Design of azimuthal-confinement-enhanced hollow-core antiresonant fibers

Hollow-core antiresonant fibers (HC-ARFs) have surpassed the minimum transmission loss of traditional silica single-mode fibers. However, this breakthrough comes at the cost of heightened structural complexity, elevated fabrication challenges. Further loss reduction demands innovative structural strategies. In this work, we propose azimuthal-confinement-enhanced HC-ARFs by integrating curved boundaries and radial walls to amplify both boundary curvature effect (BCE) and azimuthal confinement effect (ACE). Three models-optimized radial spokes, single antiresonant silica layer, and grapefruit-shaped structures-are designed and categorized into ideal (no silica jacket layer) and practical (with silica jacket layer) types. Numerical simulations reveal that optimizing dimensionless parameters f_θ and f_r, corresponding to BCE and ACE respectively, achieves a 3-4 order-of-magnitude reduction in confinement loss (CL) for ideal-type fibers (minimum CL: 2.57 × 10^-6 dB/m) and a 16-fold reduction for practical-type fibers compared to conventional designs. Critical tolerances for wavelength, silica wall thickness, and core radius are identified, ensuring robust low-loss operation. Additionally, the optimized structures exhibit enhanced minimum higher-order mode extinction ratio while maintaining bending loss and material absorption loss comparable to traditional HC-ARFs. This work establishes a paradigm for low-structural-complexity, high-performance low-loss HC-ARFs beyond nested-tube architectures, advancing their applicability across near-infrared to terahertz regimes.