A Semi-closed Form Formula to Evaluate the NLI in the Presence of Bidirectional Raman Amplifier

A semi-closed form formula to evaluate the nonlinear interference (NLI) in bidirectional Raman WDM links is proposed. The accuracy of the semi-closed formula is almost identical to that of the original GN-Model in estimating the PSD of the NLI with maximum deviation of 0.06 dB, while the computational efficiency is obviously improved.