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Beam quality β factor calculation based on two-dimensional chirp Z transformation
WANG Yan-ru, RAN Zheng-hui, DING Yu-jie
 doi: 10.37188/CO.2020-0079
Abstract(17) FullText HTML(14) PDF 2448KB(6)
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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 calculation quantum 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.
Study on orthogonal luminescence properties of a single rare-earth activator ion doped upconversion nanoparticles
LING Xiao, MEI Qing-song
 doi: 10.37188/CO.2020-0020
Abstract(23) FullText HTML(7) PDF 3130KB(4)
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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.
X-ray security inspection images classification combined octconv and bidirectional GRU
WU Hai-bin, WEI Xi-ying, WANG Ai-li, YUJI Iwahori
 doi: 10.37188/CO.2020-0073
Abstract(48) FullText HTML(16) PDF 4374KB(5)
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The active vision security inspection method has low accuracy and slow speed , it is not suitable for real-time security inspection. Aiming at this problem, this paper proposes an x-ray inspection image classification algorithm combined 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.
Research on non-uniformity correction of airborne infrared detection system
LV Bao-lin, TONG Shou-feng, XU Wei, FENG Qin-ping, WANG De-jiang
 doi: 10.37188/CO.2020-0109
Abstract(16) FullText HTML(9) PDF 6973KB(4)
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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. This paper proposes an algorithm that is 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.
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
 doi: 10.37188/CO.2020-0078
Abstract(31) FullText HTML(19) PDF 4923KB(6)
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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.
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
 doi: 10.37188/CO.2020-0064
Abstract(17) FullText HTML(13) PDF 3598KB(2)
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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.
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(435) FullText HTML(278) PDF 1978KB(14)
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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.
Research progress on nitrogen-doped carbon nanodots
LI Di, MENG Li, QU Song-nan
 doi: 10.37188/CO.2020-0035
Abstract(33) FullText HTML(19) PDF 2500KB(6)
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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.
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(7) FullText HTML(6) PDF 3894KB(3)
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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.
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(9) FullText HTML(7) PDF 3688KB(0)
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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, which can optimize the algorithm’s parameters. Then, the dynamic characteristics of a controlled object in the precise tracking system are measured with a sweep signal, and the positional information is collected with a CCD camera. 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.
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(7) FullText HTML(12) PDF 4057KB(2)
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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.
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
 doi: 10.37188/CO.2020-0022
Abstract(31) FullText HTML(22) PDF 3739KB(11)
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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 with lasers at different spot sizes. The research results show that: under 1000 W/cm2 laser irradiation, the absorption rate of the material increases with an increase in temperature. 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 dictated by 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 threshold time of fusion damage on the back surface of the target remains unchanged at 2.6 s.
Tailoring the optical properties of ZnO Nanorods doped with Al by electrodeposition
TANG Yang
 doi: 10.37188/CO.2020-0075
Abstract(12) FullText HTML(7) PDF 2288KB(1)
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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’ morphological, optical and electrical properties. ZnO nanorods arrays were fabricated by electrodeposition. The physical properties such as the crystalline quality, diameter, density, distance, Al doping, optical band gap energy, near band emission and stokes shift can be adjusted 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 morphological and optical properties.
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(4) FullText HTML(2) PDF 3555KB(0)
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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(5) FullText HTML(4) PDF 4295KB(1)
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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.
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(8) FullText HTML(10) PDF 4322KB(1)
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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 mirrors. 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.
Research on the Enhancement of Absorption Properties of Silicon via Localized Surface Plasmons Resonance in Blue Light
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(8) FullText HTML(7) PDF 4636KB(0)
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In order to enhance the blue light absorption of silicon.an array of silver nanoparticles (Ag-NPs) was designed on the surface of silicon (Si) to analyze and study the enhanced blue light absorption of silicon based on localized surface plasmons resonance (LSPR) effect. The Finite-Difference-Time-Domain (FDTD) method was used to calculate the blue-light absorption characteristic of the silicon in the Ag-NPs/Silicon composite structure. The results indicated that the extinction ability of a metal particle was related to its geometric parameters and that the intensity and frequency of LSPR could be tuned by changing the radius r, height H and period P of the Ag-NP array. If r=18.5 nm, H=45.0 nm and P=49.0 nm, the resonance absorption wavelength will be 465 nm, the blue light absorptivity of silicon will increase from 59% to 94%, the light absorption gain will be 0.57, and the gain of the number of photo-generated carriers will be 0.53. The analysis results showed that the LSPR could enhance the light absorption of silicon in the blue band. The research results have important reference value for understanding how the LSPR effect improves the blue-light absorption performance of silicon and for designing and preparing a silica-based visible light photodetector with high blue light responsiveness.
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(7) FullText HTML(5) PDF 5457KB(1)
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In view of the complex design of light sources and the poor illumination uniformity in machine vision cylinder block transverse hole detection, 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 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. If one were to move the light to the inside of the hole the non-uniformity becomes 5%, and 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 is 0.6%. The uniformity illumination surpasses 99%, which meets our requirements for machine vision detection and can be obtained by using an integrating sphere and LED dual light source.
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
 doi: 10.37188/CO.2020-0089
Abstract(7) FullText HTML(5) PDF 2487KB(0)
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To research 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.
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(10) FullText HTML(5) PDF 4088KB(2)
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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 of their various detection methods. Finally, this paper proposes the trend for the future development of target detection methods based on laser speckles.
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(6) FullText HTML(8) PDF 3432KB(0)
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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.
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(6) FullText HTML(4) PDF 3706KB(2)
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Segmented mirror technology is one of the three ways to create an 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. It introduced the development process of a segmented mirror telescope and the main structure of the segmented mirror active control system, then summarizes and analyzes 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.
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(8) FullText HTML(5) PDF 3251KB(0)
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  Objective   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.   Method   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.   Result   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.   Conclusion   The effectiveness of the delayed field ionization technique in measuring the first ionization threshold of Sm atom has been verified.
Design of resonant waveguide grating filter with reflection and transmission modes
FAN Li-na, MA Jun-shan
 doi: 10.37188/CO.2020-0072
Abstract(19) FullText HTML(11) PDF 3327KB(3)
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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 which the same device can realize two filtering modes was analyzed. The results showd that the reflection-transmission narrow-band filtering modes could be converted at the designed wavelength with the same resonant waveguide grating structure under different incident conditions.
Near-infrared BRDF study of material surfaces at varying temperatures
MA Wang-jiehui, LIU Yan-lei, CHEN Zhi-ying, LIU Yu-fang
 doi: 10.37188/CO.2019-0256
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The spectral polarized BRDF of a brass surface in the near-infrared region was measured using the absolute measurement method with a device that was designed in-house. 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.
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
 doi: 10.37188/CO.2020-0010
Abstract(29) FullText HTML(24) PDF 4343KB(9)
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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-transmitting, 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, history of reparation, etc.
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
 doi: 10.37188/CO.2020-0025
Abstract(22) FullText HTML(8) PDF 6569KB(2)
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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
 doi: 10.37188/CO.2019-0221
Abstract(29) FullText HTML(18) PDF 6596KB(1)
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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 with 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.
Time-frequency analysis of laser doppler radar vibration signals
CHEN Hong-kai, WANG Ting-feng, WU Shi-song, LI Yuan-yang, GUO Jin
 doi: 10.37188/CO.2019-0251
Abstract(28) FullText HTML(16) PDF 3283KB(4)
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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.
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(11) FullText HTML(12) PDF 4041KB(0)
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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 16PFS. 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.
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(12) FullText HTML(7) PDF 3502KB(0)
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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.
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(11) FullText HTML(10) PDF 3413KB(0)
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To resolve problems with 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 is 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 they can be as high as 0.92 for carbon fiber epoxy composites. The coupling coefficient measured by the actual thermal radiation spectrum is higher than that of a 6000 K blackbody, 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.
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(8) FullText HTML(5) PDF 1988KB(0)
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  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.
Development status and trend of micro-satellite laser communication systems
GAO Shi-Jie, WU Jia-Bin, LIU Yong-Kai, MA Shuang, NIU Yan-Jun
 doi: 10.37188/CO.2020-0033
Abstract(30) FullText HTML(16) PDF 7392KB(5)
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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. This is especially true 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, the technology’s 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 summarized
Research on 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
 doi: 10.37188/CO.2020-0003
Abstract(36) FullText HTML(32) PDF 3498KB(7)
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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 of immediate significance for 3D super-resolution fluorescence microscopy imaging, which can save computing time and achieve real-time imaging.
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(14) FullText HTML(12) PDF 3901KB(2)
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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 using the Gabor Filter Convolutional Neural Network (GF-CNN). 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 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 imagery.
Differentiation of polarization scattering characteristics of surface nanoparticle defects
GAO Ping-ping, LU Min, WANG Zhi-le, GUO Ji-kai, HE Xiao-bo
 doi: 10.37188/CO.2020-0083
Abstract(30) FullText HTML(15) PDF 6056KB(2)
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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 of 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 the trend of the change of the bidirectional reflection distribution function value of the p-polarized light incident on the surface and the detection of the p-polarized light with the scattering azimuth angle 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.
Differential chromatic confocal roughness evaluation system and experimental research
ZOU Jing-wu, YU Qing, CHENG Fang
 doi: 10.37188/CO.2020-0029
Abstract(36) FullText HTML(26) PDF 5333KB(6)
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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 for 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 in the proposed system with six repeats 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 requireme nts of most engineering applications.
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
 doi: 10.37188/CO.2019-0195
Abstract(224) FullText HTML(115) PDF 2220KB(10)
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.
Optical coherence tomography: principles and recent developments
LU Dong-xiao, FANG Wen-hui, LI Yu-yao, LI Jin-hua, WANG Xiao-jun
 doi: 10.37188/CO.2020-0037
Abstract(34) FullText HTML(39) PDF 3753KB(11)
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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.
Flat-field calibration method for large diameter survey mirror aperture splicing
LU Shi-tong, ZHANG Tian-yi, ZHANG Xiao-hui
 doi: 10.37188/CO.2019-0252
Abstract(32) FullText HTML(25) PDF 5059KB(4)
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.
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
 doi: 10.37188/CO.2020-0027
Abstract(39) FullText HTML(31) PDF 4487KB(8)
Abstract:
In view of the urgent need for seed selection technology in agriculture and for grading detection of the vigor of peeled 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 designe a near-infrared absorption spectroscopy system that detects seed viability and measure the NIR spectra of husked rice seeds that are picked over three different years. 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 (PIS-DA) model is established. The analysis showed that the transmission absorption spectrum detection system designed in this paper combined with the PLS-DA discrimination model could classify rice seeds of different vigor with an accuracy of 94.44% and 95.92%. After screening, the germination rate of rice seeds could 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.
Texture mapping of multi-view high-resolution images and binocular 3D point clouds
DU Rui-jian, GE Bao-zhen, CHEN Lei
 doi: 10.37188/CO.2020-0034
Abstract(24) FullText HTML(27) PDF 3754KB(3)
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.
TDLAS detection of propylene with complex spectral features
ZHONG Li, SONG Di, JIAO Yue, LI Han, LI Guo-lin, JI Wen-hai
 doi: 10.37188/CO.2019-0203
Abstract(2143) FullText HTML(495) PDF 6850KB(17)
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.
Reviews
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](613) [FullText HTML](246) [PDF 1212KB](60)
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](443) [FullText HTML](240) [PDF 8130KB](46)
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](333) [FullText HTML](197) [PDF 4354KB](32)
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](141) [FullText HTML](68) [PDF 1380KB](24)
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.
Original Article
Method of enhancing the quality of in-line holographic images for micro-milling tool
CHENG Ya-ya, YU Hua-dong, YU Zhan-jiang, XU Jin-kai, ZHANG Xiang-hui
2020, 13(4): 705-712.   doi: 10.37188/CO.2019-0217
[Abstract](565) [FullText HTML](318) [PDF 5008KB](30)
Abstract:
When tool setting with digital in-line holography, the zero-order image and defocused twin-image can form strong and complex background noise, which gets superimposed on the real image and seriously reduces the quality of the reconstructed image. To improve quality of interferential images in digital in-line holography, a holographic image enhancement method using an improved self-snake model is proposed. The improved self-snake model selects a diffusion intensity according to the gradient of the initial image. The experimental results show that the improved self-snake model can avoid the appearance of jagged edges and “pseudo-contours” caused by large gradient background noise during the diffusion process. This improvement outweighs the shortcomings of the self-snake model in holographic imaging. In addition, compared with the phase retrieval and multi-plane reproduction approaches, the improved self-snake model filtering method proposed in this paper not only has better suppression for interferential images but also can enhance the edge of the tool, which is conducive to the actualization of tool-setting using on digital in-line holography.
Influence of proximity focusing structure and electric field distribution on electron trajectory in the EBCMOS
WANG Wei, LI Ye, CHEN Wei-jun, SONG De, WANG Xin
2020, 13(4): 713-721.   doi: 10.37188/CO.2020-0063
[Abstract](77) [FullText HTML](57) [PDF 3437KB](22)
Abstract:
In order to obtain high-resolution Electron Bombarded CMOS (EBCMOS) imaging devices, we study the effect of electric field distribution on the electron trajectory in proximity focusing EBCMOS devices. Three different electric field distributions are obtained by designing different EBCOMS structure, namely, the nonparallel, partially parallel, and parallel equipotential surfaces between the photocathode and the Back-side Bombarded CMOS (BSB-CMOS). The electron trajectories in each case are simulated according to electromagnetism theory and monte carlo simulation method. The results indicate that, when the BSB-CMOS is bombarded by photoelectrons, the scattering diameter can be reduced to 30 μm under the condition that the surface of the electron multiplying layer is covered with 30 nm ultra-thin heavily doping layer and the voltage between electrodes is maintained at 4000 V while the distance between photocathode and BSB-CMOS is 1 mm. This structure is helpful to realize electrons focusing and achieve EBCMOS with high resolution. Then, the influence of the distance and voltage between the photocathode and BSB-CMOS on scattering diameter is studied. The results indicate that the electric field strength increases with the decrease of proximity distance and the increase of the acceleration voltage. This work will provide theoretical guidance for improving the resolution characteristics of EBCMOS imaging devices.
Fan-shaped mid-infrared chiral metamaterials based on indium tin oxide and their circular dichroism
ZHU Ye-xin, LI Ya-nan, SHI Wei-jie, ZHANG Wen-tao, YAN Chang-chun
2020, 13(4): 722-727.   doi: 10.37188/CO.2019-0190
[Abstract](606) [FullText HTML](376) [PDF 1177KB](29)
Abstract:
A mid-infrared chiral metamaterial was designed to overcome the problems of large volume and high cost of traditional mid-infrared laser polarization state controls, The fan-shaped chiral structure material made of Indium Tin Oxide (ITO) was designed and its Circular Dichroism (CD) characteristics in the mid-infrared band were studied. The CD variation characteristics of the structure were discussed by changing the filling material, the thickness, the size, the number, and the material of fan blades. The simulation results show that when the filling material is silicon and the number of fan blade is six, the strongest CD signal of 0.052 is obtained near the wavelength of 5.3 μm by selecting the appropriate fan thickness and size. Moreover, compared with the silver and gold, the structure made of ITO exhibits broadband circular dichroism, which provides a new idea for the design of broadband polarization-state control devices in the mid-infrared band.
Light intensity and spatial coherence characteristics of laser coherent detection in a turbulent atmosphere
REN Jian-ying, SUN Hua-yan, ZHAO Yan-zhong, ZHANG Lai-xian
2020, 13(4): 728-736.   doi: 10.37188/CO.2019-0194
[Abstract](624) [FullText HTML](555) [PDF 2560KB](18)
Abstract:
In this paper, the cross-spectral density function of target reflected light in laser detection is obtained by using generalized Huygens-Fresnel principle and Goodman target scattering theory. On the basis of above, the expression of intensity distribution and spatial coherence length of target reflected light is derived. The influence of different light source and target reflected light parameters on the intensity distribution and coherent length of the target reflected light is simulated by using the expressions obtained in this paper under turbulent atmospheric conditions. The results show that the coherence length of the light source has little effect on the normalized light intensity distribution; the coherence length of the received light is smaller with a larger beam waist radius and reflected light radius, and the coherence length increases at a slower rate as the transmission distance increases. In the process of weak turbulent atmospheric transmission, the influence of light source parameters on the received light is much stronger. The larger the beam waist radius, the smaller the received light intensity and coherence length value. During strong turbulent atmospheric transmission, the influence of atmospheric turbulence on the received light is dominant.
A femtosecond laser-inscribed fine-core long-period grating with low temperature sensitivity
MING Xin-yu, GUO Qi, XUE Zhao-kang, PAN Xue-peng, CHEN Chao, YU Yong-sen
2020, 13(4): 737-744.   doi: 10.37188/CO.2020-0015
[Abstract](212) [FullText HTML](142) [PDF 5819KB](24)
Abstract:
In order to reduce crosstalk caused by temperature during refractive index and strain testing, the temperature, refractive index and strain response characteristics of fine-core long-period fiber gratings were studied. A long-period fiber grating with a period of 50 μm was successfully prepared on a single-mode fiber with a core diameter of 6 μm using the femtosecond laser direct writing method. The results show that long-period fiber gratings processed with low laser energy in fine-core fibers have lower temperature sensitivity, and maintain a larger extinction ratio and better spectral quality. The loss peak of this fine-core long-period fiber grating drifts only 1.7 nm in the 20~700 °C temperature range. The grating is also highly responsive to changes in the refractive index. when ambient refractive index is in the range of 1.4065~1.4265, its sensitivity reaches 882.51 nm/RIU, and its strain sensitivity is −2.2 pm/με. This fine-core long-period fiber grating can better reduce crosstalk caused by temperature in the refractive index and strain tests.
Generation of a 49-GHz, high-repetition-rate, all-polarization-maintaining, frequency-locked multicarrier
WANG Chao, XIAO Yong-chuan, LIN Shu-qing, YU Cai-bin, QU Peng-fei, LI Ru-zhang, SUN Li-jun
2020, 13(4): 745-751.   doi: 10.37188/CO.2019-0191
[Abstract](262) [FullText HTML](146) [PDF 2295KB](16)
Abstract:
Frequency-locked multicarrier with high repetition rate is an ideal tool for microwave channelization and optical communications. To meet the needs of those applications, we propose a multicarrier laser with a repetition frequency of 49 GHz. The I/Q Modulator (IQM) works at the Single-Frequency Shifting (SSB) state by carefully optimizing the Radio Frequencies (RFs) and their three bias points, resulting in a signal-to-noise ratio of 27.5 dB. The Recirculating Frequency Shifter (RFS) architecture is employed to generate an optical comb with high flatness. By optimizing the power of RFs for the balance of gain and loss of intracavity, we successfully generate 28 frequency-locked subcarriers with flatnesses lower than 3 dB and Tone-to-Noise Ratios (TNR) larger than 29 dB. Meanwhile, an Fabry-Perot (FP) etalon is used to increase the repetition-rate, resulting in 14 frequency-locked subcarriers with flatnesses lower than 2.7 dB, TNR larger than 19 dB, average powers of more than 9 dBm and carrier spacings at 49 GHz. By applying all-polarization-maintaining components and integrated technology, the system shows one-push and long-term running properties. The standard deviation of power jitter of the multi-carrier frequency comb through the half hour is only 0.5%, which shows that this scheme has great potential applications in channel communications and microwave channelization.
Panoramic peripheral vision imaging and display technology based on a deformation eyepiece and OLED
LUO Jie-chao, GUO Jun-da, MI Feng-wen, QIU Su, DUN Xiong, JIN Wei-qi
2020, 13(4): 752-759.   doi: 10.37188/CO.2019-0214
[Abstract](200) [FullText HTML](123) [PDF 18830KB](29)
Abstract:
In narrow spaces, vehicles, carriers or for single guards on duty, traditional displays have a dilemma wherein it is difficult to balance a display’s field of view and its resolution. This paper studies panoramic/periodic imaging technology and a system based on deformable eyepieces, which is expected to provide a technical solution to effectively solve the above problems. The system uses three low-light cameras with 4 mm focal length lens to form a panoramic imaging field of view of 150°. Panoramic image analysis, stitching, correction, and display are carried out by adopted FPGA processing platform. It also has a real-time zoom display; a display system consisting of OLED micro-displays, an anamorphic eyepiece group and large eyepiece enlarges the video image horizontally by a factor of 3 and displays a panoramic high-resolution dynamic scene image in real time. The experiment verifies the feasibility of a day and night panoramic imaging display. The system has a wide array of possible applications inside and outside of the military.
An automatic focusing method of a telescope objective lens based on the defocusing estimation of a circular edge response
LUO Qi-jun, GE Bao-zhen
2020, 13(4): 760-769.   doi: 10.37188/CO.2019-0247
[Abstract](245) [FullText HTML](208) [PDF 4781KB](26)
Abstract:
A new defocusing estimation algorithm based on the response curve of a circular edge is proposed, through which the calibration of some focusing parameters and the automatic focusing of the telescope objective lens are achieved. The relationship between the gray-scale response of the edge of the circular pattern and the defocusing radius is established. Using the double threshold mean filtering of the defocusing radius around the circle, the accurate defocus radius of the blurred image is calculated and the influence of motion blur and noise is reduced. According to the linear relationship between defocus radius and focus distance, the broken line fitting method is used to obtain the focus distance. Then, by using multiple object and focus image distances, the parameters of the focusing model of the ranging method are optimized and the automatic focusing of the imaging system is achieved. Through simulation and experimentation, the feasibility and robustness of the defocusing estimation algorithm are verified. The images taken by the calibrated autofocus imaging system are clear, have a physical resolution that reaches half of their theoretical value, and have a resolvable line width better than 0.354 mm when the shooting distance is between 43 m and 52 m.
Analysis of the corneal surface and peripheral defocus after orthokeratology
LIU Bao-kai, LIU Yong-ji, XIE Pei-ying, GUO Xi, GU Jian-da, YU Hao
2020, 13(4): 770-777.   doi: 10.37188/CO.2019-0248
[Abstract](250) [FullText HTML](145) [PDF 1329KB](12)
Abstract:
A new method of corneal shape analysis method is proposed. It not only eliminates the influence of corneal thickness on the shape of cornea after orthokeratology, but also reflects the asymmetry of a cornea. A reference surface is introduced into the analysis of the height data of the anterior surface of the cornea to eliminate the influence of corneal thickness. On the basis of above, anterior surface of the cornea is divided into the optical zone, transition zone and peripheral zone. The results show that the optical zone diameter is (1.9±0.27) mm, and the curvature radius is (8.32±0.38) mm; the transition zone diameter is (6.56±0.38) mm, and the curvature radius is (7.48±0.55) mm; the curvature radius of the peripheral zone is (10.49±1.83) mm. After orthokeratology, the horizontal refraction of the transition zone is lower than its vertical refraction. The refraction of the nasal side is greater than that of the temporal side and the refraction of the upper side is greater than that of the lower side. A semi-customized eye model is established based on the obtained parameters and the results show that its peripheral defocus is myopic after orthokeratology and its defocus is asymmetrical in each direction, which is consistent with clinical observations.
Variable image distance bending using an elliptical bending mechanism with a constant cross-section mirror
ZHOU Bo-wen, WANG Nan, ZHU Wan-qian, XUE Song, TIAN Ying-zhong
2020, 13(4): 778-786.   doi: 10.37188/CO.2019-0250
[Abstract](248) [FullText HTML](150) [PDF 10078KB](15)
Abstract:
In this paper, the surface shape error of latest elliptical bending mechanism with a constant cross-section mirror is studied when the object distance is fixed (when the position of the mirror in the light path is invariable) and the image distance is adjusted drastically (when the position of the sample is changed). Based on theoretical analysis and the finite element analysis, theoretical slope error is calculated when it is caused by bending a mirror with a width equal to an elliptical cylinder with a different shape (different image distances at the reflection point). Then, a bending experiment of a prototype of the elliptical bending mechanism is conducted. Experimental results and analysis indicate that the slope error between the bending mirror and an ideal elliptic cylinder will increase with a decrease in image distance, and the slope error of the mirror will increase more quickly as the image distance is shortened. When the initial slope error of the reflecting mirror is 0.397 μrad, the slope error of the bent mirror in the whole range of image distance (21.5~3.8 m) is 0.402~0.560 μrad and the repeatable accuracy is 0.051 urad, which meets the design requirements of the beamline of the Shanghai Synchrotron Radiation Facility (SSRF). It is proven that in elliptically bending mirrors, continuous adjustment of the image distance from the focusing mirror can be achieved by using a bending mechanism with constant cross-section mirror.
Design and analysis of stress-free clamping of mirrors used in free-electron laser beamlines
ZHAO Chen-hang, LU Qi-peng, SONG Yuan, GONG Xue-peng, WANG Yi, XU Bin-hao
2020, 13(4): 787-794.   doi: 10.37188/CO.2019-0131
[Abstract](918) [FullText HTML](307) [PDF 8805KB](25)
Abstract:
The reflector is an important optical element in free-electron laser beamlines. Deformation error caused by gravity can seriously affect the image quality of a beamline. To reduce deformation error, a gravity compensation scheme based on the Bessel point theory is proposed and a stress-free clamping device is designed. Taking a 440 mm × 50 mm × 50 mm mirror as an example, the analysis results indicate that the deformation error in the bottom surface of a mirror clamped with the traditional support method is 1.647 μrad. Adopting the newly designed device proposed in this paper, the results of a finite element analysis showed that the deformation error reduced to 0.085 7 μrad, which is better than the engineering index of 0.1 μrad. To prevent the mirror from moving when switching modes, a small clamping force of no more than 2 N can be added to the mirror, at which point the surface error of the mirror becomes 0.093 9 μrad. Additionally, a dynamic analysis of the device is also carried out, which indicates that the device mutes the low natural frequency, which means that resonance will not occur during operation. Therefore, this scheme satisfies our requirements for the beamline.
Modification of Soluble Solids Content sorting line based on light source transmitting and receiving integrated probe
LIU Yan-de, RAO Yu, SUN Xu-dong, XIAO Huai-chun, JIANG Xiao-gang, XU Hai, LI Xiong, XU Jia, WANG Guan-tian
2020, 13(4): 795-804.   doi: 10.37188/CO.2019-0165
[Abstract](932) [FullText HTML](969) [PDF 6550KB](11)
Abstract:
Traditional quality sorting methods have been unable to meet people's increasing demands for fruit flavour and quality. Producers must therefore develop their traditional quality sorting methods to achieve sugar content sorting and ensure favourable flavour and quality. To address this, the near-infrared reflection spectra of navel oranges were collected separately through two different detection methods. The spectral energy of their ring transmission and diffuse reflection had to be stronger than that of the multi-point transmission and diffuse reflections. The positions of their peaks and troughs had to be approximately the same. The near-infrared diffuse reflectance spectra were preprocessed using baseline correction, multivariate scattering correction, first and second derivatives to reduce the influence of stray light and noise. A Partial Least Squares (PLS) model for the sugar content information that was collected through the two different reflection detection methods was established for their comparison and analysis. The experimental results show that the baseline correction preprocessing method produced the best results between the two methods. Its predicted correlation coefficient of sugar under ring transmission and diffuse reflection detection was 0.81 and its root mean square error was 0.46° Brix. The estimated correlation coefficient of the sugar content model using the multi-point transmission and diffuse reflection detection method was 0.76 and its root mean square error was 0.53° Brix. This research shows that it is feasible to use PLS modeling and near-infrared diffuse reflectance spectrum to upgrade the sugar content sorting methodology used on production lines.
Optimal design of a 2.7 m standard spherical inspection mirror support
GAO Jing-jing, JIAO Chang-jun, HUANG Shen, ZHANG Zhen, BI Yong
2020, 13(4): 805-813.   doi: 10.37188/CO.2019-0225
[Abstract](223) [FullText HTML](116) [PDF 13445KB](15)
Abstract:
Aiming at the problem that the decrease of inspection accuracy caused by an increase in the diameter of a spherical inspection mirror, the weight support parameters of the 2.7-meter standard spherical mirror are optimized and the structural design of its adjustment frame and support system is implemented. Firstly, the 54-point equal-force support ring is optimized for the mirror body using a finite element and genetic algorithm. In order to increase the rigidity of the mirror body when increasing the nesting hole, the bottom support force and the side support force of each ring are optimized separately and the influence of support radius and support force error on the support deformation is statistically analyzed. Finally, based on the analysis results, a structural frame of the standard inspection mirror and a support system are designed. The analysis results show that after optimization of the 54-point support position of the standard spherical mirror, the bottom support force and the side support force of each ring and under the condition that the spherical mirror support deformation is less than 1/115λ(λ=632.8 nm), the bottom support position is disturbed by ±2 mm, the side support position is disturbed by ±0.6 mm, and the support force disturbance is ±3 N, the support deformation is less than 1/70λ, which shows little deterioration. This meets the requirements of standard spherical mirror support.
Optical system design and simulation of a wide-area fundus camera
CHEN Wei-lin, CHANG Jun, ZHAO Xue-hui, JIN Hui
2020, 13(4): 814-821.   doi: 10.37188/CO.2020-0066
[Abstract](154) [FullText HTML](100) [PDF 8659KB](28)
Abstract:
A wide-area fundus camera used for screening the retinae of infants was designed. In this paper, the design methods of the device’s illuminating and imaging systems were investigated. Based on James Polans’ wide-field human eye model and a set of ophthalmic anatomy data, an infant eye model was established. Then, a tapered fiber scheme was proposed for wide area illumination. Finally, the design method of a wide-area fundus camera imaging system, including the contact lens and relay lens, is introduced. The design example shows that the Field Of View (FOV) of the wide-area fundus camera can reach 130°, and the object resolution of the fundus can reach 10 μm. The design results meet the national standards YY0634-2008 for fundus imaging equipment and meet the requirements for infant retina screening.
Optical system design and stray light suppression of catadioptric space camera
LÜ BO, FENG Rui, KOU Wei, LIU Wei-qi
2020, 13(4): 822-831.   doi: 10.37188/CO.2019-0036
[Abstract](281) [FullText HTML](143) [PDF 8184KB](31)
Abstract:
A lens group is used as an aberration correction group to solve the limited field of view angle and low imaging contrast at a large field of view in the coaxial two-mirror optical system. The lens group adopts reasonable optical power and pitch, it expands the field of view of two-reflection mirrors and improves imaging quality in the camera's full field of view. Taking an engineering application as an example, we design and develop an optical system with a 750 mm focal length, a field of view of 2ω=3.45°, an average transfer function better than 0.2 at 108 lp/mm, and an optimized design for its secondary mirror hood that suppresses stray light without a main mirror barrel hood. Simulation stray light was optimized by using TracePro software. The results show that the stray light Point Source Transmittance (PST) in the non-imaging field of view ranges from 10−3 to 10−6. The system meets the requirements for traditional ground target detection and imaging, the feasibility of a compact large-field refracting optical stray light suppression structure is verified, and a certain reference for the design and optimization of commercial coaxial refracting optical systems is provided.
Non-symmetrical design of a compact, lightweight HMD optical system
HUANG Song-chao, FENG Yun-peng, CHENG Hao-bo
2020, 13(4): 832-841.   doi: 10.37188/CO.2019-0193
[Abstract](333) [FullText HTML](160) [PDF 3484KB](38)
Abstract:
In non-symmetric optical systems, the field of view is narrow, the diameter of their exit pupil is narrow, their optical structure is complicated, their cost of manufacturing is high, and assembly adjustment is troublesome. To address these problems, free-form mirror is applied in the system. The design requirements and working principle of the dual mirror non-symmetrical optical system are firstly discussed. Then, the off-axis structure control method of the three-mirror non-symmetric optical system is analyzed. Finally, the XY polynomial free-form mirror is used to fold the optical path, eliminating the obstruction, enlarging the field of view, correcting the off-axis aberration, and a non-symmetrical optical system is designed suitable for Helmet-Mounted Display(HMD). The designed dual mirror non-symmetrical optical system has a field of view of 60° × 30° and a pupil diameter of 8 mm. At a cutoff frequency of 52 lp/mm, the full field of view Modulation Transfer Function(MTF) value is greater than 0.25 and system distortion is less than 5%. This monocular system’s weight is about 190 g. The design results show that the non-symmetrical optical system has an improved field of view and image quality, it is compact and lightweight, and can be applied to a HMD.
Design of a freeform curved prism imaging spectrometer based on an anastigmatism
ZHANG Jia-lun, ZHENG Yu-quan, LIN Chao, JI Zhen-hua
2020, 13(4): 842-851.   doi: 10.37188/CO.2019-0049
[Abstract](323) [FullText HTML](204) [PDF 1481KB](26)
Abstract:
In this paper, an algorithm for calculating the initial structure of the Offner freeform curved prism imaging spectrometer with secondary mirror external reflection is designed. The ray tracing method is used to obtain the formula for the propagation of light on the optical surfaces of an Offner spectrometer with secondary mirror external reflection. The formula can determine the structural parameters of the optical component. The off-axis beam astigmatism theory commonly used in the analysis of off-axis systems is used to analyze image quality, and a reasonable threshold is set to judge the structure algorithm. The initial structure that meets the design requirements is obtained through iterative optimization in Matlab and the initial structure is optimized in Zemax. To verify the performance of the proposed algorithm, the initial structure of a free-form prism spectrometer with a spectral range of 380~780 nm, a numerical aperture of 0.15 and a spectral resolution of 6 nm is designed. After being optimized in Zemax, the system reached the design index and the spectral line bending and color distortion are both less than 0.1 pixels. The algorithm proposed in this paper can quickly calculate the initial structure such that the requirements are satisfied, and can simplify its complexity.
Algorithmic study of total petroleum hydrocarbons in contaminated soil by three-dimensional excitation-emission matrix fluorescence spectroscopy
GU Yan-hong, ZUO Zhao-lu, ZHANG Zhen-zhen, SHI Chao-yi, GAO Xian-he, LU Jun
2020, 13(4): 852-865.   doi: 10.37188/CO.2019-0216
[Abstract](909) [FullText HTML](347) [PDF 3396KB](17)
Abstract:
Assessment of Total Petroleum Hydrocarbons (TPHs) from contaminated soils demands reliable measurement to analyze the types and contents of mixed petroleum hydrocarbons in soils. Three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy has been demonstrated as a powerful technology for rapidly analyzing mixed petroleum hydrocarbons by identifying its abundant spectral information. However, detection precision in soil still demands improvement. This study investigates the correction methods of 3DEEM fluorescence spectra to correct the complicated matrix and scattering effects of soils. To improve the analytical accuracy, parallel factor analysis (PARAFAC) and the Alternating Trilinear Decomposition method (ATLD) were used to qualitatively and quantitatively analyze mixed petroleum contaminated soils. The methods were used to assess three commonly observed petroleum hydrocarbons: machine oil, lubricating oil, and diesel oil. Compared with the results of PARAFAC, the average recoveries of ATLD increased from 85% to 95%, implying that ATLD can effectively distinguish between similar fluorescence spectra and is more effective in the detection of the components and total content of petroleum in soil. This work can have applications of risk assessment and remediation techniques.
The effects of metallic contacts on the lasing characteristics of organic thin films
HAO Ya-ru, DENG Zhao-qi
2020, 13(4): 866-872.   doi: 10.37188/CO.2020-0007
[Abstract](287) [FullText HTML](120) [PDF 1242KB](15)
Abstract:
Optical loss caused by metallic contacts are thought to be a major obstacle to the achievement of organic laser diodes. We find that multi-channel emissions and Surface Plasmons (SPs) by designing a proper distributed feedback structure can allow successful lasing in organic thin films in the presence of contacting electrodes and even show better lasing performance when compared to metal-free cases. In this paper, a lower threshold (0.026 mJ/pulse) laser emission is achieved with the Ag metal electrode on the grating structure with a period of 740 nm. Since there is no increase in device thickness, the electrical properties are not reduced when the optical properties are improved.
Fabrication and characterization of ultra-thin GaN-based LED freestanding membrane
LI Xin, SHA Yuan-qing, JIANG Cheng-wei, WANG Yong-jin
2020, 13(4): 873-883.   doi: 10.37188/CO.2019-0192
[Abstract](601) [FullText HTML](339) [PDF 1097KB](19)
Abstract:
In order to deliver the emergent light of Light Emitting Diode (LED) active layer easily, we studied the fabrication process, morphological characterization and optical characterization of submicron-level LED freestanding membrane. We prepared ultra-thin GaN-based LED freestanding membrane based on GaN-on-silicon wafer by using the backside process with photolithography, deep reactive ion etching and fast atom beam etching. Through a white light interferometer, we found that the deformation of the prepared ultra-thin LED freestanding membrane is positively correlated with the diameter of membrane, but negatively correlated with the thickness of membrane. The deformation as a whole is a smooth nanoscale arch deformation. Through the reflection spectrum test, we found that the number of reflection modes of LED freestanding membrane is much smaller than that of unprocessed silicon-based gallium nitride wafer and that the overall light intensity of reflection spectrum of the membrane is obviously improved. In the photoluminescence test, we found that due to the stress release, the emergent spectral peak of LED freestanding membrane has a blue shift of 8.2 nm compared with silicon-based gallium nitride wafer. Moreover, obvious outgoing light can be detected on the backside of the ultra-thin LED freestanding membrane with most of epitaxial layer removed. It demonstrates that LED freestanding membrane is more beneficial to deliver the emitted light in the photoluminescence test. In this study, the LED freestanding membrane with small thickness, large area, small deformation and excellent optical properties has been realized. It provides a new way for the application of GaN-based LED in the field of Micro-Optical Mechanic Electronic System (MOMES).
Influence of turbulent atmosphere on the effect of coherent beam combining
SONG Ji-kun, LI Yuan-yang, CHE Dong-bo, GUO Jin, WANG Ting-feng, LI Zhi-lai
2020, 13(4): 884-898.   doi: 10.37188/CO.2019-0197
[Abstract](1194) [FullText HTML](863) [PDF 4000KB](21)
Abstract:
Coherent beam combining is a promising technology for achieving a high-power laser beam with good beam quality. However, turbulent atmosphere is one of the key factors that restrict its application and development. This paper focuses on the influence of atmospheric Greenwood frequency on the correction effect of the coherent combination system based on Stochastic Parallel Gradient Descent (SPGD) algorithm. At first, the influence of different turbulence intensities on the correction effect of coherent combination systems is analyzed by numerical simulation under static atmospheric conditions. Then, a set of rotating phase screens that meet Kolmogorov’s statistical law are generated by numerical calculation to simulate the turbulent atmosphere and study the correction effect of coherent combination system at different atmospheric Greenwood frequencies. Finally, an experimental platform is established to demonstrate the coherent combination effect of two laser beams. The simulated and experimental results show that when the system's control algorithm iteration frequency (350 Hz) is constant, the disturbance of turbulent atmosphere to the phase and light intensity of laser beams will increase with atmospheric Greenwood frequency, making the effect of coherent combination worse.
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(613) FullText HTML(246) PDF 1212KB(60)
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(443) FullText HTML(240) PDF 8130KB(46)
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(333) FullText HTML(197) PDF 4354KB(32)
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(141) FullText HTML(68) PDF 1380KB(24)
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(1629) FullText HTML(692) PDF 2774KB(133)
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
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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(1266) FullText HTML(686) PDF 4890KB(67)
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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(837) FullText HTML(435) PDF 2481KB(34)
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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(1078) FullText HTML(635) PDF 4222KB(58)
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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(1433) FullText HTML(872) PDF 2768KB(112)
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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(875) FullText HTML(512) PDF 8834KB(64)
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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(1011) FullText HTML(543) PDF 6598KB(50)
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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(841) FullText HTML(398) PDF 4338KB(40)
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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.
Research progresses of planar super-oscillatory lenses for practical applications
LI Wen-li, YU Yi-ting
2019, 12(6): 1155-1178.   doi: 10.3788/CO.20191206.1155
Abstract(189) FullText HTML(70) PDF 14797KB(13)
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Due to the diffraction limit, it is difficult to achieve far-field super-resolution focusing and imaging for traditional optical systems. The appearance of planar superlenses based on the super-oscillation principle provides a possible solution to the problem. It can achieve far-field super-resolution focus without using evanescent waves. By precisely adjusting the diffraction and interference effects among the diffractive elements, electric field oscillation that is higher than the highest spatial frequency of the system can be measured in the local area of the focal plane, and thus the transverse and axial sizes of the diffractive focal spot can be precisely controlled. Compared with conventional optical lenses, planar Super-Oscillatory Lenses(SOLs) hold advantages for their arbitrary control over the optical field, large degree of freedom in design and easy integration with optical systems. Due to the above-mentioned reasons, SOLs have attracted extensive attention from researchers in the fields of diffractive optics and micro-nano optics. In this paper, concerning practical applications, the research state-of-the-art and application scenarios of planar SOLs are presented and discussed. Finally, the system's problems and its corresponding solutions are also described.
Review on progress of variable-focus liquid lens
HUANG Xiang, LIN Si-ying, GU Dan-dan, BU Zhen-xiang, YI Wei-jin, XIE Pei-qin, WANG Ling-yun
2019, 12(6): 1179-1194.   doi: 10.3788/CO.20191206.1179
Abstract(201) FullText HTML(64) PDF 5581KB(15)
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Compared with the traditional mechanical zoom lens, the variable-focus liquid lens has a smaller lens, faster response time, lower cost and higher integration capabilities. These lenses are widely used in image acquisition, target tracking and feature recognition. The performance and applications of liquid lenses are determined by the focal length adjustment method. This paper summarizes the progress of liquid crystals, dielectrophoresis, electrochemistry, electrowetting principle-based function control variable-focus lenses, electrostatic force, electromagnetic force, pressure regulation, and environmental-response-technology-based mechanical driven variable-focus lenses. The integrated applications of variable-focus liquid lenses in optofluidic chips are introduced. Also, the major obstacles and the settlement are described. Furthermore, the development potential and future research direction of the variable-focus liquid lens are also predicted and summarized.
Spectroscopic ellipsometry and its applications in the study of thin film materials
ZHU Xu-dan, ZHANG Rong-jun, ZHENG Yu-xiang, WANG Song-you, CHEN Liang-yao
2019, 12(6): 1195-1234.   doi: 10.3788/CO.20191206.1195
Abstract(658) FullText HTML(77) PDF 11094KB(19)
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Spectroscopic ellipsometry is used to measure the relative amplitude and phase change of linearly polarized light reflected by a material surface, so as to obtain the ellipsometric parameters. The optical properties of a material can be deduced by fitting these parameters. This technique is advantageous for being non-contact, highly sensitive, non-destructive, so it is widely used in physics, chemistry, materials science and microelectronics, etc, being an indispensable optical measurement method. This article first introduces the development history of the technology, and then presents the basic principle of the traditional ellipsometer. According to different measurement principles, ellipsometers can be divided into two types:extinction and photometric. The basic structure, measurement principle and related application of these two different types of ellipsometer are briefly clarified. After comparing these various ellipsometers, their advantages and disadvantages are introduced. At this point, a double Fourier transform infrared ellipsometry system developed by Fudan University is highlighted. Then, according to the basic steps of ellipsometric parameter manipulation, a measurement, modeling and fitting process is introduced. The equations of various optical dispersion models used for parameter fitting are introduced in detail and application examples are illustrated. Finally, the future development direction of spectroscopic ellipsometry is proposed.
Research progress in optical methods for noninvasive blood glucose detection
GUO Shuai, SU Hang, HUANG Xing-can, LIU Jian
2019, 12(6): 1235-1248.   doi: 10.3788/CO.20191206.1235
Abstract(434) FullText HTML(162) PDF 2348KB(13)
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Continuous monitoring of blood glucose levels is a prerequisite for controlling diabetes and its complications. Noninvasive methods have attracted great attention for their lack of injury and widespread acceptance. With the improvement of measurement accuracy in recent decades, optics-based methods of noninvasive blood glucose detection have shown great potential in clinical applications. In this paper, the main optics-based methods of noninvasive blood glucose detection, such as polarimetry, optical coherence tomography and infrared spectroscopy, are reviewed with regards to their principles, advantages, accuracy, problems and the possible solutions to those problems. By comparison, it concludes that the method of infrared spectroscopy has obvious advantages in detection accuracy. In the future, major challenges will be in increasing the signal-to-noise ratio of instruments, eliminating background interference and establishing universal calibration models.
Research progress of remote detection with ultraviolet Raman spectroscopy
HE Yu-qing, WEI Shuai-ying, GUO Yi-xin, ZHAO Man, JIN Wei-qi, REN Lin-mao
2019, 12(6): 1249-1259.   doi: 10.3788/CO.20191206.1249
Abstract(258) FullText HTML(86) PDF 1488KB(7)
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Ultraviolet Raman spectroscopy is a relatively effective and promising method for the detection of long-distance dangerous items. It has broad applications in the fields of anti-terrorism, drug control and food safety. Based on an analysis of the basic principles of Raman spectroscopy remote detection, this paper summarizes the advantages of ultraviolet Raman detection technology and comprehensively analyzes its research status. The module's design methods, key techniques and existing problems are analyzed from the perspective of laser emission, optical receiving system, spectral reception and spectral processing. The research difficulties and development trends of remote detection technology with ultraviolet Raman spectroscopy are summarized.
Progress of research on satellite-borne laser communication technology
DONG Quan-rui, CHEN Tao, GAO Shi-jie, LIU Yong-kai, ZHANG Yu-liang
2019, 12(6): 1260-1270.   doi: 10.3788/CO.20191206.1260
Abstract(771) FullText HTML(114) PDF 3842KB(35)
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In this article we explain the advancement and importance of spaceborne laser communication comparing with traditional microwave communication, introduce the basic components of laser communication systems, and briefly describe the working process of the system. After that, the foreign satellite-borne laser communication projects and development plans are summarized, focusing on the research status of satellite-borne laser communication in Japan, the United States and Europe in recent years. Besides, we also concisely describe the research progress in domestic universities and research institutes and point out the difficulties of current spaceborne laser communication and summarize the key technologies related to it. Finally, the future of the development of spaceborne laser communication is prospected.
Research and development of medium/high volume fraction SiCp/Al composites
CHENG Si-yang, CAO Qi, BAO Jian-xun, ZHANG Ge
2019, 12(5): 1064-1075.   doi: 10.3788/CO.20191205.1064
Abstract(196) FullText HTML(53) PDF 2208KB(5)
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Compared to traditional alloys, medium/high volume fraction SiCp/Al composites offer tailorable mechanical and thermophysical properties that could be beneficial for a variety of applications. In this paper, the main fabrication methods and applications of medium/high volume fraction SiCp/Al composites in precision instruments, optical systems, electronic packaging and thermal control are reviewed and summarized. Finally, the future development strategy of medium/high volume fraction SiCp/Al is proposed.
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(1760) FullText HTML(437) PDF 2700KB(49)
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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(725) FullText HTML(371) PDF 4295KB(87)
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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(1365) FullText HTML(486) 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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