A Dual-Band Spaceplate: Contracting the Volume of Quasi-Optical Systems

Abstract

A ‘spaceplate’ approximates the angular response of free space with a much thinner non-local metamaterial. They have the potential to significantly shrink the volume of optical and quasi-optical systems, by allowing elements such as lenses to be moved closer together. However, spaceplates exhibit a trade off between their operational angular and spectral bandwidth. In this work, we present a new space-compression concept: a dual-band spaceplate – capable of operating in two distinct frequency bands simultaneously. This allows the limited spectral bandwidth to be targeted to application specific parts of the spectrum. Our design is composed of a multi-layer stack of semi transparent mirrors separated by free-space voids. These layers act as a system of coupled Fabry-Perot cavities – the guided-mode ´ resonances of which emulate the effect of free-space propagation. The stack is engineered to exhibit two resonant sub-bands, with the frequency separation a tunable parameter in the design. We numerically and experimentally demonstrate a dual-band spaceplate exhibiting space-compression at two distinct frequency sub-bands centered about 21.4 and 23.7 GHz.