Parametric Optimization for Low Loss Negative Curvature Hollow Core Fiber With Elliptical Tube

Negative curvature hollow core fiber (NC-HCF) with elliptical tubes is beneficial for low confinement loss (CL) due to the rich degree of freedom in tube curvature. In this paper, an empirical formula for optimizing the structural parameters of NC-HCF with elliptical tubes is presented, which is aimed at the minimum CL. It is obtained by analyzing the trade-off between the mode coupling induced loss and the gap induced leakage loss, according to the theory of mode coupling between core fundamental mode and tube ring mode, and the geometric arrangement. Consequently, a relationship between gap and elliptical tube diameter in the radial direction has been found to be 1/2, with corresponding formula validated by the numerical investigation and simulation for a wide wavelength range and different elliptical tube numbers. The parametric optimization formula provides a design guideline for low loss NC-HCF, which can be an effective tool for further exploration and application.