Improved carrier phase recovery for high-capacity optical communication systems with high-order modulation formats

A modified Viterbi-Viterbi (MVV) carrier phase recovery (CPR) algorithm is comprehensively studied based on the quadrature phase-shift-keying (QPSK) partition scheme. By improving the QPSK partition scheme for the 16-ary quadrature amplitude modulation (16QAM), MVV algorithm is developed for the optical fiber communication systems with the modulation formats of dual-polarization 64-QAM (DP-64QAM) and DP-256QAM. Numerical simulations have been carried out in a 9-channel Nyquist-spaced 32-Gbaud optical transmission system for different modulation formats and the performance of MVV CPR with respect to pilot-aided (PA) CPR has been examined. Results show that MVV CPR can significantly mitigate the laser phase noise in the system using high-order modulation formats. Compared to PA CPR, MVV CPR performs better with the increase of the transmission distance, where the impact of equalization enhanced phase noise has to be taken into account. Furthermore, MVV has been compared with other CPR approaches in terms of the performance and the computational complexity.