Intra-group principal modes in graded-index multimode fibers used for mode group division multiplexing transmission

By considering very strong intra-group mixing while neglecting inter-group mixing in mode group division multiplexing (MGDM) transmission, we theoretically introduce and describe the physical model of intra-group principal modes (IGPMs) in graded-index (GI) multimode fibers (MMFs), from the view of fiber transmission matrices for both cases of one- and dual-polarization. Proof-of-concept numerical calculations for an exemplary mode-group-channel with the two lowest-order degenerate mode groups (namely the three lowest-order fiber eigenmodes) show that IGPMs can exhibit potential possibilities of the MGDM channel with minimal mode mixing/dispersion-induced signal distortion over a GI MMF.