoration is one of the most improtant research topics in the field of computer vision. It is also a typical ill-posed problem in mathematics. Its goal is to estimate a clear image from a blurred image when the point spread function is known. Its research focuses on how to make an appropriate compromise between improving clarity and suppressing noise. In the past 50 years, non-blind image restoration has made great progress. From the Wiener filtering to deep learning based methods, scholars have proposed hundreds of non-blind image restoration algorithms and applied them in various academic fields. This paper first introduces the basic concept and research significance of non-blind image restoration, then classifies and summarizes the main non-blind image restoration algorithms according to the algorithm attributes, which are generally divided into traditional methods and deep learning based methods. The traditional methods are divided into the direct method and iterative method, then are analyzed for their advantages and disadvantages. The performance of representative restoration algorithms is compared in a varity of typical experiments. Finally, the development trend and important research directions of non-blind image restoration algorithms are proposed.

Overview of key technologies for segmented mirrors of large-aperture optical telescopes
HUO Yin-long, YANG Fei, WANG Fu-guo
2022, 15(5): 973-982.   doi: 10.37188/CO.2022-0109
Abstract(226) FullText HTML(102) PDF 5408KB(196)
Abstract:

With the continuous development of astronomical exploration, the aperture of telescopes is getting larger and larger. Segmented mirror technology offers a viable and much simpler alternative to a large single monolithic primary mirrors, and has become an important way of designing the primary mirror of large-aperture telescopes. This paper summarizes the current development status of various technologies with reference to the primary mirror design of typical segmented telescopes such as the JWST and TMT, and elaborates on the performance differences and mirror supports of different segmented primary mirror schemes under the background of large-scale sub-mirrors. Potential future development trends of this technology and co-phasing detection technology are provided. This research acts as a reference for the independent development of the next generation of very large aperture optical infrared telescopes in China.

Original Article
Dynamic MTF modeling and analysis of digital domain TDI CMOS remote sensing camera
TAO Shu-ping, FENG Qin-ping, CHEN Xiao-long, ZHENG Liang-liang, ZHANG Zi-yu, GAO Tan
2022, 15(5): 983-991.   doi: 10.37188/CO.2022-0111
Abstract(121) FullText HTML(63) PDF 2818KB(115)
Abstract:

The modulation Transfer Function (MTF) is an important evaluation index for remote sensing cameras, but at present, the research on the dynamic MTF characteristics of digital domain TDI CMOS cameras is very limited. In order to deeply research its image quality degradation mechanism, combined with the principle of digital domain Time Delay Integration Complementary Metal Oxide Semiconductor (TDI CMOS) imaging, a mathematical model of digital domain TDI imaging MTF degradation caused by pixel, electronic shutters, exposure time and vibration is established. Combined with the derived model, the prediction analysis and experimental verification are carried out. The results show that the regional distribution of effective pixels of the sensor will affect the image MTF with a greater intluence from smaller opening rates, and the rolling shutter of the CMOS sensor will lead to the decrease of the digital domain TDI imaging MTF with a more serious impact for slower rolling shutter speeds. When the rolling shutter speed changes from 6 μs to 10 μs, the corresponding image MTF decreases from 0.191 to 0.177. As the exposure time shortens, the MTF grows higher, especially when there is low-frequency image shift mismatch. When the exposure time is reduced from 180 μs to 100 μs, the MTF increases from 0.126 to 0.155 with some influence on the image signal-to-noise ratio. Therefore, the exposure time should be reasonably controlled in practical applications.

Detection of large aperture flat mirror based on the differential optics transfer function method
AN Qi-chang, JIANG Xi-wen, LI Hong-wen, TANG Jing
2022, 15(5): 992-999.   doi: 10.37188/CO.2022-0122
Abstract(130) FullText HTML(78) PDF 8130KB(108)
Abstract:

In order to realize the in-situ detection of large aperture plane mirrors, wavefront detection is achieved by a combination of the Ritchey-Common method and holographic detection through the differential transfer function, combined with the actual Ritchey-Common detection architecture, and through the occlusion code of the pupil. Firstly, the principle of large aperture plane mirror detection based on differential transfer function method is derived, and the existing large aperture wavefront is compared with the reconstructed wavefront. Finally, the detection light path is built by using deformable mirrors. The correlation between the surface shape obtained by this method and the input surface shape is not less than 70%. This paper is of great significance to the fundamental cosmological propositions such as the detection of the "first light" of the universe and the "one black, two dark and three origins".

Large-scale splicing focal plane error distribution based on optical-structural-thermal integration analysis
NIU Sheng-guang, GUO Liang, LU Zhen-yu, HAN Kang
2022, 15(5): 1000-1006.   doi: 10.37188/CO.2022-0094
Abstract(142) FullText HTML(73) PDF 3562KB(141)
Abstract:

As the requirements of space astronomy, situational awareness, environmental monitoring and other fields grow higher, space telescopes are developing toward large fields of view and large apertures. Large-scale focal plane stitching technology is the key technology of large-field space telescopes. The allocation method of the main focal plane flatness error (P-V value) is generally a direct assignment method based on experience, which is prone to unreasonable error allocation.In this paper, a method of splicing focal plane error allocation is proposed, which can accurately allocate important parameter errors through optical-structural-thermal integration analysis. Taking 4×4 mechanical direct splicing focal plane with 16 pieces of Complementary Metal Oxide Semiconductor(CMOS) image sensor as an example, an error tree of splicing focal planes is established. The influence of important parameters such as gravity and temperature on the flatness of splicing focal plane is analyzed by the method of optical-structural-thermal integration analysis. The error distribution result is finally given. The analysis shows that the flatness errors caused by gravity under two different attitudes are 0.28 μm and 1.55 μm respectively, and the total flatness error caused by temperature is 5.5 μm. After leaving a 30% margin, the assigned values of the flatness error caused by gravity and temperature are determined to be 2 μm and 7.2 μm, respectively.

Compact pulsed CO2 laser with wavelength automatic tuning
PAN Qi-kun, MIAO Fang-chen, SI Hong-Li, SHEN Hui, GAO Fei, YU De-Yang, ZHANG Kuo, ZHANG Ran-ran, ZHAO Chong-Xiao, CHEN Fei, GUO Jin
2022, 15(5): 1007-1012.   doi: 10.37188/CO.2022-0107
Abstract(155) FullText HTML(80) PDF 2539KB(133)
Abstract:

In order to meet the application requirements of airborne laser differential absorption lidar for small and lightweight light sources, a compact pulsed CO2 laser is developed with automatic wavelength tuning. First, the aperture matching relationship between an RF waveguide intracavity beam and a free space optical chopper beam was studied, and a beam conversion system was designed with real focus on the intracavity. The influence of the chopper aperture on a laser pulse waveform was verified experimentally. Secondly, the wavelength tuning characteristics of CO2 laser were studied, and the diffraction angle difference between adjacent laser spectral lines was analyzed. Tunable operation in the CO2 laser was realized using a high-precision electric turntable and metal blazed grating. Finally, the integration of a compact automatic tuning pulsed CO2 laser was completed using small lightweight modules. Experimental results indicate that the laser operates stably at 1 kHz with a pulse width of 350 ns and a peak power of 3.7 kW. There are 30 lines within 9.2~10.7 μm waveband. The total weight of the laser is 18 kg. It provides a miniaturized detection light source for airborne laser differential absorption lidar.

Control system design of 515-nm high power laser
DONG Quan-rui, ZHANG Zhen-dong, WANG Wei-guo, CHEN Tao, CHEN Fei
2022, 15(5): 1013-1018.   doi: 10.37188/CO.2022-0133
Abstract(162) FullText HTML(71) PDF 2210KB(103)
Abstract:

In order to realize the stable and safe output of lasers, a control system based on a 515-nm high-power laser is designed. Firstly, the pump drive module of the system is studied. The analog sampling of the module is completed by Field Programmable Gate Array (FPGA) and the calculation output is completed in Digital Signal Processing (DSP). The closed-loop control of the constant current source is completed by using the digital Proportion-Integral-Derivative (PID) algorithm. Secondly, a Thermo Electric Cooler (TEC) is used to achieve the stable temperature control of the frequency doubling crystal module, and the Negative Temperature Coefficient (NTC) is used as the feedback to realize the temperature control. Finally, the human-computer interaction system of the laser is designed, which realizes the real-time monitoring, judgment and storage of the internal state of the laser. In order to verify the effectiveness of the control system, a pump is selected for testing. The experimental results show that the pump drive module can work continuously and stably, and the control system can monitor the internal state of the laser in real time, which is safe and reliable. The laser output center wavelength after frequency doubling is 514.98 nm, the power can reach 170 W, and the optical power stability is ±0.07 dB. All devices and equipment for the control system are made in China, meeting the system design requirements of 515-nm high-power laser.

Light-and-small optical systems by metal-based additive manufacturing
FU Qiang, YAN Lei, TAN Shuang-long, LIU Yang, WANG Ling-jie, ZHANG Xin
2022, 15(5): 1019-1028.   doi: 10.37188/CO.2022-0128
Abstract(141) FullText HTML(73) PDF 6336KB(141)
Abstract:

In order to realize the target of light and small, low radiation and large field of view of the long-wave infrared catadioptric optical system for deep-space low-temperature target detection, the local cooling optical system, topology optimization, metal-based mirror design, additive manufacturing, Single Point Diamond Turning (SPDT) for metal mirrors and surface modification are studied. First of all, a compact catadioptric optical system with partially cooled is designed, in which the aperture is 55 millimeters, the focal length is 110 millimeters and the field of view is 4 degrees by 4 degrees. Secondly, the primary mirror assembly, the secondary mirror assembly and the connecting baffle are designed using the topology optimization theory, and the third order mode and fourth order mode reach 1213.7 Hz. Then, the front group optical mirrors assembly are developed by means of additive manufacturing, SPDT, surface modification and surface gold plating. We complete the optical mechanical assembly using the centering assembly method. Finally, the performance of the system after optical mechanical centering is tested. The test results show that the Modulation Transfer Function (MTF) curves of the optical system reach the diffraction limit in the whole field of views, and the weight is only 96.04 grams. Additive manufacturing method can be used as an effective means to improve the performance of optical systems.

Hyperspectral resolution ultraviolet dual channel common optical path imaging spectrometer
ZHANG Lu, LI Bo, LI Han-shuang, GU Guo-chao, WANG Xiao-xu, SHAO Ying-qiu, LIN Guan-yu, YE Xin
2022, 15(5): 1029-1037.   doi: 10.37188/CO.2022-0125
Abstract(150) FullText HTML(58) PDF 5353KB(156)
Abstract:

Based on the requirement of multichannel detection for hyperspectral resolution imaging spectrometer, we design a hyperspectral resolution ultraviolet dual channel common optical path imaging spectrometer whose telescopic system adopts an off-axis three mirror structure with an off-axis field of view, and whose spectroscopic system applies a modified small and light weight Offner structure. Through the theoretical analysis of Offner spectrometer structures, initial structural parameters of a dual channel common optical path Offner that met the requirements of hyperspectral resolution were achieved. In order to improve the imaging quality of the imaging spectrometer, meniscus lenses were introduced into Offner structure, and the system was gradually optimized. Eventually, a dual channel common optical path imaging spectrometer was obtained with operating bands of 280~300 nm and 370~400 nm. When the Nyquist frequency is 27.8 lp/mm, the modulation transfer function (MTF) of both channels is better than 0.8, the full field mean square root radius (RMS) is less than 9 μm. and the spectral resolution is better than 0.1 nm. The design of this imaging spectrometer has important implications for the miniaturization and integration design of space-based hyperspectral detection imaging spectrometers.

Narrow line width and magnetism-free vertical-cavity surface-emitting lasers for quantum sensing
ZHANG Xing, ZHANG Jian-wei, ZHOU Yin-li, Xue Hong-bo, NING Yong-qiang, WANG Li-jun
2022, 15(5): 1038-1044.   doi: 10.37188/CO.2022-0135
Abstract(163) FullText HTML(108) PDF 4184KB(126)
Abstract:

In order to realize single mode, narrow linewidth and low magnetism field intensity operation of lasers, Vertical-Cavity Surface-Emitting Lasers (VCSEL) with integrated micro-lens extended cavity was designed and fabricated. First, an epitaxial structure suitable for the micro-lens integration was designed and grown by Metal Organic Chemical Vapor Deposition (MOCVD). The fabrication steps of the micro-lens integrated VCSEL was carried out and the magnetism-free material was used in the electrode deposition. Experimental results indicate that the operating temperature is 90 °C, the laser wavelength is 896.3 nm, the laser power is 1.52 mW, the side mode suppression ratio is as high as 36.3 dB and the operating magnetic field intensity is less than 0.03 nT. A narrow line width and magnetism-free VCSEL suitable for quantum sensing was demonstrated.

Pixel mapping variable-resolution spectral imaging reconstruction
XIAO Shu-lin, HU Chang-hong, GAO Lu-yao, YAN Ke-xiong, YANG Chun-ji, LI Hong-li
2022, 15(5): 1045-1054.   doi: 10.37188/CO.2022-0108
Abstract(128) FullText HTML(102) PDF 4907KB(135)
Abstract:

In this paper, the basic principle and reconstruction method of random filter spectral coding-decoding are discussed. According to the automatic feature extraction mechanism of a deep learning undercomplete autoencoder, a pixel mapping variable-resolution spectral imaging reconstruction network with high reconstruction accuracy and low delay is constructed. The parallel training of a 2×2 and 4×4 pixel array spectral reconstruction network is implemented by transforming the pixel mapping relationship. Finally, the network’s performance is verified by the remote sensing data with 512×616 with 120 bands spectral images. For a 2×2 pixel array with 40 bands, the reconstruction PSNR is 53 dB, the reconstruction MSE is less than 0.002, and the reconstruction time is 0.85 s. For a 4×4 pixel array with 120 bands, the reconstruction PSNR is 64 dB, the reconstruction MSE is less than 10−5, and the reconstruction time is 0.5 s. The experimental results show that the pixel mapping variable-resolution spectral imaging reconstruction network has the dynamic transformation performance of high accuracy and low delay.

Real-time semantic segmentation of microvascular decompression images based on encoder-decoder structure
BAI Rui-feng, JIANG Shan, SUN Hai-jiang, LIU Xin-rui
2022, 15(5): 1055-1065.   doi: 10.37188/CO.2022-0120
Abstract(118) FullText HTML(62) PDF 4699KB(92)
Abstract:

Aiming at the problems of large parameters and low semantic segmentation accuracy of real-time semantic segmentation networks for true-color microvascular decompression (MVD) images. This paper proposes a U-shaped lightweight fast semantic segmentation network U-MVDNet (U-Shaped Microvascular Decompression Network) for MVD scenarios, which consists of encoder-decoder structure. A Light Asymmetric Bottleneck Module (LABM) is designed in the encoder to encode context features. Feature Fusion Module (FFM) is introduced in the decoder to effectively combine high-level semantic features and underlying spatial details. Experimental results show that for the MVD test set, U-MVDNet achieves 0.66 M parameters, 76.29% mIoU (mean Intersection-over-Union), and 140 frame/s speed on NVIDIA GTX 2080Ti. And when input image size is 640 × 480, the real-time (24 frame/s) semantic segmentation is realized on NVIDIA Jetson AGX Xavier embedded development board. The proposed network has no pretrained model, fewer parameters, and fast inference speed. The semantic segmentation performance is superior to other comparison methods, and a good trade-off between segmentation accuracy and speed is achieved. Furthermore, U-MVDNet can also be easily developed and applied on embedded platform with superior performance and easy deployment.

Integrated optimization design of mirror semi-active support system based on Warping Harness
ZHANG Ben-lei, YANG Fei, WANG Fu-guo, LU Bao-wei
2022, 15(5): 1066-1078.   doi: 10.37188/CO.2022-0121
Abstract(103) FullText HTML(64) PDF 6497KB(128)
Abstract:

The semi-active support is based on the semi-active optical technology, and the correction force is converted into a correction torque through a Warping Harness(WH) spring blade to correct the mirror low-order aberration introduced by error sources such as gravity and temperature. Aiming at the defects of traditional empirical design of mirrors, a new optimal design method for a mirror support system is proposed, that is, a comprehensive design optimization method of mirror support system based on structural size optimization combined with empirical design, and a set of semi-active mirror support systems based on WH is established. Firstly, the initial structure of the support system is designed according to the empirical formula; an L-shaped hollow WH spring blade is designed, and the nonlinear analysis and fatigue analysis are carried out to determine that the blade thickness is 2 mm and the service life is 1.2×106 times. Then, the RMS value of the mirror surface in the vertical and horizontal states of the optical axis was reduced from 119 nm and 106 nm to 13.3 nm and 4.8 nm by optimizing the position of the mirror support point, the position of the triangular plate flexure joint, and the key dimension parameters of the support system’s flexible parts; under the state of 1 °C temperature difference, the specular aberration is reduced from 2.8 nm to 1.9 nm; the first-order resonance frequency is increased from 80 Hz to 130 Hz. Finally, this method is used to verify the correction ability of the semi-active support system. The results show that the correction rate of the semi-active support system for mirror defocus, primary astigmatism, primary coma and primary spherical aberration can reach up to 99%. The amplitude of each aberration is less than 1 nm; the correction rate of the RMS value of the mirror’s surface shape can reach up to 46.5% under it′s own weight state at room temperature, and the correction rate is 31.28%.

Flexural mounting technology of a 1.8 m space-borne rectangular mirror
LI Zong-xuan, ZHANG Chang-hao, ZHANG De-fu, MA Bin, LI Yun-feng
2022, 15(5): 1079-1091.   doi: 10.37188/CO.2022-0131
Abstract(111) FullText HTML(61) PDF 7637KB(87)
Abstract:

The rectangular primary mirror with aperture of 1.8 m×0.5 m is the crucial component of an off-axis Three Mirror Anastigmat (TMA) space optical system. In order to guaranty the structural stability and reliability of the Primary Mirror Assembly (PMA) and the surface figure error (RMS value) of the mirror, a bi-axial flexural support has been proposed for the large-size rectangular mirror. First, based on the principle of kinematic equivalent, the initial structure of the bi-axial flexural support was designed and the analytical formula for stiffness and its characteristic was studied as well. Then the mounting position and the key dimensions of the flexural supports were studied and optimized. Finally, the final optimization design scheme of the PMA was determined. Experimental results indicate that the surface figure error (RMS value) of the PMA under 1 G gravity in X and Y directions are 4.81 nm and 6.09 nm respectively when the optical axis is placed horizontally, which are less than λ/50 (λ=632.8 nm). The first-order natural frequency is 104 Hz, which can satisfy the design requirements. The dynamic tests have shown that the dynamic characteristics of the mirror assembly are good, and the flexural support system is stable and reliable. Now the mirror has been polished to have a surface figure better than λ/30 RMS. Zero Gravity optical testing has been performed under ±1 G respectively, which shows good coincidence with the analytical results.

Panoramic bispectral infrared imaging interference spectrum measurement inversion instrument
LV Jin-guang, LIANG Jing-qiu, ZHAO Bai-xuan, ZHAO Ying-ze, ZHENG Kai-feng, CHEN Yu-peng, WANG Wei-biao, QIN Yu-xin, TAO Jin
2022, 15(5): 1092-1104.   doi: 10.37188/CO.2022-0114
Abstract(115) FullText HTML(99) PDF 5407KB(142)
Abstract:

In order to satisfy the urgent needs of on-line real-time monitoring and analysis instrument for industrial pollution emission and sudden safety accidents, a panoramic bispectral infrared imaging interference spectrum measurement inversion instrument is proposed. Through the collaborative design of dual channel interference system, dual spectral imaging system, azimuth and elevation axis system, the measurement of image spectrum information of target scene with large field of view, wide spectral band and high resolution is realized. First, based on Fourier optics theory, the scalar diffraction theoretical model of interference imaging spectrum is established. Then based on broadband sampling and narrowband sampling theory, the sampling design of dual channel interference system is carried out. Based on the analysis of the interference imaging characteristics, the optical design of the dual band imaging system is carried out. Finally, the principle prototype is completed, and the telemetry experiment of the gas plume emitted by the chimney is carried out. The instrument can realize spectral measurement with resolution of 4 cm−1 in large field of view by 360°×60° and wide spectral range from 3~5 μm to 8~12 μm. The instrument can satisfy the application requirements of qualitative identification and quantitative analysis for gas emission monitoring.

Review of optical systems′ desensitization design methods
MENG Qing-yu, QIN Zi-chang, REN Cheng-ming, QI Yun-sheng
2022, 15(5): 863-877.   doi: 10.37188/CO.2022-0096
Abstract(359) FullText HTML(196) PDF 6933KB(247)
Abstract:

The effective realization of desired optical system performances depends not only on the design results of imaging quality, but also on the realizability of various tolerances such as optical manufacturing tolerances, assembly tolerances, and environmental tolerances. An optical system with low error sensitivity relaxes tolerance requirements, which can better resist image quality degradation disturbed by errors. While reducing manufacturing costs, it effectively improves the realizability of an optical system, thereby reducing error sensitivity. It is an important link that should be considered in optical system design. This paper analyzes and summarizes the research status of optical system error sensitivity, summarizes typical optical system desensitization methods, and summarizes the application of these methods in optical system design. Finally, potential future development directions for low error sensitivity design methods for optical systems are provided.

Research progress of single molecule biological detection methods and applications
ZHOU Wen-chao, LI Zheng-hao, WU Jie
2022, 15(5): 878-894.   doi: 10.37188/CO.2022-0129
Abstract(206) FullText HTML(110) PDF 7451KB(182)
Abstract:

Single molecule biological detection technology is an efficient technology to understand the dynamic characteristics of various biomolecules at the single molecule level and explore their structure and function. The advantage of this technology is that it can detect the heterogeneity of free energy on a single molecule, which is beyond the traditional methods. Therefore, researchers use it to solve long-standing problems in complex biological systems, heterogeneous catalysis, biomolecular interactions, enzyme systems and conformational changes. In terms of medical detection, detecting specific information about single molecules or their interactions with biological factors is not only crucial for the early diagnosis and treatment of various diseases such as cancer, but also has great potential for real-time detection and precision medicine. The advantages of high specificity and high precision of single-molecule bioassays are used to real-time detection of single biomolecules in molecular populations, and can be combined with multiple high-throughput analysis for the precise diagnosis of clinical samples. In this paper, the principle of single molecule detection and the application of biosensing are introduced, and the detection methods and related applications are summarized. Finally, the prospect and development direction of this research direction are discussed.

Recent advances in lateral mode control technology of diode lasers
WANG Li-jie, TONG Cun-zhu, WANG Yan-jing, LU Huan-yu, ZHANG Xin, TIAN Si-cong, WANG Li-jun
2022, 15(5): 895-911.   doi: 10.37188/CO.2022-0143
Abstract(256) FullText HTML(105) PDF 4726KB(190)
Abstract:

High power diode lasers are widely used for pumping solid-state lasers and fiber lasers, material processing, laser radars, free-space optical communication, security and defense. However, conventional diode lasers suffer from large far-field divergence angles, poor beam quality and low brightness, which restricts their direct applications. Broad-Area diode Lasers (BALs) can achieve high output power and efficiency. However, their lateral mode is usually influenced by many physical mechanisms, leading to a large number of guided lateral modes at high-power operation. It results in a rapid increase of the far-field width and strongly deteriorated beam quality, limiting the improvement of diode lasers′ brightness. Therefore, the lateral modes should be carefully controlled. In this paper, the factors influencing the diode lasers′ lateral modes are reviewed, and the lateral mode characteristics, optical field distribution and their relations with the device construction are analyzed. Then, the current lateral mode control technologies are described in detail. The beam quality and brightness of the output beam can be enhanced via the suppression of high-order lateral modes and the far-field blooming effect. As a result of advanced lateral mode control, novel high-brightness diode lasers can be developed at the chip level, which is beneficial for developing new diode lasers applications and reducing their system cost.

Review of ultraviolet photodetectors based on micro/nano-structured wide bandgap semiconductor oxide
CHEN Xing, ZHOU Chang, LIU Ke-wei, SHEN De-zhen
2022, 15(5): 912-928.   doi: 10.37188/CO.2022-0132
Abstract(267) FullText HTML(151) PDF 6212KB(147)
Abstract:

Ultraviolet photodetection technology is another dual-use detection technology after infrared detection and laser detection technology, which has broad application prospects. Vacuum photomultiplier tubes and Si-based photodiodes are common commercial UV detectors, but vacuum photomultiplier tubes are susceptible to high temperatures and electromagnetic radiation, and need to work under high pressure while Si-based photodiodes require expensive filters. Wide bandgap semiconductor ultraviolet photodetectors have overcome some of the problems faced by the above two devices, and are becoming the research hotspot. Among them, wide bandgap oxide materials have attracted extensive attention, due to the advantages of easy preparation for high response and high gain devices, and rich micro-structures and nano-structures. In this paper, ultraviolet photodetectors based on micro/nano-structured wide bandgap semiconductor oxide are combed, and some related researches in recent years are reviewed. The oxide materials involved include ZnO, Ga2O3, SnO2 and TiO2, etc. and the device structures involved include metal-semiconductor-metal devices, Schottky junction devices and heterojunction devices, etc.

Review of physical implementation architecture in compressive spectral imaging system
LI Yun-hui
2022, 15(5): 929-945.   doi: 10.37188/CO.2022-0104
Abstract(177) FullText HTML(67) PDF 16648KB(144)
Abstract:

Different from the traditional point-to-point mapping imaging method, computational optical imaging combines the physical regulation of the front-end optical signal with the processing of the back-end digital signal to make the image information acquisition more efficient. This new imaging mechanism is expected to alleviate the contradiction between low manufacturing cost and high performance indicators under the framework of traditional imaging technology, especially in the acquisition of high-dimensional image information. Since the system architecture supported by physical devices is the cornerstone of computational optical imaging, aiming at the sub-technical field of compressive spectral imaging, in this paper, we introduce the existing optical devices that can realize spatial or spectral modulation. Based on this, the architecture of multi-type compressive spectral imaging system is sorted out and summarized, which can be categorized as single-pixel spectral imaging, coded aperture spectral imaging, spatial-spectral dual-coded spectral imaging, microarray spectral imaging and scattering medium spectral imaging, based on the information modulation process. We focus on the information modulation and acquisition principles of various system architectures and their modulation effects on the spatial-spectral data cube, and then analyze and explore the common issues. Finally, the technical challenges faced are given, and the future development trend is discussed.

Research progress of high-speed vertical-cavity surface-emitting laser in CIOMP
TIAN Si-cong, TONG Cun-zhu, WANG Li-jun, BIMBERG Dieter
2022, 15(5): 946-953.   doi: 10.37188/CO.2022-0136
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Abstract:

High-speed vertical-cavity surface-emitting laser (VCSEL) is one of the main light sources for optical communication. Driven by the rapid growth of data traffic, the high-speed VCSEL is developing towards larger bandwidth and higher bit rate. By optimizing the epitaxy design and the growth of VCSELs, the design and the fabrication of VCSELs, and the high-frequency characterization techniques, much remarkable progress of high-speed VCSELs with different wavelengths have been achieved in modulation bandwidth, transmission rate, mode, power consumption in Changchun Institute of Optics, Fine Machanics and Physics (CIOMP). The research progress of high-speed VCSELs includes: high-speed single-mode 940 nm VCSEL with 27.65 GHz modulation bandwidth and 53 Gbit/s transmission rate; 200 Gbit/s optical link based on 850 nm, 880 nm, 910 nm and 940 nm high-speed VCSELs via wavelength division multiplexing; ultra-low power consumption as low as 100 fJ/bit of high-speed VCSEL via optimization of photon lifetime; 1030 nm high-speed VCSEL with 25 GHz modulation bandwidth; 1550 nm high-speed VCSEL with 37 Gbit/s transmission rate. The developed high-speed VCSELs have important application prospects in optical communication.

Survey of non-blind image restoration
YANG Hang
2022, 15(5): 954-972.   doi: 10.37188/CO.2022-0099
Abstract(297) FullText HTML(143) PDF 3076KB(173)
Abstract:

Non-blind image restoration is one of the most improtant research topics in the field of computer vision. It is also a typical ill-posed problem in mathematics. Its goal is to estimate a clear image from a blurred image when the point spread function is known. Its research focuses on how to make an appropriate compromise between improving clarity and suppressing noise. In the past 50 years, non-blind image restoration has made great progress. From the Wiener filtering to deep learning based methods, scholars have proposed hundreds of non-blind image restoration algorithms and applied them in various academic fields. This paper first introduces the basic concept and research significance of non-blind image restoration, then classifies and summarizes the main non-blind image restoration algorithms according to the algorithm attributes, which are generally divided into traditional methods and deep learning based methods. The traditional methods are divided into the direct method and iterative method, then are analyzed for their advantages and disadvantages. The performance of representative restoration algorithms is compared in a varity of typical experiments. Finally, the development trend and important research directions of non-blind image restoration algorithms are proposed.

Overview of key technologies for segmented mirrors of large-aperture optical telescopes
HUO Yin-long, YANG Fei, WANG Fu-guo
2022, 15(5): 973-982.   doi: 10.37188/CO.2022-0109
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Abstract:

With the continuous development of astronomical exploration, the aperture of telescopes is getting larger and larger. Segmented mirror technology offers a viable and much simpler alternative to a large single monolithic primary mirrors, and has become an important way of designing the primary mirror of large-aperture telescopes. This paper summarizes the current development status of various technologies with reference to the primary mirror design of typical segmented telescopes such as the JWST and TMT, and elaborates on the performance differences and mirror supports of different segmented primary mirror schemes under the background of large-scale sub-mirrors. Potential future development trends of this technology and co-phasing detection technology are provided. This research acts as a reference for the independent development of the next generation of very large aperture optical infrared telescopes in China.

Research progress of optical fiber Fabry-Perot interferometer high temperature sensors
LI Ai-wu, SHAN Tian-qi, GUO Qi, PAN Xue-peng, LIU Shan-ren, CHEN Chao, YU Yong-sen
2022, 15(4): 609-624.   doi: 10.37188/CO.2021-0219
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Abstract:

The high temperature sensor of the optical fiber Fabry-Perot interferometer has the advantages of small size, a simple manufacturing process, high sensitivity, high temperature resistance and anti-electromagnetic interference, which make it widely used in the aerospace energy industry, environmental monitoring and other fields. Firstly, this paper introduces the sensing principle, sensing performance, sensing characteristics and fabrication method of optical fiber Fabry-Perot interferometer high temperature sensors. Secondly, the temperature, pressure and strain sensitivity and measurement range are summarized and the domestic and foreign research progress and the performance parameters of optical fiber Fabry-Perot interferometer high temperature sensors are summarized. Thirdly, the cross-sensitivity problems of temperature and pressure of optical fiber Fabry-Perot interferometer sensors and it’s solutions, and the high-temperature sensing characteristics of Fabry-Perot interferometers based on different kinds of optical fibers are introduced. Fourthly, according to the recent research progress of fiber Fabry-Perot interferometer high temperature sensors, several fiber Fabry-Perot interferometer high temperature sensors for two-parameter measurement are introduced. Finally, the future development trend and prospect of optical fiber Fabry-Perot interferometer high temperature sensors are prospected.

The principle, performance characterization and research progress of nonlinear optical limiting materials
LV Ze, FANG You, FENG Tiao, ZONG Nan, LI Yun-fei, ZHANG Shen-jin, XIE Zheng, PENG Qin-jun
2022, 15(4): 625-639.   doi: 10.37188/CO.2021-0195
Abstract(481) FullText HTML(306) PDF 6386KB(195)
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Laser protection materials are of great significance in protecting human eyes and optical components from strong laser pulses. Among them, solid optical limiting materials based on the principle of nonlinear optics will be the main carriers for laser protection. This article introduces the research background, working mechanism, parameters and testing techniques of optical limiting materials, and reviews the research progress of various optical limiting materials with practical prospects, including inorganic semiconductor materials, conjugated organic polymers, inorganic metal clusters, carbon nanomaterials, and two-dimensional materials. And the development prospects of optical limiting materials are discussed.

Research progress on nonlinear optics of polyvinylidene fluorid and its copolymers films
LIU Yong, LIU Wei-guo, NIU Xiao-ling, HUI Ying-xue, DAI Zhong-hua, WANG Zhi-heng, GUO Wen-hao
2022, 15(4): 640-659.   doi: 10.37188/CO.2021-0191
Abstract(332) FullText HTML(190) PDF 6400KB(108)
Abstract:

Polyvinylidene fluoride (PVDF) and its copolymers films have been extensively used in photoelectric functional devices such as photoelectric conversion, optical regulation, optical switch. They are the most important polymeric ferroelectricity materials with excellent electro-active properties, high diffraction efficiency and significant nonlinear optical effect. We summarize the progress in nonlinear optical effect of polyvinylidene fluoride and its copolymers films both in domestic and foreign research within the last several years. We illustrate that the development direction of the films will be nanoscale-doping, blending modification and ultrathin. The nonlinear optical properties should be investigated by the first-principle and photonic band gap calculations, and measured by the means of the high sensitivity Z-scan, Marker fringe combing with ellipsometry. This study can provide an insight for the development and utilization for polyvinylidene fluoride and its copolymers films in future.

Research progress of terahertz super-resolution imaging
CAO Bing-hua, ZHANG Yu-meng, FAN Meng-bao, SUN Feng-shan, LIU Lin
2022, 15(3): 405-417.   doi: 10.37188/CO.2021-0198
Abstract(1366) FullText HTML(487) PDF 5252KB(418)
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Terahertz (THz) imaging technology has recently become one of the most cutting-edge technologies in many fields and has made great progress in its development over the past two decades. With the increasing demands of scientific research, medical treatment, military and industrial applications, high-resolution THz images have become indispensable. To obtain high-resolution THz images, super-resolution imaging has become a research hotspot. In this paper, the imaging methods of a THz system are reviewed, including continuous wave imaging and pulse wave imaging. On this basis, THz super-resolution imaging systems and THz signal processing technologies are described in detail. The super-resolution imaging systems include near-field imaging, super lens and terajet effect, etc. The THz signal processing technologies could be grouped as either super-resolution reconstruction and convolution calculations. Finally, the shortcomings of current super-resolution imaging technologies were discussed. There are still some bottlenecks that need to be resolved such as the high manufacturing process requirements of the system, the slow acquisition speed, and the low resolution of the learning samples used to reconstruct images. With this analysis, the research direction of super-resolution imaging is proposed.
Advances in research and applications of optical aspheric surface metrology
LIANG Zi-jian, YANG Yong-ying, ZHAO Hong-yang, LIU Sheng-an
2022, 15(2): 161-186.   doi: 10.37188/CO.2021-0143
Abstract(1503) FullText HTML(625) PDF 5743KB(430)
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Optical Systems using aspheric components (especially for free-form ones) have remarkable advantages over traditional spherical systems in that they can satisfy complicated requirements with simple optical-mechanical structures relying on abundant optional design parameters. Surface testing is an essential process for ensuring accuracy in manufacturing. Therefore, plenty of testing methods have been developed to meet varying testing demands of different types of surfaces at different stages in manufacturing. This paper summarizes the history of aspheric surface testing technology, classifies available techniques by whether they use interferometry, then introduces corresponding technical indexes, applicable conditions, research progress and applications. This paper highlights the high-precision interferometric methods, basic principles, optical layout and testing performances of every measurement method classified into Null and Non-null testing. The pros and cons of each method are compared, relative algorithms are introduced and precise adjustment methods are discussed.
Common failure modes and mechanisms in oxide vertical cavity surface emitting lasers
ZHANG Yu-qi, ZUO Zhi-yuan, KAN Qiang, ZHAO Jia
2022, 15(2): 187-209.   doi: 10.37188/CO.EN.2021-0012
Abstract(1180) FullText HTML(567) PDF 7522KB(322)
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Oxide Vertical Cavity Surface Emitting Lasers(VCSELs) are widely used in high-speed optical communications. The reliability of VCSELs is a very important index that requires a high lifetime and low failure rate in the application process. Understanding the root causes and mechanisms of VCSEL failure is necessary and helpful to improve device reliability. In this paper, we summarize and analyze the most common failure modes, causes and mechanisms observed in oxide VCSELs from the perspective of design, manufacturing and application, then apply some appropriate measures and suggestions to prevent or improve them. Moreover, the three dominating factors leading to the failure of VCSELs including oxide layer stress, Electronic Static Discharge (ESD) and humidity corrosion are introduced in more detail. At last, we simply introduce the VCSEL failure cases encountered in the actual accelerated aging verification process. This article can be used as a good VCSEL failure analysis library for chip development and production researchers.
Overview of 3D point cloud super-resolution technology
BI Yong, PAN Ming-qi, ZHANG Shuo, GAO Wei-nan
2022, 15(2): 210-223.   doi: 10.37188/CO.2021-0176
Abstract(896) FullText HTML(409) PDF 6613KB(231)
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With the development of the computer vision technology, research on recording and modeling the real world accurately and efficiently has become a key issue. Due to the limitation of hardware, the resolution of a point cloud is usually low, which cannot meet the applications. Therefore, it is necessary to study the super-resolution technology of point clouds. In this paper, we sort out the significance, progress, and evaluation methods of 3D point cloud super-resolution technology, introduce the classical super-resolution algorithm and the super-resolution algorithm based on machine learning, summarize the characteristics of the current methods, and point out the main problems and challenges in current point cloud data super-resolution technology. Finally, the future direction in point cloud super-resolution technology is proposed.
Research progress of lithium niobate thin-film modulators
LIU Hai-feng, GUO Hong-jie, TAN Man-qing, LI Zhi-yong
2022, 15(1): 1-13.   doi: 10.37188/CO.2021-0115
Abstract(1953) FullText HTML(1090) PDF 3910KB(684)
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Electro-optic modulators based on lithium niobate (LiNbO3, LN) thin-film platforms are advantageous for their small volume, high bandwidth and low half-wave voltage. They have important application prospects in the field of optical fiber communication and optical fiber sensing, and thus have became a heavily researched topic in recent years. In this paper, the research progress of the waveguide structures, coupling structures and electrode structures of LN thin-film modulators are reviewed in detail. The fabrication process of a LN thin-film waveguide is summarized, and the performances of different modulator structures are analyzed. Based on SOI and LNOI, a platform modulator is realized with VπL<2 V∙cm, a bilayer inversely tapered coupling scheme achieves a coupling loss <0.5 dB/facet , and a traveling wave electrode structure achieves a modulation bandwidth >100 GHz. Thin-film LN modulators are better than commercial LN modulators in most aspects. It can be predicted that in the near future, with the further improvement in waveguide technology, thin-film LN will become a popular scheme of LN modulators. Finally, the potential directions for the future of their research are proposed.
Two-dimensional material photodetector for hybrid silicon photonics
HU Si-qi, TIAN Rui-juan, GAN Xue-tao
2021, 14(5): 1039-1055.   doi: 10.37188/CO.2021-0003
Abstract(2672) FullText HTML(1000) PDF 10280KB(561)
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Two-dimensional (2D) materials provide new development opportunities for silicon-based integrated optoelectronic devices due to their unique structure and excellent electronic and optoelectronic properties. In recent years, 2D material-based photodetectors for hybrid-integrated silicon photonics have been widely studied. Based on the basic characteristics of several 2D materials and the photodetection mechanisms, this paper reviews the research progress of silicon photonic integrated photodetectors based on 2D materials and summarizes existing device structure and performance. Finally, prospects for strategies to obtain high-performance silicon photonic integrated 2D material photodetectors and their commercial applicability are presented with considerations for large-scale 2D material integrations, device structure, and metal-semiconductor interface optimizations, as well as emerging 2D materials.
Research progress on coherent synthesis of optical frequency comb
MA Jun-chao, MENG Li-li, ZHANG Rui-xue, ZHUO Xiao, NI Kai, WU Guan-hao, SUN Dong
2021, 14(5): 1056-1068.   doi: 10.37188/CO.2021-0071
Abstract(1140) FullText HTML(413) PDF 5700KB(257)
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Optical Frequency Comb (OFC) possesses unique time(frequency) domain characteristics such as narrow pulse width, high frequency precision, stable frequency comb teeth and well-defined optical coherence, etc. Therefore, it has become a hot research topic in various fields including ultra-fast laser technology and metrology science in recent years. Meanwhile, OFC has also been developed into an important scientific research instrument. Recently, a novel light source based on the coherent synthesis of OFCs has been developed, which can realize the periodical, high-speed (up to radio frequency) and stable modulation of the polarization or the orbital angular momentum of light. In this review, we try to introduce recent developments on the fundamental principles, experimental techniques and characterization methods of the novel light source based on the coherent synthesis of OFCs, starting from the basic concepts of OFC and mainly covering two aspects: polarization modulation and orbital angular momentum modulation respectively. We also try to provide some perspectives on the applications of OFC based on the coherent synthesis techniques in the fields of solid-state spectroscopy, optical manipulation and the interaction between light and matter, etc.
Progress of tunable micro-nano filtering structures
YU Xiao-chang, XU Ya-qing, CAI Jia-chen, YUAN Meng-qi, GAO Bo, YU Yi-ting
2021, 14(5): 1069-1088.   doi: 10.37188/CO.2021-0044
Abstract(1464) FullText HTML(646) PDF 12124KB(234)
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Because of the large size and immobility working modes, traditional spectral imaging systems struggle to meet increasingly complex practical needs. Tunable micro-nano filtering structures show unique advantages for their lighter weight and greater flexibility, so they are promising candidates for achieving adaptive and intelligent operation in the future. This article summarizes a variety of tunable filtering methodologies and their operational principles both in domestic and foreign research within the last several years. It illustrates static tunable methods such as utilizing liquid crystal and phase-change materials, some dynamic tunable filtering structures such as Fabry-Pérot cavity, micro-nano tunable grating as well as some driving approaches like mechanical stretching, electrostatic driving, optical driving, etc. Meanwhile, this article also introduces some frontier researches based on microfluidic chips and graphene. In the end, it discusses the barriers, challenges and future trends of development for tunable micro-nano filtering structures.
Research progress of elastic emission machining in optical manufacturing
LI Jia-hui, HOU Xi, ZHANG Yun, WANG Jia, ZHONG Xian-yun
2021, 14(5): 1089-1103.   doi: 10.37188/CO.2021-0022
Abstract(1093) FullText HTML(422) PDF 7589KB(194)
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The requirements of modern optical engineering in fields such as deep ultraviolet lithography, extreme ultraviolet lithography and advanced light sources drive the continuous development of advanced optical manufacturing technology. Modern optical engineering requires the surface roughness of ultra-smooth optical components to reach the atomic level and the surface shape profile error in the full spatial frequency to reach RMS(Root Mean Square) sub-nanometer or even a few dozen picometers. This drives the manufacturing requirements of ultra-smooth optical components to approach the processing limits. At present, there are still technical challenges to achieve the ultra-smooth polishing technology and equipment required for the above ultra-high precision needs. Atomic level ultra-smooth polishing of complex surfaces such as cylinders, ellipsoids and toroids is still a primary direction of research at both domestically and abroad. Elastic emission machining is an atomic-level ultra-smooth processing method with stable removal functionality and ultra-low subsurface defect creation, which can be used for manufacturing optical components with the above-mentioned accuracy requirements. We summarize the research progress of elastic emission machining and equipment at both domestically and abroad, the principles of elastic emission machining which contains fluid characteristics, the movement characteristics of polishing particles and chemical characteristics, the equipment of elastic emission machining, and the factors affecting the improvement of surface roughness and material removal rate of elastic emission machining. Then we analyze the problems faced by elastic emission machining and equipment and look forward to their prospects. It is expected that this paper will provide a reference for the further development and application of elastic emission machining.

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

CODEN ZGHUC8

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