Principle and experimental study of self-stability of reflector based on two magneto-optical crystals and two mirrors under effect of temperature and radiation
1.State Key Laboratory of Air Traffic Management System and Technology, Nanjing 210007, China 2.College of Air Traffic Control & Navigation, Air Force Engineering University, Xi'an 710077, China 3.Information and Navigation College, Air Force Engineering University, Xi'an 710077, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 61601497).
Received Date:27 March 2019
Accepted Date:15 May 2019
Available Online:01 August 2019
Published Online:20 August 2019
Abstract: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. Keywords:polarization state/ polarization independent reflection/ temperature/ radiation
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2.双旋光双反射结构自稳定性的量子化模型双旋光双反射结构的光路如图1所示, 其中入射光$ \overrightarrow {\rm{O}} $经过反射镜m1和m2的反射, 出射光$ \overrightarrow {\rm{O}} $与$ \overrightarrow {\rm{O}} $之间夹角为90°. 其中两面反射镜采用同样的材料, 且两个入射角分别为θ1 =θ2 = $\dfrac{3}{8}{\text{π}}$. A1和A2分别为两个旋光角为90°的旋光晶体. 图 1 双旋光-双反射结构光路图 Figure1. Optical path diagram of reflection structure based on two magneto-optical crystals and two mirrors.
在两轮的双旋光双反射结构实验中, 光路均按照据文献[13]给出的双旋光双反射结构装调, 在第一轮实验中, 首先测试了双旋光双反射结构的温度变化特性. 从图6中可以看出, 所有的测量点均分布在邦加球面上, 即入射光和反射光均为完全偏振光, 且不同温度下的入射光和反射光几乎完全重合. 图 6 高低温影响下的双旋光双反射结构反射光偏振态 Figure6. Polarization of reflecting light of reflector based on two magneto-optical crystals and two mirrors under the effect of high-low temperature.
为了量化分析温度变化情况下的双旋光双反射结构的保偏反射能力, 将斯托克斯矢量转换为琼斯矢量[17], 并按照(15)式计算偏振反射光的偏振保持度, 如图7所示. 当温度在–45 ℃—85 ℃之间变化时, 反射光的偏振保持度在99.99%—99.43%之间变化, 14次测试的均值为99.77%. 从图7中可以看出在–5 ℃—55 ℃之间时, 反射光的偏振保持度能够较为稳定地保持在99.8%左右, 而在低温区间和高温区间偏振保持度的起伏都很大. 这有可能是由于旋光晶体(钇铁石榴石)是在常温环境下制备的, 因此在极端的高温和低温环境下会造成其厚度的轻微变化, 进而影响其偏振特性. 但是旋光晶体的这种变化对双旋光双反射结构的影响是非常微弱的. 图 7 高低温影响下的反射光偏振保持度 Figure7. Polarization retention of the reflecting light under the effect of high-low temperature.
23.3.双旋光双反射结构的高低温-辐射实验 -->
3.3.双旋光双反射结构的高低温-辐射实验
本轮实验将两面反射镜和两枚旋光晶体全部进行400 Gy的总剂量辐照, 而后再放入高低温箱中进行高低温实验. 实验方法和实验过程与第一轮实验完全相同. 但是包括激光器在内的所有光学元件全部重新装调, 因此入射光偏振态与第一轮略有差别. 图8为入射光和反射光的偏振态, 图9为反射光的偏振保持度. 图 8 辐射和高低温影响下的双旋光双反射结构反射光偏振态 Figure8. Polarization of reflecting light of reflector based on two magneto-optical crystals and two mirrors under the effect of high-low temperature and radiation.
图 9 辐射和高低温影响下的反射光偏振保持度 Figure9. Polarization retention of the reflecting light under the effect of high-low temperature and radiation.