CD and PMD Effect on Cyclostationarity-Based Timing Recovery for Optical Coherent Receivers

TL;DR

This paper investigates how chromatic dispersion and polarization mode dispersion affect cyclostationarity-based timing recovery in optical coherent systems, proposing models and detectors that are robust to these impairments.

Contribution

It introduces a novel model for analyzing CD and PMD effects on cyclostationarity-based timing recovery and proposes a detector immune to both impairments.

Findings

The cyclic correlation matrix contains full timing and PMD information.

A determinant-based timing phase detector is immune to CD and PMD.

Experimental validation confirms the robustness of the proposed methods.

Abstract

Timing recovery is critical for synchronizing the clocks at the transmitting and receiving ends of a digital coherent communication system. The core of timing recovery is to determine reliably the current sampling error of the local digitizer so that the timing circuit may lock to a stable operation point. Conventional timing phase detectors need to adapt to the optical fiber channel so that the common effects of this channel, such as chromatic dispersion (CD) and polarization mode dispersion (PMD), on the timing phase extraction must be understood. Here we exploit the cyclostationarity of the optical signal and derive a model for studying the CD and PMD effect. We prove that the CD-adjusted cyclic correlation matrix contains full information about timing and PMD, and the determinant of the matrix is a timing phase detector immune to both CD and PMD. We also obtain other results such as a completely PMD-independent CD estimator, etc. Our analysis is supported by both simulations and experiments over a field implemented optical cable.