Coupling efficiency of a plane wave to few-mode fiber in the presence of beam random angular jitter

Using few-mode fiber to receive spatial light is an important method to obtain high coupling efficiency in long-distance free space optical communication systems. Here, we deal with the influence of random angular jitter on few-mode fiber coupling. First, the expression of mean-coupling efficiency from a spatial plane wave to few-mode fiber in the presence of random angular jitter is given. We find that few-mode fiber can obtain higher mean-coupling efficiency than single-mode fiber. Under the same coupling efficiency requirement, the tolerance of random angular jitter standard deviation of four-mode fiber and seven-mode fiber is more than twice that of single-mode fiber. Furthermore, the effect of random angular jitter on the optimal f -number of an optical fiber coupling system is studied. The theoretical models and results reported in this paper will be helpful to the design and optimization of the few-mode fiber coupling system.