Dependence of Waveguide Properties of Anti-Resonant Hollow-Core Fiber on Refractive Index of Cladding Material

Anti-resonant hollow-core fiber is featured by the broadband and low-loss transmission of light in the hollow core thanks to the optical property of anti-resonance cladding design. In this paper, we numerically explore the antiresonance of cladding from a new angle and confirm unique and important roles of refractive index of cladding material played in the confinement, bend and material losses of modes in anti-resonant hollow-core fibers. The numerical simulations demonstrate the dependence of confinement loss in anti-resonant hollow-core fiber on the cladding material refractive index which differs from the capillary waveguide and 1.5 refractive index is found favorable to achieve the lowest confinement loss ever in anti-resonant hollow-core fiber. Meanwhile, higher material refractive index can more effectively mitigate the material absorption and consequent contribution to the overall fiber loss in the anti-resonant hollow-core fiber than in the tube waveguide, by reducing the modal overlap factor. Besides, to the best of our knowledge, it is for the first time to discover that the modal dispersion of anti-resonant hollow-core fiber can be effectively altered by the cladding material refractive index, which was usually regarded to be determined by the core dimension and filled-in gas only. The refractive index around 1.8 is preferred to achieve a flattened profile of group dispersion over the transmission spectral window in anti-resonant hollow-core fibers. Our results bring in a new perspective to investigate the guidance mechanism of anti-resonant hollow-core fibers and provides guidance for material selection in the fiber design for optimization of waveguide properties.