Spin-decoupled multifunctional terahertz metasurface based on vanadium dioxide

The dynamic and precise control of circularly polarized electromagnetic waves is critical for cutting-edge fields such as chiral-molecule sensing, quantum information processing, and next-generation communications. Metasurfaces present an ideal platform for realizing miniaturized and integrated functional devices due to their sub-wavelength precision in manipulating electromagnetic waves. However, conventional metasurfaces suffer from spin-locking and functionality-freezing limitations, which prevent them from meeting the multi-functional demands of complex scenarios. To overcome these challenges, we propose a switchable, multi-functional terahertz metasurface based on the phase-change material vanadium dioxide (VO₂). By synergistically engineering the propagation phase and the Pancharatnam-Berry phase, the device achieves complete decoupling of left- and right-circularly polarized light (LCP/RCP) at 1 THz: at room temperature (dielectric state), it simultaneously deflects reflected LCP and focuses reflected RCP; above the phase-transition temperature (metallic state), it selectively absorbs LCP while converting reflected RCP into a Bessel beam. The metasurface functionality can be dynamically reconfigured on demand by varying the incident polarization and temperature. Featuring high efficiency, low crosstalk, and a compact footprint, this design provides a new design strategy and a practical pathway for developing reconfigurable terahertz devices such as beam splitters, isolators, and imaging systems.