Design of a microstructure optical fiber supporting 52 vortex beams

Abstract

We propose a newly designed optical fiber with a microstructure based on SiO2 that supports the transmission of 52 vortex beams. By optimizing the radius of the center air hole and small air holes encircling the center air hole, the effective refractive index difference between adjacent vortex beams is higher than 10−4, which is large enough to support the transmission of vortex beams. Through a numerical analysis, the dispersion of vortex beams is lower than 189.00 ps ⋅ nm−1⋅ km−1 and maintains a flat trend. The confinement loss is as low as 10−9 dB ⋅ m−1 at 1550 nm, and the nonlinear coefficient of the vector modes is on the order of 10−4. The HE31 mode has the longest stable transmission distance among the vector modes, 630.83km at 1550nm. The vortex beams’ purity is analyzed to quantify the spin–orbit coupling (SO coupling) effect. The modes’ purity is higher as the topological charge (L) increases, and the spin–orbit aligned modes’ purity is higher than the spin–orbit anti-aligned mode at the same L. The MOF’s geometric parameters affect vortex beams’ purity.