Optical Performance Monitoring for Intra-LP-Mode Dispersion in Weakly-Coupled Mode-Division Multiplexed Systems

Weakly-coupled mode-division multiplexing (MDM) technique based on linearly-polarized (LP) modes in ultralow-modal-crosstalk few-mode fiber (FMF) has been considered as a promising candidate for capacity enhancement of next-generation optical transmission systems. Similar to polarization mode dispersion in single-mode fibers (SMFs), signals in weakly-coupled FMFs suffer from the impacts of intra-LP-mode dispersion (ILMD) for both degenerate and non-degenerate LP modes.In this paper, we propose an effective method for ILMD monitoring in weakly-coupled MDM systems. The ILMD evaluation method for degenerate LP modes is designed by the analysis of channel transfer matrix in a digital coherent receiver. Then the ILMD monitoring scheme is experimentally validated for all the 6 LP mods in a weakly-coupled FMF. The influences of chromatic dispersion, optical signal to noise ratio and inter-LP-mode crosstalk to the method are also investigated.