Ring-engineered Ta ₂ O ₅ photonic crystal fiber for stable OAM mode transmission with tailored chromatic dispersion across the telecom band

We report a wavelength dependent modal, nonlinear, and dispersion analysis of the proposed Hollow Ring Core Ta 2 O 5 Photonic Crystal Fiber based waveguide for HE 1,1 to HE 5,1 over 1.31–1.61 µm using full vector eigenmode simulations. The group index remains weakly mode dependent, varying from 2.1587 to 2.1740 across the investigated band. With n 2 = 2.6 × 10 −20 m 2 /W, the nonlinear coefficient γ decreases monotonically from 3.9179 to 2.9071 W −1 km −1 as wavelength increases, maintaining strong nonlinear response. Dispersion is strongly engineered, with D spanning 1,967.04 to −1,215.43 ps/(nm km) and three zero dispersion crossings for HE 1,1 located near 1,350 nm, 1,426 nm, and 1,546 nm. The extracted higher order terms show β 2 from −0.00179207 to 0.00167256 ps 2 /km, β 3 negative over the reported range, and β 4 changing sign, enabling broadband dispersion managed operation. These results establish the proposed waveguide as a compact platform combining weak mode dependence, high nonlinearity, and widely tunable dispersion for mode multiplexed nonlinear photonic applications.