Nonlinear polarization dependence of fiber polarization diversity systems

The nonlinear polarization dependence (NPD) of a fiber polarization diversity system (PDS) is studied by means of the nonlinear power transfer functions (PTFs) of two orthogonally polarized beam paths (PBPs). In principle, a polarization-independent PDS can be developed when the PTF curves are centrally symmetric to each other in a certain range of input power. As an example, a data-pump four-wave-mixing-based PDS is investigated by simulation and experiment, and the probe and pump powers are optimized for the minimal NPD. Experimental results show that, by adding a power-saturated erbium-doped fiber amplifier to the PDS, the dynamic range of input power can be increased up to 26 dB, along with 4 dB extinction ratio (ER) improvement.