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Review of the active control technology of large aperture ground telescopes with segmented mirrors
FAN Wen-qiang, WANG Zhi-chen, CHEN Bao-gang, LI Hong-wen, CHEN Tao, AN Qi-chang, FAN Lei
 doi: 10.37188/CO.2020-0032
Abstract(87) FullText HTML(35) PDF 3727KB(16)
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Segmented mirror technology is one of the three ways to realize optical synthetic aperture telescope, and it is an important area of development for future large aperture telescopes. A telescope’s active control system of its segmented mirrors directly determines its large aperture mirror’s optical performance. This paper focuses on the active control technology of large aperture ground telescopes with segmented mirrors. In this paper, we introduce the development process of a segmented mirror telescope and the main structure of the segmented mirror active control system, then summarize and analyze the domestic and foreign development of active control systems of segmented mirrors. In this paper, the key technologies of segmented mirror active control systems and how they achieve active adjustment and active maintenance are summarized. Their applications and the direction of their development are also proposed with respect to deep learning theory in closed-loop control, co-phase detection and correction, system-level simulation modeling technology. This paper provides guidance for the design of a segmented mirror control system in the next generation of ground-based large aperture telescopes in China.
Review of laser speckle target detection technology
GAO Wei-ke, DU Xiao-ping, WANG Yang, YANG Bu-yi
 doi: 10.37188/CO.2020-0049
Abstract(100) FullText HTML(28) PDF 3630KB(16)
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Target detection technology based on laser speckles is a kind of laser detection technology that has been ignored for a long time. In this technology, the laser speckle, which is regarded as noise in the traditional laser detection technology, is used as a new source of information. By analyzing the formation mechanism of a laser speckle pattern, the relationship between the statistical characteristics and the physical characteristics of the target is explored, and the effective analysis and inversion methods are combined to obtain the target’s shape, size, surface roughness and dynamic parameters. Compared with traditional laser detection technology, target detection technology based on laser speckles has a simple structure, has low optical system requirements, is sensitive to the physical and fretting characteristics of the target’s surface, and has been widely used in aerospace, medicine, industry, military and other fields. This paper classifies and summarizes the various kinds of speckle-based target detection technologies from recent years, compares and analyzes their applications, advantages and disadvantages, as well as the environmental restrictions. Finally, this paper prospects the trend for the future development of target detection methods based on laser speckles.
Tailoring the optical properties of Al-doped ZnO Nanorods by electrodeposition
TANG Yang
 doi: 10.37188/CO.2020-0075
Abstract(66) FullText HTML(44) PDF 3626KB(3)
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In order to achieve the implantation of the ZnO nanorod arrays in the nanostructured solar cells, it is necessary to tailor and control the nanorods’ morphology, optical and electrical properties. ZnO nanorods arrays were fabricated by electrodeposition. The physical properties such as the crystalline quality, diameter, density, distance, Al doping concentration, optical band gap energy, near band emission and stokes shift can be adjusted by using Al(NO3)3 and NH4NO3. The ZnO nanorods’ diameter can be adjusted from 28 nm to 102 nm. The nanorod arrays’ density can be reduced to 2.7×109 /cm2 by using NH4NO3, resulting in an increase in the distance between nanorods to 164 nm. The Al/Zn weight ratio was increased to 2.92% by using NH4NO3, indicating that NH4NO3 can boost Al doping in ZnO nanorods. The ZnO nanorods’ optical band gap energy can be tailored from 3.36 eV to 3.55 eV by using Al(NO3)3 and NH4NO3 and the near band edge emission can also be adjusted. The use of Al(NO3)3 led to the increase of the Stokes shift to 200 meV, but it can be greatly reduced to 26 meV as a result of the NH4NO3. The use of Al(NO3)3 and NH4NO3 resulted in the fabrication of high-quality ZnO nanorod arrays with effectively tailored morphology and optical properties.
Energy coupling characteristic of materials under thermal radiation produced by strong explosion
GAO Yin-jun, GAO Li-hong, ZHANG Xiang-hua, MA Zhuang, LIU Feng, PENG Guo-liang, TIAN Zhou
 doi: 10.37188/CO.2020-0053
Abstract(86) FullText HTML(51) PDF 3425KB(1)
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To obtain the energy coupling characteristic of materials under strong explosive thermal radiation, a physical model for calculating radiation source parameters and atmospheric transmission is constructed, and the characteristics of the radiation spectrum at the target location under different conditions are obtained. The energy coupling coefficients of several kinds of materials are produced by spectral reflectance measurement and by calculating the average absorption coefficient of thermal radiation. The coupling coefficients of metal and ceramic materials are relatively small while it can be as high as 0.92 for carbon fiber epoxy composites. The coupling coefficient calculated from the actual thermal radiation spectrum is higher than that calculated from 6000 K blackbody radiation spectrum, and the maximum difference is about 14%. Taking aluminum material as an example, the coupling coefficient of thermal radiation decreases gradually with the increase of explosion yield and distance, but the overall variation is small.
Absorption enhancement of silicon via localized surface plasmons resonance in blue band
WANG Hao-bing, TAO Jin, LV Jin-guang, MENG De-jia, LI Yang, ZHAO Yong-zhou, WANG Jia-xian, ZHANG Jun, QIN Yu-xin, WANG Wei-biao, LIANG Jing-qiu
 doi: 10.37188/CO.2020-0056
Abstract(123) FullText HTML(49) PDF 4684KB(4)
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To enhance the blue light absorption of silicon, an array of silver nanoparticles(Ag-NPs) was designed so that they create Localized Surface Plasmon Resonance(LSPR) near the surface of silicon(Si). The properties of the enhanced optical absorption of silicon in the blue band were then observed and researched. The blue-light absorption characteristic of silicon in the Ag-NPs/Silicon composite structure were calculated using the Finite-Difference-Time-Domain (FDTD) method. The results indicated that the metallic nanoparticles' extinction capability was related to its geometric parameters and the resonance intensity and peak wavelength can be tuned according to different geometric parameters of Ag-NPs including radius, height and period. At a resonance peak wavelength of 465 nm, the optical absorption of Si in the composite structure (Ag-NPs/Si) rises from 59% to 94% with an array of radius r = 18.5 nm, a height H = 45.0 nm and a period P = 49.0 nm. It concluded that the light absorption gain was 0.57 and photogenerated carriers had a gain factor of 0.53 due to the enhanced light absorption of Si via LSPR in blue band. The results provide a significant reference for the enhancement of the blue-light absorption properties in silicon based on the LSPR effect and the design of a silicon-photodetector with a visible wide spectral resoponse.
Light field imaging target ranging technology
ZHANG Shi-lei, CUI Yu, XING Mu-zeng, YAN Bin-bin
 doi: 10.37188/CO.2020-0043
Abstract(60) FullText HTML(29) PDF 5073KB(9)
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At present, it is difficult to obtain target distance information in image guidance. In order to apply modern guidance laws to image guidance technology and improve its performance, a target ranging algorithm using light field imaging is proposed. The algorithm decodes and tunes light field data to extract sub-aperture images from an original image. Bilinear interpolation is then performed on the two sub-aperture images to improve the image’s spatial resolution, and two sub-aperture images are selected as calibration data to obtain the corresponding internal and external parameters. The parameters are used to correct the sub-aperture images, which aligns them and makes them coplanar. Finally, a semi-global matching method is used to match the images to obtain the disparity value of the target. Then, 3D transformation of parallax can be used to get the target distance. The experimental results show that the average measurement errors of the algorithm are 28.54 mm and 14.96 mm, respectively, before and after improvement. This algorithm can effectively extract target distance information in complex scenes, which has value in theoretical and real-world applications.
Gabor filter fusion network for pavement crack detection
CHEN Xiao-Dong, AI Da-Hang, ZHANG Jia-Chen, CAI Huai-Yu, CUI Ke-Rang
 doi: 10.37188/CO.2020-0041
Abstract(103) FullText HTML(61) PDF 3857KB(19)
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In pavement detection, the small sample of road crack image data makes it difficult for neural networks to extract useful features from images. To solve this problem, this paper proposes a Gabor Filter Convolutional Neural Network (GF-CNN) model. The GF-CNN model first inputs a road surface image into a small parameter prediction network, adaptively selects the parameters of the Gabor filter bank according to the input, and constructs a filter bank according to the predicted parameters, and then filters the initial road surface image to obtain the Gabor texture feature map. The texture feature map is inputted into a feature classification network constructed by the residual network to extract deep features, at the same time, to judge whether a crack exists. Test results on the GAPs pavement image dataset show that the F1 score of the GF-CNN model reaches 0.7137, which is superior to other pavement image detection methods. This model improves the feature extraction ability of CNNs by fusing texture features, and reduces the sensitivity of Gabor filter parameters to improve its ability to make generalizations. It has good applicability to pavement crack image detection.
Progress in ultrafast laser space-selective welding
ZHANG Guo-dong, CHENG Guang-hua, ZHANG Wei
 doi: 10.37188/CO.2020-0131
Abstract(39) FullText HTML(43) PDF 4987KB(18)
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The development of ultrafast laser technology has continuously injected new impetus into fundamental research and production, promoted the emergence of new disciplines and technologies. As a new materials welding and joining technique developed in recent years, ultrafast laser welding has attracted extensive attention due to the potential application in the fields of aerospace, precision machinery, optoelectronics, biomedical, etc.. Based on the intrinsic characteristic of non-linear space-selective energy deposition, ultrafast laser welding possesses extremely high material applicability and spatial selectivity, and can realize high-quality space-selective welding involving transparent materials with no need inserting an absorption layer. In this paper, we firstly give an overview on the progress of this field. Then, the physical mechanism, key influencing factors, and application scope of ultrafast laser welding are elaborated. At last, the future development and key challenges of ultrafast laser welding are discussed.
Design and verification of high-precision multi-star simulator with a wide field of view
XU Hong-gang, HAN Bing, LI Man-li, MA Hong-tao, ZHANG Peng-yu, JU De-han
 doi: 10.37188/CO.2020-0024
Abstract(53) FullText HTML(23) PDF 3778KB(9)
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In order to achieve high-precision ground calibration of star sensors and meet the needs of a high-precision multi-star simulator with a wide field of view, a high-precision star simulator which can accurately simulate the position and magnitude of 65 stars in the 20° × 40° field of view was developed. Based on the principles of star simulators and the transformation of the space coordinate systems of star simulators, a simulation star bracket was designed. By the analysis and calculation of errors that affect the pointing error of star simulations, the high-precision simulation star system was designed using key technologies such as "integrated installation of primary and secondary mirrors", "all-aluminum simulation star systems" and "star point position compensation". A space-position model of each simulation star in the o-x'y'z' coordinate system was established, and the mathematical models of pitch, yaw, single star direction and star angular distance were derived. Also, the theoretical errors in single-star direction and star angular distance, which were used as the theoretical basis for adjustment and testing, were calculated. The single-star direction error of all simulated stars was better than 1.914", and the angular distance error of any two simulated stars was better than 4.3". The accuracy of the designed high-precision wide-field-of-view multi-star simulator meets the requirements. It can be used as an important piece of equipment for ground calibration of high-precision star sensors.
Identification of opto-electronic fine tracking systems based on an improved differential evolution algorithm
DONG Quan-rui, CHEN Tao, GAO Shi-jie, LIU Yong-kai, ZHANG Jian-qiang, WU Hao
 doi: 10.37188/CO.2020-0021
Abstract(104) FullText HTML(50) PDF 3692KB(4)
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In this paper, an identification method based on an improved differential evolution algorithm is proposed for laser communication fine tracking systems. Firstly, the basic principle and calculation steps of the traditional differential evolution algorithm are introduced. Based on this, an improved algorithm is proposed, and the algorithm’s parameters are optimized . Then, the dynamic characteristics of a controlled object in the fine tracking system are simulated by a sweep signal, and the positional feed back information of the camera is collected. Finally, based on the experimental data, the differential evolution algorithm is used to identify the system, and the control model of the fine tracking system is obtained. The experimental results show that the improved differential evolution algorithm has faster convergence speed and accurate identification results. In general, this method has engineering value in the field of optoelectronic tracking.
Development status and trend of micro-satellite laser communication systems
GAO Shi-Jie, WU Jia-Bin, LIU Yong-Kai, MA Shuang, NIU Yan-Jun, YANG Hui-sheng
 doi: 10.37188/CO.2020-0033
Abstract(168) FullText HTML(66) PDF 7413KB(25)
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With its high speed, small size, light-weight and low power consumption, space laser communication has become an indispensable and effective means of high-speed communication between satellites, especially in micro-satellite applications, which can benefit more strongly from the advantages of laser communication. This paper provides a detailed introduction of the latest research progress in the field of micro-satellite laser communication technology. On this basis, key techniques such as light miniaturization of identical orbital terminals, light miniaturization of different orbital terminals and turbulence mitigation technologies are summarized, and the development trends of the technology’s applications, duplex communication, single-point to multi-point, localization and batch production capacity are concluded.
Structural optimization for the design of an ultra-lightweight SiC mirror with a diameter of 500 mm
ZHAO Yu, SU Cheng-zhi, ZHAO Gui-jun, YANG Guang
 doi: 10.37188/CO.2019-0201
Abstract(46) FullText HTML(18) PDF 5075KB(8)
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To meet the performance requirements of ultra-lightweight Φ500 mm-reflector optical system in near diffraction limit, the structure of the reflector is studied using advanced CAE simulation and modern high-performance SiC fabrication technology. Firstly, mirror materials were selected by comparing the common materials and manufacturing processes of existing mirrors. Then, with regards to the structural characteristics of circular symmetrical reflectors, the structure of proposed reflector was designed based on integrated optimization of the full stiffness method. Finally, the reflector assembly was designed with a back-support structure. The simulation results show that the mass of proposed primary mirror is less than 5 kg and the surface density is less than 20 kg/m2. The surface errors (RMS value) of the three directions of dead weight deformation at 4 ℃ temperature rise are less than λ/50. The first-order resonance frequency of the primary mirror assembly is no less than 120 Hz and the stress at the weakest point as measured by dynamic response analysis is less than 100 MPa. The structural optimization of the mirror meets its design requirements, with a remarkable lightweight effect and a structure that is both stable and reliable.
638 nm narrow linewidth diode laser with a grating external cavity
LIU Ye, LIU Yu, XIAO Hui-dong, LI Hong-ling, QU Da-peng, ZHENG Quan
 doi: 10.37188/CO.2020-0249
Abstract(49) FullText HTML(23) PDF 2239KB(6)
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In this paper, a narrow linewidth laser with an external grating cavity of 638 nm is described, wherein a reflection holographic grating was used as its external feedback element. The spectrum of the diode lasers with the grating external cavity arranged in a Littrow configuration were measured using a high-resolution monochromator and the characteristics of the threshold and tuning properties were investigated. In the experiment, reflection holographic gratings with 2400 l/mm and 1800 l/mm groove density were studied. At 120 mA injection current, the output power of the external cavity laser was 45.2 mW when the groove density was 2400 l/mm, and the threshold current of the LD was reduced from 60 mA to 51 mA and the descent rate was 11%. When the groove density was 1800 l/mm, the output power was 38.7 mW, the threshold current of the LD was reduced from 60 mA to 47 mA, and the descent rate was 24%. Furthermore, the linewidths were suppressed to within 3.5 pm, and the tuning ranges were 9.4 nm and 10.5 nm in wavelength. The experimental results showed that the performance of semiconductor lasers was improved greatly using the Littrow configuration with a reflective holographic grating.
Compensation of star image motion for a CMOS image sensor with a rolling shutter
ZHANG Bo-yan, KONG De-zhu, LIU Jin-guo, WU Xing-xing, DONG De-yi
 doi: 10.37188/CO.2020-0089
Abstract(96) FullText HTML(46) PDF 3891KB(8)
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According to the imaging principles and characteristics of a shutter CMOS image sensor, the shutter effect introduced by a shutter CMOS image detector operating on a star map is analyzed, and an image shift compensation method is proposed to rectify the image distortion introduced by this kind of imaging method. With the known frame frequency of the star images and the exposure time interval of the adjacent rows of the CMOS graphic sensor, this method can achieve high-speed calculation of star motion by extracting and matching the centroid of the star points in an adjacent star map. The centroid of the star points in a global image is calculated by combining the speed value with the row exposure time interval of the CMOS image sensor. The effect of the algorithm is tested on actual star images. The experimental results show that with the compensated star map, angle errors between the star sensors are smaller than 0.5″ when a satellite is in non-maneuver mode, and angle errors between either of the star sensors are about 0.6″ when the satellite is in maneuver mode. The experimental results not only prove the effectiveness of the algorithm, but also broaden the applications of shutter CMOS detectors to some extent, especially in aerospace engineering.
Room-Temperature Terahertz Photodetectors Based on Black Arsenic-Phosphorus
DONG Zhuo, CHEN Jie, ZHU Yi-fan, YANG Jie, WANG Zhong-chang, ZHANG Kai
 doi: 10.37188/CO.2020-0175
Abstract(16) FullText HTML(3) PDF 3680KB(2)
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Terahertz technology is indispensable in plenty of fields due to the abundant interactions between terahertz waves and matter. In order to meet the needs of terahertz applications, the development of highly sensitive and portable terahertz detectors based on distinctive physical mechanisms and various materials with excellent properties are urgently required. Black arsenic-phosphorus is a novel two-dimensional material that has a tunable band gap and transport characteristics with varying chemical composition, which has gained widespread interest in optoelectronic applications. Recent research on b-AsxP1-x mainly focuses on infrared detection, while the detection of terahertz has not yet been applied. Herein, an antenna-coupled terahertz detector based on exfoliated multilayer black arsenic-phosphorus is demonstrated. The terahertz response performance of the detector reflects two different mechanisms, which have a competitive relationship in the detection process. In particular, the detection mechanism can be tailored by varying the chemical composition of black arsenic-phosphorus. By balancing the band gap and carrier mobility, a responsivity of over 28.23 V/Wand a noise equivalent power of less than 0.53 nW/Hz1/2 are obtained at 0.37 THz. This implies that black arsenic-phosphorus has great potential in terahertz technology.
Study on quantitative methods of laser-induced two-dimensional fluorescence spectroscopy of multicomponent PAHs in soils
HUANG Yao, ZHAO Nan-jing, MENG De-shuo, ZUO Zhao-lu, CHENG Zhao, CHEN Yu-nan, CHEN Xiao-wei, GU Yan-hong
 doi: 10.37188/CO.2020-0059
Abstract(50) FullText HTML(8) PDF 3523KB(2)
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Laser-Induced Fluorescence(LIF) has become a powerful technology for quantitative analysis of Polycyclic Aromatic Hydrocarbons(PAHs) in soils due to its fast detection speed and low operational cost, without sample preparation. However, there are many types of PAHs in soils, and their similar structures lead to overlapped issues in their laser-induced fluorescence spectra. It is challenging to quantify a single PAH in complicated soil without the chemical separation. In this paper, fluorescence spectra of PAHs in agricultural soil are obtained by a 266 nm mobile LIF system, and quantification methods are investigated for PAHs, based on univariate linear regression, weighted non-negative least squares Multivariate Linear Regression(MRL) and Support Vector Regression(SVR). The results show that the correlation coefficients of anthracene and phenanthrene are both less than 0.90, and the average relative errors are both more than 20% by using univariate linear regression. Compared with univariate linear regression, MLR improves the prediction accuracy of anthracene and phenanthrene in the soil contaminated with bi-component PAHs. However, the average relative errors are still over 20% in the soil contaminated with multicomponent PAHs. Finally, a SVR model optimized by grey wolf optimization combined with differential evolution(GWO-DE) is applied for concentration measurement of anthracene and phenanthrene in agricultural soil contaminated with multicomponent PAHs. The average relative error of anthracene decreases from 23.1% (MLR) to 5.02%, while in the case of phenanthrene decreases from 20.8% (MLR) to 4.83%. This study provides an efficient method to improve the accuracy of LIF in quantifying multicomponent PAHs in soils.
Overview of 2D grating displacement measurement technology
YIN Yun-Fei, LIU Zhao-Wu, JIRIGALANTU, YU Hong-Zhu, WANG Wei, LI Xiao-Tian, BAO He, LI Wen-Hao, HAO Qun
 doi: 10.37188/CO.2020-0237
Abstract(49) FullText HTML(18) PDF 6952KB(13)
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Ultra-precision displacement measurement technology is not only the basis of precision machining, but also plays a decisive role in the chip manufacturing industry that is rapidly developing in Moore's Law. The grating displacement measurement system based on the grating pitch is widely used in multidimensional measurement system. Compared with the laser displacement measurement system, grating displacement measurement system greatly reduces the environmental requirements for humidity, temperature and pressure. In this paper, the development status of the optical structure of displacement sensing system based on two-dimensional grating in recent years is introduced. The principles of zero-difference and heterodyne grating interferometrys are introduced. The optical structure based on single-block two-dimensional grating is reviewed. The development history of the optical structure in single-block two-dimensional grating to coupling designs of multi-block two-dimensional gratings is summarized, the advantages and disadvantages of several two-dimensional grating displacement measurement systems are compared and analyzed, and the development trend of two-dimensional grating displacement measurement system is prospected. The engineering process of two-dimensional grating displacement measurement system is summarized.
Design of global-contextual detection model for optical remote sensing targets
ZHANG Rui-yan, JIANG Xiu-jie, AN Jun-she, CUI Tian-shu
 doi: 10.37188/CO.2020-0057
Abstract(78) FullText HTML(42) PDF 4929KB(3)
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To improve the detection accuracy and reduce the complexity of optical remote sensing of target images with a complex background, a global context detection model based on optical remote sensing of targets is proposed. First, a feature encoder-feature decoder network is used for feature extraction. Then, to improve the positioning ability of multi-scale targets, a method that combines global-contextual features and target center local features is used to generate high-resolution heat maps. The global features are used to achieve the pre-classification of targets. Finally, a positioning loss function at different scales is proposed to enhance the regression ability of the model. Experimental results show that the mean average precision of the proposed model reaches 97.6% AP50 and 83.4% AP75 on the NWPU VHR-10 public remote sensing data set, and the speed reaches 16 PFS. This design can achieve an effective balance between accuracy and speed. It facilitates subsequent porting and application of the algorithm on the mobile device side, which meets design requirements.
Illumination of a cylinder block transverse hole for machine vision inspection
JIANG Tao, ZHANG Gui-lin, GAO Jun-peng
 doi: 10.37188/CO.2020-0054
Abstract(116) FullText HTML(62) PDF 4288KB(12)
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In view of the complex design of light sources and the poor illumination uniformity in cylinder block transverse hole detection by using machine vision, a double light source method is provided for the detection of transverse holes. In this method, an integrating sphere is used as the background light source and an LED is used as the direct light source. To achieve uniformity of illumination on the cylinder transverse hole, a mathematical model of the light source radiation response is established in this paper. Using this imaging method, a relationship between the size of the light source, its distance and the position of the reflection point and illumination uniformity is proposed. Finally, a controlled experiment was performed to reveal the illumination uniformity developed in different light sources: an optical fiber source, an LED source, and an LED + integrating sphere source. The results of the experiment show that the non-uniformity is up to 10% with an LED light source emitting from outside the hole, and it becomes 5% when the LED light is moved to the inside of the hole; the non-uniformity of an internal optical fiber light source is 4.6%. In particular, the double light source, wherein the integrating sphere is used as a background light outside the cylinder block and the LED is used as a direct light inside the cylinder block has a non-uniformity of 0.6%. The uniformity illumination surpasses 99%, which can be obtained by using an integrating sphere and LED dual light source, meeting our requirements for machine vision detection.
Fast alignment of an offner imaging spectrometer using a spherical autostigmatic method
YANG Tuo-tuo, CHEN Xin-hua, ZHAO Zhi-cheng, ZHU Jia-cheng, SHEN Wei-min
 doi: 10.37188/CO.2020-0058
Abstract(99) FullText HTML(61) PDF 5510KB(9)
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Offner imaging spectrometers consist of a convex grating and two concave mirrors. The concentric characteristics of the optical structure allow it to have a large relative aperture, small distortion and a compact structure. In order to reduce the difficulty of aligning an Offner imaging spectrometer and improve its efficiency, this paper presents a fast alignment method for Offner imaging spectrometers based on the concentric characteristic and spherical autostigmatic method. Firstly, a spherical autostigmatic device is built, which can generate a point source. When the point source is located at the spherical mirror’s center of curvature (CoC), its reflection image point and the point source coincide. By measuring the distance between the reflection image point and the point source, the positional deviation of the spherical mirror’s CoC can be determined. The Offner imaging spectrometer is completed by locating the CoC of its primary mirror, convex grating and tertiary mirror. The results show that the location error of the two off-axis concave mirrors’ CoC can be controlled within 10 μm, and our imaging performance requirements for the imaging spectral system are satisfied. Compared with pre-existing methods, this method is easier to operate, lower in cost and has faster alignment capabilities.
Shift of the first ionization threshold of Sm atom in electric field
XU Zhao-jin, ZHANG Xiao-hu, ZHANG Wen-na, HUANG Chao-hong, SHEN Li
 doi: 10.37188/CO.2020-0071
Abstract(84) FullText HTML(58) PDF 3198KB(5)
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In order to obtain the first ionization threshold of Sm atom, the photoionization signal, self-ionization signal and field ionization signal generated by the Sm atom under multi-step excitation were distinguished, and the influence of the Rydberg state of the Sm atom with different magnetic quantum numbers on the first ionization threshold was studied. At first, by use of multi-step resonance excitation combined with polarization technology, the rare-earth Sm atoms were excited to the self-ionization or bound Rydberg state with a specific magnetic quantum number near the first ionization threshold. Then the ions generated by photoionization and self-ionization were pushed out of the action zone by the reverse electrostatic field, and a delayed pulsed electric field was applied to detect the Sm atoms of bound Rydberg state. Finally, the relationship between the first ionization threshold of Sm atom and the varying intensity of electrostatic field was acquired, and the first ionization threshold of the Sm atom with different magnetic quantum numbers under zero field was determined by fitting. The experimental results show that the first ionization threshold of Sm atom is 45519.69±0.17 cm−1, which has been compared with the results obtained by other methods. The effectiveness of the delayed field ionization technique in measuring the first ionization threshold of Sm atom has been verified.
Progress on defect and related carrier dynamics in two-dimensional transition metal chalcogenides
WANG Yunkun, LI Yaolong, GAO Yunan
 doi: 10.37188/CO.2020-0106
Abstract(647) FullText HTML(41) PDF 5820KB(20)
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Because of their unique physical properties, the monolayer and few-layer two-dimensional transition metal chalcogenides with atomic-level thickness are expected to play an important role in the next generation of optoelectronic devices. However, defects in two-dimensional materials affect their properties to a great extent. On one hand, defects reduce the fluorescence quantum efficiency, carrier mobility and other important device parameters. On the other hand, the control and utilization of defects have given birth to new techniques such as using single-photon sources. Therefore, it is very important to characterize, understand, handle and control the defects in two-dimensional materials. In this review, the research progress on defects and its related carrier dynamics in two-dimensional transition metal chalcogenides is summarized. This paper aims to sort out the great influence of defects and their related ultrafast dynamics on material performance in two-dimensional transition metal chalcogenides, and to support studies on fundamental physical properties and high-performance optoelectronic devices.
Speckle noise reduction in swept-source optical coherence tomography by retinal image registration
CAI Huai-yu, HAN Xiao-yan, LOU Shi-liang, WANG Yi, CHEN Wen-guang, CHEN Xiao-dong
 doi: 10.37188/CO.2020-0130
Abstract(28) FullText HTML(10) PDF 3775KB(3)
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The averaging of multiple B-Scans is an effective method of reducing speckle noise in swept-source optical coherence tomography (SS-OCT) and obtaining clear structural information. However, physiological characteristics such as eye tremor, drift, micro-saccade, and the optical structure of an SS-OCT system cause geometric transformation between images, resulting in poor multi-frame averaging. In this paper, we propose a registration algorithm based on the combination of gray distribution information and target geometric information. This method extracts the region of interest containing target information using the average gray distribution of an image, and corrects the transformation of the image with the collective effect of the phase correlation algorithm and the gray projection algorithm based on the fitting of the curve of its segments. Then, the process is repeated with the upper boundary of the retinal image fitted as the feature points to determine the optimal rotation parameters. The translation parameters are re-estimated again to achieve the rigid registration of the image. Finally, a one-to-one mapping method of axial scanning is used to achieve the non-rigid registration of the image with the energy function as the constraint. Experiments on live rabbit eyes show that the averaged image has clear boundaries, enhanced structural information, and its signal-to-noise and contrast-to-noise ratios are more than doubled their previous values, on average. The algorithm is suitable for the registration of B-Scan images with strong speckle noise and can meet the averaging needs of many types of OCT systems. It has high robustness and image registration accuracy.
Multi-scale singular value decomposition polarization image fusion defogging algorithm and experiment
ZHOU Wen-zhou, FAN Chen, HU Xiao-ping, HE Xiao-feng, ZHANG Li-lian
 doi: 10.37188/CO.2020-0099
Abstract(45) FullText HTML(22) PDF 4667KB(5)
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Problems with existing polarization defogging algorithms are that they are not robust and have limited image enhancement abilities. To resolve this, an image fusion defogging algorithm based on multi-scale singular value decomposition is proposed. Firstly, the redundancy in polarization measurement information is used, and the least square method is used to improve the accuracy of the polarization information in the traditional defogging algorithm for polarized images; then, with respect to the limitations of that algorithm, a qualitative analysis of the feasibility of image fusion defogging is provided, and a polarized image fusion defogging algorithm based on multi-scale singular value decomposition is proposed. Finally, for verification, an experiment under different visibility conditions is designed and quantified. The results show that compared with the classic polarized image defogging algorithm, this algorithm does not require manual parameter adjustment, has strong adaptability and robustness, and can effectively improve the overexposure of halos and sky areas that occur in the traditional algorithm. The image information entropy and the average gradient can be increased by 18.9% and 38.4% respectively, which effectively improves the quality of visual imaging under complex lighting conditions. The proposed algorithm has great application prospects.
Polarization changes of partially-coherent airy-gaussian beams in a slanted turbulent atmosphere
Cheng Ke, Lu Gang, Zhu Bo-yuan, Shu Ling-yun
 doi: 10.37188/CO.2020-0095
Abstract(21) FullText HTML(7) PDF 2044KB(1)
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Investigating polarization changes in a turbulent atmosphere holds great significance because polarization is one of the most important parameters in laser communication. Based on the extended Huygens-Fresnel principle and the unified theory of coherence and polarization, an analytical expression for the degree of polarization (DoP) in partially coherent Airy-Gaussian beams propagating in a slanted turbulent atmosphere is derived. It is then used to study the dependence of polarization changes in turbulent parameter, coherence length, zenith angle, truncation and distribution factor. The polarization between the slanted and horizontal paths is also compared. Compared with horizontal turbulence, the beams traverse a longer distance to recover their initial polarization in slanted turbulence. An increase in the zenith angle, receiving height and truncation factor, or a decrease in the coherence length can increase the DoP. A smaller distribution factor or a higher coherence length is beneficial to reducing the effect of the zenith angle on the polarization. Analysis of the influence of the distribution factor on polarization also shows that maintaining the polarization of a Gaussian beam with higher coherence in a horizontally turbulent atmosphere has a greater advantage to that of a pure Airy beam from the view of keeping polarization invariance. The results in this paper may be useful for studying atmospheric communication, and show that optical information encoding can be achieved by selecting appropriate parameters.
Influence of modulation performance on coating on repaired fused silica
JIANG Yong, LIAO Wei, WANG Biyi, ZHAO Wanli, LIU Qianghu, QIU Rong, GUO Decheng, ZHOU Lei, ZHOU Qiang, ZHANG Yuanheng
 doi: 10.37188/CO.2020-0110
Abstract(45) FullText HTML(21) PDF 3310KB(2)
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In order to address the light modulation problem on repair spots created after using a CO2 laser to repair fused silica surface damage, this paper focuses on the change of the profile and the modulation of the repaired sites before and after coating them with antireflective film. The influence of the depth and width of the repaired site on the deposition of the colloid are discussed, with some attention also given to the influence of the modulation effect. The results indicate that the colloidal material significantly enriches the pits of a repair, which can effectively improve their topographic dimensions with regards to their depth. The maximum modulation locations of a repaired site will increase after being coated with the antireflective film. However, the maximum modulation caused by the repaired site is much smaller than that of the corresponding uncoated repair point. The results of this study can provide reference for further optimization of repair processes and light modulation regime control of the surface damage sites on fused silica.
Enhanced Dye-sensitized Upconversion Luminescence Based on Nd3+-sensitized Multi-shell Nanostructures
WANG Dan, XUE Bin, TU Lang-ping, ZHANG You-lin, SONG Jun, QU Jun-le, KONG Xiang-gui
 doi: 10.37188/CO.2020-0097
Abstract(102) FullText HTML(19) PDF 3339KB(3)
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Lanthanide ion doped upconversion luminescence is limited by the small absorption cross-section and narrow absorption band of lanthanide ions, which results in weak luminescence. Recently, a dye-sensitized method has proven to be an effective strategy of increasing upconversion luminescence. However, simply attaching dye molecules to nanoparticles with classic Yb-doped nanostructures cannot effectively activate the sensitizing ability of the dye molecules. In response to this problem, we designed Nd-sensitized core/shell/shell (NaYF4: Yb/Er (20/2%)@ NaYF4: Yb (10 %)@ NaYF4: Nd (80 %)) nanostructures, which compared with the classic IR-806 sensitized NaYF4: Yb/Er nanostructure, their upconversion luminescence (500 to 700 nm) was approximately enhanced by a factor of 38. Through analysis of the nanostructure’s emission and luminescence lifetime data, the enhancement was confirmed by the effective overlap of Nd absorption with the emission of near-infrared dye molecules and the protective effects of the shell structure on the luminescent center (the lifetime of Er (4S3/24I15/2) was increased by 1.7 times). In addition, we found that the doping Yb3+ in the outermost layer will decrease the dye-sensitized luminescence intensity. Furthermore, this Nd-sensitized core/shell/shell also achieved enhancement in the sensitized upconversion luminescence of the luminescence centers of Ho and Tm, which establishes a foundation for enhanced dye-sensitized upconversion luminescence.
Research progress on portable laser-induced breakdown spectroscopy
ZENG Qing-dong, YUAN Meng-tian, ZHU Zhi-heng, CHEN Guang-hui, WANG Jie, YU Hua-qing, GUO Lian-bo, LI Xiang-you
 doi: 10.37188/CO.2020-0093
Abstract(54) FullText HTML(13) PDF 3931KB(6)
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As a new rapid element analysis technique, laser-induced breakdown spectroscopy (LIBS) has proven iteself to have great potential for applications in increasingly numerous industrial fields. However, due to harsh outdoor and industrial environments, newer and higher requirements are being demanded of the LIBS system, such as the size of its instruments and the ability to resist a harsh environment. The rapid development of new laser technology promotes instrumentation for LIBS, allowing it to gradually step outside the laboratory and into the industry, and allows the LIBS system to gradually move towards instrumentation, miniaturization and portability.In this paper, the development of a portable LIBS that was developed in recent years was reviewed. The application and latest research progress of different kinds of laser source (small lamp pumped solid-state laser, diode pump solid-state laser and micro laser, fiber laser) applied to the portable LIBS system were summarized and discussed, providing insight into both the fiber optic LIBS (FO-LIBS) and the handheld LIBS. In addition, the basic problems of current portable LIBS and the prospects of its future were proposed and discussed.
Real-time polarization imaging integrated technology for solid-state low-light imaging
LIANG Wan-yu, XU Jie, DAI Fang, CHANG Wei-jing, NA Qi-yue
 doi: 10.37188/CO.2020-0086
Abstract(66) FullText HTML(20) PDF 4215KB(9)
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High-performance night vision light detection is the future direction of development in photoelectric detection. In this paper, a real-time polarization imaging technology for low-light imaging is proposed to solve issues where polarization images show large error due to low sensitivity. By introducing white light channels and 8 polarization channels in four polarization directions, detection can be achieved on EMCCD micro-optical devices. The experiment shows that the polarization information obtained by the polarization array is highly accurate, and also has advantages for its low difficulty in processing and its low cost.
Non-destructive Testing of Red Globe Grape Sugar Content and Moisture Content Based on Visible/Near Infrared Spectroscopy Transmission Technology
GAO Sheng, WANG Qiaohua
 doi: 10.37188/CO.2020-0085
Abstract(36) FullText HTML(12) PDF 4724KB(2)
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  Objective  The sugar content and moisture of red globe grapes are important internal quality measurement indices. However, traditional detection methods use destructive biochemical detection.  Method  In this paper, a non-destructive detection method for the sugar and moisture content of red globe grapes based on visible/near-infrared spectroscopy transmission technology is studied. 360 red globe grape extract samples were collected and PLSR models were established by Standard Normal Variable transformation (SNV), SavitZky-Golay(S_G) and other spectral preprocessing methods to determine the one. Seven data dimensionality reduction methods of primary dimensionality reduction (GA, SPA, CARS, UVE) and secondary dimensionality reduction combinations (CARS-SPA, UVE-SPA, GA-SPA) were used to identify characteristic variables of spectra. PLSR and LSSVM content detection models of red globe grape extract sugar content and moisture content were established respectively, and the advantages and disadvantages of each model were compared and analyzed.  Result  The results show that the optimal PLSR model wavelength extraction method for red globe grape sugar content and moisture content is GA-SPA-PLSR, and the correlation coefficients of the optimal model were 0.958 and 0.938, respectively. The optimal LSSVM model wavelength extraction methods for red globe grape sugar and moisture content are CARS-SPA-LSSVM and UVE-SPA-LSSVM, respectively. The correlation coefficients of the optimal model are 0.969 and 0.942, respectively. The model built using LSSVM is better than that built using PLSR, but its operation time is longer.  Conclusion  The results show that: The non-destructive detection method of red globe grape sugar and moisture content based on visible/near-infrared technology is feasible, and that the detection accuracy of the two optimal detection models is high, which can meet detection requirements. Different models can be selected for different applications. The optimal model built by PLSR has shorter computation time and is suitable for online rapid detection. LSSVM has the best detection performance and can accurately predict red globe grape sugar and moisture content.
Research advances in adaptive interferometryfor optical freeform surfaces
ZHANG Lei
 doi: 10.37188/CO.2020-0126
Abstract(44) FullText HTML(13) PDF 3199KB(15)
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Optical free-form surfaces are difficult to detect due to their rich degrees of freedom. Interference detection methods are both highly precise and non-contact. However, the static compensator in a traditional interferometer faces difficulty in achieving in-situ tests of unknown surface shapes or those changing during fabrication. Therefore, programmable adaptive compensators for large dynamic ranges have become a well-researched topic in recent years. Combined with the research work in the field of freeform surface metrology, this paper introduces the latest research progress in adaptive interferometry for optical freeform surfaces. Adaptive interferometers based on a deformable mirror (DM) or liquid crystal spatial light modulator (LC-SLM) are analyzed in detail. An adaptive controlling algorithm in the adaptive interferometer is introduced as well. Finally, the advantages and development bottleneck of the above two kinds of adaptive interferometry are summarized and prospects the future development of freeform surface adaptive interferometers are proposed.
Effects of the combination of sample temperature and spatial confinement on LIBS
YU Dan, SUN Yan, FENG Zhi-shu, DAI Yu-yin, CHEN An-min, JIN Ming-xing
 doi: 10.37188/CO.2020-0118
Abstract(28) FullText HTML(11) PDF 3874KB(0)
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The signal intensity of laser-induced breakdown spectroscopy can be improved by increasing sample temperature and confining space confinement. The combination of the two techniques can further improve the spectral intensity of laser-induced breakdown spectroscopy. In this paper, the effects of increasing a sample’s temperature and spatial confinement on laser-induced breakdown spectroscopy (LIBS) are studied in air, and the time-resolved spectra of laser-induced aluminum plasma are measured. The experimental results show that increasing the sample’s temperature can increase the signal intensity of LIBS since a sample with a higher temperature can absorb more laser energy; when the cylindrical cavity is used to confine the plasma, the spectral emission is further improved. The effect of the combination of the two experimental conditions is that the signal intensity of LIBS is significantly stronger than that of either condition alone. The intensity of Al (I) 396.2 nm increases to 1.4 times at 200°C with higher temperature conditions alone, 1.3 times when spatial confinement is applied alone, and 2.1 times at 200°C with spatial confinement. The emission intensity with the combined effects is higher than the sum of that under the two individual conditions. The effect of the combination is mainly based on the fact that laser irradiation of the sample under a higher temperature generates stronger shock waves that can more effectively compress a larger-sized plasma plume, thereby further improving the spectral intensity of LIBS.
Optical design of visual and infrared large-aperture imaging system based on a space-based platform
LI Yi-ting, FU Yue-gang, WANG Ling-jie, ZHANG Yu-hui, LIU Ming-xin
 doi: 10.37188/CO.2020-0255
Abstract(52) FullText HTML(12) PDF 4802KB(5)
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To solve the data transmission difficulties and long-signal acquisition and processing time problem caused by excessive data transmission of the Geostationary Orbit array staring spectrometer, a scheme for a large-aperture visual and infrared snapshot spectrometer based on compressive sensing is proposed, which takes advantage of the fact that a geostationary orbit platform can stay over the fixed area for a long time. This paper analyzes the physical model of compressive sensing spectral imaging. The structure of the optical system is designed, and the relevant parameters are calculated. The objective lens uses a coaxial three-mirror afocal optical system, and dichroic films are used to split the spectrum. The relevant parameters were calculated according to requirements and the system was designed using optical software. After optimization, the optical system was shown to have a width of 400 km◊400 km, a visible area of 40 m GSD, an MWIR area of 400 m GSD, and an LWIR area of 625 m GSD. The results show that the MTF of the visible area is higher than 0.455 at 78.125 lp / mm. In mid-wave infrared, the MTF is higher than 0.518 at 33 lp / mm, and the MTF is higher than 0.498 at 20.8 lp / mm in long-wave infrared. The spectral resolution of the visible light is 20 nm, the mediumwave infrared region’s resolution is 50 nm, and the long-wave infrared spectrum resolution is 150 nm. The second-order spectrum of the visual area is less than 0.05 mm. The optical system has good imaging performance and the imaging quality of each part of the optical system is close to the diffraction limit, which meets the needs of applications and indicators.
Review of interrogation technology for quasi-distributed optical fiber sensing systems based on microwave photonics
WU Ni-shan, XIA Li
 doi: 10.37188/CO.2020-0121
Abstract(52) FullText HTML(18) PDF 3845KB(15)
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Quasi-distributed fiber sensing systems play an important role in the fields of civil engineering, energy surveying, aerospace, national defense, chemicals, etc. Interrogation technology for quasi-distributed fiber sensing systems based on microwave photonics is widely used in high-speed and high-precision signal demodulation and sensor positioning in optical fiber multiplexing systems. Compared to conventional optical wavelength interrogation, this technology greatly improves system demodulation rate and compensates for the defects of traditional sensor positioning methods. This paper introduces the recent research progress of quasi-distributed fiber sensing interrogation technology based on microwave photonics; compares and analyzes the advantages and disadvantages of several existing microwave demodulation systems from the perspective of their fiber grating quasi-distributed sensing and fiber Fabry-Perot quasi-distributed sensing systems, respectively; and provides a summary of the prospective direction of future research in quasi-distributed fiber sensing interrogation technology based on microwave photonics.
Investigations of optical environment changes in the dunhuang gobi site of the chinese radiometric calibration sites
LI Yuan, ZHANG Yong, HU Li-qin, LU Qi-feng, LU Nai-meng
 doi: 10.37188/CO.2020-0129
Abstract(61) FullText HTML(12) PDF 4273KB(6)
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The Dunhuang Gobi Site of the Chinese Radiometric Calibration Sites (CRCS) has an irreplaceable role in the field radiometric calibrations and quantitative applications in remote sensing satellites. In 2016, the molten salt tower concentrating solar power (CSP) project in the south side of the Dunhuang Site completed and began operation. The scattered radiation of the heat collection tower has an impact on diffused sky radiation. The influence on the optical environment of the calibration site needs to be analyzed and evaluated in detail. This paper focuses on the scattered radiation of the heat absorber on the top of the heat collection tower. The influence of the heat absorber was analyzed quantitatively based on the Monte Carlo three-dimensional radiation transmission model simulation and in situ CE318 multi-channel photometer almucantar measurements. By measuring the data with a new cloud cover automatic observing instrument ASC200, the accuracy of clear sky measurements improved, and the development of the CE318 four-quadrant location correction algorithm effectively increased the amount of valid data that meets our threshold requirements. The effective data collected from January to March 2020 shows that the molten salt tower CSP project has no significant impact on the sky diffuse radiation outside the 550 nm channel. In the 500 nm channel, under the geometric parameters corresponding to the valid data (distance 0.87−3.07 km, observation zenith angle 77.30−51.32°), the impact of the molten salt tower heat absorber on diffuse sky radiation does not exceed 0.93%. Combined with the analysis of the model simulation results, it can be concluded that the relative change of the sky diffuse radiation caused by the scattered radiation of the large power station is less than 1.62% at 2 km away, and the relative change is less than 0.93% when it is at least 3 km away. The research results have positive significance for the use of Dunhuang Site to conduct quantitative applications in remote sensing and the accurate evaluation of the uncertainties introduced by power stations.
Line-scanning confocal microscopy through virtual structured modulation
ZHAO Jia-wang, ZHANG Yun-hai, WANG Fa-ming, MIAO Xin, SHI Xin
 doi: 10.37188/CO.2020-0120
Abstract(52) FullText HTML(25) PDF 3945KB(10)
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Resolution in a confocal microscope is limited by the size of its pinhole,. Structured modulation has been proven to be able to achieve super-resolution in confocal microscopy, however, its limited speed in image acquisition limits its applicability in real-world applications. In order to improve its imaging speed, we attempt to introduce a method that achieves rapid super-resolution confocal microscopy using line-scanning and structured detection. A cylindrical lens was used to focus the light into a line, and a digital mask with a sinusoidal function was used to modulate the raw image in the light detection arm. Unlike the virtual structured method, there is no need for a subsequent frequency shift process. In order to improve the isotropic resolution of the system, a scanning angle of 0 ° and 90 ° was achieved by rotating the sample. Simulation and experiment results indicate that coherent transfer function expands and the resolution is 1.4 times as large as that of a conventional confocal microscope. This method increases the system’s imaging speed 104-fold when compared with a confocal structured modulation microscope that uses spot-scanning.
Projector calibration based on cross ratio invariance
YANG Jian-bai, ZHAO Jian, SUN Qiang
 doi: 10.37188/CO.2020-0111
Abstract(29) FullText HTML(17) PDF 3406KB(3)
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In order to improve the accuracy of the projector calibration in 3D shape measurement using digital fringe projection, a new projector calibration method that combines secondary projection technology and cross-ratio invariance is proposed. The secondary projection technology is used to compensate for the mutual interference between the projection pattern and the pattern on the calibration board, and the cross-ratio invariance method is used to avoid introducing camera calibration error. A comparative experiment is carried out to verify the effectiveness of the proposed method. Compared with the traditional method of projector calibration that requires camera parameters and that using global homography, the RMS values of reprojection error of this method is reduced from (0.2275, 0.2264) and (0.1237, 0.1098) pixels to (0.0535, 0.0468) pixels, and the maximum value of the reprojection error is reduced from 1.222 pixels and 0.5667 pixels to 0.2389 pixels. In addition, this method allows the camera to be simultaneously calibrated during operation, and therefore the parameters of the entire 3D measurement system can be acquired. The above results show that the method proposed in this paper can prevent errors in transmission of camera calibration parameters and improve the calibration accuracy of a projector.
Corrective method for spectral offset error caused by radial distortion in the large aperture static imaging spectrometer
AN Ling-ping, WANG Shuang, ZHANG Geng, LI Juan, LIU Xue-bin
 doi: 10.37188/CO.2020-0084
Abstract(54) FullText HTML(27) PDF 3791KB(5)
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In order to improve the spectral calibration accuracy of the Large Aperture Static Imaging Spectrometer when its field of view is increased, and to reduce the influence of radial distortion on its spectral accuracy, this paper proposes a corrective method for spectral calibration coefficients based on a spectral distortion correlation model. To begin the process, the wave number and wavelength correction formulas are given. Using 594.1 nm and 632.8 nm gas lasers, a spectroscopic imaging experiment was performed on the imaging spectrometer, and the data was processed and analyzed. The results show that when there is a barrel distortion of 0.3%, the inversion spectrum at the edge of the field of view shifts approximately 2 nm. After implementing the corrective method of this paper, the line shift is reduced to approximately 0.1 nm. This method only needs to be corrected according to the lens distortion parameters, which simplifies the laboratory spectral calibration process and improves work efficiency. It can also be applied to the orbit parameter correction of spaceborne interference spectral data.
Review of research on orthogonal frequency division multiplexing modulation techniques in visible light communication
XU Xian-ying, YUE Dian-wu
 doi: 10.37188/CO.2020-0051
Abstract(52) FullText HTML(18) PDF 3572KB(8)
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With its unique advantages, visible light communication (VLC) can compensate for limitations in radio frequency communication, allowing it to become a recent avid topic of research. Orthogonal Frequency Division Multiplexing (OFDM) has been widely used in VLC due to its high rate of data transfer and frequency selective fading resistance. We present a comparative performance evaluation of several OFDM modulation techniques in VLC, including unipolar schemes, enhanced schemes and hybrid schemes based on discrete Fourier transformation, as well as optical OFDM systems based on Hartley transform and LED index modulation. We perform these comparisons in terms of energy efficiency, spectral efficiency, bit error rate, and algorithm complexity. The principles of some kinds of optical OFDM systems are firstly illustrated and their spectrum efficiencies are theoretically analyzed and compared. We also provide research and analysis of the improved design of receivers in optical OFDM systems. The challenges and upcoming research of OFDM systems in VLC are summarized. We induce optical OFDM systems in this paper, providing a research reference and proposing more efficient unipolar modulation schemes to further improve the spectral efficiency and reliability of optical OFDM systems.
Luminescence properties of Bi3+ doped Lu1-xO3: x%Ho3+ metal ion phosphors
ZHAO Hai-qin, WANG Lin-xiang, TUO Juan, YE Ying
 doi: 10.37188/CO.2020-0222
Abstract(50) FullText HTML(18) PDF 4009KB(4)
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Bi3+ doped Lu1-xO3: x%Ho3+ metal ion phosphors were prepared using the high-temperature solid-phase method. The crystal structures of Bi3+ doped Lu1-xO3: x%Ho3+ phosphors, the Bi3+→Ho3+ energy transfer in Lu2O3 matrix and the luminescent properties of a synthetic powder were investigated. X-ray diffraction results showed that Bi3+ and Ho3+ doping had no effect on the cubic phase structure of Lu2O3. Lu2O3: Ho3+, Bi3+ phosphor emitted 5S25I8 transition of Ho3+ at 551 nm under an excitation wavelength of 322 nm, and exhibited 1S03P1 characteristic transition of Bi3+ at 322 nm and 5I85F1 transition of Ho3+ at 448 nm under an emission wavelength of 551 nm. When the doping concentration of Bi3+ was 1.5%, the effect was most effective for the energy transfer of Ho3+, which increased by a factor of 34.8 compared to that of the single-doped Ho3+ sample. For the synthesis of 1%, 1.5%, 2% Bi3+ doped Lu98.5%O3: 1.5% Ho3+ samples, the luminescence intensity at 551 nm under 980 nm increased by a factor of 13.3, 16.8 and 14.2, respectively, compared to that of under 322 nm of excitation. The energy transfer critical distance between Bi3+ and Ho3+ was calculated to be 2.979 nm, and the energy transfer between Bi3+ and Ho3+ was achieved by dipole-quadrupole interaction.
Recent progress and prospects of topological quantum material-based photodetectors
ZHANG Xing-chao, PAN Rui, HAN Jia-yue, DONG Xiang, WANG Jun
 doi: 10.37188/CO.2020-0096
Abstract(53) FullText HTML(43) PDF 5359KB(18)
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The discovery of the topological quantum states of matter is a major milestone in condensed matter physics and material science. Due to the existence of special surface states(e.g. Dirac fermions, Weyl fermions, Majorana fermions), topological quantum materials can usually exhibit some novel physical properties (such as the quantum anomalous Hall effect, 3D quantum Hall effect, Zero-band gap caused by topological states, ultra-high carrier mobility, etc.), which are different from conventional semiconductors. Because of this, there is an abundance of prospects for applications in low-power electronic and optoelectronic devices, especially in broad-spectrum detection. However, the application of topological quantum materials in the field of photoelectric detection is still in the exploratory stage at present. This article reviews the characteristics and preparation methods of topological quantum materials and the development status with respect to optical-sensing materials in photodetectors. The structure and performance of the devices based on topological quantum materials are also mentioned as the development prospects in the field of broad-spectrum detection.
Overview of 2D grating displacement measurement technology
LIU Zhao-Wu, YIN Yun-Fei, JIRIGALANTU, YU Hong-Zhu, WANG Wei, LI Xiao-tian, Bao He, LI Wen-hao, HAO Qun
 doi: 10.37188/CO.2019-0237
Abstract(533) FullText HTML(314) PDF 1978KB(21)
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Ultra-precision displacement measurement technology is not only the basis for precision machining, but also plays a decisive role in the chip manufacturing industry that is rapidly developing such that it is following Moore's Law. The grating displacement measurement system based on the grating pitch is widely used in multi-degree-of-freedom displacement measurement. Compared with the laser displacement measurement system, the grating displacement measurement system greatly reduces the environmental requirements for humidity, temperature and pressure. In this paper, the development status of the optical structure of displacement sensing systems based on two-dimensional gratings from recent years is introduced. The principles of zero-difference and heterodyne grating interferometrys are also introduced. The optical structure based on a single-block two-dimensional grating is reviewed. The development history of the optical structure in single-block two-dimensional grating to coupling designs of multi-block two-dimensional gratings is summarized, the advantages and disadvantages of several types of two-dimensional grating displacement measurement systems are compared and analyzed, and then the development trend of two-dimensional grating displacement measurement system is speculated. Finally, the engineering process of the two-dimensional grating displacement measurement system is summarized.
Writing nanovoids on a ZnS crystal with ultrafast bessel beams
CHANG Gai-yan, WANG Yu-heng, CHENG Guang-hua
 doi: 10.37188/CO.2020-0101
Abstract(70) FullText HTML(44) PDF 3894KB(6)
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Zinc sulfide crystal is one of the important materials for making a wide-spectrum infrared window. Ultrafast laser technology in manufacturing high aspect ratio nanovoids provides an approach to achieve some photonic devices such as the mid-infrared waveguide Fourier transform spectrometer. By using a quartz axicon, an ultrafast laser direct writing system is built with a 40-times-demagnification 4f system and a Gaussian-Bessel beam formed from a Yb: KGW laser that operates at 1030 nm wavelength, a repetition rate of 100 kHz and a pulse duration that is tunable from 223 fs to 20 ps. When its pulse energy changes from 36 μJ to 62 μJ and its pulse duration from 12.5 ps to 20 ps, nanovoid structures with a diameter of 80-320 nm are successfully inscribed on the ZnS crystal. The surface morphology, diameter and depth of the nanovoids are tested by FIB (focused ion beams) ablation and SEM (scanning electron microscopy) imaging. The relationships between pulse energy, pulse duration and void morphology are studied, and results show that under a pulse duration 20 ps and a pulse energy of 48 µJ, the depth of the nanovoid is about 270 µm.
Nanofluidic channel-resonant cavity structure for measuring micro-displacement of fluorescent substances
LI Lin-wei, CHEN Zhi-hui, YANG Yi-biao, FEI Hong-ming
 doi: 10.37188/CO.2020-0076
Abstract(73) FullText HTML(47) PDF 4057KB(8)
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In order to measure the micro-displacement of a fluorescent substance, this paper proposes a nanofluidic channel-resonant cavity structure by using the finite-difference time-domain (FDTD) method. Firstly, the structure is optimized by studying the effects that the quantum dot polarization state and structural parameters have on the relationship between fluorescence and structure. Then, the micro displacement of the fluorescent substance is detected by measuring the change in the output of optical power in the coupled structure. Finally, the factors affecting the sensitivity of the sensors are studied. The results show that, compared with the traditional method, when the refractive index of the nanofluidic channel-resonant cavity coupling structure is in the 2.8-3.3 range, the structure can sense of the micro-displacement of a fluorescent substance with high-precision and accuracy. The results also show that the sensing sensitivity can be further improved by reducing the distance between the nanofluidic channel and the resonant cavity.
Research progress of quasi-two-dimensional perovskite solar cells
WEI Jing, WANG Qiu-wen, SUN Xiang-yu, LI Hong-bo
 doi: 10.37188/CO.2020-0082
Abstract(111) FullText HTML(45) PDF 3555KB(33)
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At present, the power conversion efficiency of perovskite solar cells exceeds 25%. Their rapidly increasing efficiency has made people increasingly optimistic about their commercial application, but the stability of perovskite remains the biggest obstacle to successful commercialization. Quasi-two-dimensional perovskite solves this problem. Utilizing the hydrophobicity and thermal stability of large organic spacer cations, quasi-two-dimensional perovskite can effectively improve the stability of perovskite and improved crystal formation energy while providing a more stable structure. Quasi-two-dimensional perovskite also invites significant improvement to the morphology of perovskite films, which can replace anti-solvent processes, simplify production, and meet the industrial production requirements of perovskite. However, the relatively large band-gap and low carrier mobility caused by insulated organic spacer cations hinder ion transmission, causing quasi-two-dimensional perovskite solar cells to be far less efficient than three-dimensional perovskite solar cells. Therefore, for quasi-two-dimensional perovskite, it is necessary to further study its characteristics and device applications to achieve further optimization of device performance. This article summarizes the research progress of quasi-two-dimensional perovskite solar cells, the molecular structure of quasi-two-dimensional perovskite, the methods and principles of quasi-two-dimensional doping that improves the stability of three-dimensional perovskite, and the phase distribution and carrier transport characteristics of quasi-two-dimensional perovskite. Then this paper analyzes the problems faced by quasi-two-dimensional perovskite solar cells and looks forward to their prospects. It is expected that it will provide a reference for the preparation of efficient and stable quasi-two-dimensional perovskite solar cells.
Suppressed ion migration in halide perovskite nanocrystals by simultaneous Ni2+ doping and halogen vacancy filling
SUN Zhi-guo, WU Ye, WEI Chang-ting, GENG Dong-ling, LI Xiao-ming, ZENG Hai-bo
 doi: 10.37188/CO.2020-0060
Abstract(105) FullText HTML(32) PDF 4295KB(10)
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Lead halide perovskites(LHPs)are promising candidates for next-generation optoelectronic application. However, defect-induced ion migration causes phase degradation in LHP nanocrystals. Therefore, material stability has become an urgent problem that impedes practical applications.   Objective  To study the influence of doping cations on inhibiting the migration of halogen ions in perovskite nanocrystals. Through the measurement of ion migration activation energy and in-situ high-resolution transmission electron microscope technology, the principles of the effect of precursor dopants on the stability of LHPs were analyzed. The decomposition of LHPs was observed with a high magnification electron microscope and the ion migration activation energy was compared.  Method  Firstly, we synthesized two types of LHP nanocrystals with high crystal quality using nickel acetylacetonate and nickel bromide as precursor dopants, respectively. Secondly, the optical properties and component elements of the doped samples were analyzed by absorption-fluorescence spectroscopy, X-ray diffraction, X-ray photoelectron diffraction, and transmission electron microscopy. Finally, the ion migration activation energies of various LHP films were measure using temperature-dependent ion conductivity tests, and the influence of the precursor dopants on the stability of as-synthesized doped LHPs was compared with the results from high-resolution electron microscopy.  Result  The results showed that the activation energies of the doped CsPbBr3 samples were significantly improved compared to the intrinsic CsPbBr3 sample (0.07eV), which were determined to be 0.238 eV for nickel acetylacetonate and 0.487 eV for nickel bromide. In addition, the electron irradiation experiments showed that the nickel bromide-doped perovskite nanocrystals exhibited higher structural stability.  Conclusion  Doping and halogen vacancy filling can suppress ion migration in halide perovskite nanocrystals and synergy of Ni2+ doping and halogen vacancy filling can effectively inhibit ion migration in halide perovskite nanocrystals.
Research progress on the modulation properties of new electro-optic materials
LV Xiao-lei, ZHAO Ji-guang, DU Xiao-ping, SONG Yi-shuo, ZHANG Peng, ZHANG Jian-wei
 doi: 10.37188/CO.2020-0039
Abstract(67) FullText HTML(35) PDF 3432KB(6)
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Polarization modulation technology using electro-optic crystals is playing an increasingly important role in the field of three-dimensional laser imaging. Due to the low field of view and high half-wave voltage of LN materials, it is difficult for traditional electro-optic modulation technology to further improve 3D imaging performance. With perovskite-structured electro-optical materials becoming more and more mature, electro-optic modulation technology using new materials will become an excellent means to create a breakthrough in the detection accuracy of laser 3D imaging. PMNT, PLZT and KTN three typical materials have excellent electro-optical properties and dielectric properties that might surpass the field of view and half-wave voltage limitation. However, their applications in electro-optic modulation has lead to difficulties such as a low PMNT modulation bandwidth, poor PLZT transmission performance, and low KTN practical application bandwidth. Future research will focus on the practicality of this modulation technology. The technology’s electro-optic modulation performance can be improved with doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
Fabrication and Optoelectronic Characterization of Suspended In2O3 Nanowire Transistors
JIANG Yi-yang, CHEN Yan, WANG Xu-dong, ZHAO Dong-yang, LIN Tie, SHEN Hong, MENG Xiang-jian, WANG Lin, WANG Jian-lu
 doi: 10.37188/CO.2020-0062
Abstract(81) FullText HTML(24) PDF 3502KB(2)
Abstract:
One-dimensional (1D) semiconductor nanowires have shown outstanding performance in nano-electronics and nano-photonics. However, the electrical properties of the nanowire transistors are very sensitive to interactions between the nanowires and substrates. Optimizing the device structure can improve the electrical and photodetection performance of nanowire transistors. Here, we report a suspended In2O3 nanowire transistor fabricated by one-step lithography, showing a high mobility of 54.6 cm2v−1s−1 and a low subthreshold swing of 241.5 mVdec−1. As an ultraviolet photodetector, the phototransistor shows an extremely low dark current (~10−13 A) and a high responsivity of 1.6×105 AW−1. This simple and effective method of suspending the channel material of a transistor can be widely used in manufacturing high-performance micro-nano devices.
Research on a 10−9-order point source transmission test facility
WANG Wei, LU Lin, ZHANG Tian-yi, WANG Wei-lu, LIU Yi-chen, MENG Qing-yu, XU Shu-yan
 doi: 10.37188/CO.2020-0050
Abstract(77) FullText HTML(46) PDF 1988KB(4)
Abstract:
  Objective  In order to achieve the quantitative evaluation of the stray light attenuation in optical systems, we demonstrate a point source transmission test facility with 10−9-order sensitivity in this paper.  Method  We employed a pulsed source and measured the pulse to obtain the weak signal at the image plane, as well as to simplify the detection system. Using this scheme, we constructed a test facility with a maximum aperture of 600 mm and a test wavelength of 527 nm, and conducted the test with a 250 mm aperture optical system.  Result  Experimental results showed that the point transmission at a 60-degree incident angle is 1.68×10−9.  Conclusion  The results prove that the test error of this facility is in the order of 10−9 or below, and the test facility has the ability to test 10−9-order point source transmissions. This technology can provide quantitative evaluation for various optical systems with strict stray light requirements, like astronomical telescopes, star sensors and spaced target monitor payloads.
Research progress on nitrogen-doped carbon nanodots
LI Di, MENG Li, QU Song-nan
2020, 13(5): 899-918.   doi: 10.37188/CO.2020-0035
[Abstract](320) [FullText HTML](126) [PDF 2407KB](67)
Abstract:
In recent years, carbon nanodot (CDs) have been widely researched due to their unique luminescent properties, good biocompatibility, low toxicity and high photostability. These characteristics invite potential applications in optoelectronic devices, visible light communication, tumor therapy, biological imaging and other fields. There are a variety of CDs according to the different starting materials and synthesis routes. In this paper, we will systematically review nitrogen-doped CDs synthesized from citric acid and urea as the main precursor materials in our group in recent years, discuss their physicochemical properties, explore the methods and principles of CDs energy band regulation, and introduce the application progress of CDs.
Optical coherence tomography: principles and recent developments
LU Dong-xiao, FANG Wen-hui, LI Yu-yao, LI Jin-hua, WANG Xiao-jun
2020, 13(5): 919-935.   doi: 10.37188/CO.2020-0037
[Abstract](249) [FullText HTML](116) [PDF 4616KB](78)
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Optical Coherence Tomography (OCT) is a new imaging technique that uses interference in low coherent light by measuring the delay and magnitude of backscattered or reflected signals from the sample. OCT technology can provide real-time structural information with one-dimensional depth and two- and three-dimensional tomography at micron-scale resolution. Besides its high spatial resolution, OCT imaging is beneficial for its non-contact and non-invasive methodology. The system is also easy to operate and relatively portable. OCT technology is mainly applied in the biomedical imaging field for diagnoses, making up for the shortcomings of the low penetration depth in confocal microscopes and the low resolution in ultrasonic imaging. At present, OCT technology has been used as the clinical standard for the diagnosis of retinal diseases, and the combination of OCT technology and endoscope technology has become an important tool for the clinical diagnosis of cardiovascular and gastrointestinal diseases. It also provides references for early cancer diagnosis, surgical guidance and postoperative rehabilitation of musculoskeletal diseases. To broaden the application of OCT technology and improve its medical detection capabilities, researchers are committed to increasing the penetration depth of OCT imaging in biological tissue, improving the system's resolution and signal-to-noise ratio, and optimizing its overall performance. This review introduces the principle and classification of OCT systems, their applications and their recent progress in various biomedical fields.
Review on scientific detection technologies for ancient paper relics
YAN Chun-sheng, HUANG Chen, HAN Song-tao, HAN Xiu-li, YING Chao-nan, DU Yuan-dong
2020, 13(5): 936-964.   doi: 10.37188/CO.2020-0010
[Abstract](196) [FullText HTML](78) [PDF 4187KB](44)
Abstract:
This paper comprehensively discusses all kinds of modern scientific and technological detection methods for paper raw materials, inks, inkpads, and pigments used in ancient paper cultural relics, including imaging and spectrometric technologies. Relevant imaging methods include photography, tomography and microscopic imaging methods. Photographic methods include light transmission, infrared, ultraviolet, X-ray and neutron activation photography to display macroscopic information on a sample’s surface or inside. Tomography methods include X-ray, terahertz, and optical coherence tomographic methods to display layered information beneath the sample’s surface. Microscopic imaging methods include optical, scanning electron, transmission electron and atomic force microscopic imaging methods to display the sample’s microscopic information. Spectroscopy methods with fingerprint characteristics based on the principles of wave-matter interactions include chromatography, mass spectrometry, electron paramagnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray fluorescence spectrum, molecular fluorescence spectrum, Raman spectrum, UV-Vis-NIR-MID-THz absorption spectrum and hyperspectral methods. It shows that the comprehensive applications, complementary advantages and mutual confirmations of the above technologies are powerful means to reveal important traits of paper cultural relics, such as one’s manufacturing process, artistic features, preservation history, disease status, authenticity, method of reparation, etc.
Beam quality β factor calculation based on two-dimensional chirp Z transformation
WANG Yan-ru, RAN Zheng-hui, DING Yu-jie
2020, 13(5): 965-974.   doi: 10.37188/CO.2020-0079
[Abstract](144) [FullText HTML](64) [PDF 2495KB](22)
Abstract:
An algorithm for fast calculation of the field distribution of diffraction based on two-dimension chirp Z transformation is proposed. The proposed algorithm does not increase computation and significantly improves the resolution of the diffraction distribution and obtains a more accurate beam quality β factor. After verifying the correctness of the proposed algorithm, the corresponding relationship between the RMS (Root-Mean-Square) of the beam′s wavefront aberration and β factor is simulated. The simulation results show that with the same RMS value, the effect of a spherical aberration on the β factor is the strongest among the lower order Zernike aberrations. In order to simulate the different distribution of beam spots, the β factors are calculated based on different random Zernike wavefront aberrations. The results indicate that a larger proportion of high-order Zernike aberrations in the cumulative aberrations induces a bigger β factor with an identical RMS value.
Differentiation of polarization scattering characteristics of surface nanoparticle defects
GAO Ping-ping, LU Min, WANG Zhi-le, GUO Ji-kai, HE Xiao-bo
2020, 13(5): 975-987.   doi: 10.37188/CO.2020-0083
[Abstract](125) [FullText HTML](58) [PDF 6043KB](16)
Abstract:
In order to distinguish between the two types of surface defects such as dust on the surface and bubble particles below the surface, and to obtain the applicable environmental range and optimal observation conditions of the method, we established and verified two polarization scattering models for surface defects based on Rayleigh scattering theory and a polarization bidirectional reflection distribution function. On this basis, the effects of the different defect environments and different observation conditions on the polarization scattering characteristics of the two surface defect particles were obtained through simulation analysis. The results show that by detecting the changing trend of the bidirectional reflection distribution function value of the p-polarized light incident on the surface with the scattering azimuth angle, we can distinguish between the two surface defects; no matter how the position of the bubble particles under the surface change, it will not affect the change of the trend. Different optical element surface materials, defect particle types, and defect particle size have certain effects on the polarization scattering models of the two surface defects, but the overall relationship remains unchanged. In order to distinguish between the two types of surface defects described in this article, the incident angle and the detection scattering angle are both 45° and an incident light with a smaller wavelength is used in an experiment.
Erbium-doped fiber amplifier gain-flatness of a Sagnac loop with an erbium-doped fiber
LIU Yi, GUO Rong-rong, YI Xiao-gang, ZHENG Yong-qiu, CHEN Peng-fei
2020, 13(5): 988-994.   doi: 10.37188/CO.2020-0064
[Abstract](127) [FullText HTML](64) [PDF 4943KB](13)
Abstract:
In order to achieve the simultaneous adjustment of multi-channel gain in the communications, especially in WDM, and to develop a wide range of stable light outputs in multi-wavelength fiber lasers, a research scheme of the erbium-doped fiber amplifier gain flattening characteristic at the transmission-port of a Sagnac loop with an unpumped erbium-doped fiber is proposed. The scheme is a combination of the self-resonance mode of the Sagnac loop, the absorption characteristics of unpumped erbium-doped fiber and the resonance mode caused by birefringence beat length in the loop. By adjusting the polarization controllers properly in the loop, the gain spectrum can be partially or completely flattened at the transmission port of the Sagnac loop. The results show that, on one hand, the part of the spectrum is flatted within ±0.145 dB in the wavelength range of 14 nm at the transmission port, but on the other hand, the total spectrum is flatted within ±1.225 dB over a bandwidth of 36.5 nm in the whole C-band at the transmission port. The gain spectrum flattening scheme has a simple structure and good flatness of the output spectrum. It is expected that this technology will be used in WDM systems and multi-wavelength lasers.
Improvement of transmission efficiency in microwave photonic links using EDFA
XIAO Yong-chuan, WANG chao, ZHANG hao, ZHANG Ya-biao, YU Cai-bin, QU Peng-fei, SUN Li-jun
2020, 13(5): 995-1000.   doi: 10.37188/CO.2019-0195
[Abstract](361) [FullText HTML](179) [PDF 2202KB](22)
Abstract:
Photonics have long been viewed as an enabling technology that extends the sensing and signal processing performances of Radio Frequency (RF) remoting systems such as radar and electronic-warfare because of its inherent advantages in multi-octave operating frequencies, broad instantaneous bandwidth, low transmission loss, and good phase linearity. In order to improve the efficiency of the analog optical transmitter during electronic-to-optical conversion, an Erbium-Doped Fiber Amplifier (EDFA) combing with a low-bias modulator in an external intensity modulation direct detection link is applied. According to our analysis, the RF gain reduces linearly with modulator’s optical power output when the bias becomes close to its minimum. Thus, the gain provided by the EDFA to the optical signal was transferred to increase RF transmission efficiency. Experimental results indicated that the RF gain improved by 13.5 dB compared to that of conventional quadrature bias point transmissions. Meanwhile, a small penalty is introduced to system noise. Most importantly, this can be achieved by using off-the-shelf devices, which can drastically reduce the system’s cost. Finally, the proposed scheme can be widely used in electronic information equipment.
Integrated silicon waveguide electro-optic half-adder based on Epsilon-Near-Zero and ITO
LIANG Zhi-xun, XU Chuan-pei, ZHU Ai-jun, HU Cong, DU She-hui
2020, 13(5): 1001-1013.   doi: 10.37188/CO.2020-0078
[Abstract](159) [FullText HTML](82) [PDF 4952KB](18)
Abstract:
In order to achieve high-speed electro-optic hybrid operation of half-adders and solve their disadvantages in speed, energy consumption and size, a silicon waveguide integrated electro-optic half-adder is designed based on an Epsilon-Near-Zero and ITO electrical-tunable film. The ITO electrical-tunable film is used as the switch for the optical path, and thus achieve the half-add function of two binary numbers. Simulation results show that the device unit can complete the optical signal logic control when the applied voltage is 0 V and 2.35 V. When the hybrid electro-optic half-adder works at a wavelength of 1550 nm, the insertion loss is 0.63 dB, the extinction ratio is 31.73 dB, the data transmission rate is 61.62 GHz, the energy consumption per bit is 13.44 fJ, and the size of the whole half-adder is less than 21.3 μm×1.5 μm×1.2 μm. The device is compact and has a low insertion loss. This provides a theoretical foundation for the design of high-speed hybrid electro-optic logic devices and half-adders.
Time-frequency analysis of laser doppler radar vibration signals
CHEN Hong-kai, WANG Ting-feng, WU Shi-song, LI Yuan-yang, GUO Jin, WU Hao
2020, 13(5): 1014-1022.   doi: 10.37188/CO.2019-0251
[Abstract](163) [FullText HTML](86) [PDF 3300KB](21)
Abstract:
Most actual vibration signals measured by lidar are time-varying signals. Methods of time-frequency analysis based on Fourier transforms are effective tools for processing time-varying signals. In this paper, the properties of the Wigner-Wiley distribution, the smooth pseudo-Wigner-Wiley distribution, the spectrogram, the Bonn-Jordan distribution, and the extended modified B distribution are compared and analyzed with actual vibration signals measured by laser Doppler radar. Three kinds of vibrations are measured with a laser Doppler radar: chirps generated by a single loudspeaker, two-component chirps generated by two loudspeakers, and adult male heartbeat vibrations. Their time-frequency distribution resolution and the suppression of cross-terms are analyzed. By calculating the time-frequency concentration index, the analysis capacites of the five distributions for three vibrations are compared. Experimental results indicate that the performance of the extended modified B distribution is better than that of the other four time-frequency distributions. Therefore, the extended modified B distribution is more suitable for the detection of material resonance frequency of laser Doppler radar and the detection of heartbeat.
Effects of spot size on the temperature response of an aluminum alloy irradiated by a continuous laser
WEN Kang, LI He-zhang, MA Zhuang, GAO Li-hong, WANG Fu-chi, LI Wen-zhi
2020, 13(5): 1023-1031.   doi: 10.37188/CO.2020-0022
[Abstract](174) [FullText HTML](87) [PDF 3758KB](22)
Abstract:
In order to investigate the temperature response and thermal damage of a 6061 aluminum alloy after variations in spot size of continuous laser irradiation, a three-dimensional physical model under laser irradiation was established based on ANSYS finite element software. First, we used different laser parameters to carry out laser irradiation experiments, and then, based on the collected temperature and front surface scattered light intensity data, we calculated the dynamic changes in the absorptivity of the target during laser irradiation. Finally, the optimized model was used to analyze the temperature rise characteristics of the target irradiated by lasers at different spot sizes. The research results show that the absorption rate of the material increases with an increase in temperature under 1000 W/cm2 laser irradiation. Due to the localized characteristics of laser loading, lateral thermal diffusion affects the longitudinal temperature rise, and its effect becomes smaller when the spot is larger, as related with the alloy’s thermal diffusion length. For the 6061 aluminum alloy material with a thickness of 4 mm, when the spot size is greater than 10 cm, the effect of the spot’s size is negligible, and the time threshold of fusion damage on the back surface of the target remains unchanged at 2.6 s.
Nondestructive grading test of rice seed activity using near infrared super-continuum laser spectrum
JIN Wen-ling, CAO Nai-liang, ZHU Ming-dong, CHEN Wei, ZHANG Pei-guang, ZHAO Qing-lei, LIANG Jing-qiu, YU Ying-hong, LV Jin-guang, KAN Rui-feng
2020, 13(5): 1032-1043.   doi: 10.37188/CO.2020-0027
[Abstract](201) [FullText HTML](102) [PDF 5888KB](20)
Abstract:
In view of the urgent need for seed selection technology in agriculture and for grading detection of the vigor of three different years of unpeeled rice seeds, we proposed a new method of detecting the vigor of rice seeds based on near-infrared super-continuous laser spectrum to overcome the significant issues in pre-existing universal brown rice detection technology. Firstly, we design a near-infrared absorption spectroscopy system with which we detect seed viability and measure the NIR spectra of three different years of unpeeled rice seeds. The results show that the activity gradient of the rice seeds is correlated with the characteristic absorption peak of their NIR absorption spectrum. Then, the spectrum of seed is optimized with a pretreatment algorithm of normalization, second derivative correction and orthogonal signal correction. Finally, a Principal Component Analysis (PCA) model is established to reduce the dimension of the spectrum and determine the optimal number of principal components. A Partial Least Squares Discriminant Analysis (PLS-DA) model is established. The analysis results show that the transmission absorption spectrum detection system designed in this paper combined with the PLS-DA discrimination model can classify rice seeds of different vigor with an accuracy of 94.44% and 95.92%. After screening, the germination rate of rice seeds can reach 97.17%. The results show that it is feasible to achieve non-destructive classification of rice seed activity using near-infrared spectroscopy with high accuracy.
TDLAS detection of propylene with complex spectral features
ZHONG Li, SONG Di, JIAO Yue, LI Han, LI Guo-lin, JI Wen-hai
2020, 13(5): 1044-1054.   doi: 10.37188/CO.2019-0203
[Abstract](2256) [FullText HTML](565) [PDF 6847KB](35)
Abstract:
To satisfy the need for propylene measurement in the olefin production process, Tunable Diode Laser Absorption Spectroscopy (TDLAS) was studied to improve analytical performance. In this paper, a numerical simulation approach is proposed using absorbance from a spectral database to obtain the optimized design parameters, which is independent of spectral features. In the simulation, the effect of a wider linewidth laser on the absorbance profile was considered. Through the comparison of simulation results and experimental collection, the TDLAS-based propylene analysis apparatus was developed correspondingly. It has a 1 628.5 nm center wavelength broad-tuning DFB laser. A differential method was utilized in demodulated spectral acquisition to eliminate bias voltage. The multivariate linear regression model was employed to reduce the strong spectral interference from the background components in the analysis. Based on the simulated field test, the max relative error is 0.55% in the 0~1% range for the step test. For the long-term test, the standard deviation (1σ) is 9.3×10−6 for 0.2% propylene concentration. The best standard deviation is 1.33×10−6 at 221.9 s of integration time through Allen variance analysis. In the anti-interference test, the max error of 19.17×10−6 is demonstrated for 0.2% propylene concentration while methane and ethylene concentrations vary. The disadvantages of traditional methods such as the Gas Chromatogram (GC) and soft measurement methods are overcome by modulated absorption spectroscopy. The TDLAS system for heavy hydrocarbon detection with complex spectral features was demonstrated to have distinct advantages in precision, stability and interference suppression through multivariate regression modeling.
Texture mapping of multi-view high-resolution images and binocular 3D point clouds
DU Rui-jian, GE Bao-zhen, CHEN Lei
2020, 13(5): 1055-1064.   doi: 10.37188/CO.2020-0034
[Abstract](175) [FullText HTML](91) [PDF 3758KB](19)
Abstract:
Aiming at the fusion problem of binocular stereo vision reconstruction point cloud models and high-resolution texture images, a new texture mapping method is proposed. Adding a telephoto texture camera to the binocular stereo vision system to capture high-resolution texture images, the relationship between a texture image and a 3D point cloud model is obtained by matching the two-dimensional features of the high-resolution texture image and the binocular image. The binocular image is used as a bridge, thereby achieving the high-resolution mapping of high-rate texture images on 3D point cloud models. In view of the data redundancy of the overlapping parts of the multi-view texture images during mapping, a method of partitioning the guidance point cloud data is proposed, which effectively solves the problem. Through experimental verification, the proposed method can conveniently and accurately map multi-view texture images to binocular 3D point cloud models. Under experimental conditions, the texture of the 3D model can distinguish line pairs with an original line width of 0.157 mm, which is double the texture resolution of the 3D model directly generated by the binocular system, This verifies the effectiveness of the proposed multi-view high-resolution texture mapping method.
Three-dimensional single-molecule localization microscopy imaging based on compressed sensing
ZHANG Sai-wen, LIN Dan-ying, YU Bin, LENG Xiao-ling, ZHANG Guang-fu, TIAN Ye, TAN Wei-shi
2020, 13(5): 1065-1074.   doi: 10.37188/CO.2020-0003
[Abstract](190) [FullText HTML](93) [PDF 3497KB](23)
Abstract:
In order to achieve fast three-dimensional localization of high-density fluorescent molecular images, a three-dimensional compressed sensing model was established and studied using the CVX method, the Orthogonal Matching Pursuit(OMP) algorithm and a homotopy algorithm. The models’ measurement matrix was then designed. Firstly, the system’s theory and design were both developed using the three-dimensional point-spread function imaging theory of fluorescence microscopy. Then, the process of fluorescence microscopic imaging was simulated, through which the images generated in the established compressed sensing model were analyzed using the CVX method, OMP algorithm and homotopy algorithm. The recall rate, localization accuracy and reconstruction time were compared. Finally, the simulated biological samples and the collected cells in the laboratory were analyzed using the homotopy algorithm, and thus three-dimensional super-resolution imaging was achieved. It can be seen from the comparative results that the homotopy algorithm is two orders of magnitude faster than the CVX method when the reconstruction density and localization accuracy have little deviation. The localization accuracy of the homotopy algorithm is twice higher than that of the OMP algorithm. The homotopy algorithm is meaningful for 3D super-resolution fluorescence microscopy imaging, which can save computing time and achieve real-time imaging.
Ultrasound image segmentation based on a multi-parameter Gabor filter and multiscale local level set method
CHEN Xiao-dong, SHENG Jing, YANG Jin, CAI Huai-yu, JIN Hao
2020, 13(5): 1075-1084.   doi: 10.37188/CO.2020-0025
[Abstract](126) [FullText HTML](62) [PDF 6570KB](11)
Abstract:
To address the weakness and discontinuity of the edges and the uneven distribution of gray in ultrasonic images, an improved edge extraction algorithm based on a multi-parameter Gabor filter and multiscale local level set method is proposed. With the grayscale inhomogeneity of ultrasound images being regarded as texture in different directions, the directionalities of the Gabor wavelet are adopted to filter at different angles. An intermediate image is obtained to isolate the difference between each region and the background, which will allow the retention of the original image by maximizing it with a fusion method. The Gabor filter kernel with multi-center frequency meets the complex frequency distribution characteristics of ultrasound images, and the mean fusion method is used to maximize the information in the image while reducing noise influence. For the edge of the ultrasound image is weak and the grayscale is uneven, the local intensity clustering level set method is improved. A Gaussian convolution kernel template is applied with different variance sizes to fit the grayscale changes in different parts of the image. Testing the ultrasound images of a stomach show that correlation coefficient and sensitivity coefficient reaches 0.856 and 0.910, respectively, which is a 20.7% and 5% improvement over the traditional LIC algorithm, respectively. This method can satisfy the system requirements where non-contact, online, real-time, higher precision and rapid speed strong anti-jamming and stabilization are needed.
Design of an Offner convex grating radiation calibration light source with a wide dynamic range
XU Da, YUE Shi-xin, ZHANG Guo-yu, SUN Gao-fei, ZHANG Jian
2020, 13(5): 1085-1093.   doi: 10.37188/CO.2019-0221
[Abstract](147) [FullText HTML](78) [PDF 6659KB](23)
Abstract:
In order to satisfy the spectral radiance calibration of remote sensing instruments in different spectral distribution, reduce the influence of spectral radiance calibration light sources on the calibration coefficients of space optical remote sensing instruments, and solve technical problems of low spectral simulation accuracy and small spectral dynamic adjustment range, a design method for Offner type convex grating radiation calibration systems with a wide dynamic range based on spectral superposition and the principles of multi-spectral synthesis was presented, and its anastigmatic conditions were derived. The Offner spectral imaging optical system was designed with a cylindrical mirror with an accurate subdivision of broad spectral beams. Then, the mapping relationship between the array surface of the Digital Micro-mirror Device (DMD) and its spatial spectral radiation distribution was designed. The large dynamic range simulation of spectral distribution with the spatial light modulation characteristics of the DMD was achieved. Experiment results show that the interval of the spectral peak has an output by the adjacent unit array micro-mirror is greater than 0.5 nm, the spectral simulation accuracy of three typical color temperatures is 5.2% at T=3000 K, 4.1% at T=5000 K, and 3.2% at T=7000 K. The spectral simulation accuracy of the radiation calibration source was significantly improved, and the influence of spectral mismatch on the calibration coefficients of space optical remote sensing instruments was effectively diminished.
Flat-field calibration method for large diameter survey mirror aperture splicing
LU Shi-tong, ZHANG Tian-yi, ZHANG Xiao-hui
2020, 13(5): 1094-1102.   doi: 10.37188/CO.2019-0252
[Abstract](167) [FullText HTML](77) [PDF 5067KB](22)
Abstract:
The accurate flat-field calibration of large-diameter space survey telescopes is an important prerequisite for achieving some established scientific goals. At present, it is common practice to provide a uniform flat-field reference through a flat-field screen or a large-diameter integrating sphere, which is used to check the consistency of an image’s plane response. To address issues with the uniformity of flat-field screen illumination and the difficulty of preparing large-size integrating spheres, a flat-field calibration method based on sub-aperture scanning is proposed in this paper, which improves the uniformity of the flat-field reference and the uncertain calibration caused by stray light. First, we complete a sub-aperture flat-field calibration theory analysis, establish a sub-aperture flat-field calibration mathematical model, plan the sub-aperture scanning route and scan aperture size, and perform the initial design of the parameters of the collimation system for calibration. Secondly, we complete the image surface illumination simulation verification experiment. Finally, we set up an experiment to scan the planned sub-apertures, build full-aperture illuminance data, and verify the feasibility of the above-mentioned large-aperture space survey telescope sub-aperture stitching flat-field calibration scheme. The experimental results show that the full-aperture illuminance information can be restored using the full-aperture stitching method to scan the image surface energy of the system and by using the sub-aperture stitching method to compare and contrast the full-aperture image surface illuminance. The superimposed gray value in our experiment was 233.350 and the error was 1%. It is therefore verified that the sub-aperture stitching method can be used for flat-field calibration of large-diameter sky survey telescopes, and has practical value in real-world applications.
Differential chromatic confocal roughness evaluation system and experimental research
ZOU Jing-wu, YU Qing, CHENG Fang
2020, 13(5): 1103-1114.   doi: 10.37188/CO.2020-0029
[Abstract](187) [FullText HTML](62) [PDF 5344KB](28)
Abstract:
In order to meet the demand of large-area surface roughness measurement, a non-contact differential measurement system based on chromatic confocal sensors is presented in this paper. In the proposed system, two chromatic sensors and an optical flat, forming a differential measurement structure, are coupled with the motion system with a ball-to-socket connection. Using this differential configuration, the straightness error of the motion system is compensated and the measurement accuracy can be effectively improved. Based on this system, the methodology of surface roughness measurement, error compensation and measurement performance evaluation is established. In order to verify the measurement performance of the proposed system, standard step heights and roughness comparators are measured. For the step height measurement, the experimental results show that in the travel range of 60 mm, the standard deviation of the proposed system in six repeated measurements is 0.16 μm and the relative standard deviation RSD is 0.054%. From the results, it can be concluded that the straightness error of the motion system has been effectively overcome. When measuring the roughness comparators, the measurement errors of Ra and Rq are 0.032 μm and 0.073 μm, respectively. Therefore, the roughness measurement capability of the proposed system meets the requirements of most engineering applications.
Near-infrared BRDF of material surfaces at varying temperatures
MA Wang-jiehui, LIU Yan-lei, CHEN Zhi-ying, LIU Yu-fang
2020, 13(5): 1115-1123.   doi: 10.37188/CO.2019-0256
[Abstract](132) [FullText HTML](79) [PDF 4332KB](11)
Abstract:
The spectral polarized BRDF of a brass surface in the near-infrared region was measured using the absolute measurement method with a home-made device. The temperature range was 20~800 ℃, and the influence of temperature on the BRDF was analyzed. The results indicate that temperature has an obvious influence on the BRDF of brass. With an increase in temperature, the BRDF was almost constant at first, then increased before finally decreasing. Scanning electron microscope testing, roughness measurement and X-ray diffraction analysis of the brass surface at different temperatures were performed. The test results indicate that the influence of temperature on BRDF can be attributed to variation in surface morphology and chemical composition.
Non-uniformity correction of airborne infrared detection system based on inter-frame registration
LV Bao-lin, TONG Shou-feng, XU Wei, FENG Qin-ping, WANG De-jiang
2020, 13(5): 1124-1137.   doi: 10.37188/CO.2020-0109
[Abstract](133) [FullText HTML](69) [PDF 9563KB](22)
Abstract:
During flight, changes in environmental parameters affect the accuracy of non-uniformity correction of airborne infrared point-target detection systems to some extent. Therefore, it is necessary to perform on-board scene-based non-uniformity correction. In this paper, we propose an algorithm based on inter-frame registration to achieve on-board non-uniformity correction. It first preprocesses the images to filter out dead pixels, then calculates a cross-power spectrum with two adjacent frames and determines their registration displacement according to a correlation function that is calculated from the cross-power spectrum. After registering an image, corrective parameters are updated by minimizing the error through a function. The corrective parameters are finally obtained after the above calculations are performed. In an experimental comparison, we simulate a set of non-uniform scene image sequences as the experimental image sequence. This experiment first identified the influence of changes between frames (including displacement, rotation and scaling) on the accuracy of non-uniformity correction. It then used two representative algorithms and the proposed algorithm to process the image series, and compared the performance of the algorithms from the perspective of image quality and convergence speed. The results show that the proposed algorithm has better non-uniformity corrective performance compared with the two other methods. The PSNR increased by over 20 dB, and the SSIM exceeded 0.99. The proposed algorithm has higher complexity, but its convergence speed is much faster, and it is easy to be implemented on hardware platforms, which gives the algorithm possible applications in engineering.
X-ray security inspection images classification combined octave convolution and bidirectional GRU
WU Hai-bin, WEI Xi-ying, WANG Ai-li, YUJI Iwahori
2020, 13(5): 1138-1146.   doi: 10.37188/CO.2020-0073
[Abstract](262) [FullText HTML](110) [PDF 4373KB](18)
Abstract:
Due to the disadvantages of low accuracy and slow speed in the active vision security inspection method, it is not suitable for real-time security inspection. Aiming at this problem, we propose an x-ray inspection image classification algorithm combining octave convolution (OctConv) with attention-based bidirectional Gate Recurrent Unit (GRU). Firstly, OctConv is introduced to replace the traditional convolution operation to divide the input feature vector into high and low frequency, and reduce the resolution of low frequency features, effectively extracting the features of security image and reducing the spatial redundancy. Then, the feature weight can be adjusted by dynamic learning through attention-based bidirectional GRU to improve the classification accuracy of threat objects. Finally, a lot of experimental results on SIXRay dataset show that the classification accuracy, AUC value and PRE of 8000 test samples are 98.73%, 91.39% and 85.44%, respectively, with a time of 36.80 seconds. Compared with the current mainstream model, the proposed algorithm can improve the performance and speed of threat objects recognition in X-ray security images.
Original Article
Design of resonant waveguide grating filter with reflection and transmission modes
FAN Li-na, MA Jun-shan
2020, 13(5): 1147-1157.   doi: 10.37188/CO.2020-0072
[Abstract](145) [FullText HTML](78) [PDF 3338KB](22)
Abstract:
At present, narrow-band filter based on resonant waveguide grating structure applied to biosensors can only achieve a single filter mode of reflection or transmission. In order to expand the variety of samples and improve the accuracy of the samples testing, a resonant waveguide grating filter with both reflection and transmission modes was designed based on the guided mode resonance effect. Firstly, based on the classical one-dimensional resonant waveguide grating structure, a filter with convertible reflection-transmission mode at the same wavelength (632.8 nm) was designed by adjusting the incident conditions. In both modes, excellent filtering performance was presented, spectral efficiency was higher than 98%, and Q factor was greater than 1000. Then, the resonance mechanism for that the same device can realize two filtering modes was analyzed. The results showed that the reflection and transmission narrow-band filtering modes could be converted at the designed wavelength with the same resonant waveguide grating structure under different incident conditions.
Orthogonal luminescence properties of a single rare-earth activator ion doped upconversion nanoparticles
LING Xiao, MEI Qing-song
2020, 13(5): 1158-1170.   doi: 10.37188/CO.2020-0020
[Abstract](175) [FullText HTML](74) [PDF 3129KB](17)
Abstract:
Upconversion luminescence nanomaterials have attracted widespread attention owing to their special optical properties, while most of them emit single color luminescence. In order to achieve multicolor orthogonal upconversion luminescence and avoid the synthesis complexity and interference between multiple dopant ions, herein, we reported a novel orthogonal emissive upconversion nanoparticle, NaErF4:Yb(19.5%)/Tm(0.5%)@NaYF4:Yb(10%)@NaNdF4:Yb(10%), through thermal decomposition strategy step by step. This novel nanoparticle can give out green luminescence and red luminescence by the energy level transition of Er3+ from 2H11/2,4S3/24I15/2 and 4F9/24I15/2 under the excitation light of 980 nm and 808 nm, respectively. The particles demonstrated uniform size, stable structure and excellent dispersibility. Under the excitation of 980 nm, the emission intensity at 650 nm of red luminescence was approximately 9.46 times more than the emission intensity at 540 nm. Under the excitation of 808 nm, the emission intensity at 540 nm of green luminescence was about 5.39 times more than the emission intensity at 650 nm.
Development status and trend of micro-satellite laser communication systems
GAO Shi-Jie, WU Jia-Bin, LIU Yong-Kai, MA Shuang, NIU Yan-Jun, YANG Hui-sheng
2020, 13(6): 1171-1181.   doi: 10.37188/CO.2020-0033
Abstract(168) FullText HTML(66) PDF 7413KB(25)
Abstract:
With its high speed, small size, light-weight and low power consumption, space laser communication has become an indispensable and effective means of high-speed communication between satellites, especially in micro-satellite applications, which can benefit more strongly from the advantages of laser communication. This paper provides a detailed introduction of the latest research progress in the field of micro-satellite laser communication technology. On this basis, key techniques such as light miniaturization of identical orbital terminals, light miniaturization of different orbital terminals and turbulence mitigation technologies are summarized, and the development trends of the technology’s applications, duplex communication, single-point to multi-point, localization and batch production capacity are concluded.
Review of laser speckle target detection technology
GAO Wei-ke, DU Xiao-ping, WANG Yang, YANG Bu-yi
2020, 13(6): 1182-1193.   doi: 10.37188/CO.2020-0049
Abstract(100) FullText HTML(28) PDF 3630KB(16)
Abstract:
Target detection technology based on laser speckles is a kind of laser detection technology that has been ignored for a long time. In this technology, the laser speckle, which is regarded as noise in the traditional laser detection technology, is used as a new source of information. By analyzing the formation mechanism of a laser speckle pattern, the relationship between the statistical characteristics and the physical characteristics of the target is explored, and the effective analysis and inversion methods are combined to obtain the target’s shape, size, surface roughness and dynamic parameters. Compared with traditional laser detection technology, target detection technology based on laser speckles has a simple structure, has low optical system requirements, is sensitive to the physical and fretting characteristics of the target’s surface, and has been widely used in aerospace, medicine, industry, military and other fields. This paper classifies and summarizes the various kinds of speckle-based target detection technologies from recent years, compares and analyzes their applications, advantages and disadvantages, as well as the environmental restrictions. Finally, this paper prospects the trend for the future development of target detection methods based on laser speckles.
Review of the active control technology of large aperture ground telescopes with segmented mirrors
FAN Wen-qiang, WANG Zhi-chen, CHEN Bao-gang, LI Hong-wen, CHEN Tao, AN Qi-chang, FAN Lei
2020, 13(6): 1194-1208.   doi: 10.37188/CO.2020-0032
Abstract(87) FullText HTML(35) PDF 3727KB(16)
Abstract:
Segmented mirror technology is one of the three ways to realize optical synthetic aperture telescope, and it is an important area of development for future large aperture telescopes. A telescope’s active control system of its segmented mirrors directly determines its large aperture mirror’s optical performance. This paper focuses on the active control technology of large aperture ground telescopes with segmented mirrors. In this paper, we introduce the development process of a segmented mirror telescope and the main structure of the segmented mirror active control system, then summarize and analyze the domestic and foreign development of active control systems of segmented mirrors. In this paper, the key technologies of segmented mirror active control systems and how they achieve active adjustment and active maintenance are summarized. Their applications and the direction of their development are also proposed with respect to deep learning theory in closed-loop control, co-phase detection and correction, system-level simulation modeling technology. This paper provides guidance for the design of a segmented mirror control system in the next generation of ground-based large aperture telescopes in China.
Progress in ultrafast laser space-selective welding
ZHANG Guo-dong, CHENG Guang-hua, ZHANG Wei
2020, 13(6): 1209-1223.   doi: 10.37188/CO.2020-0131
Abstract(39) FullText HTML(43) PDF 4987KB(18)
Abstract:
The development of ultrafast laser technology has continuously injected new impetus into fundamental research and production, promoted the emergence of new disciplines and technologies. As a new materials welding and joining technique developed in recent years, ultrafast laser welding has attracted extensive attention due to the potential application in the fields of aerospace, precision machinery, optoelectronics, biomedical, etc.. Based on the intrinsic characteristic of non-linear space-selective energy deposition, ultrafast laser welding possesses extremely high material applicability and spatial selectivity, and can realize high-quality space-selective welding involving transparent materials with no need inserting an absorption layer. In this paper, we firstly give an overview on the progress of this field. Then, the physical mechanism, key influencing factors, and application scope of ultrafast laser welding are elaborated. At last, the future development and key challenges of ultrafast laser welding are discussed.
Research progress on nitrogen-doped carbon nanodots
LI Di, MENG Li, QU Song-nan
2020, 13(5): 899-918.   doi: 10.37188/CO.2020-0035
Abstract(320) FullText HTML(126) PDF 2407KB(67)
Abstract:
In recent years, carbon nanodot (CDs) have been widely researched due to their unique luminescent properties, good biocompatibility, low toxicity and high photostability. These characteristics invite potential applications in optoelectronic devices, visible light communication, tumor therapy, biological imaging and other fields. There are a variety of CDs according to the different starting materials and synthesis routes. In this paper, we will systematically review nitrogen-doped CDs synthesized from citric acid and urea as the main precursor materials in our group in recent years, discuss their physicochemical properties, explore the methods and principles of CDs energy band regulation, and introduce the application progress of CDs.
Optical coherence tomography: principles and recent developments
LU Dong-xiao, FANG Wen-hui, LI Yu-yao, LI Jin-hua, WANG Xiao-jun
2020, 13(5): 919-935.   doi: 10.37188/CO.2020-0037
Abstract(249) FullText HTML(116) PDF 4616KB(78)
Abstract:
Optical Coherence Tomography (OCT) is a new imaging technique that uses interference in low coherent light by measuring the delay and magnitude of backscattered or reflected signals from the sample. OCT technology can provide real-time structural information with one-dimensional depth and two- and three-dimensional tomography at micron-scale resolution. Besides its high spatial resolution, OCT imaging is beneficial for its non-contact and non-invasive methodology. The system is also easy to operate and relatively portable. OCT technology is mainly applied in the biomedical imaging field for diagnoses, making up for the shortcomings of the low penetration depth in confocal microscopes and the low resolution in ultrasonic imaging. At present, OCT technology has been used as the clinical standard for the diagnosis of retinal diseases, and the combination of OCT technology and endoscope technology has become an important tool for the clinical diagnosis of cardiovascular and gastrointestinal diseases. It also provides references for early cancer diagnosis, surgical guidance and postoperative rehabilitation of musculoskeletal diseases. To broaden the application of OCT technology and improve its medical detection capabilities, researchers are committed to increasing the penetration depth of OCT imaging in biological tissue, improving the system's resolution and signal-to-noise ratio, and optimizing its overall performance. This review introduces the principle and classification of OCT systems, their applications and their recent progress in various biomedical fields.
Review on scientific detection technologies for ancient paper relics
YAN Chun-sheng, HUANG Chen, HAN Song-tao, HAN Xiu-li, YING Chao-nan, DU Yuan-dong
2020, 13(5): 936-964.   doi: 10.37188/CO.2020-0010
Abstract(196) FullText HTML(78) PDF 4187KB(44)
Abstract:
This paper comprehensively discusses all kinds of modern scientific and technological detection methods for paper raw materials, inks, inkpads, and pigments used in ancient paper cultural relics, including imaging and spectrometric technologies. Relevant imaging methods include photography, tomography and microscopic imaging methods. Photographic methods include light transmission, infrared, ultraviolet, X-ray and neutron activation photography to display macroscopic information on a sample’s surface or inside. Tomography methods include X-ray, terahertz, and optical coherence tomographic methods to display layered information beneath the sample’s surface. Microscopic imaging methods include optical, scanning electron, transmission electron and atomic force microscopic imaging methods to display the sample’s microscopic information. Spectroscopy methods with fingerprint characteristics based on the principles of wave-matter interactions include chromatography, mass spectrometry, electron paramagnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray fluorescence spectrum, molecular fluorescence spectrum, Raman spectrum, UV-Vis-NIR-MID-THz absorption spectrum and hyperspectral methods. It shows that the comprehensive applications, complementary advantages and mutual confirmations of the above technologies are powerful means to reveal important traits of paper cultural relics, such as one’s manufacturing process, artistic features, preservation history, disease status, authenticity, method of reparation, etc.
Application of emerging transition metal dichalcogenides in ultrafast lasers
SUN Jun-jie, CHEN Fei, HE Yang, CONG Chun-xiao, QU Jia-yi, JI Yan-hui, BAO He
2020, 13(4): 647-659.   doi: 10.37188/CO.2019-0241
Abstract(932) FullText HTML(318) PDF 1212KB(103)
Abstract:
Ultrafast laser technology is one of the most active research frontiers in lasers, physics and information science. It is widely applied in industrial processing, biomedicine, lidar and other fields. Because of their unique physical structure and excellent photoelectric properties, two-dimensional materials have a wide operating band, controllable modulation depth and short recovery time when they are employed as saturable absorbers in ultrafast lasers. Among them, transition metal dichalcogenides have become a focus of research because their band-gap is continuously adjustable. In this paper, we introduce the characteristics of transition metal dichalcogenides and the fabrication methods of saturable absorber devices. The research progress of ultrafast lasers based on emerging transition metal dichalcogenides is reviewed, and the development trend is highlighted.
Research progress of high-precision surface metrology of a K-B mirror
ZHANG Shuai, HOU Xi
2020, 13(4): 660-675.   doi: 10.37188/CO.2019-0231
Abstract(587) FullText HTML(302) PDF 8130KB(66)
Abstract:
The advanced light source represented by the new generation of the diffraction limit synchrotron radiation source and the full-coherent X-ray free-electron laser has become an indispensable research tool in many fields. The continuous development of advanced light sources drives the rapid progress of ultra-precision optical manufacturing. The surface precision of a K-B mirror, a key focusing optical element in advanced light sources, is an important factor, which should be less than tens of nano radians. However, high precision K-B mirror surface metrology still has great technical challenges and is now a research hotspot in the scientific community. This paper introduces typical K-B mirror surface metrology, including reflection profile measuring technology such as the Long Trace Profiler (LTP), the Nanometer Optical component Measuring (NOM), and stitching interference metrology. Current K-B mirror surface shape technologies are summarized and the upcoming research progress is prospected.
Recent advances in high-power continuous-wave ytterbium-doped fiber lasers
DANG Wen-jia, LI Zhe, LI Yu-ting, LU Na, ZHANG Lei, TIAN Xiao, YANG Hui-hui
2020, 13(4): 676-694.   doi: 10.37188/CO.2019-0208
Abstract(500) FullText HTML(270) PDF 4354KB(55)
Abstract:
High power continuous-wave ytterbium-doped fiber lasers have unique advantages such as high electro-optical efficiency, excellent beam quality and good thermal management. For these reasons, these fiber lasers are widely used in industrial processing, national defense and military, and scientific research. However, their non-linear and thermal effects at high-power conditions limit the further improvement of their output power. In this paper, the formation mechanism and corresponding suppression methods of stimulated raman scattering and thermally induced mode instability are analyzed. We hope that these analyses can provide some reference for the design and integration of high-power fiber laser systems. The research results for overcoming these limited factors introduced since 2015 are then discussed in detail. This paper is concluded by predicting the development prospects of high-power continuous-wave ytterbium-doped fiber lasers.
Fiber-reinforced silicon carbide and its applications in optical mirrors
ZHANG Wei, ZHANG Ge, GUO Cong-hui, FAN Tian-yang, XU Chuan-xiang
2020, 13(4): 695-704.   doi: 10.37188/CO.2020-0052
Abstract(262) FullText HTML(136) PDF 1380KB(35)
Abstract:
Fiber-reinforced silicon carbide composites with excellent mechanical and thermal properties are widely used in aerospace, nuclear energy, automobile, chemical industry and many other fields, especially in optical mirrors. This paper introduces the characteristics of fiber-reinforced silicon carbide composites. The advantages and disadvantages of different preparation processes of fiber-reinforced silicon carbide composites are compared. The protective effects of different interface layers on fibers and composites are expounded. The application progress of fiber-reinforced silicon carbide composites in the field of optical mirrors at home and abroad is summarized. Finally, the research direction to be carried out for realizing large-scale application of fiber-reinforced silicon carbide mirror blanks is analyzed.
Research progress of deep-UV nonlinear optical crystals and all-solid-state deep-UV coherent light sources
WANG Xiao-yang, LIU Li-juan
2020, 13(3): 427-441.   doi: 10.3788/CO.2020-0028
Abstract(1764) FullText HTML(764) PDF 2774KB(146)
Abstract:
All-solid-state deep ultraviolet coherent light sources have important applications in frontier science, high technology and many other fields. An effective and feasible technical approach is to use commercially available visible and near-infrared all-solid-state lasers as the fundamental frequency light source to generate a deep ultraviolet laser through cascaded frequency conversion using nonlinear optical crystals. This paper reviews the research progress of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet coherent light sources. Taking KBBF crystals as the representative example, their discovery, crystal growth, corresponding prism-coupled device technology, main optical properties, and ability to generate deep ultraviolet coherent light are each introduced. It was proven that KBBF crystals are excellent nonlinear optical crystals that can achieve deep ultraviolet laser output through direct frequency doubling. The applications of deep ultraviolet coherent light sources based on KBBF crystals and prism-coupled technology are discussed, with special focus given to ultra-high resolution photoelectron spectrometers. Finally, the future direction of the development of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet laser technology are given.
Progress of OLEDs prepared by inkjet printing
LIU Xin, YE Yun, TANG Qian, GUO Tai-liang
2020, 13(2): 217-228.   doi: 10.3788/CO.20201302.0217
Abstract(1386) FullText HTML(795) PDF 3187KB(181)
Abstract:
In recent years, OLED(Organic Light Emitting Diode) devices have been widely used in small-and medium-sized displays, and have gradually been popularized in large area display applications, such as in TVs and lighting. With the continuous development of organic light-emitting technology, higher requirements drive research on the color and pattern of OLED devices. Compared with the traditional vacuum evaporation process, inkjet printing technology easily colors large-area devices and patterns composite functional materials. It is also simple to implement, low in cost and has a more flexible process. In this paper, the current progress of inkjet-printed OLED devices is reviewed. Furthermore, this paper systematically introduces the development of inkjet printing equipment, by optimizing bank structures to improve the resolution of their display screens, by optimizing the ink formulation and composition ratio to suppress the coffee ring effect of inkjet droplets, and improves the uniformity of display luminescence. Finally, this paper summarizes and provides prospects for the future development of this technology at home and abroad.
Research progress on rock removal by laser technology
GUAN Bing, LI Shi-bin, ZHANG Li-gang, CHEN Shuang-qing
2020, 13(2): 229-248.   doi: 10.3788/CO.20201302.0229
Abstract(1356) FullText HTML(710) PDF 4890KB(69)
Abstract:
Laser technology in rock removal is an important research direction in the field of applied optics. It is a complex, high-temperature and high-pressure physical and chemical process with multi-phase, multi-coupling and multi-scale applications. In order to clarify the core difficulties in laser-rock interaction research and to provide an effective theory reference and trend information for researchers, an overview of research on laser rock removal technology is summarized. Firstly, the mechanism of rock removal using lasers is clarified. Then, existing research of laser rock removal is summarized and analyzed from different perspectives, including laser equipment for petroleum drilling and completion, its influencing factors, the phase-change heat transfer of temperature fields, its physical and mechanical properties, and its feasibility in the oil and gas industry. Finally, the advantages of rock removal by laser technology compared with traditional drilling and completion methods are elaborated. In view of the existing problems in laser-rock interaction research, the future development trend of rock removal by laser technology is predicted. The research results show that rock removal by laser technology can lead to research breakthroughs in field-supporting facilities, multi-factor evaluation, multi-field coupling mechanisms and theoretical systems of underground applicability.
Application of planar antenna in field-effect transistor terahertz detectors
WANG Xiao-Dong, YAN Wei, LI Zhao-feng, ZHANG Bo-wen, HUANG Zhen, YANG Fu-hua
2020, 13(1): 1-13.   doi: 10.3788/CO.20201301.0001
Abstract(919) FullText HTML(473) PDF 2481KB(40)
Abstract:
In order to improve the responsivity and reduce the noise equivalent power of Field-Effect Transistor (FET) THz detectors, a suitable planar antenna structure is necessary.In this paper, we investigate the research progress of FET THz detectors integrated with planar antenna structures. Firstly, we analyze the working principle of FET THz detectors and clarify that an integrated planar antenna could effectively improve the detector's performance by enhancing its coupling efficiency with terahertz waves. Secondly, we present some typical planar antennas and discuss their pros and cons. These include the dipole antenna, the patch antenna, the slot antenna, the grating-gate, and others, which are each compared with respect to responsivity for the detectors. Finally, we find that the responsivity of the FET THz detectors can be greatly improved when applying planar antenna structure and that each type of antennas contributes uniquely. This work introduces several planar antennas integrated into FET THz detectors, including the performance and research progress of various antennas.Some existing problems are described and some predictions of the future development trends for this technology are summarized.
Progress of quantum dot backlight technology
YE Yun, YU Jin-hui, LIN Shu-yan, CHEN En-guo, XU Sheng, GUO Tai-liang
2020, 13(1): 14-27.   doi: 10.3788/CO.20201301.0014
Abstract(1193) FullText HTML(697) PDF 4222KB(70)
Abstract:
Quantum dots (QDs) have received widespread attention because of their adjustable emitted wavelength of light, color purity and high quantum efficiency, which have great potential in applications requiring high-color-quality displays with photoluminescence. In this paper, the progress of QD backlights based on each QDs on-chip, QDs on-surface and QDs on-edge are reviewed, including their principle, structures and current applications. Then, several other novel QD backlight structures are also introduced, prompting a proposal for two novel QD backlight technologies. One is the QDs scattering diffusion plate, which is prepared by injecting molding with a mixture of QDs and polymer at a low temperature. The other is a QD microstructure light guide plate, which is fabricated by transferring QDs on the surface of a light guide plate through screen printing or inkjet printing. Both of these two QD plates can achieve high color gamut while being simple to process, being low in cost and holding high production efficiency. These have wide applications in high color gamut liquid crystal displays.
Research progress on laser-produced plasma light source for 13.5 nm extreme ultraviolet lithography
ZONG Nan, HU Wei-min, WANG Zhi-min, WANG Xiao-jun, ZHANG Shen-jin, BO Yong, PENG Qin-Jun, XU Zu-yan
2020, 13(1): 28-42.   doi: 10.3788/CO.20201301.0028
Abstract(1708) FullText HTML(1013) PDF 2768KB(135)
Abstract:
The semiconductor industry is the backbone of the high-tech and information age. Lithography technology, one of the core technology of the semiconductor industry, has become a key research subject all around the world. This article mainly discusses the light source of 13.5 nm Extreme Ultraviolet Lithography (EUVL) by using Laser-Produced Plasma (LPP). It makes a brief introduction to the principles behind this technology and the development history of this field at home and abroad. The introductions include the materials used in the multilayer mirror, and rationale for the selection of materials, the shape and design of the target and the type of laser. At the same time, this article points out that the main problems for the EUVL are light debris reduction and the conversion efficiency improvement of EUV light.This paper also gives special analysis of the light source output devices of 13.5 nm EUVL machines produced by international famous companies——Gigaphoton of Japan and ASML of the Netherlands, which can generate more than 100 W level EUV power. Finally, this article summarizes and forecasts future research related to this technology.
Recent progress in tunable metalenses
LIN Yu, JIANG Chun-ping
2020, 13(1): 43-61.   doi: 10.3788/CO.20201301.0043
Abstract(944) FullText HTML(546) PDF 8834KB(74)
Abstract:
Emerging optical devices demand miniaturized, integrated and intelligent optical zoom systems, thus stimulating development in nano-optoelectronics. Metalenses are two-dimensional planar structures with lens function composed of arrays arranged specifically to equally focus wavelengths of light. Due to their ultrathin and lightweight properties and their ease of integration, it is expected that they will revolutionize optics by replacing the conventional bulky, curved lenses used that pervade optical devices. However, once the micro/nano-structures of a metalens are fabricated, their shape and size cannot be modified, which can not realize the real-time adjustment of focusing and will limit the further development of metalenses' functions and applications. Currently, substantial effort is being devoted to solving this problem. One of the most attractive aspects of metalenses is in the way they combine metasurface lenses with smart materials. In this article, we first provide an overview of novel tunable metalenses. Then, we elaborate and analyze their regulatory principles and device performance, respectively. Finally, we summarize the current problems and difficulties facing the development of tunable metalenses and describe the direction of their future development.
Research progress of quantum dot enhanced silicon-based photodetectors
ZHU Xiao-xiu, GE Yong, LI Jian-jun, ZHAO Yue-jin, ZOU Bing-suo, ZHONG Hai-zheng
2020, 13(1): 62-74.   doi: 10.3788/CO.20201301.0062
Abstract(1134) FullText HTML(606) PDF 6598KB(65)
Abstract:
Silicon-based photodetectors have been widely investigated due to their high reliability, easy integration and low cost. With the development of artificial intelligence and autonomous vehicles, research and performance enhancement of silicon-based photodetectors is an important field of research. Quantum dots are excellent light-conversion and light-modulation materials due to their superior absorption coefficient, tunable spectra, high photoluminescence quantum yield and simple integration. The tunable light absorption and phototuminesence properties of quantum dots make them suitable materials for enhancing the detection. Quantum dots enhanced silicon-based photodetectors are emerging as a new technique to advance the performance of detection and imaging. In particular, they show potential to expand the functionality of CCD and CMOS devices and further satisfy increasing demands for detection. In this review, we summarized the progress of quantum dot-enhanced silicon-based photodetectors in the field of ultraviolet detection, infrared imaging, polarization detection and spectral detection, hoping to attract the attentions of domestic colleagues.
Development of additively manufacturing metal mirrors
TAN Song-nian, DING Ya-lin, XU Yong-sen, LIU Wei-yi
2020, 13(1): 75-86.   doi: 10.3788/CO.20201301.0075
Abstract(981) FullText HTML(433) PDF 4338KB(48)
Abstract:
With the rapid development of optical measurement and remote sensing, the demand for weight, volume and environmental adaptability in folding optical systems are continuously increasing. Metal mirrors based on additive manufacturing technology are gradually gaining the attention and research of scholars at home and abroad for their easy to realize optimum design, rapid manufacturing process and high processing performance. Compared to conventional metal mirrors, additively manufacturing metal mirrors strengthen the stiffness of the mirror and achieve a higher degree of weight reduction simultaneously. Furthermore, additively manufacturing mirrors can meet the environmental adaptability and rapidity requirements of optical systems. This paper first discusses the evaluation indicators of metal mirrors. Second, the development status and technical parameters of metal mirrors based on additive manufacturing technology are reviewed. The design and preparation of metal mirrors for additive metal fabrication and the post-treatment of substrates are discussed. Then, through analysis, the preparation process and key technologies of additively manufacturing metal mirrors are summarized. Finally, prospects for additively manufacturing mirror applications are presented.
Image processing method for ophthalmic optical coherence tomography
CAI Huai-yu, ZHANG Wei-qian, CHEN Xiao-dong, LIU Shan-shan, HAN Xiao-yan
2019, 12(4): 731-740.   doi: 10.3788/CO.20191204.0731
Abstract(1876) FullText HTML(498) PDF 2700KB(56)
Abstract:
Optical coherence tomography(OCT) has become a hot research topic in the field of clinical medicine due to its features including micron-level high resolution, non-invasive imaging and instantaneity, which has developed rapidly and made much progress and break throughs in recent years. In this paper we briefly review the applications of OCT in ophthalmology, discuss the methods of speckle noise reduction in the spatial and frequency domains of OCT images, and summarize the precise positioning and stratification method of each layer of tissue in the OCT anterior segment and retina image. The advantages and disadvantages of the segmentation methods based on gray value search, active contour model, graph and pattern recognition algorithms are analyzed and compared. In addition, the existing problems with segmentation methods are discussed and the corresponding solutions and feasible optimization schemes are proposed. Analysis and evaluation of clinical diagnostic indicators of ophthalmic diseases are discussed. According to the needs in ophthalmology and the current status of OCT image processing, the development trends and level of OCT image processing are discussed and analyzed.
The regularized phase tracking technique used in single closed interferogram phase retrieval
WANG Xian-min, LIU Dong, ZANG Zhong-ming, WU Lan, YAN Tian-liang, ZHOU Yu-hao, ZHANG Yu-peng
2019, 12(4): 719-730.   doi: 10.3788/CO.20191204.0719
Abstract(818) FullText HTML(389) PDF 4295KB(96)
Abstract:
Different kinds of modulation methods are usually adopted when physical quantities, such as temperature, forces and deformation, are measured in interference. Fringe patterns carry measurement information of those quantities and are usually later analyzed for its retrieval. Single closed fringes are generally what is recorded by CCD. When the experimental conditions are not conducive to phase shifting, loading wave and other modulation means, the regularized phase tracking(RPT) technique can retrieve a continuous phase map directly from a single interferogram, making it the most effective method. In recent years, RPT technique has been improved to achieve higher processing power, algorithm robustness and retrieval accuracy for complex fringe patterns, ultimately making it more practical. In this paper, we introduce the basic algorithm principle and how the RPT technique is applied in the retrieval of single interferograms, review the technique's relevant modifications and developments in recent years, cite some examples used for phase retrieval and speculate the direction of its future development.
Realization of a watt-level 319-nm single-frequency CW ultraviolet laser and its application in single-photon Rydberg excitation of cesium atoms
WANG Jun-min, BAI Jian-dong, WANG Jie-ying, LIU Shuo, YANG Bao-dong, HE Jun
2019, 12(4): 701-718.   doi: 10.3788/CO.20191204.0701
Abstract(1496) FullText HTML(554) PDF 8142KB(80)
Abstract:
In order to meet the demand for single-photon Rydberg excitation of cesium atoms in the field of atomic physics, we investigated the key technolgies of single-frequency continuous wave(CW) tunable ultraviolet(UV) laser at 318.6 nm. Combining the fiber lasers, fiber amplifiers and the nonlinear crystals, we achieved 318.6 nm UV laser over 2 Watt output with cavity-enhanced second-harmonic generation following the sum-frequency generation of two infrared lasers at 1 560.5 nm and 1 076.9 nm in PPLN crystal. The typical root-mean-square fluctuation of UV laser power was less than 0.87% within 30 minutes. The electronic side-band locking scheme based on a temperature controlled hyper-fine ultra-stable ultra-low-expansion cavity placed in an ultra-high vacuum chamber was used to achieve the continuously tuning of UV laser in a wide range while still keeping it locked. The continuously tunable range was larger than 4 GHz and the residual frequency fluctuation of UV laser was about 16 kHz. We employed this high-power single-frequency continuously tunable UV laser system for the direct 6S1/2nP3/2(n=70-100) Rydberg excitation of cesium atoms with atomic vapor cells in experiments. After that, relevant theoretical analysis and research have been done. With a magneto-optical trapped cesium atomic ensemble, single-photon Rydberg excitation using the UV laser system was achieved with a pure optical detection scheme.

Supervisor: Chinese Academy of Sciences

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

Editor-in-Chief: Wang Jiaqi, Academician

ISSN 2095-1531

CN 22-1400/O4

CODEN ZGHUC8

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