| Space laser communication not only has wide band,high speed,long distance,strong anti-interference ability,but also has outstanding advantages of light and small size,which makes it very suitable for inter-satellite and deep space link communication and can meet the increasing demand for information transmission at present.At the same time,it is also the development trend of space communication in the future.Due to the high speed,miniaturization and networking requirements of space laser communication,the communication terminal based on polarization splitting and coherent detection communication system is the best solution.Laser communication systems using these two communication systems both use polarized light for signal transmission.The polarization state of signal light will affect the performance of the communication system,so it has strict requirements on the polarization state of signal light.However,the polarization characteristics of the optical system will change the polarization state of the signal light,thus affecting the performance of the communication system.Based on the research project of a certain type of space laser communication optical terminal,aiming at the problems of polarized light transmission efficiency of optical system and coaxial calibration of communication receiving and transmitting optical paths,the following research work is carried out around the polarization characteristics of space laser communication optical system:1.The principle,system composition and workflow of space laser communication optical system based on polarization splitting are introduced.Based on the principle of coherent detection and the principle of coaxial calibration of the transmitting and receiving optical axes of laser communication,the influence of the polarization state of light on the efficiency of the optical system of laser communication and the coaxial calibration of the transmitting and receiving optical axes of communication are analyzed respectively,which shows that the signal-to-noise ratio of coherent detection will be reduced when the polarization state of the signal light is inconsistent with that of the local oscillator light,and the polarization state of the signal light will also affect the intensity distribution of the calibration spot,thus affecting the coaxial calibration accuracy of the communication receiving and transmitting optical axis.2.According to the laser communication optical system of polarization splitting and coherent detection,the polarized light transmission models of the communication receiving optical path and the communication transmitting optical path are established,and the mathematical models between the optical transmission efficiency of the communication receiving optical path and the transmitting optical path and the polarization characteristics of each component in the optical system are deduced respectively.The influence of the polarization effects of the optical telescope,the quarter wave plate,the communication transmitting mirror group and the communication receiving mirror group on the optical transmission efficiency is analyzed through numerical simulation,which provides a theoretical basis for the polarization maintaining design and index quantification of the laser communication optical system.3.According to the laser communication optical system of polarization splitting,the polarized light transmission model of the coaxial calibration optical path of the communication transmitting and receiving optical axis is established.The polarization characteristics of total inner reflection type and Ag-coated film type corner cube are analyzed respectively,and the polarization characteristics of calibration light paths using total inner reflection type and Ag-coated film type corner cube are mathematically simulated and experimentally tested.The simulation and experimental results show that in the calibration system using Ag-coated film type pyramid prism,the calibration light has approximately the same complex amplitude distribution of light field under different propagation paths,and the calibration light spot intensity distribution meets Ellie distribution,which is more conducive to improve the coaxiality calibration accuracy of the communication transmitting and receiving optical path.4.According to the design index of space laser communication optical system,a set of laser communication optical system based on polarization splitting is completed.According to the requirements of transmission efficiency of polarized light in communication optical path,the design requirements of polarization maintaining film system are analyzed and the design of polarization maintaining film system is completed.Polarization loss simulation and experimental measurement are carried out on the coated optical telescope,communication transmitting mirror group and communication receiving mirror group.The simulation and experimental results show that the polarization loss of the coated optical system is less than 0.1%,and the polarization transmission efficiency loss caused by the coating can be calculated to be less than 0.1%,which indicates that the optical system has very high polarization maintaining performance.According to the operating conditions of quarter wave plate in the system,the polarisation-maintaining assembly scheme of quarter wave plate is given,and A set of system auxiliary assembling and detection device based on ShackHartmann wavefront measuring instrument is designed and built,which ensures that the defocus under the working wavelength of optical telescope meets the requirements.This paper has certain guiding significance and reference value for the relevant theoretical research and practical work of polarization characteristics of laser communication optical systems and the development of space laser communication optical systems with high polarization maintaining performance,and has certain promotion effect on the development of high efficiency,miniaturization and networking of space laser communication terminals. |
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