Analysis of Polarization Effects to Digital Timing Recovery in Coherent Receivers of Optical Communication Systems

We analyze the systematic influence of optical polarization effects on digital timing phase estimation in receivers with coherent demodulation. It is shown by analysis and by simulation that the combination of half-Baud differential group delay (DGD) in combination with certain states of polarization (SOP) attenuates the clock tone such that the timing phase can not be estimated. Proposals for mitigation schemes with low complexity and robust timing phase estimation are presented.