Highly Reversible Tuning of Light‐Matter Interactions in Van der Waals Materials Coupled with Hydrogel‐Assisted Optical Cavity

Abstract Controlling light‐matter interactions via cavity systems manifested by Rabi splitting is paramount important for nanophotonics. However, achieving conveniently accessible and active tuning of light‐matter interactions remains a formidable challenge. Traditional approaches often necessitate either sophisticated design or meticulous nanofabrication to address this issue. Here, a handy strategy is experimentally demonstrated to build an adjustable coupling system featuring reversibly modulated responses based on dielectric‐hydrogel‐metal resonators. By controlling the top tungsten disulfide layer thickness, the flexible manipulation of weak‐intermediate‐strong transitions in exciton‐cavity interactions is revealed on a large‐scale hydrogel membrane without nanopositioning or lithography. Crucially, by leveraging the inflation sensitivity of the hydrogel, the coupling strength can be reversibly tailored with excellent reproducibility by modulating the resonator's dry/immersed states. The combined merits of captivating design and daily stimulus render the novel hydrogel‐based nanocavities as a groundbreaking step toward the development of active and practical integrated optical devices, such as polariton lasing, switches, and sensors.