Maximum Likelihood Estimation of Polarization States in Coherent Optical Communications

In this paper, a polarization state estimation algorithm in coherent optical communication systems is proposed based on the maximum likelihood (ML) method. Through the derivation, we obtain the analytical solutions of the polarization states and deduce the corresponding Cramér-Rao Lower Bounds (CRLBs). The proposed ML estimator not only can achieve the optimum estimation with merely 16 pilot symbols, but also shows great tolerance to the additive white Gaussian noise (AWGN) and linear phase noise (LPN). Simulation results verify the accuracy, efficiency and robustness of the proposed ML estimator.