Single-Shot Characterization of Frequency-Resolved Imbalance in Coherent Transceivers Based on Inter-Channel Response Ratio

The compensation for in-phase/quadrature (IQ) and polarization imbalance residing at the coherent transceivers is crucial to the overall performance of high-speed transmission systems. To simultaneously characterize the frequency-dependent IQ/polarization imbalance by a single-shot measurement for either the transmitter or receiver, we propose a simple, but efficient and accurate method based on inter-channel response ratio in the frequency domain. The characterization of the transmitter-side frequency-resolved imperfections only requires one single-ended photodetector (PD) for direct detection while the coherent receiver characterization is based on the classical polarization-diversity coherent receiver configuration without modification. Experimental results have demonstrated the excellent performance of our proposed method to estimate these frequency-dependent imperfections. The estimation accuracy for the IQ/polarization skew residing at both transmitter and receiver can reach tens of femtoseconds (fs). The transmission experiment for a 75-Gbaud dual-polarization (DP) probabilistic constellation-shaped (PCS) 256- quadrature amplitude modulation (QAM) signals with 1.05-Tb/s raw data rate confirms the effectiveness of our proposed method for both IQ/polarization skew and frequency-dependent imbalance.