Receiver in-phase and quadrature skew tolerant baud-rate timing recovery scheme for short-reach coherent optical interconnection

A baud-rate sampling timing recovery (TR) scheme with receiver IQ skew tolerance is proposed and experimentally demonstrated. The proposed scheme performs independent TR for the in-phase and quadrature (IQ) tributary signals, thereby tracking the sampling phase error while naturally compensating for receiver IQ skew. The robustness of the IQindependent TR to frequency offset (FO) and phase noise is theoretically analyzed. To address IQ misalignment caused by the IQ-independent TR, the use of pseudo-noise (PN) sequences for IQ frame synchronization is proposed. The proposed scheme achieves accurate timing recovery with hardware-efficient baud-rate sampling in the presence of receiver IQ skew, laying the foundation for stable performance of subsequent baud-rate equalization. The performance of the scheme is validated in a 56 GBaud polarization division multiplexed (PDM) 16QAM coherent experimental system. Experimental results demonstrate that the proposed scheme achieves similar BER performance to the modified Gardner+real-valued multiple-input multiple-output (RVMIMO) (@2 SPS) scheme. Moreover, the proposed scheme exhibits robustness to arbitrary IQ skew compared to the ABSPD + RVMIMO (@1 SPS) scheme.