Randomly coupled trench-assisted multicore fibers with different arrangements for high tolerance of manufacturing errors

Randomly coupled multicore fibers (RC-MCFs) are promising candidates for long-haul transmission. However, the degree of coupling between the homogeneous cores of an RC-MCF is weakened if manufacturing errors appear. Therefore, a low-index trench layer is introduced into the coupled cores to investigate the effects of its position and thickness on the group index to enhance the tolerance of manufacturing errors. A depressed region is designed in the center of the core to solve the problem of the effective area decreasing because of the confinement of the low-index trench. Additionally, it is important to study the effective arrangement of the coupled cores to obtain a smaller group delay spread (GDS) within the limited 125-mu m cladding; we discuss the single-layer and double-layer arrangements. A moderate range is found for both the bending radius and core pitch to minimize the GDS. For the single-layer arrangement, the degree of mixing is weak, and the degeneracy state does not easily change the bending conditions; thus, it may be a good candidate for designing systemically coupled multicore fibers. For the double-layer arrangement, the bending and twisting factors can induce sufficient mixing among the different modes to reduce GDS; thus, this arrangement is more suitable for the design of RC-MCFs.