Modeling Nonlinear Interference with Sparse Raman-Tilt Equalization

We investigate the impact of accumulated stimulated Raman scattering (SRS) on the nonlinear interference (NLI) variance due to sparse gain-tilt equalization along the optical link. We propose simple modifications to analytical models available in the literature, such as the Gaussian noise (GN) or the enhanced Gaussian noise (EGN) models, for reliable NLI estimation in the presence of accumulated SRS. We additionally generalize closed-form expressions of the NLI variance in a GN framework to the new scenario. We validate the models through split-step Fourier method simulations showing the importance of including the gain-tilt equalization period in the model to preserve the accuracy. The proposed model is then used to provide insights on the interplay between the NLI and accumulated SRS.