Research On The Key Technologies Of Large Aperture Telescope Ground Station For Satellite-to-Ground Laser Communications

When the local mobile communication system is progressing to the 5th generation wireless systems of Gbps rate,the satellite-to-ground communication system,which is based on wireless microwave,still stays at Kbps rate.This is largely due to the ultra-long link distance.The power consumption,volume and quality of the communication terminals will increase in order to realize a high-rate communication system,and result-ing in the doubling of satellite manufacturing and launching costs.At the same time,the complex electromagnetic environment in space also limits the application of high-rate wireless microwave communication system.With the advent of big data era of satel-lite communications,laser communication is expected to become the main transmission mode of the next generation of satellite-to-ground communication system.At present,the satellite has been gradually developed to the direction of miniatur-ization,lightening and low power consumption.The launch cost and risk of failure of the satellite with large mass and complex system structure is extremely high.As a re-sult,the power,quality and system complexity of satellite terminals are greatly limited.Therefore,a series of technical problems with the establishment of satellite-to-ground laser communication systems need to be solved by improving the performance of the ground station,including improving the detection ability,resolution ability,tracking ability,atmospheric turbulence overcoming ability,fiber coupling ability and so on.The combination of large aperture receiving telescope and adaptive optics is a reason-able development route.On the one hand,it can make full use of the great advantages of large aperture telescope in detection and tracking,on the other hand,the effect caused by atmospheric turbulence can be compensated by adaptive optics technology.This thesis focuses on the acquisition and tracking technology,coaxial emission technology,turbulence compensation technology and optical fiber coupling technology,which are urgently needed to be solved in the establishment of satellite and ground laser communication ground station with large runoff adaptive optics.Firstly,the magnitude of the satellite and the relationship between the aperture of the telescope and the magnitude of the limit detection are calculated through theoretical analysis,and various acquisition schemes are compared,which reflects the fast acquisi-tion ability of the large-aperture telescope in the case of long distance and low brightness of the satellite.Secondly,in the transmitting system,a rotary polarization isolation scheme is pro-posed to solve the problem of large interference of common optical path and same fre-quency transmitter-receiver,and the transmitter-receiver isolation degree of this scheme is about 90dB.Aiming at the interference of telescope truss to multi-mode beacon laser emission,the active coaxial transmission scheme is proposed,and the multi-mode fiber coaxial algorithm based on SPGD is studied in detail.The experimental results show that the scheme and algorithm can realize the active coaxial emission of four-path bea-con in 2 seconds.Then,the influence of atmospheric turbulence on the communication quality is analyzed through theoretical derivation and numerical simulation.The results show that even in the case of weak turbulence,atmospheric turbulence will have a serious impact on the communication quality.Through simulation and modeling,the requirements of the adaptive optical system for satellite-ground laser communication are analyzed.The results show that the turbulence compensation ability of the adaptive optical system for satellite-ground laser communication is higher than that of the adaptive optical system for astronomical imaging.Furthermore,in order to meet this requirement,an independent integral weighted direct slope control algorithm is proposed to suppress the non-uniform flicker of the star-earth laser beam,so as to improve the correction accuracy of the adaptive opti-cal system.Experimental results show that the algorithm can improve the accuracy of adaptive optics by more than 10%when the edge flicker is severe.Then,three exper-iments of adaptive optical space laser communication under different conditions were carried out,and the experimental results were analyzed to verify the relevant key tech-nologies,indicating that the adaptive optical technology can significantly improve the communication quality.Finally,a coherent detection coupling technique is proposed to solve the problem of low detection sensitivity and coupling efficiency in fiber coupled systems.This tech-nique not only makes full use of the high sensitivity of coherent detection,but also can compensate the high frequency jitter error of the coupling system.Simulation results show that the proposed method can achieve high coupling efficiency with very low coupling power.The research on the key technologies of the large aperture telescope ground sta-tion for laser communication system carried out above can provide guidance for the construction of the ground station and provide strong technical support for the develop-ment of China's space engineering.