The dramatic optical property change of optical phase change materials (O-PCMs) between their amorphous and crystalline states potentially allows the realization of reconfigurable photonic devices with enhanced optical functionalities and low power consumption, such as reconfigurable optical components, optical switches and routers, and photonic memories. Conventional O-PCMs exhibit considerable optical losses, limiting their optical performance as well as application space. In this talk, we present the development of a new group of O-PCMs and their implementations in novel meta-optic devices. Ge-Sb-Se-Te (GSST), obtained by partially substituting Te with Se in traditional GST alloys, feature unprecedented broadband optical transparency covering the telecommunication bands to the LWIR. A drastic refractive index change between the amorphous and crystalline states of GSST is realized and the transition is non-volatile and reversible.
Optical metasurfaces consist of optically-thin, subwavelength meta-atom arrays which allow arbitrary manipulation of the wavefront of light. Capitalizing on the dramatically-enhanced optical performance of GSST, transparent and ultra-thin reconfigurable meta-optics in mid-infrared are demonstrated. In one example, GSST-based all-dielectric nano-antennae are used as the fundamental building blocks for meta-optic components. Tunable and switchable metasurface devices are developed, taking advantage of the materials phase changing properties.