Switchable bifunctional metasurfaces: nearly perfect retroreflection and absorption at the terahertz regime

Here we make use of vanadium dioxide (VO₂) to design a bifunctional metasurface working at the same targeted frequency. With the increase of temperature, the functionality of the designed metasurface can switch from a multichannel retroreflector to a perfect absorber, caused by the phase transition of VO₂ from insulator to conductor. Different from traditional bifunctional metasurfaces designed by simple composition of two functionalities, our proposed bifunctional metasurface is based on the interaction between two functionalities. The device shows good potential for the combination of wavefront manipulation and optical absorption, therefore providing a promising approach for switchable detection and antidetection devices.