Equalization-Enhanced Phase Noise Compensation in Coherent Fiber Receivers

Dispersion uncompensated fiber links are widely used due to their nonlinear benefits. In such links, dispersion requires electronic compensation after down-conversion by the receiver laser. Therefore, laser phase noise inevitably affects the received signal. While, in an optimal receiver, the phase noise should be compensated before dispersion, practical phase estimation is only feasible when dispersion is already compensated. Unfortunately, compensating receiver phase noise after dispersion compensation gives rise to equalization-enhanced phase noise (EEPN), which limits the system's performance, especially for high data rates over long system reaches. In this paper, we demonstrate that EEPN can be mitigated through signal processing. We derive the compensation expression and propose two different compensators depending on the availability of the receiver phase noise. Our study demonstrates that by using a simple time-variant finite impulse response filter, one can effectively compensate for EEPN. The simulation study validates these theoretical findings, revealing improved system performance, including enhanced system reach, optimal launch power, and reduced bit error rate compared to existing EEPN-controlled methods. Importantly, we show that the complexity of our compensators is comparable to existing methods, demonstrating its feasibility for practical implementation.