Polarization-independent anti-resonant hollow-core fiber coupler

In this paper, we numerically demonstrate a silica-glass-based polarization-independent symmetric (50:50) coupler tailored for nested anti-resonant nodeless fibers; however, the design methodology should be applicable for all other anti-resonant tubular designs of the hollow-core fibers as well. The device design is optimized using finite-element method simulations. By incorporating a lateral core offset on the facing side of the missing nested tube structure, the coupler exhibits strong modal interaction, compact device length, and high tolerance to fabrication variations. Our analysis shows very low confinement loss (<0.001dB/m) in a wide wavelength range of 1.36–1.625 µm. The coupler has a coupling ratio 50±2% in a wavelength range of 1.55−1.59µm. Our proposed design remains tolerant to cladding-tube ellipticity variations of up to 5% from the ideal value while keeping the confinement loss below 0.002 dB/m. These results establish a pathway toward low-loss and polarization-independent components for a fully integrated hollow-core fiber network.