Optimization method for low-loss single-mode bending negative curvature anti-resonant hollow-core fiber designed by mode modification

A method of designing negative curvature anti-resonant hollow-core fibers (NC-AR-HCFs) with bending resistance is proposed, by which the fundamental mode (FM) and higher-order mode (HOM) can be adjusted. An asymmetric double-ring negative curvature hollow-core fiber (ADR-NC-HCF) is proposed to verify the method. The ADR-NC-HCF achieves the FM loss of 0.8 dB/km at 1550 nm under the bending radius of 20 mm. The coupling relation between the modes in ADR-NC-HCFs is analyzed revealing the physical principle of the design method. Based on the principle, the fiber can be directionally optimized to achieve a lower loss of the FM or higher-order mode extinction ratio.