Complete spectral gap in coupled dielectric waveguides embedded into metal

TL;DR

This paper demonstrates the existence of a complete spectral gap in a symmetric plasmonic coupler with coupled dielectric waveguides embedded in metal, achieved without periodic structures.

Contribution

It introduces a novel symmetric four-waveguide structure that achieves a complete spectral gap through coupled modes, without relying on periodicity.

Findings

Spectral gap exists despite non-periodic structure.

Complete spectral gap achieved in symmetric four-waveguide system.

Contradirectional and codirectional mode interactions are key.

Abstract

We study a plasmonic coupler involving backward (TM_01) and forward (HE_11) modes of dielectric waveguides embedded into infinite metal. The simultaneously achievable contradirectional energy flows and codirectional wavevectors in different channels lead to a spectral gap, despite the absence of periodic structures along the waveguide. We demonstrate that a complete spectral gap can be achieved in a symmetric structure composed of four coupled waveguides.