Statistical distribution of fiber-coupling efficiency in the satellite-to-ground downlink

In the satellite-to-ground downlink lasercom systems, efficient coupling of atmospherically distorted spatial light into single-mode fibers is a key technology for fiber-coupled optical receiver. Statistical distribution of fiber-coupling efficiency is important to analyze the performance of a receiver. We use the simulation of beam propagation to examine statistical distribution of fiber-coupling efficiency for the satellite-to-ground downlink. The distributions of the fiber-coupling efficiency for different numbers of speckles are obtained, and the cumulative density functions of the fiber-coupling efficiency are also given. In order to validate the accuracy of numerical simulation method, the dependence of average fiber-coupling efficiency on the ratio of lens size to speckle size is attained, which is highly consistent with the prior theoretical works. The results will be helpful in the design of the satellite-to-ground downlink lasercom system based on fiber-coupling technology.