Study of frequency-guided-assisted residual optical carrier algorithms in low-cost coherent optical communication

This paper investigates a phase noise suppression scheme based on residual optical carrier (ROC) for low-cost distributed feedback (DFB) lasers exhibiting MHz-level phase noise. The core of the ROC scheme is generating an auxiliary residual optical carrier with a frequency pilot tone (FPT). This is done by slightly offsetting the bias of the IQ modulator at the transmitter. This setup lets the receiver perform frequency offset estimation (FOE) and carrier phase recovery (CPR) at the same time. Through systematic numerical simulations and experimental validation, we analyze the impact of critical parameters—including carrier-to-signal power ratio (CSPR), low-pass filter (LPF) characteristics (type, bandwidth), guard interval, and laser linewidth tolerance—on the system performance. The results demonstrate that a third-order Gaussian LPF with 360 MHz bandwidth achieves optimal phase noise suppression with a 1 GHz guard interval. The proposed scheme offers a low-complexity solution for short-range coherent optical communication systems.