Effects of Mode Dispersion on the Nonlinear Interference in Few-Mode Fiber Transmissions

We investigate the effect of mode dispersion on the variance of the nonlinear interference (NLI) in weakly-coupled coherent space-division multiplexed (SDM) transmissions based on few-mode fibers (FMFs). We present an extended Gaussian noise model that incorporates mode dispersion in both the intra- and inter-group NLI. We show that the random spatial mode dispersion (SMD) of quasi-degenerate mode groups has a significant role in setting the dependence of the NLI variance on the systematic and deterministic differential mode group delay (DMGD) between mode groups. After validating the model by comparison with the split-step Fourier method, we use it to isolate different nonlinear effects and provide insights into how they interact with SMD and DMGD. The theoretical model exhibits great accuracy in fast computation times, making it a valuable tool for a comprehensive investigation of nonlinear FMF transmissions.