Assessment of intra-channel fiber nonlinearity compensation in 200-GBaud and beyond coherent optical transmission systems

In this paper, we investigate and assess the performance of intra-channel nonlinearity compensation (IC-NLC) under the influence of polarization mode dispersion (PMD) in long-haul coherent optical transmission systems with a symbol rate of 200 GBaud and beyond. We first evaluate the proportion of self-channel interference (SCI) in 4 THz systems using the split-step Fourier method (SSFM) based simulation with either lumped amplification or distributed Raman amplification. As the symbol rate increases to 300 GBaud, the SCI proportion exceeds 65%. On the other hand, the non-deterministic PMD will impact the effectiveness of IC-NLC, especially for ultra-high symbol rate systems. Therefore, we investigate the power spectral density of the residual nonlinear noise after ideal IC-NLC in the presence of PMD, and propose its expression for lumped and distributed Raman amplifier (DRA)-amplified systems. The results indicate that the gain of ideal digital backpropagation (IDBP) decreases by 3.85 dB in 300-GBaud single-channel erbium-doped fiber amplifier (EDFA)-amplified standard single-mode fiber (SSMF) links with a transmission distance of 800 km and a PMD parameter of 0.05 ps/km 1/2 , and by 5.09 dB in 800-km 300-GBaud single-channel DRA-amplified SSMF links with a PMD parameter of 0.05 ps/km 1/2 . Furthermore, the theoretical results are consistent with the numerical results. Finally, we evaluate the gains of IC-NLC in multi-channel wavelength-division multiplexing (WDM) systems using the low-pass-filter assisted digital backpropagation (LDBP). As the symbol rate increases from 100 GBaud to 300 GBaud, the gain of 20-step-per-span (20-stps) LDBP increases from 0.53 dB to 0.87 dB for 800-km EDFA-amplified SSMF links, and from 0.89 dB to 1.30 dB for 800-km DRA-amplified SSMF links. Our quantitative results show that for 200-GBaud and beyond systems, IC-NLC is able to achieve performance gain even under the significant influence of PMD.