Coupling of Plasmon Modes in Graphene Microstructures

TL;DR

This paper develops a coupled-mode theory for graphene plasmonic structures, enabling accurate prediction of mode interactions and dynamics, validated through experiments on coupled graphene strip arrays with tunable spacing.

Contribution

It introduces a quantitative coupled-mode theory for graphene plasmons, bridging the gap between theory and experiment for complex coupled structures.

Findings

Coupled-mode theory accurately predicts plasmon coupling in graphene structures.

Experimental tuning of spacing modifies plasmon frequencies as theory suggests.

Good agreement between theoretical predictions and experimental results.

Abstract

A variety of different graphene plasmonic structures and devices have been proposed and demonstrated experimentally. Plasmon modes in graphene microstructures interact strongly via the depolarization fields. An accurate quantitative description of the coupling between plasmon modes is required for designing and understanding complex plasmonic devices. Drawing inspiration from microphotonics, we present a coupled-mode theory for graphene plasmonics in which the plasmon eigenmodes of a coupled system are expressed in terms of the plasmon eigenmodes of its uncoupled sub-systems. The coupled-mode theory enables accurate computation of the coupling between the plasmon modes and of the resulting dynamics. We compare theory with experiments performed on the plasmon modes in coupled arrays of graphene strips. In experiments, we tune the coupling by changing the spacing between the graphene strips in the array. Our results show that the coupling parameters obtained from the coupled-mode theory and the plasmon frequency changes resulting from this coupling agree very well with experiments. The work presented here provides a framework for designing and understanding coupled graphene plasmonic structures.