Capacity Expansion in Submarine Cable Systems With Bidirectional Transmission Using 4-Core-or-More MCF and MC-EDFA

Bidirectional transmission in a multicore fiber (MCF) reduces core-to-core crosstalk, changing optimal MCF design and multicore submarine cable systems, compared with conventional unidirectional transmission systems. We first demonstrate analytically the increase in capacity with bidirectional transmission in submarine systems. From the perspective of the capacity of one MCF, we show that bidirectional transmission enables an optimum design based on a 6-core MCF with a standard cladding diameter, taking advantage of the reduction of XT. For multicore submarine cable systems, we demonstrate that 6-core MCF systems with bidirectional transmission offer the highest cable capacity for regional Asian systems in the range of 3,000 km. We further discuss a multicore erbium doped fiber amplifier (MC-EDFA) system even for bidirectional transmission to improve the energy efficiency in submarine systems, and we show that 6-core MCF systems offer the highest capacity up to 6,000 km because of MC-EDFA. We also show a 10\% larger capacity for a 3,000 km 6-core MCF system, and 43\% larger capacity for a 9,000 km 4-core MCF system in bidirectional transmission with MC-EDFA, compared with the conventional repeater amplifier in FIFO devices. In addition, we investigated the potential increase in the cable capacity with the future cable system assumption, especially concerning cable supply voltage.