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Optimum index profile of few-mode coupled multicore fibers for reducing the group delay spread.

We numerically investigate the group delay spread (GDS) characteristics in few-mode coupled multicore fibers (FM-CMCFs) in weak random-bending conditions by using a coupled-wave theory. We qualitatively show the modal coupling between modes in the intra- and the inter-mode group generated by bending. The results indicate that the modes of FM-CMCFs are less likely to couple with each other in weak random-bending conditions in contradiction to single-mode coupled multicore fibers. To resolve this problem, we demonstrate an optimum index profile and core pitch, where the GDS can be reduced even if the different mode groups do not couple strongly.