Random Polarization-Mode Coupling Effects in Heterogeneous Multi-Core Fibers With Different Cladding Diameters

We investigate the relationship between the inter-core crosstalk (IC-XT) and polarization-mode dispersion (PMD) of multi-core fibers (MCFs) with differing cladding diameter ( dCL ). The study is based on the assumption that the IC-XT is primarily characterized by random coupling occurring between polarization-modes along the propagation process. Our investigation involved the analysis of two 2-core weakly-coupled heterogeneous MCFs, sharing almost identical cores but differing in dCL . Here, we introduce a method to estimate the birefringence parameters for each core, obtained from a combination of measured and numerically calculated data of IC-XT and PMD. Under the assumption that both cores have identical birefringence beat length LB values, the results reveal an opposite relationship between the IC-XT and PMD characteristics, where increasing the dCL results in an improvement of the IC-XT, but at the cost of the deterioration of the PMD. The same behavior was observed even when minor differences in LB between cores were considered. Moreover, our estimated values of the birefringence parameters for each fiber core are several orders of magnitude smaller than those reported in conventional single-mode fibers.