Directional Scattering Switching from an All-Dielectric Phase Change Metasurface

All-dielectric metasurfaces are a blooming field with a wide range of new applications spanning from enhanced imaging to structural color, holography, planar sensors, and directionality scattering. These devices are nanopatterned structures of sub-wavelength dimensions whose optical behavior (absorption, reflection, and transmission) is determined by the dielectric composition, dimensions, and environment. However, the functionality of these metasurfaces is fixed at the fabrication step by the geometry and optical properties of the dielectric materials, limiting their potential as active reconfigurable devices. Herein, a reconfigurable all-dielectric metasurface based on two high refractive index (HRI) materials like silicon (Si) and the phase-change chalcogenide antimony triselenide (Sb₂Se₃) for the control of scattered light is proposed. It consists of a 2D array of Si-Sb₂Se₃-Si sandwich disks embedded in a SiO₂ matrix. The tunability of the device is provided through the amorphous-to-crystalline transition of Sb₂Se₃. We demonstrate that in the Sb₂Se₃ amorphous state, all the light can be transmitted, as it is verified using the zero-backward condition, while in the crystalline phase most of the light is reflected due to a resonance whose origin is the contribution of the electric (ED) and magnetic (MD) dipoles and the anapole (AP) of the nanodisks. By this configuration, a contrast in transmission (ΔT) of 0.81 at a wavelength of 980 nm by governing the phase of Sb₂Se₃ can be achieved.