Numerical Design of a Semicircular Composite-Cladding Hollow-Core Antiresonant Fiber for Higher-Order-Mode Suppression

We propose and numerically evaluate a fourfold hollow-core antiresonant fiber with integrated cladding units that combine a semicircular outer element, a circular antiresonant capillary, and nested elliptical and circular rings. This composite topology combines membrane-thickness and nested-boundary control to obtain low fundamental-mode leakage together with strong higher-order-mode attenuation. After geometric optimization, the calculated confinement losses at 1550 nm are 6.44×10−4 and 3.64×102 dB/km for the fundamental mode (FM) and the lowest-loss identified core-guided higher-order mode (HOM), respectively, corresponding to a confinement loss-based higher-order-mode extinction ratio (HOMER) of 5.65×105. The calculated wavelengths satisfying FM confinement loss ≤0.01 dB/km and HOMER above 103 form two sampled ranges, 1.250–1.575 and 1.650–1.675 μm. Within the investigated geometric perturbations, membrane-thickness errors and elliptical-ring circularization substantially affect modal-loss discrimination. The results provide a quantitative design basis for mode-selective composite cladding and identify the geometric features that must be controlled to retain its modal-loss discrimination.