The influence of alignment tolerance on coupling efficiency of FSOC system based on few-mode fiber

Using optical fiber devices at the terminal is an important means to improve the performance of free space optical communication systems. We proposed a Fraunhofer diffraction integral based method to calculate the coupling efficiency between spatial light and few-mode fiber, and studied the influences of alignment tolerance on coupling efficiency. Numerical simulations confirm that the results obtained by this new method are consistent with the traditional calculation method. What is more, a few-mode fiber has flatter response characteristics to F-number mismatch, fiber lateral offset and defocus. Compared with single mode fiber, few-mode fibers can not only improve the maximum coupling efficiency, but also their coupling efficiency is much less sensitive to deviations from ideal conditions, thereby making them a more practical option for real world applications.