NEC Corporation, its subsidiary OCC Corporation and Sumitomo Electric Industries, Ltd. have completed the first trial of uncoupled 4-core submarine fibre cable and verified its transmission performance to meet the exacting demands of global telecommunications networks.

International data usage is expected to expand by 30-40% CAGR from 2020-2026, driven by factors such as the growth of 5G mobile data, and the need to share ever more content between data centres distributed around the world. To meet this demand, submarine networks are adopting space division multiplexing (SDM) technology, where the number of independent spatial channels is increased to maximise total system capacity, reduce power consumption and optimise cost per bit. Multicore fibre is now expected to further increase the number of parallel optical fibre cores without increasing the submarine cable size and structure, enabling the second generation of submarine SDM systems.

Multicore fibre submarine cable features Conventional single-mode fibre has a single core within an individual fibre. In contrast, each multicore fibre contains multiple cores (4 cores in this case). This represents a four-fold enlargement in the number of spatial channels for the same amount of optical fibres and with the same fibre structure: each fibre being 250µm diameter (0.25mm) after coating.

The uncoupled 4-core fibre is being deployed within the OCC SC500 series LW (Lightweight) cable, which has a 17mm outer diameter and withstands 8,000-metre water depth. This cable can accommodate up to 32 fibres. With multicore fibre, the number of cores can be increased without increasing the cable diameter, with corresponding benefits in the cost per bit of the cable system.

Transmission performance demonstration

NEC and OCC have demonstrated that the cable’s optical transmission performance in the water fully meets the exacting requirements of modern long-haul submarine cables. They further showed that the process of cabling Sumitomo Electric’s multicore fibre has no effect on its optical characteristics, achieving excellent attenuation properties.

This research was supported by the Ministry of Internal Affairs and Communications (MIC), Japan, under the initiative “Research and Development of Innovative Optical Network Technology for a Novel Social Infrastructure” (JPMI00316).

Image source: Courtesy of Sumitomo Electric

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