Optical properties of Fano-resonant metallic metasurfaces on a substrate

TL;DR

This paper investigates how substrates influence Fano resonances in metallic metasurfaces in the mid-IR range, introducing a semi-analytical model to describe these effects and challenging existing effective medium theories.

Contribution

A new semi-analytical technique and minimal model are developed to analyze substrate effects on Fano resonances in metallic metasurfaces.

Findings

Substrate presence suppresses Wood's anomalies.

Different Fano resonances respond uniquely to substrate contrast.

Spectral positions depend on substrate and superstrate permittivities.

Abstract

Three different periodic optical metasurfaces exhibiting Fano resonances are studied in mid-IR frequency range in the presence of a substrate. We develop a rigorous semi-analytical technique and calculate how the presence of a substrate affects optical properties of these structures. An analytical minimal model based on the truncated exact technique is introduced and is shown to provide a simple description of the observed behavior. We demonstrate that the presence of a substrate substantially alters the collective response of the structures suppressing Wood's anomalies and spatial dispersion of the resonances. Different types of Fano resonances are found to be affected differently by the optical contrast between the substrate and the superstrate. The dependence of the spectral position of the resonances on the substrate/superstrate permittivities is studied and the validity of the widely used effective medium approaches is re-examined.