Transceiver Imbalances Compensation and Monitoring by Receiver DSP

In-phase and quadrature (IQ) imbalances in optical transceiver, such as amplitude imbalance, phase imbalance, and IQ skew, can cause serious system performance degradation, especially when high order modulation formats are used. In this work, we present a method to isolate and separately monitor these various impairments from received signals by coherent digital signal processing (DSP). Receiver amplitude and phase imbalances could be compensated and monitored by Gram-Schmidt orthogonalization procedure (GSOP) and receiver skew could be compensated and monitored by a 4 x 4 or 4 x 2 multiple-input and multiple-output (MIMO) equalizer. Transmitter imperfections compensation and monitoring take place behind the residual frequency offset compensation and carrier phase recovery by a 4 x 4 MIMO equalizer based on minimal mean square error (MMSE) criterion. By these methods, we analyze and investigate the interaction of transceiver's impairments impact on each monitor numerically. After that, we conduct an experiment to verify the feasibility of the proposed method. All of these results show that each monitor could operate very robust even when multiple co-exist.