Nonlinearity and Phase Noise Mitigation Using Feed-forward Carrier Phase Estimation and Digital Backward Propagation in Coherent QAM Transmission

We numerically investigate the performance of Viterbi-Viterbi (VV) carrier phase estimation (CPE) and feed-forward decision directed (DD) CPE along with digital backward propagation (DBP) to mitigate laser phase noise, linear and nonlinear fiber impairments for polarization multiplexed (PM) 4 and 16-ary quadrature amplitude modulation (QAM) coherent systems. For 16-QAM, DD-CPE is compared with quadrature phase shift keying (QPSK) partitioning method that is based on the modification of VV-CPE. When the laser phase noise is negligible, both CPE methods exhibit a similar performance when employed after DBP. However, in the presence of phase noise, non-decision directed VV-CPE (for 4-QAM) and QPSK partitioning (for 16-QAM) methods outperform DD-CPE with greater phase noise tolerance and reduced complexity. (C) 2014 Published by Elsevier B.V.