Acceleration and parallelization methods for the ISRS-EGN model

The enhanced Gaussian noise (EGN) model, which incorporates inter-channel stimulated Raman scattering (ISRS), offers a highly accurate and comprehensive physics-based framework for evaluating nonlinear interference (NLI) in optical fiber communication systems. However, its practical applicability is limited by its high computational cost. In this work, we identify the oscillatory behavior of the integrand in the four-wave mixing (FWM) efficiency factor as a key bottleneck and propose an approximation method that yields an accurate closed-form expression for the FWM efficiency factor. Numerical results demonstrate that the proposed method achieves a low mean absolute error (MAE) of approximately 0.0033 dB under strong ISRS conditions, while reducing computation time by more than 99.6% compared to the full integral evaluation. Additionally, we develop and optimize a parallel computation strategy that exploits independent regions of the integration domain, further enhancing overall computational efficiency.