Active metasurfaces for manipulatable terahertz technology*

Abstract

Metasurface is a kind of two-dimensional metamaterial with specially designed sub-wavelength unit cells. It consists of single-layer or few-layer stacks of planar structures and possesses certain superior abilities to manipulate the propagating electromagnetic waves, including the terahertz (THz) ones. Compared with the usual passive THz metasurfaces whose optical properties are difficult to be controlled after fabrication, the active materials are highly desirable to enable dynamic and tunable control of THz waves. In this review, we briefly summarize the progress of active THz metasurfaces, from their physical mechanisms on carrier concentration modulations, phase transitions, magneto-optical effects, etc., for various possible THz applications mainly with low-dimensional materials, vanadium dioxide films, and superconductors.