在采用光纤耦合接收方式的星地下行激光链路中，空间光至单模光纤耦合光功率是决定链路通信成败的关键因素。激光链路的大气湍流效应和跟瞄误差导致耦合光功率随机起伏。本项目首先研究并建立耦合光功率概率分布理论，其次作为该理论的应用，研究耦合光功率概率分布与激光链路通信误码率之间依赖关系，为基于光纤耦合接收的星地下行激光链路系统优化设计奠定理论基础。研究耦合光功率概率分布理论包含三方面工作，即通过理论分析和实验验证，建立耦合光功率概率分布函数对大气湍流光强闪烁指数和相位起伏方差依赖关系；建立光纤耦合过程中相位起伏方差的正交化分解方法，获得耦合光功率概率分布函数与各个正交分解项依赖关系，利用自适应光学降低甚至消除这些正交分解项的影响，获得高水平的稳定耦合光功率；建立耦合光功率概率分布函数对跟瞄误差方差的依赖关系。上述研究对优化星地下行链路激光通信系统设计和推动卫星激光通信技术的发展与应用具有重要意义。

In satellite-to-ground downlink based on fiber coupling receiving technology, coupling optical power from space to single mode fiber deceide link communication success. Random fluctuation of coupling optical power resulted form atmospheric turbulence and tracking error in link. Firstly, this item presents probability distribution theory of coupling optical power. Secondly, the dependence between probability distribution and bit-error-rate of laser link will be given. This work can provide some foundations for the optimization design of satellite-to-ground laser communcation system based on single-mode fiber receiving technology. The research of probability distribution theory of coupling optical power include three aspects. Firstly, probability distribution function of coupling optical power will be built, the interrelation between this function and optical intensity scintillation index and phase fluctuation variance will be given. Secondly, orthogonal decompositon method of phase fluctuation variance will be built in fiber coupling problem. The interrelation between probability distribution function of coupling optical power and orthogonal terms will be obtained. Then we can use adaptive optics technology to decrease and eliminate the fluence of orthogonal terms, and obtain high-level and stable coupling optical power. Thirdly, The interrelation between probability distribution function of tracking error variance will be obtained. The aforementioned research is significant in the optimizing design of satellite-to-ground downlink laser communication system and the development and application of satellite laser communication technology.