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Issue 6 ， 2022
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Design of MWIR Hadamard coded imaging spectrometer
Abstract：In a space Hadamard transform spectral imager （SHTSI） system， encoding the template using digital mirror devices （DMDs） can ensure that the system is miniaturized and lightweight， and has high resolution and high frame rate. However， modulation using DMD causes the focus plane of SHTSI to tilt； consequently， the resultant image obtained from the spectrometer does not match the cooled shield of the detector. This causes image degradation and field of view loss. In this paper， a novel SHTSI system design is proposed to improve the quality of the final image. The design also addresses the issues of cold stop aperture mismatch and field of view accuracy. In this scheme， the design of the front lens contains a tilted and off-center lens， which tilts the image of the object by 24° with respect to the primary focus plane. Based on this method， a SHTSI optical system is designed， and the spot diagram RMS of the full field of the system was calculated to be less than 5 µm. This ensures that the system generates an even image. According to this design scheme， a SHTSI principle model machine is developed. The experiment results show that the evaluation of the restored spectral angular distance of the SHTSI system is better than 0.052.Keywords：optical designing;Hadamard transform spectral imager;MWIR spectral imaging;digital mirror devices- 244
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Published：2022-04-26 -
High-accuracy characterization of areal micro-nano steps measured with optical microscopes
Abstract：The measurement data of areal micro-nano steps using optical microscopes are multi-dimensional topographical data. They are huge and complex with low correlation. It is very difficult to characterize such a type of measurement. Additionally， the measurement usually includes bad points that deteriorate its accuracy. This paper proposes a method for characterizing areal micro-nano steps using optical microscopic profilometries. First， the measurement system is selected， and the measurement method is designed according to the structural characteristics of the micro-nano steps to obtain the measurement data. Second， the reconstruction method is developed for the areal topographic measurement data， decreasing the complex multi-dimensional data into sequenced 2D coordinates. Subsequently， quantitative characterization models are created for parameterization of step heights， identifying outliers while mapping the centroid of 2D points into step height parameters. Finally， the accuracy and robustness of the algorithm is further improved by iterative convergence. Experiments on two step height standard artefacts are carried out. The results show that the method can accurately characterize the steps for data with measurement defects. A comparison with certified values shows that the measurement and characterization error is below 1.5%.Keywords：3D nano structures;step height;optical microscopic measurement;parameterization;areal topography- 225
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Published：2022-04-26 -
Three dimensional isolation system for large ground-based optical telescope
Abstract：Seismic hazards are an important issue for both observatory and telescope structures. In order to meet the anti-seismic requirements of large ground-based optical telescopes， a three-dimensional isolation system with unique characteristics is proposed and designed. A hydraulic damping system， which consists of additional passive components in the hydraulic supporting system of the telescope， senses critical oscillations and initiates the isolation system of the telescope before critical acceleration values are reached， in order to limit the loads to acceptable values. Finite element analysis results indicate that responses of the telescope main structure without the isolation system show significant dynamic amplification， and their amplification to input ratios for the NS， EW， and UD directions are about 142%， 145%， and 369%， respectively. By contrast， the isolation system suppresses response acceleration compared with input， and their amplification ratios for the NS， EW， and UD directions are about 22%， 38%， and 4%， respectively. Simulation analyses show that the isolation system can achieve adequate seismic isolation performance and meets the anti-seismic design requirements of large ground-based optical telescopes.Keywords：seismic hazard;large ground-based telescope;isolation system;hydraulic damping;finite element analysis- 182
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Published：2022-04-26
Modern Applied Optics
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Research on absolute linear time-grating displacement sensor with one-pole-difference structure and analysis of measurement error characteristics
Abstract：Focusing on the problems of complex coding and strict lithography for absolute displacement sensors， a “precise number of pole + precise displacement within a pole” method of absolute displacement measurement using time-grating sensors with a one-pole-difference structure is proposed. The fixed ruler of the sensor comprises two rows of excitation windings with a one-pole-difference structure， which comprises cosine windings and sine windings arranged orthogonally in space. The orthogonal excitation current is applied to the excitation windings， and sinusoid induction windings in the moved ruler are employed to induce a time-varying magnetic field. Then， the two traveling wave signals with one-pole-difference are obtained. After signal decoupling， the absolute displacement can be obtained using the “precise number of pole + precise displacement within pole” method. Measurement accuracy caused by installation height and installation error is analyzed. The results demonstrate that the deflection angles of installation led to an amplitude increases in DC and second harmonics， and after error correction， the measuring accuracy reached ±1.2 µm within the range of 90 mm. Theoretically， the resolution reached 0.1 µm.Keywords：absolute displacement measurement;time-grating sensor;one-pole-difference structure;measurement error analysis- 189
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Published：2022-04-26 -
Design and parameter optimization of frictionless cylinder based on aerostatic bearing
Abstract：A frictionless cylinder with an air bearing was proposed to satisfy the demand of an ultra-precision vertical axis for a frictionless and stable gravity balance system. The parameters of the air bearing are optimized. First， the initial parameters of the air bearing are determined； then， an analysis model using ANSYS is established. The calculation results based on the engineering method and the experimental results are used to verify the analysis model. Then， the response surface optimization method is used to obtain the bearing capacity， air consumption， and bending moment under different orifice arrangements （corresponding to the optimal air film thickness）， based on the established model. According to the above results， the optimal air bearing parameters are selected. The results demonstrate that a non-linear relationship exists between the bearing capacity and the number of orifices. As the number of orifices increases， the bearing capacity increases rapidly and then remains constant. The arrangement of double-row orifices can ensure a sufficient bending moment with fewer orifices. Finally， the cylinders before and after parameter optimization are tested. The results demonstrate that the bearing capacity increases by about 7.7% and the bending moment increases by about 15.7% after parameter optimization. The parameter optimization of air bearing based on the response surface is efficient and feasible. The proposed air bearing frictionless cylinder can satisfy the requirements of the gravity balance system.Keywords：frictionless cylinder;aerostatic bearing;finite element analysis;ultra-precision vertical axis;parameter optimization- 188
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Published：2022-04-26 -
A compensation method for spatial geometric error of double roller-rail involute measuring instrument
Abstract：To solve the difficult problem of precision measurements of class-1 gear involute artefacts， this paper proposes a new method of spatial geometric error compensation of a double roller-rail involute measuring instrument. First， a mathematical model of the mapping relationship between the spatial geometric error and involute tooth profile deviation is established. Subsequently， the comprehensive installation error of the gear involute artefact， the base discs， and the mandrel， and the roundness error of the base discs are analyzed based on the established model. Finally， the tooth profile deviations of the gear involute artefact are measured by changing parameters such as the arc segment of base discs corresponding to the roll path length of involute， the comprehensive installation eccentricity， and phase. The following conclusions are drawn. The difference between the measured and theoretical values of the tooth profile deviation caused by the roundness error of the base discs is no more than 0.04 μm. Considering the eccentricity e of 3.46 μm as an example， when the pure rolling component is assembled according to the maximum profile slope deviation phase （λ1=λ2=λ3=70°）， the measured value of the profile slope deviation differs from the theoretical value by -0.16 μm， and the relative error is about 4 %. When assembled according to the maximum profile form deviation phase （λ1=λ2=λ3=160°）， the difference between the measured and theoretical values of the profile form deviation is 0.01 μm， and the relative error is about 2%. The experimental results demonstrate the effectiveness of the spatial geometric error compensation method， which provides measurement means for realizing the high-precision manufacturing of class-1 gear involute artefact.Keywords：spatial geometric error;tooth profile deviation;gear involute artefact;error compensation;measurement of the involute- 130
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Published：2022-04-26 -
Experimental study on rolling and brittle fracture to single crystal silicon and sapphire by diamond cutter wheel
Abstract：Rapid partitioning of integrated circuit chips is a key process in semiconductor device manufacturing. Usually， a fixed single-point diamond tool blade is used for scribing and cutting. However， the process can result in irregular cracks and damage chip circuits. Therefore， for two chip materials， i.e.， single crystal silicon and sapphire， a 2.5 mm diameter diamond cutter wheel was used for rolling brittle fracture processing experiments. We analyzed the stress distribution under different machining processes and discussed the effects of the cutter wheel geometry and process parameters on crack extension and the rolling brittle fracture quality of different materials. The results show that the concentrated tension stress at the cutter wheel edge end generates and expands micro-cracks， which gradually shape micro-cutting marks in the rolling direction， leading to the final brittle fracture. However， this produces lateral cracks that make it easier to break the brittle fracture edge. Under a suitable tension stress， edge breakage is as low as approximately 1 μm and the brittle section quality is high. In addition， the greater the hardness and fracture toughness of the chip material， the smaller the cutter wheel angle and the greater the rolling pressure. When the rolling pressure of single crystal silicon is 0.015 MPa， the tensile stress at the edge contact is approximately 100 MPa， the rolling pressure of sapphire is 0.095 MPa， and its tensile stress is approximately 350 MPa， crack expansion of the fracture section after rolling and brittle fracture is relatively uniform， and the quality of the fracture surface is optimal. Finally， the experimental result showed that the quality of integrated circuit chips cut with the diamond cutter wheel with a micro-serrated structure is better.Keywords：single crystal silicon;sapphire;diamond cutter wheel;crack extension;precision rolling and brittle fracture- 146
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Published：2022-04-26 -
Droplet motion between closed and open regions on digital microfluidic chips
Abstract：In order to facilitate the implementation of complete and highly automated biochemical analyses on digital microfluidic chips， two conventional configurations were integrated on a flexible substrate to establish a hybrid configuration. The motion between the closed and open regions was studied. First， the motion characteristics of a droplet at the boundary were analyzed according to the force balance analysis method. Based on this， the conditions for crossing the boundary were deduced， and optimization methods to realize two-region motion were developed. Then， the two-region reciprocating motions of the droplet were realized on three types of flexible substrates. Finally， the influence of the horizontal and vertical positions and the thickness of the top plate on the closed region on the droplet movement between the two regions was analyzed. The experimental results show that lateral position mode II and a thin top plate are conducive to the free reciprocating motions of the droplets and can reduce the driving voltage； to realize bidirectional cross-region movement of 0.8-1.2 μL droplets， the gap between the plates in the closed region on the polyethylene terephthalate-based flexible chip should be within 150-350 μm. The experimental results demonstrate that the droplets can move back and forth freely between the closed and open regions， and the hybrid structure facilitates droplet operation and highly automated analysis on a single chip.Keywords：digital microfluidic;electrowetting-on-dielectric;two-region motion;hybrid configuration- 168
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Published：2022-04-26
Micro/Nano Technology and Fine Mechanics
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Image dehazing method quality assessment
Abstract：In recent years， responding to subjective assessment results in assessment methods by targeting the quality of dehazing algorithms has become common， but this lacks quantitative description. However， existing objective quality assessment methods and subjective assessment have been inconsistent， and the two sometimes diverge. Therefore， to improve the objective quality assessment performance of a dehazing method， a full reference dehazing method quality assessment based on artificially synthesized images is proposed here. First， a synthetic image dataset is established that includes reference haze-free， synthetic hazy， and dehazed images obtained by using eight state-of-the-art dehazing algorithms on these synthetic hazy images. Second， we classify quality problems that might be introduced by the dehazed images. Third， by combining clarity-related features and existing objective methods of image quality assessment， a dehazing method quality assessment is proposed through mutual integration of image visibility， structural similarity， and color recovery. In the synthetic image dataset， this paper’s method is compared with existing image quality assessment methods for experiments. The experimental results showed that， for the synthetic image dataset， the proposed method performed optimally in SRCC， PLCC， and RMSE metrics. The consistency of this paper’s method with subjective assessment was better， which was more favorable to support research on dehazing algorithms.Keywords：image dehazing;objective quality assessment;synthetic hazy images;image dataset- 258
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Published：2022-04-26 -
SLIC super-pixel segmentation algorithm base on NMI features used in remote sensing image
Abstract：The state-of-the-art super-pixel segmentation algorithm based on simple linear iterative clustering （SLIC） has the problem of over segmentation and discontinuity when processing remote sensing images with extensive details. Here， we propose a remote sensing image segmentation method that combines the NMI-based similarity measure between super-pixel blocks to improve the segmentation effect. First， a guided filtering is used to smooth the pepper noise in the image. Second， the image is segmented at a pixel level using the SLIC algorithm to generate initial super-pixels. Third， to achieve image segmentation， the micro super-pixels are determined based on some criterion and then merged into the adjacent super-pixel blocks with the least difference by calculating the similarity measure with its adjacent super-pixel blocks. This paper’s method reduces the sensitivity of super-pixel to noise and improves the precision of image segmentation compared with traditional segmentation algorithms. The experimental results indicate that the proposed algorithm reduced the number of segmented super-pixel blocks from 4 171 to 282 and reduced the number of micro super-pixel blocks by more than 60%. It also reduced the influence of noise points and improved the over segmentation defects of existing algorithms.Keywords：simple linear iterative clustering;super pixel;regional consolidation;normalized moment of inertia- 155
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Published：2022-04-26 -
Research on aberration correction method of coherent optical communication based on CNN-SPGD algorithm
Abstract：In order to reduce the influence of atmospheric turbulence on the transmission performance of free-space optical communication systems， an adaptive optical correction system is established to correct high-order aberrations. The mixing efficiency， bit error rate， and iteration times of the system are studied. First， the Zernike coefficient of the image is divided into 8 categories and 256 sub-categories， and the categories of input spots are predicted by a CNN model. For each small class of aberrations， the midpoint of the coefficient range of each order is taken as the standard point to form a standard Zernike coefficient vector， and its corresponding standard voltage is taken as the initial correction voltage. The experimental results show that the number of iterations required by the SPGD algorithm to achieve mixing efficiencies of 0.80， 0.85， and 0.9 is 110， 161， and 280， respectively. To reach the same mixing efficiencies， the number of iterations required by the CNN-SPGD algorithm is 4， 37， and 141. For the same number of iterations， the mixing efficiency of the CNN-SPGD algorithm in the system is higher and the bit error rate is lower. Moreover， the CNN-SPGD algorithm has a faster aberration correction speed compared to the SPGD algorithm. The CNN-SPGD algorithm can considerably reduce the number of iterations required by traditional adaptive optics systems and meet the various needs of laser communication.Keywords：free space optical communication;wavefront sensorless;mixing efficiency;bit error rate- 240
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Published：2022-04-26
Information Sciences
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