Blind Receiver Skew Compensation and Estimation for Long-Haul Non-Dispersion Managed Systems Using Adaptive Equalizer

Imbalances between the four sampling channels of a coherent detector with polarization diversity can rapidly degrade system performance. One of these imbalances, namely the receiver skew, becomes increasingly important when higher symbol rates, higher modulation orders, and low roll-off pulse shapes are used. Here, we evaluate the performance of receiver skew compensation based on a complex-valued multiple-input multiple-output 4 × 2 adaptive equalizer that is tolerant to large residual chromatic dispersion. In addition, we derive skew estimation from converged equalizer taps. Both the adaptive equalizer and the derived estimator are validated experimentally with offline processing through long-haul transmission of 46 Gbaud signal over a non-dispersion-managed test bed. The transmitted signal is Nyquist pulse shaped with a root-raised-cosine filter with 0.1 roll-off factor, polarization division multiplexed, and modulated with 16-ary quadrature amplitude modulation.