Actively Switchable Beam‐Steering via Hydrophilic/Hydrophobic‐Selective Design of Water‐Immersed Metasurface

Abstract Liquid immersion on metasurface was earlier demonstrated to realize spectral control. However, it remains a great challenge to achieve tunable phase modulation and versatile beam‐steering performance, which are critical for practical optoelectronic devices. Here, a new liquid‐immersive mechanism with metasurfaces for active beam‐steering is proposed and experimentally realized. Based on the dielectric‐on‐metal nanostructure with selective hydrophilic/hydrophobic properties, the switchable beam‐steering is initiated and successfully presented in the broadband visible regime with a large reflection angle of ≈±30°. Specifically, the beam diffraction direction is tuned between two opposite‐directional channels by water immersion or drying in a repeatable and controllable manner. The proposed straightforward tuning strategy enjoys great convenience in structural patterning and large‐area implementation, instead of requiring any complicated contact patterning or external modulation. This study provides an alternative optical platform for switchable beam‐steering functionality, which is promising for potential applications in tunable display, directional emission, sensing technologies, etc.