Liquid‐Crystal‐Switchable Quasi‐BIC Metasurface for Erasable Display in Visible Band

Active control of quasi‐bound states in the continuum (q‐BICs) in the visible spectrum remains restricted by lithographic fabrication tolerances and the difficulty of achieving low‐loss, reversible, and scalable operation. Here, we demonstrate a liquid‐crystal (LC)‐switchable q‐BIC metasurface enabling erasable optical display. The platform employs HfO 2 nanoblock pairs on an Ag mirror to realize a high‐quality (high‐Q) q‐BIC resonance. An electrically reoriented LC cell modulates the surrounding refractive index and dynamically controls radiative coupling. We design the unit cell for a resonance at 608 nm with a full width at half maximum (FWHM) of ∼1.62 nm (Q ≈ 375) and a modulation depth (MD) of ∼10.80 dB, producing voltage‐controlled reveal/erase of encoded images. Furthermore, to improve fabrication tolerance, we introduce a permittivity‐asymmetric design using geometrically identical nanoblocks by selectively coating one block with PMMA. This optimized structure supports an ultrasharp resonance at 640 nm with FWHM ∼0.67 nm (Q ≈ 956) and an MD of ∼15.63 dB. The proposed LC‐integrated metasurfaces exhibit low optical loss, electrical addressability, and compatibility with large‐area fabrication, offering a compact and efficient platform for fast, reversible, and rewritable visible displays as well as optical information encryption.