Propagation in few modes fiber with strongly coupled groups of modes

In this paper, we propose a design of a multimode step index fiber where the first six modes can propagate simultaneously. We investigate the propagation of six strongly coupled groups of modes which are very important for spatial division multiplexing (SDM) optical communications. We solve numerically the six coupled Manakov equations and we find that fundamental solitons propagating in different groups of modes travelling with the same speed due to spectral shifts for each soliton. This phenomenon is known as soliton trapping and is a consequence of the intermodal nonlinear coupling based on cross phase modulation. This fiber is very promising to increase the capacity of SDM systems by more than a tenfold factor compared to single mode systems.