Multiple path interference and differential modal delay reduction using spatial filters in a 4F system.

Multiple path interference (MPI) and differential modal delay (DMD) are two major impairments in fiber optic communication systems. MPI can be found in a few mode fibers in which a higher order mode propagates as a weak replica of the signal and interferes with the fundamental mode at the output of the fiber link. DMD in multimode fibers (MMF) leads to intersymbol interference, which limits the bit rate-distance product of the system. A simple method is proposed to reduce MPI and DMD effects using spatial filters in a 4F system. Higher order modes have higher spatial frequency components. Therefore by choosing a proper spatial filter with a suitable bandwidth, a fraction of the unwanted higher order modes can be suppressed, and therefore MPI and DMD effects can be reduced.