Bend-insensitive optical vortex guiding enabled by dual-ring photonic crystal fiber engineering

This work presents a detailed numerical analysis of a Bend-Insensitive Dual-Ring OAM Photonic Crystal Fiber (BIDRO-PCF) engineered for stable guidance of HE m,1 and OAM-like modes. The fiber incorporates a hollow core surrounded by two high-index functional rings of LiNbO 3 and B 2 O 3 -modified silica, embedded within a silica PCF lattice. Simulations across 1.32–1.62 μm band show that all guided modes maintain effective indices in the 2.080–2.123 range with modal separation below 0.01, while the imaginary part of the index remains on the order of 10 −10 , confirming low intrinsic loss. The effective area increases from 31.9 to 35.1 μm 2 over the band, corresponding to nonlinear coefficients decreasing from 3.88 to 3.03 W − 1 km −1 . Dispersion calculations reveal strictly normal behaviour, with chromatic dispersion varying from, 95 to 33 ps nm −1 km −1 and higher-order terms β 2 , β 3 , and β 4 following smooth, well-structured trends. Bend modelling demonstrates strong robustness, bend-modified effective index remains near 2.092 for radii R B ≥ 3 cm, and significant distortion appears only at extreme curvature, where R B = 0.01 cm produces n eff values up to 2.167 for higher-order modes. These results confirm that the BIDRO-PCF supports stable multi-mode and OAM-compatible operation with high bend tolerance, making it suitable for advanced optical communication and nonlinear photonic applications.