Polarization-Insensitive Phase Conjugation of QPSK Signal Using Bragg-Scattering FWM in SOA

We experimentally demonstrate polarization-insensitive phase conjugate generation in a semiconductor optical amplifier (SOA) using a counter-propagating and cross-polarized degenerate pump. The polarization-insensitive operation is achieved in both the ports of the SOA through Bragg scattering four-wave mixing. The nature of polarization transformation of the process necessitates the selection of frequency of the signal to be larger than that of the pump for the penalty-free performance of the polarization-insensitive conjugate generation. We demonstrate the phase conjugate generation of 10 GBd PM-QPSK signal, simultaneously in both input and output ports of the SOA, with a penalty of <1.5 dB.