LiNbO ₃ /Ta ₂ O ₅ dual ring core photonic crystal fiber: dispersion engineering and supercontinuu

Abstract

A dual ring core photonic crystal fiber is numerically designed to achieve low loss guidance, dispersion control, and broadband nonlinear spectral broadening. The structure employs a silica microstructured background with a hollow air core and concentric LiNbO ₃ and Ta ₂ O ₅ rings, with air hole diameters of 0.6 µm, 1.0 µm, and 2.0 µm and a hollow core radius of 13 µm. Guided modes are computed using a full vector Maxwell eigenmode solver based on the finite element method with a perfectly matched layer, and robustness is assessed through a 600 mode sweep. The Ta ₂ O ₅ ring thickness is selected as 0.8 µm because the effective index spectrum remains well separated across the computed modes and the imaginary part of the effective index is reduced. Over 1.40–1.60 µm, the investigated HE modes exhibit confinement loss below 10 ⁻⁸  dB/m and mode purity close to 0.99. Dispersion analysis shows a sign transition in D with corresponding β ₂ reversal, while β ₃ and β ₄ remain bounded within the studied band. Nonlinear propagation results demonstrate progressive spectral broadening with fiber length from 0.1 to 20.0 mm and peak power from 2 to 10 kW, supported by temporal and spectral evolution maps. These results indicate that the proposed dual ring core platform supports stable guidance and dispersion tailored broadband generation in a compact length scale.