Non-volatile tunable optics by design: From chalcogenide phase-change materials to device structures

Integration of chalcogenide phase-change materials (PCMs) with planar multilayer structures, metasurfaces, waveguides and photonic integrated circuits has sparked extensive research in non-volatile tunable optical devices. The optical performances of these devices are determined not only by the light interference or localization using layered or patterned device structures, but also by the change in dielectric function of PCMs upon phase transition. In this review, we summarize latest progress on high-performance tunable optical PCM devices, which are promoted by the successful designs of both new materials and novel device structures. First, we present an in-depth understanding of the optical properties of PCMs at the atomic level and discuss how to tailor the optical properties via materials design. Then we discuss multiple emerging non-volatile optical applications utilizing the tunable transmission, color, absorption, emission and phase shift of PCM optical devices that are enabled by waveguide integration, multilayer deposition as well as metasurface patterning. Recent progress on microheater fabrication that enables electronic-photonic integration is also highlighted. Finally, we outline the opportunities that lie ahead for optical PCMs and non-volatile nanophotonics.