Terahertz Broadband Bimodal Multiplexing Detection Based on Quasi‐Bound States in the Continuum and Guided‐Mode Resonance

Abstract Grating metasurfaces supporting guided‐mode resonance (GMR) can provide ultra‐sharp resonances for light‐matter solid interactions, facilitating their applications in various fields such as sensing, lasers, and imaging. Bound states in the continuum (BICs) are unique resonant modes located in the radiative continuum domain but fully bound without energy leakage. BIC can be transformed into quasi‐bound states in the continuum (QBICs) and coupled to external radiation to meet the demand for high‐Q resonances. Here, a broadband dielectric terahertz (THz) sensor is presented for GMR, which facilitates the generation of BIC whose QBIC states can reach a quality factor of 10 3 . The sensor has a signal enhancement factor of more than 10 dB over the entire frequency range of 1.25–2.20 THz and can accurately analyze three absorption peaks of explosive materials. The design breaks through the single‐peak scanning of THz detection by cross‐fertilizing BIC with GMR, generating an angular manipulation ultra‐broadband in the THz spectrum. It provides a powerful tool for ultrasensitive trace analysis and will facilitate many new THz sensing applications. Meanwhile, the structure will support the combination of metasurfaces with flexible materials, improving the performance of flexible devices and broadening their applications in optoelectronic devices.