Joint interference of laser linewidth, chromatic dispersion, and multipath interference mitigation in self-coherent detection

Self-coherent detection is a promising solution for extended range (ER) and ze best range (ZR) transmission in data centers due to its ability to recover the optical field with low complexity. However, in practical applications, the interaction between laser phase noise and fiber chromatic dispersion (CD) can lead to equalization-enhanced phase noise (EEPN) and phase-to-amplitude (P2A) noise, while multipath interference (MPI) can also severely degrade system performance. In this study, we investigated the combined impact of laser linewidth, fiber CD, and MPI on self-coherent optical communication systems. We demonstrate that the interaction between the laser linewidth, fiber CD, and MPI after direct detection results in phase noise-induced cascaded interference (PNICI). By analyzing the characteristics of PNICI, we propose a joint carrier extraction-based equalization (CEE) and recursion-based maximum likelihood (R-ML) phase estimation algorithm to mitigate PNICI. The CEE effectively mitigates MPI-induced interference through channel estimation, while the R-ML algorithm mitigates the phase noise of PNICI with significantly lower computational complexity compared to the original ML. Simulations verify the effectiveness of the proposed CEE + R-ML scheme using a 56 GBaud 16-ary quadrature amplitude modulation (16-QAM) optical single-sideband (SSB) signal in a Kramers-Kronig receiver. Results show that the proposed CEE + R-ML scheme can increase the signal-to-interference ratio (SIR) tolerance by 5.4 dB with a laser linewidth of 1 MHz after 100 km fiber transmission. Moreover, after 100 km fiber transmission, the 7% forward error correction (FEC) threshold can be achieved under the SIR of 25 dB and laser linewidth of 4 MHz.