Immersion‐Triggered Switchable Quasi‐BIC with Optical Encryption from 1.5D Metagratings

Actively tuning quasi‐bound states in the continuum (q‐BIC) has emerged as a prominent theme in nanophotonics due to its tailored light–matter interaction. However, the practical controllable q‐BIC metadevices still exhibit critical challenges for achieving convenient tuning in the visible regime with strong reversibility and large‐area implementation. Herein, an immersion‐triggered tuning approach is demonstrated for switchable q‐BIC in the visible regime using 1.5D metagratings. Moreover, by employing the water as the trigger, active q‐BIC‐based optical information encryption is demonstrated due to the spectra alternation. In addition, the proposed q‐BIC is insensitive to incident angles regarding quality factor, resonant wavelength, and modulation depth (MD). This immersion‐triggered strategy for q‐BIC offers a practical tuning approach for achieving dynamic switchable optical functionalities, with potential applications in metasurface‐empowered active q‐BIC optical devices.