OTDR Enabled Multiple-Loopback Measurement of Inter-Core Crosstalk in MCF

As a fundamental limiting factor in the space division multiplexing (SDM) system based on weakly coupled multi-core fiber (MCF), inter-core crosstalk (IC-XT) requires measuring conveniently and efficiently during MCF deployment. In this paper, we propose an effective IC-XT measurement method based on optical time domain reflectometer (OTDR). By connecting the designed bridge single-mode fibers (SMFs) structure at the beginning end of the MCF and launching optical pulse signal into one core under test at the far end, multiple loopback IC-XT peaks can be read on the OTDR, from which the IC-XT levels from the core under test to all other cores can be simultaneously calculated. Two bridge schemes for IC-XT measurement are proposed and experimentally verified on a 41 km 7-core fiber. The first scheme supports bidirectional IC-XT measurement, while the second performs better in the OTDR dynamic range and computational complexity. Both schemes demonstrate good measurement accuracy, with < 1 dB of errors. We believe that the proposed method will certainly provide convenient and efficient IC-XT evaluation during future MCF deployment.