Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber

TL;DR

This paper introduces a novel hollow fiber design with a thin ITO layer that supports epsilon-near-zero modes, enabling highly confined waveguiding with potential applications in sensing, filtering, and nonlinear optics.

Contribution

It demonstrates the excitation of ENZ modes in a new fiber structure through coupling of core and thin-film modes, with tunable phase matching based on internal refractive index.

Findings

ENZ mode excitation observed near specific wavelengths

Mode coupling depends on internal refractive index

Potential for in-fiber sensing and nonlinear applications

Abstract

We report a novel optical waveguide design of a hollow step index fiber modified with a thin layer of indium tin oxide (ITO). We show an excitation of highly confined waveguide mode in the proposed fiber near the wavelength where permittivity of ITO approaches zero. Due to the high field confinement within thin ITO shell inside the fiber, the epsilon-near-zero (ENZ) mode can be characterized by a peak in modal loss of the hybrid waveguide. Our results show that such in-fiber excitation of ENZ mode is due to the coupling of the guided core mode to the thin-film ENZ mode. We also show that the phase matching wavelength, where the coupling takes place, varies depending on the refractive index of the constituents inside the central bore of the fiber. These ENZ nanostructured optical fibers have many potential applications, for example, in ENZ nonlinear and magneto-optics, as in-fiber wavelength-dependent filters, and as subwavelength fluid channel for optical and bio-photonic sensing.