Architecture and planning of a regional multicore fiber submarine network comprising core selective switch-based branching units

We propose a novel branching unit (BU) architecture based on a $1 \times 2$ core selective switch (CSS) for regional multicore fiber (MCF) submarine systems. The proposed BU architecture requires only three CSS pairs and no fan-in fan-out devices, which reduces component cost, conserves space resources in the BU body, and halves the number of MCFs in branching cables resulting in a significant cable cost savings. For further component cost and space savings, we propose and discuss two approaches to achieve a higher-core-count CSS: one is to employ 16-CFs in a CSS for input and output ports and the other is to employ four bundled 4-CFs. These architectures increase the number of reconfigurable cores in a single CSS. While the proposed CSS-based BU architecture has the advantage of halving the number of MCFs in the branch cable, the aggregation of MCFs in the branch cable leads to core identification number (ID) contention, which increases the number of cores required if traditional same-core-ID assignment in the upstream and downstream is employed. We develop a bidirectional core assignment method that addresses this issue by assigning different core IDs in the upstream and downstream and validate its efficacy using the linear integer planning method.