High Figure–of–Merit Multi–Core Fiber with Standard Cladding Diameter for Long–Haul and Wide–Band Transmission

A weakly coupled multi–core fiber with the standard 125–μm cladding diameter has shown promise as a next–generation large–capacity transmission medium for long–haul networks that can provide multiple optical paths while maintaining the existing cable structure. In this paper, we numerically and experimentally demonstrate a standard cladding 4–core fiber (4CF) with a superior transmission performance in terms of figure–of–merit (FOM), which is defined as the relative spectral efficiency to a conventional G.654 fiber, by simultaneously optimizing the design of its effective area and loss and crosstalk characteristics for submarine transmission. By considering a counter–propagation configuration among neighboring cores, we can obtain larger effective area of the optimized 4CF design because of the relaxed tradeoff relationship with the crosstalk. Specifically, we report a 10,140–km transmission with the spectral efficiency of 7.52 bit/s/Hz using a counter–propagation configuration, which indicates we can exceed a 1 Pbit/s cable capacity when considering a conventional 17–mm–diameter submarine cable. We also investigate the applicability of the standard cladding 4CF to wide–band transmission in the C+L band to see if it is appropriate for a long–distance terrestrial system. Our findings show that our design of 4CF to maximize the FOM for co– and counter–propagation between cores enables us to obtain a higher FOM in not only the C band but also the C+L band.