• Acta Photonica Sinica
  • Vol. 52, Issue 4, 0411001 (2023)
Liang FANG1、2、4、*, Weimin WANG5, Qiang WANG1、3, Xin CHENG1、2, Zhenjie FAN1、2, Hui ZHANG1、2、4, Rujin ZHAO1、2、4, and Enhai LIU1、2、4
Author Affiliations
  • 1Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
  • 2Key Laboratory of Science and Technology on Space Optoelectronic Precision Measurement, Chinese Academy of Sciences, Chengdu 610209, China
  • 3State Key Laboratory of Optical Technologies on Nano-fabrication and Micro-engineering, Chinese Academy of Sciences, Chengdu 610209, China
  • 4University of Chinese Academy of Sciences, Beijing 100049, China
  • 5Defense Key Disciplines Laboratory of Novel Micro-nano Devices and System Technology, Chongqing University, Chongqing 400044, China
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    DOI: 10.3788/gzxb20235204.0411001 Cite this Article
    Liang FANG, Weimin WANG, Qiang WANG, Xin CHENG, Zhenjie FAN, Hui ZHANG, Rujin ZHAO, Enhai LIU. Microshutter Array Design of Field-of-view Gated Imaging Systems for All-time Star Sensor[J]. Acta Photonica Sinica, 2023, 52(4): 0411001 Copy Citation Text show less

    Abstract

    Traditional all-time star sensors usually have a narrow Field of View (FOV) and adopt single star tracking mode. Because of only one target star in the FOV, the optical system should be installed on a two-dimensional rotation/scanning platform, or multiple telescopes are used to achieve synchronous measurement, which can lead to many shortcomings such as large volume, low reliability and poor autonomy. The optical imaging system based on FOV gated technology can obtain the wide FOV and strong sky background radiation suppression ability at the same time by combining a large total FOV with a narrow gated FOV, which is expected to achieve multi-star detection and star pattern recognition in the daytime. It has the advantages of small volume, light weight and good autonomy. In the FOV gated optical imaging system, it is necessary to use a key device of microshutter array to quickly switch the gated FOV. Microshutter arrays need to have the characteristics of large element size, high duty cycle and high response speed. At present, there is no microshutter array that meets the requirements can be used. In this paper, a short-wave infrared band FOV gated imaging system principal prototype is designed. In this system, two sets of microlens arrays are used, the aperture of the microlens element is 4 mm, the FOV gated imaging channel number is 7×7, and each imaging channel can obtain near diffraction limit imaging quality. The microshutter array is placed behind two sets of microlens arrays, and the size of the microshutter element is also 4 mm. The position of the microshutter element corresponds to that of the microlens element one by one. In order to meet the application requirements of the FOV gated imaging system, the main design parameters of the microshutter element are determined as follows. The area duty cycle is not less than 90%, the switching response time is not less than 25 ms, and the drive voltage is not more than 120 V. Based on the principle of electrostatic parallel plate capacitive drive and the MEMS bulk silicon process, two rectangular silicon thin plates are designed as light shields for microshutter elements. Furthermore, the light shields are also used as upper electrodes, and the lateral sides of silicon substrate are used as lower electrodes. By loading and removing the drive voltage, the switching of the open and closed states of a microshutter element can be realized. Considering the material characteristics, parameters such as electrode width, cantilever beam width and thickness are first determined. Then, according to the mathematical model of the microshutter element, the influence of different number and length of cantilever beam on the drive voltage and response time is analyzed. The calculation results show that the driving voltage increases with the number of cantilevers beams and decreases with its length. In order to minimize the driving voltage, the number of cantilevers beams should be 2, and the beam length should be greater than 200 μm. On the other hand, since the longer the cantilevers beam, the longer the response time of the microshutter element. In order to meet the 25 ms response time requirement, the beam length of the cantilevers beam is determined as 200 μm.The Ansoft Maxwell electromagnetic field simulation software is used to simulate the electrostatic moments of the microshutter at different torsion angles and then the Comsol Multiphysics finite element analysis software is used to calculate the torsional elastic coefficient of the cantilever beam. According to the balance conditions of the electrostatic moment and the elastic recovery moment, the variation of the torsion angle and the drive voltage is presented. The results show that the microshutter element can be opened when the drive voltage is 106.4 V, which is basically consistent with the theoretical calculation result of 114 V and demonstrates the feasibility of the design parameters of the microshutter array. In addition, since only one microshutter element is turned on under normal operating conditions, the light incident to the other unopened microshutter elements can be reflected or absorbed. The reflected light can form stray light within the optical system, which will affect the distribution of sky background radiation on the image surface of the detector. Therefore, according to the structural layout of the designed FOV gated imaging system, the effect of the surface reflectivity of the microshutter element on the stray light in the system is simulated and analyzed by using the advanced stray light analysis software ASAP. The results show that as the surface reflectivity of the microshutter element increases from 3% to 80%, the average illumination of the sky background radiation at the image plane on the surface of the detector increases very little, and the impact on stellar detection is almost negligible. Therefore, in the design of microshutter arrays, there is no special requirement for the reflectivity of the microshutter surface. This study provides a theoretical basis for the processing of microshutter array in FOV gated imaging system.
    Liang FANG, Weimin WANG, Qiang WANG, Xin CHENG, Zhenjie FAN, Hui ZHANG, Rujin ZHAO, Enhai LIU. Microshutter Array Design of Field-of-view Gated Imaging Systems for All-time Star Sensor[J]. Acta Photonica Sinica, 2023, 52(4): 0411001
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