Tunable multifunctional full-space metalens based on photosensitive silicon and VO 2

Abstract Aiming at the bottleneck that existing metalenses struggle to achieve efficient full-space dynamic modulation at the same frequency, this study proposes a full-space terahertz meta-atom based on photosensitive silicon (PS) and VO 2 , enabling dynamically switchable operation modes. The meta-atom employs a multi-layer composite resonant structure, allowing independent manipulation of the reflection and transmission wavefronts of circularly polarized (CP) waves at a fixed frequency. When both PS and VO 2 are in the metallic states, rotating the PS double-open ring enables reflection-type cross-polarization conversion and 2 π phase coverage in the 0.43–0.99 THz frequency band. When PS transitions to the insulating state, rotating the PS-Au ring maintains high-efficiency reflection cross-polarization conversion and 2 π phase coverage in the 0.65–1.2 THz band. When both PS and VO 2 are in the insulating states, the meta-atom switches to transmission mode, achieving efficient cross-polarization conversion and 2 π phase coverage within the 0.83–0.97 THz range. Based on this meta-atom, we further designed four types of phase-reconfigurable full-space metalenses, including bifocal tuning for a single-focus metalens, bifocal tuning for a dual-focus metalens, single-point focusing to dual-point focusing switching, and single-point focusing to focused orbital angular momentum (FOAM) generator switching. Simulation results demonstrate that by controlling the phase states of PS and VO 2 , the operating mode and wavefront of the metalens can be dynamically reconfigured, enabling focal length variation and functional switching. This research provides a novel solution for dynamic terahertz wavefront control, with significant application potential in terahertz super-resolution imaging, high-speed communication, and intelligent information processing.