Thermally switchable terahertz wavefront metasurface modulators based on the insulator-to-metal transition of vanadium dioxide.

Active use of phase transition phenomena for reversibly tuning the properties of functional materials in devices currently is an attractive research area of materials science. We designed and fabricated two kinds of metasurface modulators for dynamically controlling the wavefront of terahertz (THz) radiation based on the temperature-induced insulator-to-metal phase transition of vanadium dioxide (VO2). The modulators designed are based on the C-shaped slot antenna array. The slot antennas are made of the VO2 films on c-sapphire substrates. The C-shaped slot antennas are active only when the VO2 is in its metallic phase, i.e. at temperatures T > TC ∼68 °C. At T > TC, the first kind acts as a THz multi-focus lens which converges an incident THz plane wave into four focal spots and the second kind as an Airy beam generator. We characterized the function of two THz wavefront modulators over a broad frequency range, i.e. from 0.3 to 1.2 THz. Such thermally switchable THz wavefront metasurface modulators with a capability of dynamically steering THz fields will be of great significance for the future development of THz active devices.