Fiber Nonlinearity Mitigation of WDM-PDM QPSK/16-QAM Signals using Fiber-Optic Parametric Amplifiers based Multiple Optical Phase Conjugations

We demonstrate fiber nonlinearity mitigation by using multiple optical phase conjugations (OPCs) in the WDM transmission systems of both 8 × 32-Gbaud PDM-QPSK channels and 8 × 32-Gbaud PDM-16-QAM channels, showing improved performance over a single mid-span OPC and no OPC in term of a nonlinear threshold and a best achievable Q2 factor after the transmission. In addition, after an even number of multiple OPCs, signal wavelength can be preserved after the transmission. In the WDM-PDM-QPSK transmission system over 3600 km, by using multiple OPCs the nonlinear threshold was increased by ~5 dB compared to the case of no OPC and increased by ~2 dB compared to the case of mid-span OPC. In the WDM-PDM-16-QAM transmission system over 912 km, by using the multiple OPCs the nonlinear threshold was increased by ~7 dB compared to the case of no OPC and increased by ~1 dB compared to the case of mid-span OPC.