Electrically Tunable VO₂-Based Metasurface for Shared-Aperture Terahertz Molecular Fingerprint Sensing and...

Metasurfaces enable spatially programmable control of far-field wavefronts, while broadband molecular sensing relies on strong near-field confinement and enhanced light-matter interaction. The mismatch between far-field radiation and near-field localization makes their monolithic integration in a single shared aperture challenging. Here, we report an electrically tunable terahertz (THz) VO₂-based metasurface designed under temporal coupled mode theory (TCMT). The device adopts a metal-insulator-metal (MIM) architecture integrating a VO₂ microbridge and bowtie antenna, enabling bias-controlled switching between molecular fingerprint sensing and programmable wavefront manipulation in a shared aperture. At zero bias, the metasurface operates in an over-coupled regime, supporting a broadband low Q resonance over 0.8-1.2 THz with strong local field enhancement for molecular fingerprint sensing demonstration, serving as a passive near-field sensing mode. Under the metallic state condition induced by the VO₂ phase transition, the unit cell exhibits an approximately 180° reflection phase shift with nearly invariant amplitude. An electrically assisted programmable addressing implementation is proposed by exploiting the electrothermal switching capability of VO₂. Each unit cell thus functions as a 1-bit programmable meta-atom. By reconfiguring the spatial coding sequence, the device realizes anomalous reflection and beam splitting, which are further extended to refractive index sensing: thin analyte layers (<10 μm) are detected via anomalous reflection, whereas thicker layers are detected via beam splitting when the anomalous beam is suppressed. This constitutes a far-field active sensing mode. Both functionalities originate from the same over-coupled radiative loss mechanism: enhanced near fields enable fingerprint sensing, while the open radiative channel supports far-field refractive index sensing through programmed phase coding. This shared aperture design unifies near-field and far-field, passive and active sensing, offering a compact platform for THz integrated sensing and communication.