Diffraction limited focusing and routing of gap plasmons by a metal-dielectric-metal lens

TL;DR

This paper demonstrates the experimental realization of a metal-dielectric-metal lens capable of diffraction-limited focusing and routing of gap plasmons in a planar waveguide, advancing integrated plasmonic photonic devices.

Contribution

It introduces a novel high numerical-aperture metal-dielectric-metal lens for gap plasmon focusing and routing, with detailed fabrication and optical characterization.

Findings

Achieved diffraction-limited focusing of gap plasmons.

Measured focal distance and spot size match theoretical predictions.

Demonstrated propagation length of surface plasmon polaritons.

Abstract

Passive optical elements can play key roles in photonic applications such as plasmonic integrated circuits. Here we experimentally demonstrate passive gap-plasmon focusing and routing in two-dimensions. This is accomplished using a high numerical-aperture metal-dielectric-metal lens incorporated into a planar-waveguide device. Fabrication via metal sputtering, oxide deposition, electron- and focused-ion- beam lithography, and argon ion-milling is reported on in detail. Diffraction-limited focusing is optically characterized by sampling out-coupled light with a microscope. The measured focal distance and full-width-half-maximum spot size agree well with the calculated lens performance. The surface plasmon polariton propagation length is measured by sampling light from multiple out-coupler slits.