Transmission resonances on metallic gratings with very narrow slits

TL;DR

This paper demonstrates that metallic gratings with very narrow slits can produce high transmission resonances at wavelengths larger than the grating period, via surface plasmon polaritons or waveguide resonances.

Contribution

It introduces a transfer matrix and modal expansion model to explain transmission resonances in narrow-slit metallic gratings, highlighting two distinct excitation mechanisms.

Findings

High transmittance achieved at specific resonances

Resonances occur at wavelengths larger than the grating period

Two excitation mechanisms identified: surface plasmons and waveguide modes

Abstract

In this paper we show how transmission metallic gratings with very narrow and deep enough slits can exhibit transmission resonances for wavelengths larger than the period of the grating. By using a transfer matrix formalism and a quasi-analytical model based on a modal expansion, we show that there are two possible ways of transferring light from the upper surface to the lower one: by the excitation of coupled surface plasmon polaritons on both surfaces of the metallic grating or by the coupling of incident plane waves with waveguide resonances located in the slits. Both mechanisms can lead to almost perfect transmittance for those particular resonances.