Boosting Optical Nanocavity Coupling by Retardation Matching to Dark Modes

TL;DR

This paper demonstrates that controlling the surrounding refractive index enables efficient frequency tuning and enhances optical coupling in plasmonic nano-antennas by activating dark modes through retardation matching.

Contribution

It introduces a novel approach of tuning plasmonic nano-antennas via refractive index control to activate dark modes, bypassing shape-dependent limitations.

Findings

Refractive index control enables dark mode activation.

Retardation matching improves in/output coupling.

Enhanced optical functionalities in plasmonic nano-antennas.

Abstract

Plasmonic nano-antennas can focus light to nanometre length-scales providing intense field enhancements. For the tightest optical confinements (0.5-5 nm) achieved in plasmonic gaps, the gap spacing, refractive index, and facet width play a dominant role in determining the optical properties making tuning through antenna shape challenging. We show here that controlling the surrounding refractive index instead allows both efficient frequency tuning and enhanced in/output-coupling through retardation matching as this allows dark modes to become optically active, improving widespread functionalities.