Tunable dielectric metasurfaces by structuring the phase-change material

Metasurfaces have made great progress in the last decade for generating miniature and integrated optical devices. The optical properties of metasurfaces can be tuned dynamically by integrating with phase-change materials. However, the efficiency of tunable metasurfaces remains a bit low, which is a disadvantage for the realistic applications of metasurfaces. Here, we demonstrate the tunable dielectric metasurfaces by structuring the phase-change material Ge₂Sb₂Te₅. The unit cell of metasurface is composed of several Ge₂Sb₂Te₅ nanopillars with different geometric parameters, and the incident light interacts with different nanopillars at diverse phases of Ge₂Sb₂Te₅, leading to various functions. By elaborately arranging the Ge₂Sb₂Te₅ nanopillars, various tunable optical devices have been realized, including tunable beam steering, reconfigurable metalens and switchable wave plate. The refractive direction, focal length and polarization state can be tuned through the phase transition of Ge₂Sb₂Te₅. The phase-change metasurfaces based on Ge₂Sb₂Te₅ nanostructures could be used in cameras, optical microscopy and adaptive optics.