Dynamic Channel Characterization of Equalization Enhanced Phase Noise in Coherent Optical Receivers

We present a dynamic closed-form model that captures the impulse response of equalization-enhanced phase noise (EEPN) in a single-carrier coherent system. The model reveals that EEPN appears as a time-varying spectral phase perturbation on each transmitted pulse, governed by a truncated segment of LO phase noise. The center of this segment drifts slowly over time, reflecting the dynamic nature of EEPN across successive pulses. Leveraging this model, we accurately reproduce both the received waveform and the dynamic signal-to-noise ratio (SNR). In a 252-Gbaud 16QAM system with 20 ns/nm chromatic dispersion (CD), the predicted SNR closely matches simulation results, with a deviation of less than 0.7 dB.