Mode Analysis and Characterization of Negative Curvature Hollow-Core Fiber under Bending

Negative curvature hollow-core fiber (NC-HCF) is a promising waveguide candidate for long haul transmission, high power laser delivery and macro-/micro-bend sensing. It is important to study in details of its bending characteristics, among which the critical bend radius is a crucial parameter. In this paper, a new semi-analytical model is reported to calculate the critical bend radius accurately. This model is then validated numerically and experimentally. Meanwhile, the influence of structural parameters and bend radius on the fundamental core mode effective index is discussed. The model can also be used to predict the peak values in loss spectrum under bending condition. Generally, it supports the design of NC-HCF and related devices to meet the requirements about broad bandwidth in telecommunication as well as high bending sensitivity in sensing application.