Observation of enhanced epsilon-near-zero effects in resonant stratified media

Abstract

Epsilon-near-zero (ENZ) materials have gained recent interest due to their exotic optical properties, but their potential is limited by intrinsic material losses. Enhanced epsilon-near-zero (eENZ) materials are periodically stratified media consisting of alternating ENZ and dielectric layers. In this study, we demonstrate the fabrication and optical characterization of 15-layer ENZ-dielectric thin film stack, wherein indium tin oxide functions as the ENZ material and titanium dioxide as the dielectric. We experimentally show the enhanced optical transmission of the structure over a bare ENZ film with similar thickness. Further, we display the giant polarization dependent optical response of the material, which is characterized by the narrowing from 56° to 14° in half-width at half-maximum of the transmission cone. These properties are physically attributed to guided-waves, Fabry–Pérot resonances, and Ferrell–Berreman plasmons within the film stack. The experimental realization of our material paves the way for devices utilizing eENZ-materials, such as coherence switchable lasers and light sources with directional emission.