Local Energy Velocity of the Air-Core Modes in Hollow-Core Fibers

Abstract

In this paper, we consider the behavior of the local energy flow velocity of the fundamental air-core mode at the core-cladding boundary in two types of hollow-core fibers: hollow-core fibers with a negative curvature of the core boundary and single-capillary fibers with similar geometrical parameters. It is demonstrated that the behavior of both axial and radial components of the local energy velocity of the fundamental air-core mode is completely different for these two types of hollow-core fibers. The negative curvature of the core boundary leads to an alternating behavior of the radial projection of the local energy velocity and a decrease of two orders of magnitude compared to the values of this projection for a single capillary. In our opinion, this behavior of the local energy velocity of the fundamental air-core mode is caused by a periodic set of Poynting vector vortices that appear in the cladding capillary walls.