Reduction of multipath interference in a few mode fibers using spatial filters

摘要

Multipath interference (MPI) is caused by the beating between a signal and its weak replica. In a few mode fibers, a replica of the signal propagates as a higher order mode. Since the optical path length of a higher order mode is different from the fundamental mode, it leads to interference pattern at the output end of the fiber, which degrades the system performance. In this paper, a simple method is proposed to reduce such kind of MPI effect by using a spatial filter in a 4F system. A higher order mode has higher spatial frequency components and therefore, choosing a low pass spatial filter with a suitable cutoff frequency, some part of the unwanted higher order mode can be suppressed and then MPI can be reduced. The idea is validated by simulation results.