Two-stage constant modulus algorithm equalizer for singularity free operation and optical performance monitoring in optical coherent receiver

A two-stage constant-modulus-algorithm (CMA) equalizer for polarization-demultiplexing in a polarization-division-multiplexed coherent receiver is demonstrated. The equalizer eliminates the singularity problem of CMA equalizers and provides an effective way to monitor polarization-mode dispersion and polarization-dependent loss.