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 (d(C)(L)). 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 d(C)(L). 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 L-B values, the results reveal an opposite relationship between the IC-XT and PMD characteristics, where increasing the d(C)(L) 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 L-B 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.