Robust manipulation of light using topologically protected plasmonic modes

TL;DR

This paper introduces a topological plasmonic crystal structure that leverages topologically protected defect modes for robust light manipulation, including mode filtering and beam-splitting, resilient to fabrication imperfections.

Contribution

It presents a novel topological plasmonic design based on the SSH model, demonstrating defect modes and functional devices with robustness to errors.

Findings

Existence of topological defect modes with sub-wavelength localization

Construction of spatial mode filters and beam-splitters using kinks

Robustness of structures to fabrication errors within the topological band gap

Abstract

We propose a topological plasmonic crystal structure composed of an array of parallel nanowires with unequal spacing. In the paraxial approximation, the Helmholtz equation that describes the propagation of light along the nanowires maps onto the Schr\"{o}dinger equation of the Su-Schrieffer-Heeger (SSH) model. Using full three-dimensional finite difference time domain solution of the Maxwell equations we demonstrate the existence of topological defect modes, with sub-wavelength localization, bound to kinks of the plasmonic crystal. Furthermore, we show that by manipulating kinks we can construct spatial mode filters, that couple bulk modes to topological defect modes, and topological beam-splitters that couple two topological defect modes. Finally, we show that the structures are robust to fabrication errors with inverse length-scale smaller than the topological band gap.