Vanadium dioxide-based terahertz metasurfaces for manipulating wavefronts with switchable polarization

As a unique phase transition material, vanadium dioxide (VO2) has been widely applied in switchable and modulating metasurfaces. In this work, VO2-based reflective meta-atoms are designed to achieve wavefront reconfiguration in terahertz frequency. When VO2 is metal, four optimized meta-atoms with 90o phase difference provide a full phase coverage, and they achieve high polarization conversion efficiency. After phase transition of VO2, the capability in the metallic state is lost. Thus, the corresponding phase coverage is switched from 360° to 0°, and the phenomenon of polarization conversion almost vanishes. Assembled by these meta-atoms, three metasurfaces are numerically presented. When VO2 is in the state of metal, they are anomalous reflector, metalens, and vortex beam generator. The presented metasurfaces own the abilities of wavefront manipulation and polarization conversion. When VO2 is in the insulating state, three metasurfaces are switched to specular reflector. Simulations are conducted to verify their abilities of wavefront modulation and polarization control. The proposed metasurfaces may have potential applications in the fields of terahertz switching, communication, and focusing.