A Robust Timing Recovery Algorithm With Enhanced DPLL Performance for Nyquist Digital Multi-Band Optical Systems

We propose a novel timing recovery algorithm (TRA) for Nyquist digital multi-band optical coherent systems. The proposed TRA employs two complementary metrics to cover all states of polarization (SOP) and differential group delays (DGD), and the extracted timing error is also robust to residual chromatic dispersion (rCD), phase noise and residual frequency offset (RFO). 1.12-Tbit/s simulations and 320-Gbit/s experiments are conducted to verify the proposed theory. It is shown that compared to the conventional Gardner, Godard and sGardner algorithms, the proposed TRA eliminates the singularity problem when the DGD is equal to odd times of half symbol period and the susceptibility to the signal spectral roll-off factor. This method also enhances the performance of the digital phase-lock loop with higher tolerance to clock frequency offset and loop delay than the conventional TRAs and our recently proposed TRA.