Efficient unidirectional nanoslit couplers for surface plasmons

TL;DR

This paper introduces a novel back-side slit-illumination method with periodic indentations that achieves unidirectional surface plasmon polariton launching, improving coupling efficiency and directionality for ultracompact plasmonic devices.

Contribution

The paper presents a new slit-illumination technique using periodic indentations to control SPP directionality, overcoming previous coupling limitations.

Findings

Unidirectional SPP launching achieved

Suppression of SPP in one direction demonstrated

Enhanced coupling efficiency shown

Abstract

Plasmonics is based on surface plasmon polariton (SPP) modes which can be laterally confined below the diffraction limit, thereby enabling ultracompact optical components. In order to exploit this potential, the fundamental bottleneck of poor light-SPP coupling must be overcome. In established SPP sources (using prism, grating} or nanodefect coupling) incident light is a source of noise for the SPP, unless the illumination occurs away from the region of interest, increasing the system size and weakening the SPP intensity. Back-side illumination of subwavelength apertures in optically thick metal films eliminates this problem but does not ensure a unique propagation direction for the SPP. We propose a novel back-side slit-illumination method based on drilling a periodic array of indentations at one side of the slit. We demonstrate that the SPP running in the array direction can be suppressed, and the one propagating in the opposite direction enhanced, providing localized unidirectional SPP launching.