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Research progress on nonlinear optics of poly(vinylidene fluorid) and its copolymers films
LIU Yong, LIU Wei-guo, NIU Xiao-ling, HUI Ying-xue, DAI Zhong-hua, WANG Zhi-heng, GUO Wen-hao
 doi: 10.37188/CO.2021-0191
Abstract(0) FullText HTML(0) PDF 2494KB(0)
Poly vinylidene fluoride (PVDF) and its copolymers films have been extensively used in photoelectric functional devices such as photoelectric conversion, optical regulation, optical switch ,which are the most important polymeric ferroelectricity materials with excellent electro-active properties, high diffraction efficiency and significant nonlinear optical effect. This article summarizes the progress in nonlinear optical effect of poly(vinylidene fluoride) and its copolymers films both in domestic and foreign research within the last several years.It illustrates the development direction of the films will be nanoscale-doping ,blending modification and ultra-thin.The nonlinear optical properties should be investigated by the first-principle and photonic band gap calculations,and measured by the means of the high sensitivity Z-scan ,Marker fringe combing with ellipsometry.This study may provide an insight for the development and utilization for poly(vinylidene fluoride) and its copolymers films in future .
Alignment method of plane reflecting mirror system for aerial remote sensor
ZHANG Jian, WANG Jian-fei, FANG Xin, SONG lai-yun, LIU Shao-ming, WANG Xue
 doi: 10.37188/CO.2021-0187
Abstract(0) FullText HTML(0) PDF 3727KB(0)
It is a common design method to reduce the volume and mass of aerial remote sensor by using the plane mirror to turn the light path. However, the introduction of the plane mirror puts forward higher requirements for the alignment of the aerial remote sensor. This paper introduces an alignment method for plane mirror system of an aerial remote sensor. The mathematical model of theodolite measurement is established by the coordinate transformation method, and the corresponding relationship between the angular deviation (pitch deviation and azimuth deviation) of single plane mirror assembly and plane mirror system and the measured value of theodolite is deduced. Then a method of measuring and adjusting the angle deviation of plane mirror system with theodolite is proposed. Finally, the pitch angle deviation and azimuth angle deviation between the lens optical axis and the normal of the focal plane mounting surface meet the index requirements of no more than 2'. More than 10 sets of aerial remote sensor plane mirror systems have been aligned by using this method, which is convenient and efficient. At the same time, this method can provide a solution for the angle calibration and alignment of plane mirror in various optical instruments.
Study on Si impurity induced quantum well intermixing
WANG Yu-xiao, ZHU Ling-ni, ZHONG Li, KONG Jin-xia, LIU Su-ping, MA Xiao-yu
 doi: 10.37188/CO.2021-0200
Abstract(8) FullText HTML(2) PDF 3571KB(0)
Catastrophic optical mirror damage (COMD) on the cavity surface is one of the main factors that restricts the output power and reliability of semiconductor lasers. Quantum well intermixing technology is one of the most commonly used methods to solve COMD. In this paper, Silicon dielectric layer is used as the diffusion source for the study of Silicon impurity induced disordering with the method of annealing in a tube furnace. The effects of the dielectric film thickness, annealing conditions, quantum barrier material and sacrificial layer material on the wavelength blue shift of InGaAs/GaAs(P) quantum wells were analyzed. The wavelength blue shift of the InGaAs/GaAsP structure is 70.5 nm under 780 ℃ annealing temperature at a duration of 10 hours. GaAsP bariier structure has a larger blue shift than that of GaAs-barrier. Besides, epitaxial layer with an InGaP sacrificial layer has a larger blue shift than the AlGaAs sacrificial layer.
Optimal design of variable cross-section compression-bending ellipsoidal cylindrical mirror
LI Tong, WANG Nan, ZHU Wan-Qian, REN Zu-Yang, JIN Li-Min, XUE Song
 doi: 10.37188/CO.2021-0179
Abstract(14) FullText HTML(2) PDF 3146KB(0)
  Objetive  In order to meet the needs of the station project under construction, the project of variable cross-section bending ellipsoidal cylindrical mirror was proposed.   Method  This scheme is based on the design theory of variable-width bending elliptical cylindrical focusing mirrors, deduces the calculation formula of the slope error of the variable-section (with sagittal focus) mirror, and optimizes the design. This project is designed based on the optical parameters of the focusing lens (object distance p, image distance q and grazing incidence angle θ),   Result  The results show that under this requirement, the optimal widths at both ends of the mirror are 49.5 mm and 90.5 mm. After calculating, simulating and optimizing the bending moments at both ends of the mirror, the slope error RMS value is reduced from ~5.1368 μrad To ~0.0636 μrad (take 1 m length),   Conclusion  Close to the system error (~0.0407 μrad), meeting the design requirements.
Staticaberration correction technique for adaptive optics system based on focal-plane copyapproach
ZHANG Tian-yu, WANG Gang, ZHANG Xi, DOU Jiang-pei
 doi: 10.37188/CO.2021-0183
Abstract(8) FullText HTML(2) PDF 4949KB(0)
A key factor limiting the performance of the adaptive optics system is the non-common path aberration (NCPA) caused by the difference between wavefront sensor path and science image path, and the static aberration will inevitably be introduced in the common path of AO system at the same time. Therefore, this paper proposes a correction technology based on the copy of focal-planepoint spread function (PSF) to eliminate static aberration in scienceimage path of AO system.This technology uses the PSF generated by the laser point light source as the reference PSF, and copies the reference PSF to the science image path of the AO system through iterative optimization algorithms.Experimental results show that theStrehl Ratio (SR) is increased from the initial 0.312 to 0.995 after correction. This technology canstillobtain the global optimization resultsstablyandquickly,especially when the initial static aberration of the system is large.
Electrically controlled polarization rotator based on liquid crystal optical waveguide
ZHA Zheng-tao, ZHANG Qian-shu
 doi: 10.37188/CO.2021-0213
Abstract(1) FullText HTML(0) PDF 3893KB(0)
In this study, the gradient characteristic of field-induced reorientation of nematic liquid crystal was considered to analyze the polarization conversion length (PCL) and polarization conversion efficiency (PCE) of electronically controlled polarization rotator based on liquid crystal optical waveguide more accurately. Firstly, according to the eigenvalue equation obtained from the liquid crystal magnetic field coupling equations, the corresponding relationship between PCL and the applied voltage was constructed. Then the explicit expression of the iterative equations of alternating direction implicit beam propagation method (ADI-BPM) was obtained by transverse finite-difference discretization of the electric field transmission equation, which was used to solve the propagation field in the liquid crystal optical waveguide and calculate the PCE. Finally, the eigenmode and propagation field are solved through a simulation experiment, and then the effects of the gradient characteristics of liquid crystal director on PCL and PCE are analyzed. The results show that the effect of the gradient of the liquid crystal director on the PCL can be ignored, but the maximum PCE is about 20% lower than that of the uniform reorientation of the liquid crystal. This result will provide a certain theoretical reference for the practical development of an electronically controlled polarization rotator based on a liquid crystal optical waveguide.
Non-contact perception of physiological parameters from videos of faces
JI Xiao-qiang, LIU Zhen-yao, LI Bing-lin, RAO Zhi, LI Gui-wen, SU Li-wei
 doi: 10.37188/CO.2021-0157
Abstract(67) FullText HTML(46) PDF 4256KB(7)
Non-contact detection of various physiological parameters in daily life. In this paper, a method of estimating physiological parameters based on imaging photoplethysmography from videos of people’s faces recorded by mobile phone is proposed. First, a "wavelet transform-principal component analysis-blind source separation" algorithm is proposed to extract the video’s RGB three-channel pulse wave signal with a high signal-to-noise ratio. Then, the green channel signal is processed separately in the frequency and the time domains to estimate heart and respiratory rates. The pulse wave signals of the red and blue channels are processed and combined with the oxygen saturation detected by an oximeter to perform data fitting, and the best linear equation for estimating the oxygen saturation value from the facial video is found. Finally, the error of the estimation results of various physiological parameters under natural light is compared, and the estimation results of each parameter under three lighting environments are analyzed. The results show that under the three lighting environments, the average error of heart rate detection is 0.5512 bpm , the average error of respiration rate is −0.6321 brpm , and the average error of oxygen saturation is −0.2743%. In summary, the non-contact physiological parameter estimation method proposed in this paper is highly accurate, universally applicable and stable. Its estimation results are highly consistent with the measurement result of standard instruments, which meets the needs of daily physiological parameter measurement.
Iterative solution of underwater scattering light field
HE Da-hua, LI Yang-yang, ZHOU Shao-jie
 doi: 10.37188/CO.2021-0162
Abstract(42) FullText HTML(7) PDF 5071KB(5)
The scattering of light by water is an important factor in the deterioration of underwater image quality. In order to quantitatively analyze the influence of water scattering under the irradiation of a specific light source, the scattering model of underwater light transmission is established, and the Fredholm integral equation for solving the distribution of underwater light field is derived. Under conditions where the light energy underwater decays exponentially with an increase in distance and the volume scattering function of the water is constant, the numerical iterative solution method of the integral equation with boundary conditions is given and the high-precision underwater light field distribution can be obtained. Taking the sun, uniform sky brightness, and underwater and overwater point light sources as examples, the calculation results of their underwater light fields when the water surface is calm are given. This method can be extended to solve the distribution of underwater light fields under arbitrary light source configurations and arbitrary boundary conditions, which lays a foundation for strictly deriving a point spread function and modulation transfer function for water bodies.
Research progress of terahertz super-resolution imaging
CAO Bing-hua, ZHANG Yu-meng, FAN Meng-bao, SUN Feng-shan, LIU Lin
 doi: 10.37188/CO.2021-0198
Abstract(14) FullText HTML(2) PDF 3214KB(0)
Terahertz (THz) imaging technology is one of the most cutting-edge technologies in many fields recently, and has made great progress in the development of recent two decades. With the increasing demand of scientific research, medical treatment, military and industrial applications, high-resolution THz images become indispensable. In order to obtain high-resolution THz images, super-resolution imaging have become a research hotspot. Firstly, the imaging methods of a THz system are reviewed, including continuous wave imaging and pulse wave imaging. On this basis, THz super-resolution imaging systems and THz signal processing technologies are introduced in detail. The super-resolution imaging system includes near-field imaging, super lens and terajet effect, etc. The THz signal processing technologies basically could be identified as: super-resolution reconstruction and convolution calculation. Finally, the shortcomings of current super-resolution imaging are discussed. There are still some bottlenecks that need to be resolved, such as the high manufacturing process requirements of the system, the slow acquisition speed, and low resolution of the learning samples used to reconstructed the image. On this analysis, the research direction of super-resolution imaging is prospected.
IR radiation characteristics of high-altitude off-orbit engine plume
ZHENG Hong-ru, MA Yan, FAN Lin-dong, REN Xiang
 doi: 10.37188/CO.2021-0232
Abstract(10) FullText HTML(2) PDF 1547KB(0)
When a hypersonic vehicle maneuvers at a high Angle of attack, the jet generated by its off-orbit engine interferes strongly with the high-speed thin atmospheric flow, and the flow field is complicated. The infrared radiation generated by the flow field is also a landmark event of space-based infrared system detection. In this paper, aiming at the hypersonic flight vehicle engine and thin flow interference situation, Navier-Stokes equations are numerically solved to simulate the interference flow field, and infrared radiation characteristics of gas are obtained by line-by-line integration method, combined with the backward Monte Carlo method. The aircraft flight altitude is 94 kilometers, cases of no wind, different incoming flow attack angle and velocity are considered, and the observability of low orbit satellites is evaluated. The simulation results show that for a given observation position, the intensity of infrared radiation in each band is low under the condition of no wind, and the maximum value is 10−9 W/m2. Under the influence of incoming flow attack angle, the infrared signal intensity of flow field increases significantly, the greater the attack angle and velocity, the greater the intensity, and the maximum value is 10−6 W/m2. Atmospheric attenuation effect has great influence on observability of different observation positions. The results can provide reference for infrared warning and anti-missile of hypersonic vehicle.
Research on photonics generation of broadband millimeter wave noise signals with high excess noise ratios
HUANG Hai-bi, LIU Wen-jie, SUN Yue-hui, WANG An-bang, QIN Yu-wen, WANG Yun-cai
 doi: 10.37188/CO.2021-0158
Abstract(57) FullText HTML(13) PDF 3698KB(4)
The Excess Noise Ratio (ENR) of traditional noise sources is usually less than 20 dB due to the limitation of the working frequency and the power of electronic devices. To solve the problem, this paper proposes a technology to generate a millimeter-wave noise source with a high ENR by two incoherent light beams beating. First, two optical filters are used to filter and shape the broadband amplified spontaneous emission light source. Then, the two obtained beams of amplified spontaneous radiation light with different frequencies are coupled to the photodetector for the beat frequency, which can generate electrical noise signals. A theoretical analysis predicts that a noise source with an ENR larger than 50 dB can be obtained by adjusting the optical spectral, linewidth and optical power of the two incoherent light beams filtered from an amplified spontaneous emission source under the current level of photodetector responsivity. A proof-of-concept experiment achieved a millimeter-wave noise source with an ENR higher than 50 dB. This method could also generate millimeter-wave and even terahertz-wave noise with a high ENR if a higher-speed photodetector was used.
Blade reflection suppression technology based on surface structured light on machine detection
LI Mao-yue, LIU Ze-long, ZHAO Wei-xiang, XIAO Gui-feng
 doi: 10.37188/CO.2021-0194
Abstract(11) FullText HTML(2) PDF 4187KB(1)
In the process of structured light detection, the thin-walled blade is easy to produce strong reflection due to its small surface roughness, which affects the solution of the principal value of fringe phase, so it can not accurately reconstruct the three-dimensional point cloud. In this paper, the blade in the machining process is taken as the research object, and an image enhancement processing based on Retinex algorithm is proposed to restore the information of stripes in the high reflective position. Firstly, the reflective characteristics of thin-walled blades are analyzed. The gray range and ideal gray value of the optimal exposure are calibrated by experiments. The camera response curve model of aperture rotation angle and image average gray level is established, and the gray level interval of the optimal exposure is used as the detection condition by adjusting the aperture and exposure time. Secondly, the fringe image is processed based on Retinex algorithm. The improved bilateral filter replaces the commonly used Gaussian filter, which effectively retains the edge information of the fringe while removing the illumination. Finally, the monocular structured light detection is carried out on the thin-walled blade. The experimental results show that, for the fringe image processed by this proposed algorithm, the number of stripes detected by Canny operator is the largest, the average growth rate of image information entropy is 18.21%, the phase principal value error of the solution is the smallest. Through the deviation analysis with the standard point cloud detected by the handheld laser scanner, the positive and negative deviations of the point cloud are reduced to 0.0589 mm and −0.0590 mm, which are reduced by 44.6% and 44.1% respectively compared with the deviation of the origin cloud, and the surface quality is significantly improved. The image enhancement algorithm proposed effectively suppresses the reflection of metal surface in the process of surface structured light detection.
Method and Device for Testing Stray Light Characteristics of Digital Micro-mirror Devices (DMD)
YAO Xue-feng, GAO Yi, LONG Bing, Yu Chenyang, LI Wen-hao, YU Hong-zhu, ZHANG Jing, LI Xiao-tian
 doi: 10.37188/CO.2021-0132
Abstract(142) FullText HTML(48) PDF 5342KB(15)
  Objetive  In order to obtain the true optical characteristics of a Digital Micro-mirror Device (DMD), a test method for the stray light distribution of the micro-mirror unit was proposed and an experimental device was built to test the stray light distribution of a micro-mirror unit in the 2×2 array area.  Method  First, a stray light test method is proposed. Then, in view of the small size of the micro-mirror unit and the flexible configuration mode, an illumination system with a continuously adjustable convergent spot size and an imaging system that can clearly image the micro-mirror unit was designed. Finally, the stray light distribution of the micro-mirror unit in the 2×2 array area was obtained through experimentation.  Result  The test results show that the reflection energy near the center channel of a single micro-mirror unit is strong, while the reflection energy near the edge is relatively weak. In addition, the micro-mirror unit also reflects part of the energy outside the test area. The maximum absolute stray light intensity of the micro-mirror unit in the test area appears near the central channel, and its gray value is 6.86. The maximum absolute stray light intensity of the micro-mirror unit close to the test area also appears near the central channel, and its gray value is 4.01, which indicates that the stray light near the central channel is strong. The relative intensity of stray light in the test area is relatively weak, which increases sharply from the edge of the test area and reaches a peak value of 293.5% after about two micro-mirror units, and then decreases sharply.   Conclusion  The above research results can play a guiding role in the development of various instruments using DMD in the future.
Common failure modes and mechanisms in oxide vertical cavity surface emitting lasers
ZHANG Yu-qi, ZUO Zhi-yuan, KAN Qiang, ZHAO Jia
 doi: 10.37188/CO.EN.2021-0012
Abstract(134) FullText HTML(58) PDF 7512KB(32)
Oxide Vertical Cavity Surface Emitting Lasers(VCSELs) are widely used in high-speed optical communications. The reliability of VCSELs is a very important index which requiring a high lifetime and low failure rate in the application process. Understanding the root causes and mechanisms of VCSEL fails is necessary and helpful to improve device reliability. In this paper, we summarize and analyze the most common failure modes, causes and mechanisms observed in oxide VCSELs from three main aspects of design, manufacturing and application, and some appropriate measures and suggestions are applied to prevent or improve them. Moreover, the three dominating factors leading to the failure of VCSELs including oxide layer stress, ESD and humidity corrosion are introduced in more detail. This article can be used as a good VCSEL failure analysis library for chip development and production researchers. At finish, we will simply introduce the VCSEL failure cases encountered in the actual accelerated aging verification process for more references.
Design of automatic image measuring system
FENG Qi-yin, QIU Guo-hua, YAN De-xian, Li Ji-ning, Li Xiang-jun
 doi: 10.37188/CO.2021-0174
Abstract(16) FullText HTML(5) PDF 5468KB(1)
A wide-band and narrow-band switchable dual-functional metamaterial absorber is presented in this paper. The phase change material vanadium dioxide (VO2) is introduced, and different functions can be achieved by using only a single switchable metasurface. The mutual conversion of different functions is realized by the reversible phase transition between the VO2 insulating state and the metal state. When VO2 is in metallic state, the designed structure can be regarded as a metamaterial broadband absorber. The simulation results show that the absorption is over 98% in the frequency range of 1.55 THz to 2.21 THz. When VO2 is in the insulating state, the structure acts as a narrow band absorber, and the absorption at resonance frequencies of 2.54 THz, 2.93 THz and 3.34 THz is over 95%. In addition, the effect of geometric parameters on the absorption of metamaterial absorber is discussed. Because of the symmetry of the element structure, the absorber is insensitive to the polarization when the electromagnetic wave is vertically incident, and it can keep good absorption performance with the large incident angle. Therefore, the switchable dual-functional metamaterial absorber proposed in this paper can be widely used in terahertz modulation, thermal emitters and electromagnetic energy acquisition, etc.
Aberration coupling characteristics of axial and lateral misalignments of off-axis three-mirror telescopes
BAI Xiao-quan, GUO Liang, MA Hong-cai, XU bo-qian, JU Gou-hao, XU Shu-yan
 doi: 10.37188/CO.2021-0164
Abstract(29) FullText HTML(8) PDF 10681KB(6)
To ensure the imaging quality of the off-axis three-mirror space telescope during the ground adjustment and on-orbit adjustment stages, this paper uses the Nodal aberration theory to reveal the coupling characteristics of the axial misalignment and the lateral misalignment on aberration from the internal mechanism level. This paper focuses on the compensation relationship generated by the coupling characteristics of two types of misalignments: (1) Axial misalignment compensates for lateral misalignment, which reveals a type of working condition where the system image quality may be at a local extreme during the alignment process on the ground. (2) Lateral misalignment compensates for axial misalignment. A compensation strategy wherein astigmatisms and comas introduced by lateral misalignment can compensate for astigmatisms and comas induced by axial misalignment is proposed (defocus cannot be corrected) in orbit. Taking the off-axis three-mirror system in the laboratory as an example, the accuracy of the analytical relationships can be verified. Simulations and experiments have proven that the imaging quality of the system may reach the diffraction limit (1/14λ), but the system’s image quality is at a local minimum in the presence of axial and lateral misalignment. When the telescope is misaligned in orbit and the defocus is small, the system image quality can be corrected by properly aligning the lateral misalignment first. The RMS wavefront error after compensation changes less than 0.03λ compared with the design state (the best state of installation and alignment).
Analysis of photoelectric characteristics and performance of a light-damaged schottky perovskite detector
QU Jia-yi, WANG Yun-peng, SUN Jun-jie, CHEN Fei, ZHAO Dong-xu, TIAN Can-can
 doi: 10.37188/CO.2021-0196
Abstract(21) FullText HTML(7) PDF 4786KB(3)
To understand the effects of femtosecond lasers on the optical performance of the photodetectors, the damage characteristics of a CsPbBr3 back-to-back Schottky photodetector irradiated by femtosecond pulses and its photoelectric performance under various laser energy densities were evaluated. A CsPbBr3 microcrystal film on the ITO interdigital electrode was deposited by chemical vapor deposition and a back-to-back Schottky type all-inorganic perovskite photodetector was prepared. The CsPbBr3 photodetector was irradiated with a Ti:Sapphire femtosecond laser with a pulse width of 35 fs. The damage morphology of the CsPbBr3 polycrystalline film was observed using a microscope under different laser energy densities, and the photoelectric performance of the Schottky-structure perovskite photodetector after damage from different energy densities was evaluated. Results suggest that the damage threshold of the self-made all-inorganic metal halide Schottky photodetectors is high at 2.1 W/cm2, and when the sample is slightly damaged, the photoelectric characteristics of the sample are improved to a certain extent as the spectral responsivity is broadened by 50 nm. As part of the film is heated off, the sample still maintains a certain level of detection performance.
Infrared dim small target detection based on visual saliency and local entropy
ZHAO Peng-peng, LI Shu-zhong, LI Xun, LUO Jun, CHANG Kai
 doi: 10.37188/CO.2021-0170
Abstract(21) FullText HTML(13) PDF 3236KB(11)
  Objective  To improve the high false-alarm rate and poor real-time capability in detecting infrared small dim targets, a novel algorithm based on visual saliency and local entropy is proposed in this paper.   Method  This method solves the problem of detecting coarse and fine small targets. First, a local entropy method is used to obtain the region of interest. Then, an improved visual saliency method is used to calculate local contrast. Finally, a threshold segmentation method is used to extract dim infrared small targets.   Result  : The method is verified using a contrast test with TOPHAT and LCM, and the results show the performance of this method precedes the TOPHAT algorithm and LCM algorithm. The false alarm rate of this method decreases to 62.5% and 33.3% compared with the two other algorithms, and the time cost decrease to 38.6% of that of LCM.   Conclusion  The method can achieve accurate detection of infrared dim and small targets in a complicated environment, solving the high false alarm rate and poor real-time capability issues to some extent.
High-performance self-powered photodetectors based on the carbon Nanomaterial/GaAs vdW heterojunctions
HUO Ting-ting, ZHANG Dong-dong, SHI Xiang-lei, PAN Yu, SUN Li-jie, SU Yan-jie
 doi: 10.37188/CO.2021-0149
Abstract(114) FullText HTML(45) PDF 4736KB(11)
With the advantages such as simple structure, simple process and easy interface control, the photoelectric devices based on carbon nanomaterial/bulk semiconductor van der Waals (vdW) heterojunctions can fully utilize the ultrahigh carrier mobility of carbon nanomaterials and the excellent photoelectric properties of bulk semiconductors. Especially, the novel mixed-dimensional vdW heterojunctions with atomic-level interfaces, whose bandgaps are matched with those of bulk semiconductors, can be formed by controlling the diameter/chirality and Fermi level of single-walled carbon nanotubes (SWCNTs). Here, we reported a self-powered broadband photodetector based on the pn vdW heterojunctions by combining (6, 5)-enriched semiconducting SWCNT film with n-type GaAs, and used graphene to reduce the probability of carrier recombination in SWCNT film and to promote the carrier transport. The experimental results suggest that the self-powered device exhibits high-sensitivity photoelectric response toward the incident photons in the 405~1064 nm range, and that the max photoelectric responsivity of 1.214 A/W and the specific detectivity of 2 × 1012 Jones could be achieved at zero bias.
Overview on point cloud super resolution technology
BI Yong, PAN Ming-qi, ZHANG Shuo, GAO Wei-nan
 doi: 10.37188/CO.2021-0176
Abstract(48) FullText HTML(27) PDF 6609KB(15)
With the development of the computer vision technology, the research on recording and modeling the real world accurately and efficiently has become one of the key issues. Due to the limitation of hardware, the resolution of the point cloud is usually low, which cannot meet the needs of application. Therefore, it is necessary to study the super-resolution technology of point cloud. This paper sorts out the significance, progress, and evaluation methods of point cloud super-resolution technology, introduces the classical super-resolution algorithm and the super-resolution algorithm based on machine learning, summarizes the characteristics of the current methods, and points out the main problems and challenges in the current point cloud data super-resolution technology. Finally, the future direction in point cloud super-resolution technology is proposed.
Averaged intensity and spectral shift of partially coherent chirped optical coherence vortex lattices in biological tissue turbulence
KE Cheng, ZHU Bo-yuan, SHU Ling-yun, LIAO Sai, LIANG Meng-ting
 doi: 10.37188/CO.EN.2021-0010
Abstract(55) FullText HTML(31) PDF 1216KB(5)
Averaged intensity and spectral shift of partially coherent chirped optical coherence vortex lattices (PCCOCVLs) in biological tissue turbulence are investigated, where optical lattice structures in monochromatic optical field and spectral rapid transitions in polychromatic optical field are stressed. It is found that the beam profile evolves from annular structure with vortex core into a periodic array of lobes with dark zone, and it finally present a Gaussian-like pattern in biological tissue. Although lattice parameter modulates beam profile, it cannot affect spectral behavior in biological tissue turbulence. The analysis of spectral shift also shows that a smaller distance is beneficial to spectral rapid transition, where the transverse coordinate decreases with an increase of chirp parameter and a decrease of pulse duration. The accumulated turbulences in a longer distance can suppress not only spectral transition, but spectral shift. The reduction of spectral shift is accompanied by a stronger biological tissue turbulence. The results have the application possibility in image recognition, medical device and noninvasive optical diagnose in biological tissue.
Luminescence enhancement mechanism of Er3+ ion by Ag@SiO2 core-shell nanostructure in Tellurite glass
CHEN Xiao-bo, LI Song, ZHAO Guo-ying, LIU Hong-Zhen, GUO Jing-hua, MA Yu, WANG Ke-zhi, GENG Zhu-feng
 doi: 10.37188/CO.2021-0142
Abstract(63) FullText HTML(24) PDF 1251KB(6)
In present manuscript, we introduce the prepared Ag@SiO2 nanostructure directly into tellurite luminescence glass 70TeO2-25ZnO-5La2O3-0.5Er2O3. We find that the maximum enhancement of visible and infrared excitation spectra intensity of (A) Ag(1.6×10−6 mol /L)@SiO2(40 nm) @Er3+(0.5%):tellurite glass relative to (B) Er3+(0.5%):tellurite glass is about 149.0% and 161.5% respectively. Their maximum enhancement of visible and infrared luminescence spectra intensity is 155.2% and 151.6%, respectively. We also find that sample (A) has a large increase for lifetime compared with sample (B). Because surface plasmon absorption peak of Ag@SiO2 is located just at 546.0 nm, it completely resonates with the luminescence peak of erbium ion at 546.0 nm. Therefore, the resonance enhancement action of Ag@SiO2 on the luminescence of erbium-doped tellurite luminescence glass is obvious. The Ag@SiO2 nano core-shell structure studied in present paper is pre-fabricated in advance. Thanks to advantages of the step-by-step realization of the silver nano core-shell structure and the production of glass: it can successfully smoothly control the size of Ag@SiO2, it also has the advantage of strong operability in the manufacturing process of Ag@SiO2@Er:telluride luminescence glass. It also has the advantages of low price and minor cost. Moreover, it can not only ensure that the silver is not oxidized, but also it can successfully control the distance between the rare earth ion luminescence center and the silver surface plasma, and it can also successfully reduce the back energy transfer, therefore which promotes the silver surface plasma to more effectively enhance the intensity of photo-luminescence. These results are of great significance for enhancing the luminescence intensity of rare earth luminescent materials and promoting their wider application prospects.
Study on the damage characteristics of 532 nm picosecond pulse laser to monocrystalline silicon
WANG Jia-min, JI Yan-hui, LIANG Zhi-yong, Fei Chen, ZHENG Chang-bin
 doi: 10.37188/CO.2021-0160
Abstract(89) FullText HTML(24) PDF 4758KB(13)
With the development of optoelectronic countermeasures and ultrashort pulse laser technology, the study of the interaction between ultrashort pulse laser and monocrystalline silicon has very important theoretical and practical significance. However, there are few reports about the damage effect of 532 nm picosecond pulse laser on monocrystalline silicon. Therefore, in order to further clarify the damage mechanism of 532 nm picosecond pulsed laser to monocrystalline silicon, we have carried out an experimental study to measure the damage threshold, clarify the damage mechanism, and discuss the pulse accumulation effect at low flux. Firstly, using a laser with a wavelength of 532 nm, a pulse width of 30 ps and a metallurgical microscope, based on the 1-on-1 laser damage test method, the zero damage probability threshold is determined to be 0.52 J/cm2.Secondly, the damage effect of picosecond laser irradiated monocrystalline silicon was studied under different laser flux, and it was found that the damage of 532 nm picosecond laser to monocrystalline silicon is manifested as heated-effect damage and plasma impact damage. The increase of energy density can be divided into three stages according to the main damage mechanism: thermal effect (0.52~3 J/cm2), thermal ablation (3~50 J/cm2) and plasma effect (>50 J/cm2), and the damage areas are corresponded to different growth laws with the laser energy density, respectively. Finally, an experiment of multi-pulse cumulative effect was carried out at low laser flux, and it was found that at a laser energy density of 0.52 J/cm2, the surface was irradiated continuously for 16 shots.The formation of a heat-affected zone confirms that the cumulative effect of multiple pulses can lower the laser damage threshold of monocrystalline silicon.
Design of optical system for quality evaluation of large rectangular aperture laser beam
PAN Guo-tao, YAN Yu-feng, YU Xin, ZHANG Lei, SUN Kuo, BAI Su-ping, SUN Hong-shen
 doi: 10.37188/CO.2021-0130
Abstract(108) FullText HTML(19) PDF 4690KB(32)
Adaptive optical correction technology can effectively improve the beam quality of solid slab lasers, but with the increase of laser output power, the output beam aperture and the system volume gradually increase, which makes the design of adaptive optical correction systems difficult. Therefore, under the premise of meeting the requirements of conjugate detection in the adaptive optical correction system, it is of certain research significance to optimize the size parameters of the detection system as a whole, and realize the detection of multiple parameters such as wavefront phase and beam quality. In this paper, we achieve the multi-parameter detection of a 160 mm×120 mm rectangular beam emitted by a slab laser when the overall size of the system is 350 mm×180 mm×220 mm (length × width × height). According to the technical requirements of large detection apertures, there are limitations in tube length and long exit pupil distance. Firstly, the dual-Gaussian initial structure was used to eliminate the aberration. Combined with the aspheric surface technology, the design scheme of splitting detection after high-ratio beam compression was adopted to achieve the simultaneous detection and evaluation of multiple parameters. Secondly, the initial parameters of the system were determined based on the principles of telephoto imaging and conjugate imaging. Thirdly, the simulation model of the detection system was established to analyze the imaging quality and the tolerance of the system, which were carried out to provide the basis for the construction of the experiment. Finally, the experiments were built to verify the design results. Results indicate that the conjugate wavefront detection, light intensity uniformity detection and beam quality evaluation of a 160 mm × 120 mm rectangular beam can be realized under the object-image conjugation and size constraint conditions. In the experiment, the β factor of the measured beam is 1.24 times the diffraction limit, and the uniformity is 73.8 %, which meets the technical requirements.
Statistical characteristics of multi-channel cooperative dynamic speckle metric
CHE Dong-bo, WANG Ting-feng, ZHANG Shao, HAN Yue, YI Yuan-yang
 doi: 10.37188/CO.2021-0152
Abstract(74) FullText HTML(29) PDF 3751KB(6)
To improve the accuracy and efficiency of dynamic speckle metric for nondestructive detecting the far-field target hit-spot intensity in target-in-the-loop (TIL) system, a multi-channel cooperative detection system for acquiring speckle signals is established. And the theory of dynamic speckles, the simulation model of this system and the spatial-temporal spectral fusion characteristics are investigated. As a first step, the power spectrum is obtained by filtering, auto-correlating and Fourier transforming the intensity fluctuations of dynamic speckle detected by the point detector. Then, the feasibility of speckle-metric, obtained by multiplying the spectrum with weights, is explored to monitor the target-focused spot. As a second step, the approach of splicing the temporal signals obtained from different spatial locations on the receiving plane is proposed. Moreover, the prerequisites of this approach are listed. Finally, the effectiveness of the proposed speckle metric obtained by fusing spectrum is verified through simulations and experiments. The results show that speckle metric decreases with the increase of the hit-spot size, and four-channel space-averaging metric can improve the accuracy by 2 times when each group of signals is uncorrelated. Besides, the metric obtained by spatial-temporal fusion spectrum not only guarantees accuracy but also increases the system bandwidth by 4 times. Therefore, the multi-channel cooperative acquisition of speckle metric can monitor the hit-spot change of far-field moving target more rapidly.
Advances in research and application of optical aspheric surface metrology
LIANG Zi-jian, YANG Yong-ying, ZHAO HONg-yang, LIU Sheng-an
 doi: 10.37188/CO.2021-0143
Abstract(161) FullText HTML(59) PDF 5699KB(36)
Optical Systems using aspheric components (especially for free-form ones) have remarkable advantages over traditional spherical systems that they can realize complicated requirements with simple optical-mechanical structure relying on abundant optional design parameters. Surface testing is an essential process for the ensurance of accuracy in manufacture. Therefore, plenty of testing methods have been developed to meet varying testing demands of different types of surface or different stages in manufacture. This paper retrospects the history of aspheric surface testing technology, classifies available techniques by the criterion of the using interferometry or not, then introduces corresponding technical indexes, applicable conditions, research progress as well as application cases.This paper highlights the high-precision interferometric methods, illustrate basic principles, optical layouts as well as testing performances of every method classified into Null and Non-null testing. The pros and cons of each method are compared, some relative algorithms are explained and precise adjustment methods of testing path are discussed.
Error correction of glass medium in high temperature digital image correlation deformation measurement
REN Ming-yang, WANG Li-zhong, FU Bai-qiang, CHEN Ren-hong, WU Hong, WANG Yan-peng
 doi: 10.37188/CO.2021-0144
Abstract(114) FullText HTML(48) PDF 4496KB(7)
In order to correct the measurement error caused by glass medium in high temperature deformation measurement, this paper takes glass medium as a part of camera calibration model. Based on photogrammetry technology and digital image correlation method, a binocular camera calibration method in complex environment is proposed and applied to high temperature deformation measurement. Firstly, aiming at the calibration difficulty caused by the poor image quality in complex environment, the camera imaging model with distortion correction is adopted to complete the binocular camera calibration by bundle adjustment camera calibration method, which improves the success rate and stability of calibration. Secondly, aiming at the problem of low calibration accuracy of binocular camera in complex environment, the influence of lens focal length, ambient light interference and the distance between glass and camera on the calibration results is analyzed, and the optimal calibration parameters are given, so that the calibration reprojection error is reduced from 0.832 pixels to 0.132 pixels. Finally, the measurement error of calibration with and without glass is compared by using the measurement environment with glass medium, which proves that this method can greatly reduce the measurement error. The test results show that this method can effectively reduce the measurement error of displacement field caused by glass medium in high temperature environment. The maximum decrease of measurement error of displacement field in X, Y and Z axes is 76.26 %, 75.02 % and 42.02%, respectively. The method in this paper can achieve high-precision camera calibration in complex environments, and has good calibration stability. It is an effective way to realize accurate measurement of high temperature deformation.
Fabrication of gold microarray electrode based on DMD lithography and electrodeposition
YANG Dong-fang, LU Zi-feng, LIU Hua, SHAN Gui-ye
 doi: 10.37188/CO.2021-0109
Abstract(43) FullText HTML(36) PDF 5919KB(10)
In order to improve the detection efficiency of micro array electrodes (MAE) and reduce the production cost, a technology combining digital micromirror device (DMD) maskless projection lithography with electrochemical deposition was proposed. Firstly, a user-defined micro structure array was fabricated by using the advantages of PZS high resolution motion and DMD flexibility. And a uniform Au micro array electrode (Au/MAE)was fabricated by electrodeposition. Then, the electrochemical properties of Au/MAE with different structures were compared by cyclic voltammetry, and the optimized structural parameters were obtained. Finally, the current response of optimized Au/MAE to glucose with different concentrations and pH values were studied, and the anti-interference of Au/MAE in glucose detection was tested by chronoamperometry. Electrochemical analysis shows that the simple Au/MAE has a significant amperometric response and strong anti-interference ability for the electrochemical detection of glucose with a sensitivity of 101 μA·cm−2·mM−1. This method has the advantages of high resolution, high consistency, simple process and low cost, which provides a feasible operation scheme for the fabrication of biosensor array.
Coaxial holographic reconstruction method of micro-milling tool pose
SUN Yi-yang, XU Jin-kai, YU Zhan-jiang, ZHANG Xiang-hui, CHENG YA-ya, YU Hua-dong
 doi: 10.37188/CO.2021-0089
Abstract(279) FullText HTML(119) PDF 4455KB(16)
When a micro-milling tool has a clamping angle on its spindle, the wear of the tool edge will accelerate and shorten the tool’s lifespan. In order to accurately observe the inclination state of the micro-milling tool on the machine, a three-dimensional pose reconstruction method based on the depth of field of a micro-milling tool is proposed. The laser coaxial digital holographic experimental device is used to obtain the micro-milling tool hologram, and the reconstruction image is obtained through the Fresnel reconstruction algorithm. The tool edge points are extracted as the key points in the reconstruction image, the wavelet transform local variance operator is used to obtain the degree of focus of the key points, and then the axial position corresponding to the milling tool is determined. The least square method is used to fit the key points and correct the reconstruction error, from which the three-dimensional pose reconstruction of the micro-milling tool is realized. The experimental results show that the reconstruction error of the micro-milling tool obtained by the three-dimensional pose reconstruction method is better than 0.1. This method can accurately measure a three-dimensional pose of a micro-milling tool, which can provide a reference for the subsequent correction of micro-milling tool clamping accuracy.
Design of a control system for a visible/near-infrared real-time imaging spectrometer
WU Chang-kun, ZHANG Wei, HAO Ya-zhe
 doi: 10.37188/CO.2021-0119
Abstract(244) FullText HTML(99) PDF 5328KB(21)
A visible/near-infrared real-time imaging spectrometer is designed for hyperspectral imaging. The spectrometer is designed on the basis of an acousto-optic tunable filter (AOTF). Its operating band range is 1.3 μm, in which the visible light camera works in the 400 nm−1000 nm band and the near-infrared camera works in 1000 nm−1700 nm band. A field-programmable gate array (FPGA) is used as the core processing unit of the spectrometer control system. The Cameralink interface is used to collect camera data, the AOTF frequency is controlled by the serial port. Through the organic combination of AOTF synchronization signal and the trigger signal outside the camera, the one-to-one correspondence between a continuous image and multi-wavelength cyclic acquisition is realized. Finally, the image data is transmitted to the upper computer through the USB3.0 interface for real-time display. The field test shows that the imaging quality of the spectrometer is good and the system works stably. For images with a 1024*1024 resolution, the real-time transmission rate of the image can reach up to 120 frame/s, which meets the design requirements. In practical engineering applications, the control system has a rich interface, high reliability, flexible interface and strong expansibility.
High-precision surface reconstruction technology for elliptical flat mirrors
YAN Gong-jing, LUO Wang, ZHANG Bin-zhi
 doi: 10.37188/CO.2021-0106
Abstract(216) FullText HTML(90) PDF 5885KB(7)
In order to realize the high-precision surface measurement of large-diameter elliptical optical flat mirrors and improve the image quality of large-aperture telescope systems, the absolute measurement algorithm for flat elliptical mirrors is studied in this paper. Firstly, the orthogonal polynomials fitting of an elliptical optical flat mirror is studied. Then, the absolute testing algorithm is studied theoretically. The orthogonal absolute testing algorithm can effectively separate the face error of the reference mirror from the mirror to be measured, which can realize the high-precision surface reconstruction of the elliptical flat mirror to be measured. To prove the actual testing accuracy of the above method, we carried out an absolute testing simulation and experiment on a 250 mm*300 mm mirror. In the simulation, the possibility that the reference surface error is high was considered. In the experiment, a 250 mm*300 mm elliptical testing area was selected in the Zygo300 mm standard flat surface. The above-mentioned elliptical area was tested by the 150 mm Zygo interferometer, and the surface reconstruction was realized based on the above-mentioned orthogonal absolute testing algorithm. The experimental results show that the surface error separation between the reference mirror and the elliptical mirror can be achieved by using the method described in this paper, and the residual RMS (Root-mean square) value of the absolute testing result is 0.29 nm, which proves the feasibility and accuracy of the method described in this paper. The high-precision surface reconstruction of the elliptical flat mirror can be achieved using the above method.
Research progress of lithium niobate thin-film modulators
LIU Hai-feng, GUO Hong-jie, TAN Man-qing, LI Zhi-yong
2022, 15(1): 1-13.   doi: 10.37188/CO.2021-0115
[Abstract](526) [FullText HTML](203) [PDF 3910KB](165)
Electro-optic modulators based on lithium niobate (LiNbO3, LN) thin-film platforms are advantageous for their small volume, high bandwidth and low half-wave voltage. They have important application prospects in the field of optical fiber communication and optical fiber sensing, and thus have became a heavily researched topic in recent years. In this paper, the research progress of the waveguide structures, coupling structures and electrode structures of LN thin-film modulators are reviewed in detail. The fabrication process of a LN thin-film waveguide is summarized, and the performances of different modulator structures are analyzed. Based on SOI and LNOI, a platform modulator is realized with VπL<2 V∙cm, a bilayer inversely tapered coupling scheme achieves a coupling loss <0.5 dB/facet , and a traveling wave electrode structure achieves a modulation bandwidth >100 GHz. Thin-film LN modulators are better than commercial LN modulators in most aspects. It can be predicted that in the near future, with the further improvement in waveguide technology, thin-film LN will become a popular scheme of LN modulators. Finally, the potential directions for the future of their research are proposed.
Original Article
Complex non-diffraction beams generated using binary computational holography
YANG Jing-yu, REN Zhi-jun, HUANG Wen-jun, XU Fu-yang
2022, 15(1): 14-21.   doi: 10.37188/CO.2021-0061
[Abstract](205) [FullText HTML](40) [PDF 3682KB](50)
The diffraction of optical fields is a universal phenomenon that can cause beams to spread during propagation in free space. Ideal non-diffracting (spatially stable) structured beams can propagate in free space without changing their initial field distribution at any plane orthogonal to the direction of propagation. Moreover, the non-diffracting structured beams also have the ability for self-recovery after encountering obstacles. Hence generating non-diffracting beams or structured beams is a very important field of research for overcoming the diffraction behavior of beams during propagation in free space. Any non-diffracting structured beams with a certain intensity, phase distribution, and propagation properties have special applications in the field of optics. Lately, some non-diffracting beams with complex structures are introduced one after another, such as Mathieu beams, parabolic beams, Lommel beams, asymmetric Bessel beams, and so on. The complex amplitude modulation is necessary to produce the non-diffracting beams with abundant structures. At present, no commercial optical modulator can modulate the phase and amplitude of light waves simultaneously. Based on binary computer-generated holography that can encode the two-dimensional transmission function distribution, a binary real amplitude computer-generated hologram with complex amplitude modulation functionality is designed and constructed. Binary real amplitude computer-generated holograms, which are a kind of binary optical diffracting element that generate non-diffracting beams with complex optical morphology, are designed and constructed by encoding the complex optical filed information by using the Lohmann-type detour phase coding method. For the Lohmann-type detour phase coding method, the coding principle is mainly that the complex field distribution information is transformed into amplitude and phase information. The complex field distribution is sampled, and one can obtain a matrix of point sources. Here, we extract the amplitude and phase information as input information to generate two 2D real value matrices for detour phase coding. By using the homemade projection imaging lithography system, the silver salt halide plate was exposed, developed and fixed, and then a binary mask is precisely machined. The homemade projection imaging lithography system can machine holograms with an ultrahigh resolution of 79874 × 79874 dpi and a maximum output of 156 mm × 156 mm. Using the mask, the non-diffracting beams with abundant structures can be produced accurately. Taking the non-diffracting Mathieu beam as an example, two kinds of binary real amplitude computer-generated holograms for generating Mathieu beams are constructed by using the Roman type detour phase coding method. In the process of the machine, the photolithography file is firstly divided into 47 unit patterns of 600 pixel × 600 pixel, where each unit pattern is automatically inputted into a DMD (Digital Micromirror Device) in proper sequence, and then subsequently scanned line-by-line for projection exposure. When the lithography is complete, the silver halide plate is processed to obtain the mask. In this experiment, the calculated CGH is 28000 pixel × 28000 pixel, and the size of a pixel is 318 nm×318 nm. The size of the produced binary masks is 8.9 mm × 8.9 mm. The non-diffracting Mathieu beams with elliptic coefficient q=10 and topological charge number m=0, 1 are generated, which belong to the even type Mathieu beams of the first kind. Undoubtedly, the classes of non-diffracting Mathieu beams, including the even type Mathieu beams of the second kind, odd type Mathieu beams of the first kind, and odd-type Mathieu beams of the second kind can also be generated using the same encoding method and experimental setup. Since one can encode both the amplitude information and the phase information of optical field in sole spatial light modulation, the experimental system is simple in structure. The experimental results show that the coding method of binary computer-generated holography is an accurate, convenient and efficient way to generate high-quality non-diffracting beams with abundant structures.
Visual method for measuring forming limit curve of pliable composite film
CHEN Ren-hong, LIANG Jin, YE Mei-tu, REN Mao-dong, ZHANG Ji-yao
2022, 15(1): 22-33.   doi: 10.37188/CO.2021-0101
[Abstract](271) [FullText HTML](81) [PDF 4639KB](20)
To address the difficulty in measuring the strain limit of pliable composite film forming tests, a measurement method based on binocular stereo vision combined with digital image correlation is proposed. Firstly, to address the image matching problem in large deformations or cracks in thin films, a weak-correlation step-by-step matching method based on adaptive updating of image matching benchmarks is proposed according to the continuity of adjacent state deformation of series images. Then, according to the differences in the surface strain distribution of the film material with that of the steel parts, a strain field is proposed to fit the limit strain curve of the film material. The software and hardware system of visual measurement is built, and the limit strain curve of a Q235 steel specimen is measured and compared to results from the coordinate grid method. The limit strain accuracy can be improved by 0.02%, which proves the feasibility and accuracy of this method. The pliable composite film specimens prepared by PET, Nylon, Al foil, PP were each measured. The method and system successfully completed the measurement of the forming limit curve of the pliable composite film. The comparative experiments show that the proposed method can quickly and accurately measure the surface strain distribution of pliable composite film during forming. Compared with the coordinate grid method, it has obvious advantages and provides a highly reliable and highly precise method for solving the forming limit strain curve of film materials.
Nighttime image dehazing with a new light segmentation method and a linear image depth estimation model
LV Jian-wei, QIAN Feng, HAN Hao-nan, ZHANG Bao
2022, 15(1): 34-44.   doi: 10.37188/CO.2021-0114
[Abstract](184) [FullText HTML](83) [PDF 4156KB](21)
Image with the scene of haze at night has low contrast, non-uniform illumination, color cast and significant noise. These cause nighttime haze removal from single image to be problematic and challenging. In this paper, we put forward a method that can remove nighttime haze from images and improve image quality. The input image is first decomposed into a glow layer and a haze layer with a modified color channel transformation for glow artifacts and color correction. A new light segmentation function is proposed next by using gamma correction of the channel difference and setting the threshold levels as the probability of a pixel belonging to a light source region. Then we estimate the ambient illuminance map by combining the maximum reflectance prior value with the aforementioned probability and computing the atmospheric light in the light and non-light regions. Finally, we establish a novel linear model to build the connection between the image depth map and three image features including luminance, saturation and gradient map for the light source regions while using the dark channel prior for the non-light source regions. The result of the light segmentation is 0.07, and the parameters of the linear depth estimation are 1.0267, −0.5966, 0.6735 and 0.004135. Experimental results show the proposed method is reliable for removing nighttime haze and glow of active light sources, reducing significant noise and improving visibility.
3D position angle measurement based on a lens array
DU Ming-xin, YAN Yu-feng, ZHANG Ran, CAI Cun-liang, YU Xin, BAI Su-ping, YU Yang
2022, 15(1): 45-55.   doi: 10.37188/CO.2021-0129
[Abstract](80) [FullText HTML](21) [PDF 4206KB](24)
Accurate measurement of three-dimensional attitude angle is widely used in aviation, aerospace, national defense and other fields. In order to realize convenient and accurate measurement of three-dimensional attitude angle, an optical system based on a lens array is designed and an analysis model of micro-three-dimensional attitude angle measurement is established in this paper. In the system, the collimated parallel beam passes through four array lenses arranged in a pyramid shape to form regular array spots on a CCD. By analyzing the distance between the spots on the CCD image, the distance between the adjacent aperture on the lens array and the inclination angle between the lens array and CCD, the beam pitch angle and azimuth angle relative to the receiving system can be obtained. By using the angle of the lines of the array spots relative to the horizontal or vertical plane, the roll angle about the Z axis can also be obtained. Compared with the measurement results of the high-precision autocollimator, the measurement accuracy of the proposed method is verified to be RMS≤0.1″. The results show that the proposed method can realize the measurement of three-dimensional attitude angle.
Risley-prism inverse algorithm based on equivalent vector model
FENG Jian-xin, WANG Qiang, WANG Ya-lei, XU Biao
2022, 15(1): 56-64.   doi: 10.37188/CO.2021-0117
[Abstract](234) [FullText HTML](76) [PDF 4310KB](17)
In order to further improve the calculation accuracy and reduce the calculation time of the inverse algorithm in the Risley-prism structure, a new algorithm is proposed. It combines the forward iterative method with the equivalent vector model of the Risley-prism to produce an equivalent vector iterative method of calculation. Firstly, the equivalent vector model of the wedge is established according to its deflection. Then, the vector coordinates of the light emitted from the Risley-prism are solved through vector superposition. The equivalent vector model is then substituted into the two-step inverse solution algorithm to calculate the approximate value of the rotation angle of the Risley-prism. Finally, the inverse equivalent vector iteration algorithm is proposed by using forward iteration and gradual approximation, and the rotation angle of Risley-prism is obtained. The experimental results show that the accuracy of the algorithm reaches 10 μm and the calculation time is less than 0.1 ms. The algorithm can effectively improve calculation accuracy, reduce calculation time, and has application prospects in the field of high-precision beam pointing.
Optical design of a wide-spectrum ultraviolet imager based on a single material
LI Han-shuang, LI Bo, LI Hao-chen, LIN Guan-yu
2022, 15(1): 65-71.   doi: 10.37188/CO.2021-0127
[Abstract](154) [FullText HTML](61) [PDF 3696KB](25)
Ultraviolet detection technology is widely used in various fields of production and human life. It is thus greatly significant to study wide-spectrum ultraviolet (UV) imager systems. Through deducing the theoretical formula of chromatic aberration, a scheme for correcting the chromatic aberration of the optical system of the wide-spectrum UV imager with the lenses made of single material was proposed. Combined with the performance index of a high-sensitivity dynamic UV imaging detector, the optical system of the 210~400 nm wide-spectrum UV imager with only one lens material and all lenses being spherical was designed. The optical design software CODE V was used to optimize the system and evaluate the image quality. The results demonstrate that the Modulation Transfer Function (MTF) in the entire field of view and waveband of the system is better than 0.6 at the Nyquist frequency of 40 lp/mm and RMS<7.8 μm. Thus, the system has good imaging quality. The system does not contain aspheric optical elements, which makes it not only easy to process and assemble, but also reduces its cost and lays a technical foundation for the development of a wide-spectrum UV imaging spectrometer.
Design of cooled long-wavelength infrared imaging optical system
SHAN Qiu-sha, XIE Mei-lin, LIU Zhao-hui, CHEN Rong-li, DUAN Jing, LIU Kai, JIANG Kai, ZHOU Liang, YAN Pei-pei
2022, 15(1): 72-78.   doi: 10.37188/CO.2021-0116
[Abstract](181) [FullText HTML](62) [PDF 3955KB](34)
Aiming at 640×512 long-wavelength infrared cooled detectors, a cooled long-wavelength infrared optical system was designed to track and detect an infrared target. The optical system adopts the secondary imaging structure to ensure 100% cold-shielding efficiency, and adopts a combination of optical material Ge and ZnS to achieve aberration correction and achromatic design. By introducing the high-order aspheric surface, the high aberration of the system is well-corrected, thus the system structure is simplified. The optical system is composed of 6 lenses. The focal length is 400 mm, the working bands are 7.7~9.3 μm, the field of view is 1.37°×1.10°, and the F-number is 2. The design results show that at a spatial frequency of 33 lp/mm, the MTF of off-axis field of view is more than 0.24, which approaches the diffraction limit and has high imaging quality. In the operating temperature range of −35~+55 ℃, the focusing lens is used to ensure the imaging quality under high and low temperature environments, which can be used for infrared tracking detection over a wide range of temperatures.
Longitudinal chromatic aberration compensation method for dual-wavelength retinal imaging adaptive optics systems
ZHU Qin-yu, HAN Guo-qing, PENG Jian-tao, RAO Qi-long, SHEN Yi-li, CHEN Mei-rui, SUN Hui-juan, MAO Hong-min, XU Guo-ding, CAO Zhao-liang, XUAN Li
2022, 15(1): 79-89.   doi: 10.37188/CO.EN.2021-0009
[Abstract](111) [FullText HTML](39) [PDF 4821KB](21)
Dual-wavelength retinal imaging adaptive optics systems are suitable for high contrast and resolution imaging of retinal capillaries. The compensation of the Longitudinal Chromatic Aberrations (LCAs) in dual-wavelength adaptive systems is researched. The LCA is measured, the measured wavefronts are analyzed, and the arbitrary wavefront LCA compensation method is given. An adaptive correction experiment is carried out and the experimental results indicate that the root mean square error of the wavefront is reduced to 0.16 λ (λ=589 nm) and the retinal capillary resolution is improved to 6 μm. This work may be used for the clinical applications of retinal imaging.
Calibration of single optical wedge compensation test system error by computer generation hologram
CAI Zhi-hua, WANG Xiao-kun, HU Hai-xiang, CHENG Qiang, WANG Ruo-qiu, ZHANG Hai-dong
2022, 15(1): 90-100.   doi: 10.37188/CO.EN.2021-0004
[Abstract](193) [FullText HTML](106) [PDF 3891KB](24)
As a testing method for large convex aspheric surface, the single optical wedge compensation test has good applicability, robustness and flexibility. However, various errors are coupled with one another during the test process and these errors are difficult to decouple. This affects the accuracy and reliability of the tests. To address this, a method is developed to calibrate the system error of single optical wedge test paths using a Computer Generation Hologram (CGH). We first analysed the source of system error in the optical path of a single optical wedge compensation test as well as the feasibility of using CGH for the calibration of an optical wedge compensation test system. In combination with engineering examples, a CGH was designed for optical wedge compensators with a diameter of 150 mm. Based on the analysis results, the calibration accuracy of the CGH was 1.98 nm RMS, and after calibration the test accuracy of single wedge compensation was 3.43 nm RMS, thereby meeting the high-precision test requirements of large convex aspheric mirrors. This shows that CGH can accurately calibrate the pose of single optical wedge compensators and the test system errors of optical paths. Thus we address the problems affecting error decoupling in test optical paths, and improve the accuracy and reliability of the single optical wedge compensation method. Meanwhile, using CGH calibration, the system errors of the test optical paths, Tap#2 and Tap#3, were 0.023 and 0.011 λ RMS, respectively.
High-sensitivity surface plasmon resonance sensor based on the ten-fold eccentric core quasi-D-shaped photonic quasi-crystal fiber coated with indium tin oxide
LIU Qiang, JIANG Yu, HU Chun-jie, LU Wen-shu, SUN Yu-dan, LIU Chao, LV Jing-wei, ZHAO Jin, TAI Sheng-nan, YI Zao, CHU Paul K
2022, 15(1): 101-110.   doi: 10.37188/CO.EN.2021-0006
[Abstract](159) [FullText HTML](70) [PDF 3662KB](16)
A high-sensitivity Surface Plasmon Resonance (SPR) sensor comprising of an eccentric core ten-fold Photonic Quasi-crystal Fiber (PQF) with a D-shaped structure and partially coated with Indium Tin Oxide (ITO) is designed and numerically analyzed. The eccentric core D-shaped structure makes the analysis of liquids more convenient and also strengthens the coupling between the core mode and Surface Plasmon  Polariton (SPP) mode to improve the sensing sensitivity. The characteristics of the sensor are investigated by the Finite Element Method (FEM). The wavelength sensitivity increases with increasing Refractive Indexes (RIs) and the maximum wavelength sensitivity and resolution are 60000 nm/RIU and 1.67×10−6 RIU, respectively. The sensor delivers excellent performance and has large potential applications in the measurement of liquid refractive indexes.
Experimental investigation on propagation characteristics of vortex beams in underwater turbulence with different salinity
LU Teng-fei, LIU Yong-xin, WU Zhi-jun
2022, 15(1): 111-118.   doi: 10.37188/CO.EN.2021-0001
[Abstract](179) [FullText HTML](98) [PDF 3754KB](20)
It is very important to study the propagation characteristics of light beams in ocean turbulence. In order to get closer to the actual situation, we build a device which can control both the salinity and the intensity of underwater turbulence to study the propagation characteristics of vortex beams and a Gaussian beam in underwater turbulence. The results show that compared with the underwater turbulence without sea salt, the light spot will be more diffuse and the light intensity will be weaker in the underwater turbulence with sea salt. When the topological charge m is 2, the scintillation index of the vortex beam in the underwater turbulence with salinity of 4.35‰ is larger than that in the underwater turbulence with salinity of 2.42‰, no matter it is strong turbulence or weak turbulence. When the vortex beam with m=2 propagates to the same distance, the scintillation index increases with the increment of the salinity and the intensity of underwater turbulence. Under different salinity conditions, the radial scintillation index of the vortex beam with m=2 decreases firstly and then increases with the increase of the radial distance. In addition, we set up another experimental device which can transmit a longer distance. The scintillation index of the vortex beam with m=2 is much higher than that of the Gaussian beam in the underwater turbulence within 20 m propagation distance, and the scintillation indices of both the vortex beam with m=2 and the Gaussian beam increase with the increase of the propagation distance.
Fabrication of an ultra-narrow band-pass filter with 60 pm bandwidth in green light band
WANG Kai-xuan, CHEN Gang, LIU Ding-quan, MA Chong, ZHANG Qiu-yu
2022, 15(1): 119-131.   doi: 10.37188/CO.2021-0092
[Abstract](215) [FullText HTML](72) [PDF 5106KB](24)
Owing to the strong penetrating ability in the atmosphere, 532 nm-wavelength green laser has wide applications including free-space optical communications and laser three-dimensional mapping. A spectral filter, with a half-power bandwidth of less than 100 pm, is an important optical element to suppress the interference of background light. Therefore, an ultra-narrow band-pass filter based on optical interference film is designed and fabricated in this paper. The high and low refractive index film are made of tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2), respectively. The designed optical thin films are deposited on a fused quartz substrate by double-ion-beam sputtering deposition method. The transmission spectra of the filters are measured by a tunable laser and a power meter. The half-power bandwidths of the filters are (60±2) pm, and the transmittance reaches 62.6%.
Illustrating the Helmholtz-Kohlrausch effect of quantum dots enhanced LCD through a comparative study
JI Hong-lei, CHENG Shang-jun, LI Peng-fei, ZHANG Yan, GE Zi-yi, ZHONG Hai-zheng
2022, 15(1): 132-143.   doi: 10.37188/CO.2021-0058
[Abstract](364) [FullText HTML](135) [PDF 7571KB](58)
Helmholtz-Kohlrausch effect (H-K effect) describes the influence of color purity on the perceived brightness of a colored object. Quantum dots (QD) based backlights can enhance the color quality of Liquid Crystal Display (LCD) with improved perceived brightness due to the well-known H-K effect. However, the H-K effect of QD embedded TVs (also known as QLED TV) has not been fully demonstrated. In this paper, we investigated the H-K effect of QLED TVs through a comparative study between QLED backlights and YAG-LED backlights. By comparing the viewers’ experimental results with the Kaiser and Nayatani model, we demonstrate that a QLED TV shows significant H-K effect. To achieve the same perceived brightness with YAG-LED TV, the physical brightness of QLED TV was greatly decreased to 75% for pure red, 86% for pure green, and 74%-88% for bright colorful images. Moreover, QLED TVs are strongly preferred over YAG-LED TVs even when both QLED TV and YAG-LED TV show the same perceived brightness. The results imply the bright future of QLED TVs toward healthly displays.
Enhancing the fluorescence emission by flexible metal-dielectric-metal structures
CAO Wen-jing, SUN Li-ze-tong, GUO Fu-zhou, SONG Jian-tong, LIU Xiao, CHEN Zhi-hui, YANG Yi-biao, SUN Fei
2022, 15(1): 144-160.   doi: 10.37188/CO.2021-0084
[Abstract](220) [FullText HTML](99) [PDF 4337KB](20)
The technology of enhancing fluorescence emission can increase the sensitivity of fluorescence detection and the brightness of Light Emitting Diodes (LEDs), and is of great significance in improving the performance of light-emitting devices. Since the metal structure has a good effect in enhancing the local field and fluorescence emission, and the flexible dielectric material has flexible bendability characteristics, on the basis of above, we propose a flexible structure composed of Metal-Dielectric-Metal (MDM) to enhance the fluorescence emission. The influence of the structure on the directional emission enhancement of quantum dots is systematically studied by using the finite difference time domain method. Theoretical calculations show that the local undulations and arcs of the flexible MDM structure can promote fluorescence enhancement and increase the quantum efficiency of the quantum dots located at the center of the structure by about 7 times. They can alao change the refractive index and thickness of the dielectric to achieve the tunability of the target wavelength. At the same time, the experimental results shows that the flexible MDM structure does have a positive effect on the fluorescence enhancement. This discovery is valuable for future display technologies and flexible light-emitting devices. It is of certain guiding significance for the development and application of high-efficiency flexible devices.
Research progress of lithium niobate thin-film modulators
LIU Hai-feng, GUO Hong-jie, TAN Man-qing, LI Zhi-yong
2022, 15(1): 1-13.   doi: 10.37188/CO.2021-0115
Abstract(526) FullText HTML(203) PDF 3910KB(165)
Electro-optic modulators based on lithium niobate (LiNbO3, LN) thin-film platforms are advantageous for their small volume, high bandwidth and low half-wave voltage. They have important application prospects in the field of optical fiber communication and optical fiber sensing, and thus have became a heavily researched topic in recent years. In this paper, the research progress of the waveguide structures, coupling structures and electrode structures of LN thin-film modulators are reviewed in detail. The fabrication process of a LN thin-film waveguide is summarized, and the performances of different modulator structures are analyzed. Based on SOI and LNOI, a platform modulator is realized with VπL<2 V∙cm, a bilayer inversely tapered coupling scheme achieves a coupling loss <0.5 dB/facet , and a traveling wave electrode structure achieves a modulation bandwidth >100 GHz. Thin-film LN modulators are better than commercial LN modulators in most aspects. It can be predicted that in the near future, with the further improvement in waveguide technology, thin-film LN will become a popular scheme of LN modulators. Finally, the potential directions for the future of their research are proposed.
Two-dimensional material photodetector for hybrid silicon photonics
HU Si-qi, TIAN Rui-juan, GAN Xue-tao
2021, 14(5): 1039-1055.   doi: 10.37188/CO.2021-0003
Abstract(1331) FullText HTML(361) PDF 10280KB(370)
Two-dimensional (2D) materials provide new development opportunities for silicon-based integrated optoelectronic devices due to their unique structure and excellent electronic and optoelectronic properties. In recent years, 2D material-based photodetectors for hybrid-integrated silicon photonics have been widely studied. Based on the basic characteristics of several 2D materials and the photodetection mechanisms, this paper reviews the research progress of silicon photonic integrated photodetectors based on 2D materials and summarizes existing device structure and performance. Finally, prospects for strategies to obtain high-performance silicon photonic integrated 2D material photodetectors and their commercial applicability are presented with considerations for large-scale 2D material integrations, device structure, and metal-semiconductor interface optimizations, as well as emerging 2D materials.
Research progress on coherent synthesis of optical frequency comb
MA Jun-chao, MENG Li-li, ZHANG Rui-xue, ZHUO Xiao, NI Kai, WU Guan-hao, SUN Dong
2021, 14(5): 1056-1068.   doi: 10.37188/CO.2021-0071
Abstract(500) FullText HTML(121) PDF 5700KB(103)
Optical Frequency Comb (OFC) possesses unique time(frequency) domain characteristics such as narrow pulse width, high frequency precision, stable frequency comb teeth and well-defined optical coherence, etc. Therefore, it has become a hot research topic in various fields including ultra-fast laser technology and metrology science in recent years. Meanwhile, OFC has also been developed into an important scientific research instrument. Recently, a novel light source based on the coherent synthesis of OFCs has been developed, which can realize the periodical, high-speed (up to radio frequency) and stable modulation of the polarization or the orbital angular momentum of light. In this review, we try to introduce recent developments on the fundamental principles, experimental techniques and characterization methods of the novel light source based on the coherent synthesis of OFCs, starting from the basic concepts of OFC and mainly covering two aspects: polarization modulation and orbital angular momentum modulation respectively. We also try to provide some perspectives on the applications of OFC based on the coherent synthesis techniques in the fields of solid-state spectroscopy, optical manipulation and the interaction between light and matter, etc.
Progress of tunable micro-nano filtering structures
YU Xiao-chang, XU Ya-qing, CAI Jia-chen, YUAN Meng-qi, GAO Bo, YU Yi-ting
2021, 14(5): 1069-1088.   doi: 10.37188/CO.2021-0044
Abstract(575) FullText HTML(246) PDF 12124KB(97)
Because of the large size and immobility working modes, traditional spectral imaging systems struggle to meet increasingly complex practical needs. Tunable micro-nano filtering structures show unique advantages for their lighter weight and greater flexibility, so they are promising candidates for achieving adaptive and intelligent operation in the future. This article summarizes a variety of tunable filtering methodologies and their operational principles both in domestic and foreign research within the last several years. It illustrates static tunable methods such as utilizing liquid crystal and phase-change materials, some dynamic tunable filtering structures such as Fabry-Pérot cavity, micro-nano tunable grating as well as some driving approaches like mechanical stretching, electrostatic driving, optical driving, etc. Meanwhile, this article also introduces some frontier researches based on microfluidic chips and graphene. In the end, it discusses the barriers, challenges and future trends of development for tunable micro-nano filtering structures.
Research progress of elastic emission machining in optical manufacturing
LI Jia-hui, HOU Xi, ZHANG Yun, WANG Jia, ZHONG Xian-yun
2021, 14(5): 1089-1103.   doi: 10.37188/CO.2021-0022
Abstract(430) FullText HTML(177) PDF 7589KB(81)
The requirements of modern optical engineering in fields such as deep ultraviolet lithography, extreme ultraviolet lithography and advanced light sources drive the continuous development of advanced optical manufacturing technology. Modern optical engineering requires the surface roughness of ultra-smooth optical components to reach the atomic level and the surface shape profile error in the full spatial frequency to reach RMS(Root Mean Square) sub-nanometer or even a few dozen picometers. This drives the manufacturing requirements of ultra-smooth optical components to approach the processing limits. At present, there are still technical challenges to achieve the ultra-smooth polishing technology and equipment required for the above ultra-high precision needs. Atomic level ultra-smooth polishing of complex surfaces such as cylinders, ellipsoids and toroids is still a primary direction of research at both domestically and abroad. Elastic emission machining is an atomic-level ultra-smooth processing method with stable removal functionality and ultra-low subsurface defect creation, which can be used for manufacturing optical components with the above-mentioned accuracy requirements. We summarize the research progress of elastic emission machining and equipment at both domestically and abroad, the principles of elastic emission machining which contains fluid characteristics, the movement characteristics of polishing particles and chemical characteristics, the equipment of elastic emission machining, and the factors affecting the improvement of surface roughness and material removal rate of elastic emission machining. Then we analyze the problems faced by elastic emission machining and equipment and look forward to their prospects. It is expected that this paper will provide a reference for the further development and application of elastic emission machining.
Budget analysis of focus control in advanced lithography (I) -optical path
ZHONG Zhi-jian, LI Chen-yi, LI Shi-guang, GUO Lei, WEI Ya-yi
2021, 14(5): 1104-1119.   doi: 10.37188/CO.2021-0033
Abstract(889) FullText HTML(206) PDF 4286KB(92)
As the technology node of large-scale integrated circuits continues to shrink, the focus control of the lithographic tools becomes particularly difficult. In order to ensure the exposure quality of wafers, it is necessary to quickly and accurately adjust the wafer in the Depth of Focus (DOF) to a degree as small as few dozen of nanometers. For this reason, people need to carefully analyze the various factors that cause defocusing or process window changes in the lithographic process, make a reasonable focus control budget, and control the various error factors within a certain range. This paper focuses on Extreme Ultraviolet (EUV) lithography, reviews the factors that affect focus control in the optical path of an advanced EUV lithographic tool and summarizes their principles, simulation and experimental results. It can provide a reference when conducting advanced lithography focus control budget research.
Research progress of tunable fiber light sources with wavelength near 1 μm
DANG Wen-jia, GAO Qi, LI Zhe, LI Gang
2021, 14(5): 1120-1132.   doi: 10.37188/CO.2021-0125
Abstract(388) FullText HTML(105) PDF 6378KB(44)
Tunable fiber light sources with wavelength near 1 μm are widely used in optical fiber sensing, laser cooling, photochemical, spectroscopy and medical fields. They have thus become an area of focus in fiber light source research in recent years. The development history of fiber light sources with wavelength tuning ability is firstly summarized systematically. Then, their problems and possible solutions are analyzed. Finally, the future developments of tunable fiber light sources near 1 μm are prospected.
Research progress of optical chaos in semiconductor laser systems
KUANG Shang-qi, GUO Xiang-shuai, FENG Yu-ling, LI Bo-han, ZHANG Yi-ning, YU Ping, PANG Shuang
2021, 14(5): 1133-1145.   doi: 10.37188/CO.2020-0216
Abstract(346) FullText HTML(114) PDF 6559KB(64)
Chaotic lasers are widely used in secure communication, lidar, optical detection and other applications due to their noise-like randomness, excellent anti-interference and other advantages. Moreover, as semiconductor lasers have small size, stable structure and other advantages, it has become one of the main lasers to produce optical chaos. However, the chaotic laser output from conventional optical feedback semiconductor lasers has the problems of narrow signal bandwidth and delay characteristics, which seriously affect their applications. With consideration for these problems, a comprehensive introduction to reduce the delay characteristics and optimize the chaotic laser bandwidth are reviewed based on recent literatures. This paper also summarizes the research progresses of chaotic secret communication, which is very important in the synchronization of chaotic lasers. The chaotic output of semiconductor lasers and the applications of chaotic lasers are also summarized, and then their development and potential future applications are discussed.
Review of augmented reality display technology
SHI Xiao-gang, XUE Zheng-hui, LI Hui-hui, WANG Bing-jie, LI Shuang-long
2021, 14(5): 1146-1161.   doi: 10.37188/CO.2021-0032
Abstract(1062) FullText HTML(305) PDF 5479KB(244)
Augmented reality (AR) display technology has developed rapidly in recent years, and has become a research hotspot and development focus of the global information technology industry. It has the potential to revolutionize the ways we perceive and interact with various digital information. Recent advances in micro-displays and optical technologies offer new development directions to further advance AR display technology. This review analyzes the optical requirements of human visual systems for AR head-mounted displays and compares them with current specifications of AR head-mounted displays to demonstrate their current levels of development and main challenge. The basic principles and parameters of various micro-displays and optical combiners in AR head-mounted displays are introduced to explain their advantages and practicability, and their development trends are summarized.
3D small-field surface imaging based on microscopic fringe projection profilometry:a review
WANG Yong-hong, ZHANG Qian, HU Yin, WANG Huan-qing
2021, 14(3): 447-457.   doi: 10.37188/CO.2020-0199
Abstract(750) FullText HTML(224) PDF 2289KB(196)
Intelligent manufacturing has become more precise, miniaturized and integrated. Representative integrated circuit technology and its derived miniature sensors such as Micro-Electro-Mechanical System (MEMS) have become widely used. Therefore, it is important for intelligent manufacturing development to accurately obtain the surface morphology information of micro-devices and implement rapid detection of device surface defects. Fringe Projection Profilometry (FPP) based on structural light projection has the advantages of being non-contact, highly precise, highly efficient and having full-field measurement, which plays an important role in the field of precision measurement. Microscopic Fringe Projection Profilometry (MFPP) has been developed rapidly during recent decades. In recent years, MFPP has made great progress in many aspects, including its optical system structures, corresponding system calibration methods, phase extraction algorithms, and 3D coordinate reconstruction methods. In this paper, the structure and principle of a three-dimensional measurement system of microscopic fringe projection are reviewed, and the calibration problem of a small field-of-view system that is different from the traditional projection model is analyzed. After that, the development and improvement process of the micro-projection system structure is introduced, and the reflection in the measurment caused by the system structure and metal material is analyzed. On this basis, the prospects of the development of microscopic fringe projection of 3D measurement system are discussed.
Development progress of Fe2+:ZnSe lasers
XU Fei, PAN Qi-kun, CHEN Fei, ZHANG Kuo, YU De-yang, HE Yang, SUN Jun-jie
2021, 14(3): 458-469.   doi: 10.37188/CO.2020-0180
Abstract(717) FullText HTML(165) PDF 3598KB(107)
Mid-infrared lasers with emission spectrums located in the 3~5 μm atmospheric window have a wide range of possible applications in medical treatment, industrial processing, atmospheric remote sensing, space communication, infrared countermeasures and other fields. Transition Metal (TM) doped Ⅱ~Ⅵ group sulfide crystals can be used as the gain medium to achieve mid-infrared laser output. Among them, Fe2 +:ZnSe lasers are advantageous for their high conversion efficiency, their wide tunable range in the mid-infrared band and their compact structure. They are one of the most effective ways of achieving a short pulse with high power and high energy in the mid-infrared band. With the development of material technology in recent years, Fe2 +:ZnSe lasers have begun developing rapidly and have become a heavily researched topic. This paper reviews the development of a TM2+:Ⅱ~Ⅵ laser represented by a Fe2 +:ZnSe laser. The preparation methods of a Fe2 +:ZnSe gain medium are introduced and analyzed. The pump sources and factors affecting the performance of Fe2 +:ZnSe lasers are discussed. The output characteristics of the Fe2 +:ZnSe laser are reviewed. The latest development of Fe2 +:ZnSe lasers in room temperature and ultrashort pulse directions is summarized and prospected. The possible future development direction of Fe2 +:ZnSe lasers is discussed.
Research progress on portable laser-induced breakdown spectroscopy
ZENG Qing-dong, YUAN Meng-tian, ZHU Zhi-heng, CHEN Guang-hui, WANG Jie, YU Hua-qing, GUO Lian-bo, LI Xiang-you
2021, 14(3): 470-486.   doi: 10.37188/CO.2020-0093
Abstract(897) FullText HTML(178) PDF 3951KB(117)
As a new rapid element analysis technique, Laser-Induced Breakdown Spectroscopy (LIBS) has proven iteself to have great potential for applications in increasingly numerous industrial fields. However, due to harsh outdoor and industrial environments, newer and higher requirements are being demanded of the LIBS system, such as the size of its instruments and the ability to resist a harsh environment. The rapid development of new laser technology promotes instrumentation for LIBS, allowing it to gradually step outside the laboratory and into the industry, and allows the LIBS system to gradually move towards instrumentation, miniaturization and portability.In this paper, the development of a portable LIBS that was developed in recent years was reviewed. The application and latest research progress of different kinds of laser source (small lamp pumped solid-state laser, diode pump solid-state laser and micro laser, fiber laser) applied to the portable LIBS system were summarized and discussed, providing insight into both the fiber optic LIBS (FO-LIBS) and the handheld LIBS. In addition, the basic problems of current portable LIBS and the prospects of its future were proposed and discussed.
Research progress of the laser vibration measurement techniques for acoustic-to-seismic coupling landmine detection
LI Jin-hui, MA Hui, YANG Chen-ye, ZHANG Xiao-qing, LUO Xin-yu, WANG Chi
2021, 14(3): 487-502.   doi: 10.37188/CO.2020-0134
Abstract(736) FullText HTML(195) PDF 3467KB(54)
Acoustic-to-seismic coupling landmine detection technology based on the unique mechanical characteristics of landmines and the acoustic-to-seismic coupling principle has broad application prospects in safe and effective detection of landmines. However, a significant amount of work must be done to study the practical landmine detection system. Among them, the acoustic coupled surface vibration signals are very weak and complicated, which has always been a challenging problem to detect such signals accurately and quickly. In this paper, the non-contact laser measurement techniques of surface vibrations based on the principle of the acoustic-to-seismic coupling landmine detection technology were reviewed, including laser Doppler interferometry, electronic speckle pattern interferometry and laser self-mixing interferometry, etc., and the application feasibility of electronic speckle-shearing pattern interferometry in acoustic-to-seismic coupling landmine detection was analyzed.
Research progress on the modulation properties of new electro-optic materials
LÜ Xiao-lei, ZHAO Ji-guang, DU Xiao-ping, SONG Yi-shuo, ZHANG Peng, ZHANG Jian-wei
2021, 14(3): 503-515.   doi: 10.37188/CO.2020-0039
Abstract(940) FullText HTML(195) PDF 3438KB(102)
Polarization modulation technology based on 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 LiNiO3 (LN) materials, it is difficult for traditional electro-optic modulation technology to further improve 3D imaging performance. As the preparation technology of perovskite-structured electro-optical materials becomes more mature, electro-optic modulation technology based on new materials will become an excellent means to create a breakthrough in the detection accuracy of laser 3D imaging. PMNT, PLZT and KTaxNb1-xO3 (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 modulation bandwidth for PMNT, poor transmission performance for PLZT, and low practical application bandwidth for KTN. Future research will focus on the practicality of this modulation technology. The electro-optic modulation performance can be improved by doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
Orthogonal frequency division multiplexing modulation techniques in visible light communication
XU Xian-ying, YUE Dian-wu
2021, 14(3): 516-527.   doi: 10.37188/CO.2020-0051
Abstract(1011) FullText HTML(178) PDF 3613KB(86)
With its unique advantages, Visible Light Communication (VLC) can compensate for limitations in radio frequency communication, allowing it to become a recent avid topic of research. Orthogonal Frequency Division Multiplexing (OFDM) has been widely used in VLC due to its high rate of data transfer and frequency selective fading resistance. We compare the performance of several OFDM modulation techniques in VLC, including unipolar schemes, enhanced schemes and hybrid schemes based on discrete Fourier transformation, as well as optical OFDM systems based on Hartley transform and LED index modulation. We perform these comparisons in terms of energy efficiency, spectral efficiency, bit error rate, and algorithm complexity. The principles of some kinds of optical OFDM systems are firstly illustrated and their spectrum efficiencies are theoretically analyzed and compared. We also research and analysis the improved design of receivers in optical OFDM systems. The challenges and upcoming research of OFDM systems in VLC are summarized. The research in this paper can provide a research reference and propose more efficient unipolar modulation schemes to further improve the spectral efficiency and reliability of optical OFDM systems.
Research advances in adaptive interferometry for optical freeform surfaces
ZHANG Lei, WU Jin-ling, LIU Ren-hu, YU Ben-li
2021, 14(2): 227-244.   doi: 10.37188/CO.2020-0126
Abstract(1377) FullText HTML(298) PDF 3333KB(259)
Optical free-form surfaces are difficult to detect due to their rich degrees of freedom. Interference detection methods are both highly precise and non-contact. However, the static compensator in a traditional interferometer faces difficulty in achieving in-situ tests of unknown surface shapes or those changing during fabrication. Therefore, programmable adaptive compensators for large dynamic ranges have become a well-researched topic in recent years. Combined with the research work in the field of freeform surface metrology, we introduce the latest research progress in adaptive interferometry for optical freeform surfaces. Adaptive interferometers based on a Deformable Mirror (DM) or Liquid Crystal Spatial Light Modulator (LC-SLM) are analyzed in detail. An adaptive controlling algorithm in the adaptive interferometer is introduced as well. Finally, the advantages and development bottleneck of the above two kinds of adaptive interferometry are summarized and the prospects for the future development of freeform surface adaptive interferometers are proposed.
Interrogation technology for quasi-distributed optical fiber sensing systems based on microwave photonics
WU Ni-shan, XIA Li
2021, 14(2): 245-263.   doi: 10.37188/CO.2020-0121
Abstract(716) FullText HTML(246) PDF 3910KB(77)
Quasi-distributed fiber sensing systems play an important role in the fields of civil engineering, energy surveying, aerospace, national defense, chemicals, etc. Interrogation technology for quasi-distributed fiber sensing systems based on microwave photonics is widely used in high-speed and high-precision signal demodulation and sensor positioning in optical fiber multiplexing systems. Compared to conventional optical wavelength interrogation, this technology greatly improves system demodulation rate and compensates for the defects of traditional sensor positioning methods. This paper introduces the recent research progress of quasi-distributed fiber sensing interrogation technology based on microwave photonics; compares and analyzes the advantages and disadvantages of several existing microwave demodulation systems from the perspective of their fiber grating quasi-distributed sensing and fiber Fabry-Perot quasi-distributed sensing systems, respectively; and provides a summary of the prospective direction of future research in quasi-distributed fiber sensing interrogation technology based on microwave photonics.
Research progress of 0.9 ~ 1.0 μm near-infrared continuous-wave fiber lasers
DANG Wen-jia, LI Zhe, LU Na, LI Yu-ting, ZHANG Lei, TIAN Xiao
2021, 14(2): 264-274.   doi: 10.37188/CO.2020-0193
Abstract(552) FullText HTML(168) PDF 2460KB(121)
Near-infrared continuous-wave fiber lasers with wavelengths of 0.9~1.0 μm have important application prospects in the fields of high-power blue and ultraviolet laser generation, high-power single-mode pump sources, biomedicine and lidars. They have thus become a heavily researched topic in recent years. At present, their gain mechanisms mainly include a rare earth ion gain or a nonlinear effect gain. In this paper, the research progress of 0.9~1.0 μm fiber lasers based on these two kinds of gain mechanisms are reviewed in detail, and the technical bottlenecks and solutions of these lasers are analyzed. Furthermore, the potential directions for the future of their research are proposed.
Time-delay interferometry for space-based gravitational wave detection
WANG Deng-feng, YAO Xin, JIAO Zhong-ke, REN Shuai, LIU Xuan, ZHONG Xing-wang
2021, 14(2): 275-288.   doi: 10.37188/CO.2020-0098
Abstract(1035) FullText HTML(201) PDF 9981KB(114)
The Time-delay Interferometry (TDI) technique is of important value for China’s gravitational wave detection program and other space-based laser interferometry missions. In space-based gravitational wave detection, laser interferometry is utilized to achieve ten-picometer precision in the displacement measurements between drag-free proof masses. Laser frequency noise and clock frequency noise are the two dominant noises in the measurement. In the European LISA (Laser Interferometer Space Antenna) program for gravitational wave detection, TDI technique is used to remove laser noise and displacement noise of optical platform by time-delaying and linearly combining the twelve phase measurement data of the three satellites and thus creating an interferometer with equal-length beams. For the cancellation of clock noise, the frequencies of onboard clocks are multiplied to GHz levels and then the GHz clock signals are added on inter-satellite laser links by phase modulation. Finally, the clock noise can be extracted from the generated clock-sideband beat note, eliminating the clock noise terms in the TDI data combination. For the time-delay operation in the data post-processing of the TDI, there is also a requirement for the precise measurement of the absolute distances between three satellites. Therefore, in the TDI scheme, there are three functions applicable to the inter-satellite laser links: displacement measurement, clock sideband modulation and absolute distance ranging. The latter two functions consume the power of the optical carrier by 10% and 1%, respectively. The TDI demonstration in the LISA’s ground-based testbed shows the laser noise and clock noise can be suppressed by the factor of 109 and 5.8×104, respectively.
Development status and trend of micro-satellite laser communication systems
GAO Shi-Jie, WU Jia-Bin, LIU Yong-Kai, MA Shuang, NIU Yan-Jun, YANG Hui-sheng
2020, 13(6): 1171-1181.   doi: 10.37188/CO.2020-0033
Abstract(2006) FullText HTML(554) PDF 7413KB(292)
With its high speed, small size, light-weight and low power consumption, space laser communication has become an indispensable and effective means of high-speed communication between satellites, especially in micro-satellite applications, which can benefit more strongly from the advantages of laser communication. This paper provides a detailed introduction of the latest research progress in the field of micro-satellite laser communication technology. On this basis, key techniques such as light miniaturization of identical orbital terminals, light miniaturization of different orbital terminals and turbulence mitigation technologies are summarized, and the development trends of the technology’s applications, duplex communication, single-point to multi-point, localization and batch production capacity are concluded.

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



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