Thermally‐Switchable Metalenses Based on Quasi‐Bound States in the Continuum

Abstract Dynamic wavefront shaping with optical metasurfaces has presented a major challenge and inspired a large number of highly elaborate solutions. Here, this study experimentally demonstrates thermo‐optically reconfigurable, nonlocal metasurfaces using simple device architectures and conventional CMOS‐compatible dielectric materials. These metasurfaces support quasi‐bound states in the continuum (q‐BICs) derived from symmetry breaking and encoded with a spatially varying geometric phase, such that they shape optical wavefront exclusively on spectrally narrowband resonances. Due to the enhanced light‐matter interaction enabled by the resonant q‐BICs, a slight variation of the refractive index introduced by heating and cooling the entire device leads to a substantial shift of the resonant wavelength and a subsequent change to the optical wavefront associated with the resonance. This study experimentally demonstrates a metalens modulator, the focusing capability of which can be thermally turned on and off, and reconfigurable metalenses, which can be thermo‐optically switched to produce two distinct focal patterns. The devices offer a pathway to realize reconfigurable, multifunctional meta‐optics using established manufacturing processes and widely available dielectric materials that are conventionally not considered “active” materials due to their small thermo‐optic or electro‐optic coefficients.