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Issue 7 ， 2019
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Velocity vector measurements by hydroxyl tagging velocimetry based on crossed tagging and displaying
Abstract：To measure the two-dimensional velocity vector distribution of the flow field, a method of crossed tagging and displaying to conduct velocity vector measurement based on hydroxyl tagging velocimetry was developed. In this technique, the tagging laser beam and the displaying laser sheet are intersected to form tagging spots for flow tracing. Compared with the traditional cross-grid method to realize velocity vector measurement, this method uses a simplified experimental light path, which is advantageous to a Keywords：laser diagnostics;velocity vector measurement;hydroxyl tagging velocimetry;crossed tagging and displaying- 81
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Published：2020-08-13 -
Design of optical brightness enhancement film for direct-lit backlight in automobile head-up display
Abstract：The direct-lit backlight used in an automobile head-up display must have high brightness and a small size. To reduce the thickness of a direct-lit backlight and improve its brightness, an optical brightness enhancement film is designed. First, a two-dimensional microstructure curve for the uniform illumination of light emitted by a single light-emitting diode (LED) is designed according to Snell's law. A microstructure curve is designed and calculated with an LED as an ideal point light source. Based on the Keywords：direct-lit backlight;microstructure;brightness enhancement film;head-up display- 99
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Published：2020-08-13 -
Three-degree-of-freedom micro-vibration measurement system based on dual-frequency laser interference
Abstract：To obtain multi-degree-of-freedom micro-vibration information of an optical platform, a three-degree-of-freedom dynamic micro-vibration measurement system based on plane mirror dual-frequency laser interference is designed. The system utilizes the laser Doppler effect to obtain the three-point displacement information of the measuring mirror by using three measuring axes; calculates the overall displacement, torsion angle, and pitch angle information of the measuring mirror; and detects the three-degree-of- Keywords：micro-vibration measurement;dual-frequency laser interference;multi-degree of freedom;uncertainty analysis- 142
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Published：2020-08-13 -
Risley-prism-based beam scanning system for mobile lidar
Abstract：A beam scanning system is a fundamental component of a light detection and ranging (lidar) system, as it determines the field of view (FOV). To increase the FOV and maintain a specific angular resolution, multiple laser diodes are often used in a mobile lidar. However, the time response of different laser diodes is different, resulting in a mutual ranging difference between different ranging channels of the lidar. Risley prisms are outstanding beam pointing devices that offer good prospects for beam scannin Keywords：mobile lidar;Risley prisms;beam scanning system;two-dimensional scanning- 156
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Published：2020-08-13 -
Influence of plasma treatment on optical and damage properties of TiO2 thin films
Abstract：To improve the optical properties and laser damage threshold of TiO2 films and to ensure their wider use and greater stability in lasers, TiO2 films were deposited on K9 glass using electron beam evaporation technology, and the samples were post-treated with Ar/O mixed plasma. The effects of plasma post-treatment time on the laser damage characteristics of TiO2 thin films were analyzed by measuring the film spectral characteristics, surface defect density, surface topography, damage threshold, and damage topography. The experimental results showed that the refractive index and fill density of the films increased with increasing post-treatment time, whereas the physical thickness and surface roughness decreased. In addition, the surface defect density first decreased and then increased. After a 20-min post-treatment, the LIDT of the TiO2 film samples increased from 5.6 to 9.65 J/cm2 under a 1 064-nm laser irradiation, representing an increase of 72.3%.Keywords：TiO2 thin film;electron beam evaporation;optical constant;plasma treatment;laser damage threshold- 131
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Published：2020-08-13 -
Development of high-temperature resistant incremental encoder
Abstract：To measure the angle shift that occurs under high-temperature conditions, a fiber-based high-temperature-resistant incremental encoder was developed in this study. First, a high-temperature-resistant fiber was employed to transfer light under high-temperature conditions. A field programmable gate array was used to process the incremental encoder's electric signal, and a USB was used to transfer the angle in a normal temperature environment. Second, the effect of the collimation degree of a light beam on the Keywords：photoelectronic encoder;fiber;high-temperature resistant;LED convex lens fiber couple;incremental;FPGA+USB- 129
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Published：2020-08-13 -
Image inversion and quality enhancement for space large aperture diffractive imaging system
Abstract：To address the urgent need for ultra-large aperture and lightweight high-resolution optical payloads in the field of high-orbit military monitoring, an image inversion and quality enhancement method was proposed for large-caliber diffractive imaging systems with diffractive optical elements used as the primary mirror. First, an image inversion model was established for the diffraction imaging system based on the regularization and iso-halo block theories. Here, the multi-regularization and multi-constraint Keywords：large aperture diffractive optical system;degradation of diffraction imaging quality;inversion recovery model;imaging quality enhancement- 104
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Published：2020-08-13 -
Large aperture optical element wavefront gradient controlled by computer numerical controlled polishing
Abstract：To improve the Graphical Representation of Model Spaces (GRMS) index of optical elements, a new polishing method based on smoothing surface shape by fitting was proposed after the rules of the effects of surface shape precision and distribution on the wavefront gradient index were summarized. The fundamentals and workflow of this method were then presented. First, the surface shape discontinuity was determinedby scanning and computing the original surface shape data. Then, the new surface shape data used in Keywords：optical manufacture;optical elements;Computer Numerical Controlled(CNC) polishing;Gradient Root Mean Square(GRMS);smoothing surface shape by fitting- 116
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Published：2020-08-13 -
Strain transmission and accuracy experiment on fiber Bragg grating small-diameter shape sensors
Abstract：Small-diameter shape sensors have a variety of potential applications in medicine such as the positioning of breast tumor chest needles, shape display of intestinal endoscopes, and positioning of cardiac vascular catheters. The shape-reconstruction and end-positioning accuracies of shape sensors have always been major concerns of researchers. To improve the shape-reconstruction accuracy of a fiber Bragg grating (FBG) shape sensor, the strain transfer law of an FBG shape sensor with 90° distribution of fiber Keywords：fiber sensing;fiber Bragg grating;strain transmission;shape reconstruction- 112
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Published：2020-08-13 -
Quantum random number Gaussian noise signal generator
Abstract：The existing method used to generate Gaussian noise signals is to generate random numbers through mathematical calculation. However, this method cannot achieve a true random signal nor can it match the actual noise signal. In this study, a Gaussian noise signal generator based on a quantum random number is proposed. A single-photon detector detects the photon signal of the selected path as the source of the random number and realizes the Gaussian noise signal generator based on a true random number. The ran Keywords：Gauss noise;single photon;random number source;amplitude spectrum;power spectrum- 102
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Published：2020-08-13 -
Quantum random number Gaussian noise signal generator
Abstract：The existing way of generating Gauss noise signal is to generate random numbers by means of mathematical calculation, which can not really achieve randomness. In this paper, a true random Gauss noise signal generator is realized by detecting the photon signal of the selected path by a single photon detector as the source of generating a random number. The random number is processed by WGN Gauss algorithm to get the Gauss noise signal, which is implemented in Verilog language in FPGA. The results demonstrate that the amplitude spectrum of the generated noise signal obeys the Gauss distribution, and the power spectrum of the noise signal obeys the uniform distribution, which satisfies the characteristics of the Gauss white noise. Compared with the existing methods, based on quantum random number, its source of random number is clear, and it can achieve real randomness. It provides a simple scheme for the realization of a true random number of Gauss noise signal generator.Keywords：Gauss noise;single photon;random number source;amplitude spectrum;power spectrum- 67
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Published：2020-08-13
Modern Applied Optics
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Risley-prism-based beam scanning system for mobile lidar
Abstract：A beam scanning system is a fundamental component of a light detection and ranging (lidar) system, as it determines the field of view (FOV). To increase the FOV and maintain a specific angular resolution, multiple laser diodes are often used in a mobile lidar. However, the time response of different laser diodes is different, resulting in a mutual ranging difference between different ranging channels of the lidar. Risley prisms are outstanding beam pointing devices that offer good prospects for beam scanning of mobile lidars because of their notable features such as large FOVs and high pointing precision. In this study, the optical and mechanical configurations of a scanning system are designed based on the beampointing and scanpattern models, which can realize twodimensional scanning over a wide FOV. The horizontal and vertical FOVs of the scanning system are 360° and 30.4°, respectively. When the scanning system operates at a frequency of 5 Hz and scan lines of 30 with a 1MHz repetition rate laser, the horizontal and vertical resolutions are 0.05° and 1.0°, respectively. These performance indicators are comparable with those of mainstream mobile lidars and can meet the actual requirements of mobile lidars. Most importantly, this scanning system can eliminate ranging differences between different channels, and significantly improve the ranging precision of the lidar.Keywords：mobile lidar;Risley prisms;beam scanning system;two-dimensional scanning- 62
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Published：2020-08-13 -
Influence of Plasma Treatment on optical properties and damage properties of TiO2 Thin Films
Abstract：To improve the optical properties and laser damage threshold of TiO2 films and to ensure their wider use and greater stability in lasers, TiO2 films were deposited on K9 glass using electron beam evaporation technology, and the samples were post-treated with Ar/O mixed plasma. The effects of plasma posttreatment time on the laser damage characteristics of TiO2 thin films were analyzed by measuring the film spectral characteristics, surface defect density, surface topography, damage threshold, and damage topography. The experimental results showed that the refractive index and fill density of the films increased with increasing posttreatment time, whereas the physical thickness and surface roughness decreased. In addition, the surface defect density first decreased and then increased. After a 20-min post-treatment, the LIDT of the TiO2 film samples increased from 5.6 to 9.65 J/cm2 under a 1 064 nm laser irradiation, representing an increase of 72.3%.Keywords：TiO2 thin film;electron beam evaporation;optical constant;plasma treatment;laser damage threshold- 45
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Published：2020-08-13 -
Development of high-temperature resistant incremental encoder
Abstract：To measure the angle shift that occurs under high-temperature conditions, a fiber-based high-temperatureresistant incremental encoder was developed in this study. First, a high-temperature-resistant fiber was employed to transfer light under high-temperature conditions. A field programmable gate array was used to process the incremental encoder's electric signal, and a USB was used to transfer the angle in a normal temperature environment. Second, the effect of the collimation degree of a light beam on the performance of the optical encoder was analyzed, and then a lightemitting diode (LED) convex lens fiber couple was developed. Finally, 23 surface polyhedrons and autocollimations were used to test the accuracy, and the accuracies of the LED convex lens fiber couple and fiber direct couple were compared. The results show that this system can work normally in 100 ℃ conditions. The size of the encoder head is 62 mm× 42 mm, the resolution is 0.3", and the precision 3σ is 13.55 ″, which represent an improvement of 20.8% over that of the fiber direct couple. The system thus satisfies high-temperature conditions. .Keywords：photoelectronic encoder;fiber;high-temperature resistant;LED convex lens fiber couple;incremental;FPGA+USB- 63
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Published：2020-08-13 -
Large aperture optical element’s wavefront gradient controlled by CNC polishing
Abstract：To improve the Graphical Representation of Model Spaces (GRMS) index of optical elements, a new polishing method based on smoothing surface shape by fitting was proposed after the rules of the effects of surface shape precision and distribution on the wavefront gradient index were summarized. The fundamentals and workflow of this method were then presented. First, the surface shape discontinuity was determinedby scanning and computing the original surface shape data. Then, the new surface shape data used in guiding the processing were generated using the nonuniform rational Bspline fitting algorithm and the data between the neighbor discontinuities was reconstucted. Finally, appropriate processing parameters were established based on the generated surface shape data. An experimental study was conducted on K9 material plane mirrors of 610 × 440 mm, and results showed that the proposed method can reduce the GRMS from 11 nm/cm to less than 7.7 nm/cm in two polishing cycles while maintaining a high surface shape precision.Keywords：optical manufacture;optical elements;Computer Numerical Controlled(CNC) polishing;Gradient Root Mean Square(GRMS);smoothing surface shape by fitting- 44
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Published：2020-08-13 -
Composite Imprint Lithography Technique for Mass Producing Large-area Microstructures
Abstract：To implement low-cost mass production of large-area micro/nanostructures on large-size rigid and fragile substrates, this study presents a novel composite nanoimprint lithography technique. First, the basic principle and process of the composite imprint lithography are described. Then, the effects and rules of the key process parameters (i.e., spreading speed of the flexible mold, imprint force, imprint speed, and curing time) on the imprinted patterns are revealed by a series of experiments. Finally, through a combination of the homemade composite imprinter and optimized process parameters, four typical cases are illustrated. We fabricated largearea micro/nanostructures on three rigid substrates (glass, polymethyl methacrylate, and sapphire), including microscale columnar structures (the largest graphic area is 132 mm× 119 mm), a microscale grating structure (the largest area is 6inch round), and a nanoscale columnar structure (the graphic area is 47 mm× 47 mm). Experimental results show that the presented composite imprint lithography technique provides a novel way for the macroscopic quantity preparation of large-area micro/nanostructures and large-area patterning on rigid or fragile substrates, thus presenting a bright prospect for industrial applications.Keywords：composite imprint lithography;large-area nanoimprint lithography;composite flexible mold;non-planar substrates;large-area microstructures- 44
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Published：2020-08-13 -
Active compensation of contour error of X-Y linear motor precision motion platform
Abstract：To address the deficiencies of the traditional cross-coupling control structure, an active compensation control structure was proposed in this study to reduce the contour error of an X-Y linear motor precision motion platform. First, a permanent magnet synchronous linear motor was used to analyze the single-axis positioning tracking error, where the tracking error was related to the position reference. Therefore, adjustment to the amount of coupling compensation to the reference instruction was added to the system, which considered the disturbance of the reference command in the actual working condition. The contour error components were compensated to the position and speed loops of each axis servo and verified by a simulation and an experiment. Results show that the average value of the contour error of the X-Y axis motion platform when tracking a large curvature complex track using an active compensation method is 20.68 μm. The singleaxis tracking error is 70 μm. Compared with the traditional cross-coupling control structure, the accuracy of the active compensation structure contour error is improved by 15.5%, the single-axis tracking error is reduced, and the reference command disturbance can be suppressed.Keywords：contour error;active compensation;X-Y motion platform;linear motor;tracking error- 47
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Published：2020-08-13
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Flexible center of gravity measurement method and uncertainty evaluation
Abstract：To measure the center of gravity of a large-sized aircraft, a flexible center of gravity measurement method is proposed. A method to obtain the line that passes through the center of gravity, the coordinate transformation, and the means to obtain the center of gravity itself are also proposed. First, the projection of the line that passes through the center of gravity is measured, and a line that passes through this projection point is established and converted into a coordinate system of the body under tes Keywords：center of gravity measurement;flexible measurement method;uncertainty analysis;Monte Carlo simulation- 103
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Published：2020-08-13 -
Gringing performance degradation of diamond wheel
Abstract：Acoustic emission is the most direct and sensitive characterization of grinding interference. Therefore, to ensure high-precision grinding, acoustic emission signals were used to evaluate the degradation in grinding performance of a diamond wheel. A fused silica grinding experiment was conducted using a newly trimmed diamond grinding wheel to record the acoustic emission signal and surface morphology of the grinding wheel during its life cycle. A wavelet packet analysis was used to determine the typical low Keywords：acoustic emission;wavelet packet analysis;feature extraction;wear monitoring- 105
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Published：2020-08-13 -
Composite imprint lithography for mass producing large-area microstructures
Abstract：To implement low-cost mass production of large-area micro/nanostructures on large-size rigid and fragile substrates, this study presents a novel composite nanoimprint lithography technique. First, the basic principle and process of the composite imprint lithography are described. Then, the effects and rules of the key process parameters (i.e., spreading speed of the flexible mold, imprint force, imprint speed, and curing time) on the imprinted patterns are revealed by a series of experiments. Finally, throu Keywords：composite imprint lithography;large-area nanoimprint lithography;composite flexible mold;non-planar substrates;large-area microstructures- 186
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Published：2020-08-13 -
Minimum deviation of triaxial velocity tracking tactic arithmetic for three-axis turntable
Abstract：Few real-time methods exist for three-axis turntable tracking when attemping to solve the orientation change of targets. The alt-azimuth and alt-alt methods, which lock the roll and azimuth axes of the turntable, respectively, are mostly utilized. However, these two methods suffer from the problem of tracking in blind zones. In this study, a minimum deviation of triaxial velocity (MDTV) algorithm was proposed to improve the performance of three-axis turntable tracking. A motion model of a three-axis turntab Keywords：three-axis turntable;alt-alt tracking pedestal;alt-azimuth tracking pedestal;high precision tracking- 85
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Published：2020-08-13 -
Active compensation of contour error of
X -Y linear motor precision motion platformAbstract：To address the deficiencies of the traditional cross-coupling control structure, an active compensation control structure was proposed in this study to reduce the contour error of anX-Y linear motor precision motion platform. First, a permanent magnet synchronous linear motor was used to analyze the single-axis positioning tracking error, where the tracking error was related to the position reference. Therefore, adjustment to the amount of coupling compensation to the reference instruction was added to the Keywords：contour error;active compensation;X-Y motion platform;linear motor;tracking error- 136
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Published：2020-08-13 -
Design of repeatable locking/unlocking mechanism for spaceborne laser communication terminal
Abstract：A repetitive locking/unlocking mechanism based on a Shape Memory Alloy (SMA) wire was proposed to meet the multiple locking/unlocking requirements of the servo system of an onboard laser communication terminal during orbit. First, the working principle of a repeated locking/unlocking mechanism that used a spring component to realize locking and that of an SMA wire output return stress to unlock were analyzed. The locking principle was applied to optimize the locking force and displacement. Second, the locki Keywords：unlocking mechanism;memory alloy wire;repeatable;spring;unlocking force- 104
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Published：2020-08-13 -
Influence of radial temperature gradient on surface figure of lightweight reflective mirror
Abstract：To analyze the effects of radial temperature gradients on the surface figures of lightweight reflective mirrors, a 2-m-aperture lightweight mirror of a space camera was taken as the research object and a finite element model of the mirror was established. The effects of different radial temperature gradients and lightweight structures on the surface figure Root Mean Square (RMS) values of reflective mirrors was analyzed, and the accuracies of a simulation method and conclusions were verified through an expe Keywords：radial temperature gradient;thermal distortion;reflective mirror;surface figure;lightweight- 123
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Published：2020-08-13 -
Study on mechanical properties and random response suppression of micro-scale mechanical-sensitive component
Abstract：To solve the problem of excessive random vibration response of a micro-scale mechanical-sensitive component of an optical instrument for a space station, micro-scale and fine modeling of the component was conducted, its mechanical properties were studied, and effective measures were adopted to suppress its random response. First, the boundary coordination of the micro-scale model and the variation problem of the micro-scale finite element were discussed. On this basis and according to the characteristics of Keywords：micro-scale;fine modeling;random response;optical instrument;mechanical-sensitive component- 102
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Published：2020-08-13 -
Micro sharp groove by EDM with multi-station shape-angle electrode
Abstract：To solve the difficulty of ensuring the shape accuracy of micro grooves in a micro device, a new method of using multi-station shape-angle electrodes through Electrical Discharge Machining (EDM) was proposed. A total of 304 stainless steel samples were used as workpiece materials, and pure copper and copper-tungsten alloy (W75%) were selected and compared as electrode materials. To reduce the influence of electrode wear and installation error, multi-station shape-angle electrodes were machined by low-speed Keywords：sharp groove;constant speed and multiple cutting by WEDM;multi-station shape-angle electrode;Electrical Discharge Machining(EDM)- 124
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Published：2020-08-13
Micro/Nano Technology and Fine Mechanics
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Intelligent fault diagnosis of thin wall bearing based on information fusion
Abstract：To realize the intelligent diagnosis of bearing faults, an intelligent fault diagnosis method for the thin-wall bearing of a robot based on information fusion was studied. First, a test and multi-information data acquisition system of the thin-wall bearing of a robot was built by acquiring acoustic emission and vibration acceleration signals. Then, data from acoustic emission and vibration acceleration signals detected during the test of thin-wall bearing under different fault types, equivalent loads, and r Keywords：thin wall bearings;multi-information fusion;fault diagnosis;neural network;intelligent diagnosis- 132
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Published：2020-08-13 -
Active contour model for image segmentation based on Retinex correction and saliency
Abstract：To achieve fast and accurate segmentation of natural images with intensity inhomogeneity and complicated backgrounds, an active contour model combined with Retinex correction and saliency analysis for image segmentation was proposed. Retinex correction was applied to obtain the reflection component of objects in images; this could suppress the influence of intensity inhomogeneity caused by nonuniform illumination. Moreover, the Retinex-corrected image reflected the image essence more objectively, ensuring t Keywords：image segmentation;intensity inhomogeneity;retinex;saliency detection- 121
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Published：2020-08-13 -
Airborne LiDAR point cloud classification using transfer learning
Abstract：In order to overcome the problem that existing airborne methods for LiDAR point cloud classification have difficulties in obtaining high classification accuracy and reducing processing time simultaneously, a method using transfer learning for classifying airborne LiDAR point clouds was proposed. First, normalized height, intensity, and normal vector were calculated for each LiDAR point, by setting different sizes of neighborhood, and multi-scale point cloud feature images were generated by utilizing the pro Keywords：transfer learning;feature image;classification;airborne LiDAR point cloud- 162
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Published：2020-08-13 -
Tone mapping method combining guided filtering and nonlinear second-order features
Abstract：To improve the visualization effect and enhance the local detail information of an image, a tone-mapping method that combines guided filtering and nonlinear second-order features was proposed. First, the luminance information of an input image was extracted and the luminance image was decomposed by a multi-scale using a guide filter to obtain a base layer and a detail layer image. Second, a weighting map of the detail layer was constructed by the guided filtering method, a nonlinear second-order feature was Keywords：image processing;high dynamic range image;tone mapping;guide filter- 103
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Published：2020-08-13 -
Siamese network tracking with redetection mechanism
Abstract：To solve the insufficient tracking capability problem for a fully convolutional Siamese network (SiamFC) in complex scenarios such as those involving fast motion and large similar interference, SINT was introduced as a redetection network to improve the SiamFC. When multiple peaks appeared in the tracking response map, the proposed algorithm enabled the redetection network to redetermine the target position with higher accuracy. At the same time, a generative model was adopted to construct a template to ada Keywords：object tracking;siamese network;redetection;generative model;high-confidence update- 134
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Published：2020-08-13 -
Mesh-based adaptive planning for complex surface accurate measurement
Abstract：Layout optimization of inspection points is key for the inspection of geometric errors in models with complex surfaces. To deal with difficulties in the adaptive planning of whole inspection points of model components that were characterized by multiple surface characteristics, mesh-based adaptive planning of inspection points was studied. A complex surface model was transformed into a dense triangular mesh model, and the triangular mesh simplification method was used for adaptive planning of inspection poi Keywords：complex surface inspection;adaptive sampling;triangular mesh simplification- 122
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Published：2020-08-13 -
Extraction of line contour points from point cloud data using pattern vector method
Abstract：In this article, an extraction method of line contour points from point cloud data (for a fold-line edge and a ridge edge with a small chamfer) is proposed. In this method, multiple-direction slices were constructed to obtain section data containing line contour points. Then, according to the form characteristic of the section data, a pattern vector was constructed by using the normal angle of two adjacent points to represent the characteristic. The section data was divided into many small groups, each with Keywords：pattern vector;point cloud;line contour;multiple-direction slice- 98
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Published：2020-08-13 -
Spectral-spatial joint classification of hyperspectral image algorithm based on improved Gaussian process regression
Abstract：To solve the problems of high calculation amounts and low classification accuracy of Gaussian process regression in hyperspectral image classification, a spectral-spatial joint classification algorithm for hyperspectral images based on improved Gaussian process regression was proposed. A subset of samples was selected using maximum variance as the index to narrow the calculation range of the Gaussian process regression parameter solution, and a square root matrix decomposition method was introduced to predi Keywords：classification of hyperspectral images;Gauss process regression;maximum variance;square root matrix decomposition;spectral-spatial associated distance- 120
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Published：2020-08-13 -
Wearable fatigue monitoring glasses based on N-Range
Abstract：Current fatigue monitoring equipment is expensive, non-portable, and its algorithm has a low robustness in eye movement image processing. Existing front-end camera fatigue monitoring schemes have many limitations and greatly affect their users efficiency; as such, the development of portable and accurate fatigue monitoring systems is very challenging. In this paper, a new type of fatigue monitoring glasses and N-Range image processing algorithm is proposed to improve the robustness of eye location analysis Keywords：fatigue monitoring;PERCLOS;N-range;eye partial excision;portable wearing equipment- 102
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Published：2020-08-13
Information Sciences
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