All-optical switchable terahertz spin-photonic devices based on vanadium dioxide integrated metasurfaces

Metasurfaces based on Pancharatnam-Berry (P-B) phase can achieve strong spin angular momentum (SAM) to orbital angular momentum (OAM) conversion of light, which provides a new degree of freedom for light control and opens up a new way for the applications of metasurfaces in classical and quantum optics. With the development of high-speed, large-capacity information transmission and high-definition imaging, demand for multifunctional and tunable P-B phase metasurfaces increases. Here, we propose three switchable terahertz spin-photonic devices based on P-B phase metasurfaces for focusing (divergence), splitting and vortex generation of terahertz beams. Based on photo-induced insulator-metal phase transition of the vanadium dioxide (VO2) islands in reflective hybrid resonators, switching of the devices function between on- and off-state is obtained, and the amplitude switching efficiency is as high as 90%. This work provides new ideas for the design of active terahertz devices and facilitates the applications of terahertz spin-photonic devices based on metasurfaces.