Principle and experimental study of self-stability of reflector based on two magneto-optical crystals and two mirrors under effect of temperature and radiation
Authors: Zhao Gu-Hao , Mao Shao-Jie , Zhao Shang-Hong , Meng Wen , Zhu Jie , Zhang Xiao-Qiang , Wang Guo-Dong , Gu Wen-Yuan ,   State Key Laboratory of Air Traffic Management System and Technology, Nanjing 210007, China,   College of Air Traffic Control & Navigation, Air Force Engineering University, Xi'an 710077, China,   Information and Navigation College, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

Acquisition, tracking and pointing (ATP) is an important subsystem of satellite-based optical communication system. It controls the direction of the beam passing through the mirror, and then completes the alignment and stabilization of intersatellite/satellite-ground light path. As is well known, the ordinary mirror changes the polarization of photons, so the ATP mirrors must be specially processed in quantum communication system and coherent optical communication system. For example, in order to counteract the change of photon polarization caused by the mirror, it is usually necessary to coat the mirror. However, this membrane structure must be tested by the radiation and temperature change from the space environment. A polarization-independent reflector based on two magneto-optical crystals and two mirrors is proposed. This structure does not need any special treatment (such as coating) for the reflector. It can realize polarization-independent reflection at any angle only through the reasonable configuration of the ordinary reflector and 90° rotatory crystal. In addition, it is found that the structure has self-stability, that is, when the polarization characteristics of optical devices change due to environmental change, the overall polarization reflection characteristics of the reflective structure remain unchanged. The polarization equation of reflected light of reflector based on two magneto-optical crystal and two mirrors is derived. The polarization of reflected light under environmental influence is simulated, and the polarization independent reflection self-stability of double-rotating double-reflection structure is found. The polarization-independent self-stabilization of this structure is verified by temperature and radiation experiment. The experimental results show that the average polarization retention of the reflecting light of the reflector based on two magneto-optical crystal and two mirrors can reach 99.77% when the temperature varies from －45 ℃ to 85 ℃. The mirrors and the magneto-optical crystals are irradiated by cobalt 60 with a total dose of 400 Gy, and the average polarization retention of the reflective structure is also 99.35%. The experimental results show that the polarization-independent reflectance can be kept stable for a long time in the space environment where radiation and temperature change dramatically. Relying on this self-stability, the reflector based on two magneto-optical crystals and two mirrors can maintain high polarization-independent reflection capability for a long time in a space environment. This makes it a new option for polarization-preserving reflective components in satellite-based optical communication systems.