Exceptional Points and Asymmetric Mode Switching in Plasmonic Waveguides

TL;DR

This paper explores exceptional points in a non-Hermitian graphene waveguide system, demonstrating mode coalescence, asymmetric mode switching, and potential applications in nanoscale optical switches and sensors.

Contribution

It identifies and analyzes exceptional points in a graphene-based plasmonic system, revealing mode behavior and phase variation useful for optical device development.

Findings

EPs cause eigenvalue coalescence in graphene waveguides

Encircling EPs results in mode conversion and phase change

Input modes can lead to different outputs, enabling switching

Abstract

We investigate the exceptional points (EPs) in a non-Hermitian system composed of a pair of graphene sheets with different losses. There are two surface plasmon polaritons (SPP) modes in the graphene waveguide. By varying the distance between two graphene sheets and chemical potential of graphene, the EPs appear as the eigenvalues, that is, the wave vectors of the two modes coalesce. The cross conversion of eigenmodes and variation of geometric phase can be observed by encircling the EP in the parametric space formed by the geometric parameters and chemical potential of graphene. At the same time, a certain input SPP mode may lead to completely different output. The study paves a way to the development of nanoscale sensitive optical switches and sensors.