Fig. 1
From: Optical vortices in waveguides with discrete and continuous rotational symmetry
Schematic of an MCF with M=5 periphery cores and the central core. Geometric parameters that dominantly determine coupling coefficients C0 and C1, are the distance between the central and each of periphery cores R and the distance between two neighboring periphery cores d=2R sin(π/M). Coupling coefficients depend on the geometry and refractive index of cores. Here, all periphery cores are assumed to be identical, while the central core can be different