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.

中文翻译：

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存在光束随机角抖动时平面波与少模光纤的耦合效率

在长距离自由空间光通信系统中，利用少模光纤接收空间光是获得高耦合效率的重要方法。在这里，我们处理随机角抖动对少模光纤耦合的影响。首先，给出了存在随机角抖动时从空间平面波到少模光纤的平均耦合效率表达式。我们发现少模光纤可以获得比单模光纤更高的平均耦合效率。在相同的耦合效率要求下，四模光纤和七模光纤的随机角抖动标准偏差容限是单模光纤的两倍以上。此外，随机角抖动对最优$f$的影响研究了光纤耦合系统的数量。本文报道的理论模型和结果将有助于少模光纤耦合系统的设计和优化。