Coupling dynamics in multicore fibers: a comprehensive review of weakly-coupled and strongly-coupled MCF architectures for space-division multiplexing

Multicore fibers (MCF) can overcome the capacity limitations of the network by enabling space-division multiplexing (SDM). Based on inter-core interaction, classification puts the MCFs into two groups. The first group is weakly-coupled (WC) MCFs. The second group is strongly-coupled (SC) MCFs. WC-MCFs are the weakly-coupled MCFs that minimize crosstalk through optimized core spacing and refractive-index engineering. Many researchers consider the independent transmission channels suitable for long-haul networks, high-capacity optical links, and emerging 5G/6G fronthaul deployment due to their stability and compatibility with existing infrastructure. Recent research highlights the complementary nature of WC and SC designs: WC-MCF is better for low-crosstalk independent-channel long-haul and practical deployment, while SC-MCF is better for maximizing spatial-spectral capacity and petabit-class core transport. In terms of capacity, strongly coupled MCF (SC-MCF) is better because its supermode-based spatial multiplexing supports far higher spatial channel counts and ultra-high petabit-class throughput compared to weakly coupled MCF.