Vanadium Dioxide Based Reconfigurable Janus Metasurface for Terahertz Full Space Wavefront Manipulation

Full space beam control can achieve precise orientation of signal energy in three-dimensional space, and has important application in radar systems and wireless communications. Here, we present a reconfigurable Janus metasurface based on the phase change material vanadium dioxide (VO₂), realizing bidirectional transmission and reflection at different temperatures. The meta-atom is composed of a three-layer metal-VO₂ composite structure and two dielectric layers. When the VO₂ is in the insulating state, the metasurface operates in transmission mode, enabling linear polarization conversion and independent beam control for terahertz (THz) waves incident from both forward and backward directions. When the VO₂ is in the metallic state, the metasurface switches to reflection mode, where linear polarization conversion and phase control of reflected waves are realized through the transmission-phase principle. Furthermore, by combining transmission-phase and geometric-phase mechanisms, decoupled control of circular polarization is achieved. By arrangement of these meta-atoms, we further designed a four-channel device capable of dynamically switching between the metalens and vortex beam generator. Meanwhile, a six-channel imaging device is constructed to produce distinct letter patterns under different operating modes. The results demonstrate that the proposed metasurface device achieves versatile multi-channel multiplexing. This work provides a new strategy for enhancing the multiplexing freedom of metasurface-based wavefront manipulation, with promising applications in THz rader, imaging, communications, and related fields.