Influence of Discrete Mode Coupling on the Nonlinear Interaction in Mode-Multiplexed Systems

In this letter, we analyze the impact of discrete mode coupling on mode-multiplexed transmission links that employ few-mode fibers. We show that discrete coupling between spatial modes, as introduced, e. g., by splices, highly degrades the performance of mode-division multiplexed transmission links due to an additional nonlinear penalty. This stands in contrast to the performance improvement that is introduced by frequently appearing random mode coupling.