Impulse Response Analysis of Coupled-Core 3-Core Fibers

We analyze the experimental impulse response of coupled-core 3-core fibers and compare the results against super-mode calculations. We show that for small coupling between cores, the impulse response is dominated by core-to-core variations of the fiber parameters. Introduction Recent results in space-division multiplexed long distance transmission using multicore fibers (MCFs) [1], [2] show the potential of MCFs to overcome the capacity limit of single mode fibers (SMFs) imposed by the combination of Shannon's capacity and fiber nonlinearities. Of particular interest for MCFs is the impact of crosstalk between the cores on the transmission properties. For MCFs with low crosstalk [3], [4], theoretical modeling of fiber imperfections was performed in detail in [5], resulting in "noise like" crosstalk that accumulates linearly with the length of the MCF. In the case of moderated crosstalk [2], [6], theoretical predictions based on scalar coupled-wave theory and analysis of the resulting super-modes [7] fail to accurately describe the experimentally observed crosstalk behavior. In this work the impulse responses of two different 3-core (3C) MCFs with core spacings of 39 µm and 29 µm are calculated and analyzed in detail and compared to super-mode calculations based on a vector mode solver. The results indicate that there are multiple regimes, dictated mainly by the interplay of the core-tocore crosstalk and variations of the MCF properties from core to core. The super-mode manifestation, consisting in observing an impulse response with two peaks for the case of 3C-MCF, separated by the differential group delay (DGD) of the super-modes, has not been observed in the fibers under study.