Demonstration of Uncoupled 4-Core Multicore Fiber in Submarine Cable Prototype With Integrated Multicore EDFA

We developed a 15.2-km submarine cable prototype which can accommodate up to 16 fiber pairs (FPs) of 125 μm standard cladding diameter 4-core uncoupled multicore fiber (UC-MCF). Fiber properties such as loss, chromatic dispersion, and inter-core crosstalk were measured and compared before and after cabling. We found that the cabling process, such as fiber rewinding, copper tubing and polyethylene coating completion, did not significantly change the fiber properties such as loss. To verify the influence of cabling process on long-haul transmission performance, we fabricated a 60.8-km length 4-core UC-MCF transmission span by serially splicing four FPs from the 15.2-km length cabled 4-core UC-MCF. An experimental loop transmission setup was established using the cabled transmission span, and Q-value was measured in real-time. The 120 wavelength multiplexed channels were transmitted. The five channels were modulated by 100 Gbps 34.7 GBd polarization multiplexed quadrature phase shift keying (PM-QPSK) signal and the other channels were loading channels shaped from amplified spontaneous emission (ASE). We changed the transmission direction one core at a time in the 4-core UC-MCF based transmission line to examine the effect of inter-core crosstalk on the transmission line. The −25-dB inter-core crosstalk caused negligible signal degradation in the 4-core UC-MCF and fan-in fan-out (FIFO) a total of 88 spans. Furthermore, we found that the 5,350-km transmission using cabled 4-core UC-MCF was limited by optical signal to noise ratio (OSNR). We integrated the transmission 4-core UC-MCF with the 4-core UC-MC-erbium doped fiber amplifier (EDFA) without using FIFO and clarified experimentally a Q-value improvement of 0.6 dB by removing half number of the FIFOs.