Linear and Nonlinear Optical Tuning With Sb 2 S 3 ‐Based Metasurfaces

Phase‐change metasurfaces have attracted significant attention for reconfigurable photonic devices owing to their ability to tune optical responses between amorphous and crystalline phases. Despite their potential in optical switching, communications, and signal processing, achieving large optical modulation while maintaining low optical loss and strong field confinement remains a major challenge. Here, the unique properties of metasurfaces on monolithic and hybridized /Si platforms are experimentally demonstrated. In the telecommunications spectral range, both phases remain nearly lossless, with a large refractive‐index contrast. The monolithic metasurface enables transmission modulation depths of up to 92% and resonance shifts of 150 nm through laser‐induced phase transitions to 50% polycrystalline state. Integrating a silicon overlayer introduces hybrid resonance with enhanced near‐field confinement, achieving comparable modulation with nearly half the laser switching power required by the monolithic structure. Furthermore, the broad resonance tunability and strong third‐order nonlinearity of metasurface enable tunable third‐harmonic generation over a 40 nm spectral range. The hybrid /Si platform further demonstrates a threefold enhancement in tunable THG emission, benefiting from the combined nonlinear responses and strong resonance field confinement. These results highlight the potential of monolithic and hybrid metasurfaces for compact low‐power optical switching and tunable visible light sources.