Tunable Transmissive Metasurface Based on Thin-Film Lithium Niobate

In this work, we present a free-space transmissive light amplitude modulator based on thin-film lithium niobate on an insulator platform with an indium tin oxide meta-grating. The design leverages guided mode resonances induced by the transparent conductive oxide layer, enabling efficient electrooptical modulation in the near-infrared region. By integrating transparent conductive oxide both as electrical contact and as the resonating structure, the device eliminates the need for complex alignment during fabrication and minimizes optical losses associated with metallic contacts. We experimentally demonstrate that the device achieves a fundamental mode resonance at 968.5 nm with a quality factor of 440. The electrooptical tuning efficiency is thoroughly investigated across different modes using measurements and simulations. A notable resonance shift of 0.38 nm is observed for the fundamental mode under a ±10 V bias, while a maximum modulation amplitude of 4.6% is achieved with a higher-order mode. Furthermore, the device exploits incident angle tuning as an additional degree of freedom, effectively splitting and sensitively shifting resonances. The new resonances can provide electrooptic tunability. These results highlight the potential of this compact and scalable design for applications in spatial light modulation, optical communications, and tunable optics.