Ge₃Sb₂Te₆-based mid-infrared metasurfaces for polarization control and wavefront steering

Abstract

Benefiting from excellent properties in wavefront control, germanium antimony telluride (GeSbTe)-based photonic devices provide new opportunities for manipulating electromagnetic wave. In this paper, Ge3Sb2Te6 meta-atoms are presented to realize polarization switching for mid-infrared wave through the state transition from the crystalline Ge3Sb2Te6 to the amorphous Ge3Sb2Te6. When the crystalline Ge3Sb2Te6 is involved, the proposed meta-atoms with 90° phase shift achieve high-efficiency polarization conversion and 360° phase coverage. As Ge3Sb2Te6 is changed to the amorphous state, phase coverage drops to only 36°, and most of the cross-polarized wave vanishes. Using these designed meta-atoms, three metasurfaces are implemented at 76.5 THz. Firstly, a gradient metasurface is constructed, and it dynamically switches between specular reflection and anomalous reflection. Next, a reflective metalens is proposed to realize switching between focusing and defocusing under different states of Ge3Sb2Te6. Lastly, a focused vortex beam is presented to reconstruct the mode of orbital angular momentum (OAM). All designs realize the switching between cross-polarization and co-polarization. Our work could have possible applications in fields such as mid-infrared switching, focusing, and wireless communication.