Joint-Polarization and Joint-Subchannel Carrier Phase Estimation for 16-QAM Optical Systems

Carrier phase estimation using information from multiple subchannels and orthogonal polarization channels is proposed and experimentally verified. The concept is evaluated with a 112 Gb/s dual-channel DP-16-QAM system, but may find applications in next generation Terabit systems utilizing superchannels and containing densely packed subchannels originating from the same laser. The new technique requires an accurate carrier frequency estimation algorithm, implemented in the paper using a decision-directed method. The algorithms are tested with a narrow (100 kHz) and a broad (2 MHz) linewidth laser in the coherent receiver.