Index-Profile Modification for Increasing MDM Channel Count in Radially-Single-Mode Ring-Core Fibers

We investigate radially-single-mode ring-core fibers that feature a monotonic-graded-index-profile for the 2nd-layer, a raised-index-inner-core in the 1st-layer, and a low-index-trench in the 3rd-layer. We achieve four mode-groups with effective-index-difference between any two mode-groups ≥ 1.198×10–3.