Coupled surface plasmon and resonant optical tunnelling in symmetric optical microcavities

TL;DR

This paper investigates a symmetric optical microcavity system supporting coupled surface plasmons and resonant tunnelling, demonstrating high transmission through a model that enhances frustrated total reflection effects.

Contribution

It introduces a simple model for transmission in symmetric microcavities supporting coupled plasmons, highlighting conditions for high transmittance even with micron-scale dielectric layers.

Findings

Resonance conditions enable high transmittance in microcavities.

Coupled surface plasmons enhance optical tunnelling.

The system exhibits a quantum tunnelling-like phenomenon with metal films.

Abstract

A symmetrical structure consisting of a low refractive index dielectric layer between two metallic films, i.e. an optical cavity, surrounded by a semi-infinite dielectric medium of higher refractive index, forms an optical system capable of supporting both volume and surface resonances. The latter are associated with synchronized collective electronic oscillations in the inner surfaces of the two thin metallic films, called coupled surface plasmons. These oscillations are generated by an evanescent wave in the cavity and therefore the thickness of the cavity is limited to the micron range for visible radiation. Under suitable incident conditions, light propagating in the microcavity will resonate with these plasmonic oscillations and can be strongly transmitted into the surrounding medium. In this work, we establish a simple model of the transmission characteristics of the cavity and define resonance conditions that allow high transmittance even for inner dielectric layer thicknesses of various wavelengths. This phenomenon is an enhanced version of the optical process of frustrated total reflection between dielectrics analogous to quantum tunnelling effect. In the present situation, the phenomenon is more striking because it takes place in a system with two absorbing metal films which, under resonant conditions, favour a superior transmission.