Parabolic-Index Ring-Core Fiber Supporting High-Purity Orbital Angular Momentum Modes

Abstract

We design a graded-index ring-core fiber with a GeO2-doped silica ring core and SiO2 cladding. This fiber structure can inhibit the effect of spin-orbit coupling to mitigate the power transfer among different modes and eventually enhance the orbital angular momentum (OAM) mode purity. By changing the high-index ring core from the step-index to parabolic graded-index profile, the purity of the OAM1,1 mode can be improved from 86.48% to 94.43%, up by 7.95%. The proposed fiber features a flexible structure, which can meet different requirements for mode order, effective mode area, etc. Simulation results illustrate that the parabolic-index ring-core fiber is promising in enhancing the OAM mode purity, which could potentially reduce the channel crosstalk in mode-division-multiplexed optical communication systems.

Nonlinear localized states near the interface with nonlinear response between the medium with a parabolic index spatial profile and Kerr-type medium

“…The bending sensitivity of smooth refractive fibers, although worse than the idealized parabolic case, is significantly better than the more commonly used stepped refractive fibers, whose profiles change abruptly [85,86]. Parabolic refractive index profiles are usually obtained by doping glasses with semiconductor additives [87,88]. The most common structures are gradient cores with quartz doped with germanium or GeO 2 [89][90][91].…”