An Efficient Method for Skew Estimation and Compensation in Coherent Receivers

The performance of coherent optical systems can be seriously degraded when in-phase and quadrature (IQ) components experience misalignments crossing certain critical limits. The critical limits of IQ phase, gain, and skew misalignments are lower at higher modulation formats and in narrowband systems. In this letter, frequency-domain skew-estimation algorithm and time-domain skew-compensation technique are proposed. When compared with other published methods, the new architecture improves timing performance and relaxes requirements for a multiple-input multiple-output time-domain equalizer at low implementation price. We discuss IQ imperfections on both transmitter and receiver sides and provide an efficient compensation procedure.