Phase-Offset Estimation for Joint-Polarization Phase-Recovery in DP-16-QAM Systems

We propose a method that estimates the phase-offset between polarization-demultiplexed 16-ary quadrature amplitude modulation (16-QAM) signals, enabling the utilization of joint-polarization phase-recovery (JPPR) algorithms. The method is based on a Viterbi & Viterbi-like architecture that raises selected samples to the fourth power to remove the data dependence from the phase estimation process. Monte Carlo simulations indicate that feedforward and decision-directed JPPR algorithms using the proposed phase-offset estimation technique effectively relax the laser linewidth requirements for dual-polarization 16-QAM systems.