Terahertz state switching of holograms enabled by vanadium dioxide-based metasurfaces.

Holography is an important topic in optical research. Metasurface holography has attracted increasing attention in recent years. However, it is still challenging to achieve dynamic tuning of holograms in the terahertz band. As an excellent phase change material, vanadium dioxide (VO) is widely employed to dynamically manipulate electromagnetic waves. Here, VO meta-atoms are designed to manipulate phase and amplitude by changing the state of VO at 3.0 THz. These meta-atoms are composed of a VO block, silica spacer, and gold substrate. As the metallic VO is involved, 360° phase coverage is achieved by changing the dimension of VO. The phase difference between the VO meta-atoms is approximately equal to 90°. Holograms are generated by aligning these meta-atoms. By combining convolution operations, holograms are deflected and reproduced. As the insulating VO is involved, the phase difference between the VO meta-atoms vanishes and the reflection amplitudes of the meta-atoms almost reach 100%. Using the phase transition of VO, three types of metasurfaces are designed to manipulate holograms and they realize state switching of the hologram generator, state switching of hologram deflection, and state switching of the multi-beam hologram. Our work may find applications in optical holography and information privacy.