Tunable full-space light field manipulation based on double-layer Ge2Sb2Te5 metasurfaces

Abstract

Metasurfaces have the strong ability to reshape wave front and are attractive for a wide range of applications. However, metasurface based light field manipulation can be realized usually in either transmission or reflection space individually, which will limit its application scenario of metasuface. In this paper, we design a phase change material Ge2Sb2Te5 (GST) based double-layer dielectric metasurface in mid-infrared bands, which can achieve the light field manipulation in full space and dynamically control the focal intensity of reflected and transmitted light. As proof-of-concepts, two functional metasurfaces are designed and investigated: the first metasurface realizes the dynamically adjustable focus intensity in full-space under left circularly polarized (LCP) light incidence, the second metasurface is designed to provide spin-dependent bifocal in full space, which can generate custom designed two focal points under LCP or right circularly polarized (RCP) light incidence. Our proposed tunable full-space dielectric metasurfaces can be potentially applied for energy-harvesting, optical communication and optical imaging.