Experimentally excellent beaming in a two-layer dielectric structure

Anna C Tasolamprou,Maria Kafesaki,Costas M Soukoulis,Lei Zhang,Thomas Koschny

doi:10.1364/oe.22.023147

Abstract

We demonstrate both experimentally and theoretically that a two-layer dielectric structure can provide collimation and enhanced transmission of a Gaussian beam passing through it. This is due to formation of surface localized states along the layered structure and the coupling of these states to outgoing propagating waves. A system of multiple cascading two-layers can sustain the beaming for large propagation distances.

Highlights

Directional light emission has been found to occur in metallic subwavelength apertures when the metal surrounding them features surface corrugations [1, 2]
In analogy to the surface plasmon polaritons which under certain conditions propagate strongly bound to a metal-dielectric interface, it has been shown that similar surface states can be supported by dielectric photonic crystals [7,8,9,10]
Apart from the photonic crystals, it has been discovered that even a single dielectric layer can support such surface states, i.e. states extended along the layer and localized in the perpendicular direction [14]

Summary

Introduction

Directional light emission has been found to occur in metallic subwavelength apertures when the metal surrounding them features surface corrugations [1, 2]. The enhanced directionality and transmission is is due to these surface corrugations that enable the coupling of the highly confined at the metal surface and non-radiative surface plasmon polaritons to outgoing propagating modes. To the metallic surface corrugations, a layer of scatterers on top of the modified layer, often call grating layer, facilities the coupling of the surface waves to radiation modes and results in enhanced beaming [11,12,13]. Placing a proper additional grating layer provides coupling to the radiation modes and directional propagation and by using several two-layer structures, referred as bilayers, the beaming can be sustained for long distances. The first layer of each bilayer supports surface states and the rear, grading layer couples the surface states to radiation modes. Given that the materials involved are dielectrics, the bilayer structure can be scaled down to μm, giving the same beaming response in the optical regime

Systems and investigation methods

8.2-12.4 GHz 2 Narda horn

Numerical investigation of a single layer of dielectric rods

Conclusions