Enhanced Electro-Optic Modulation in Resonant Metasurfaces of Lithium Niobate

In display technologies or data processing, planar and subwavelength free-space components suited for flat photonic devices are needed. Metasurfaces, which shape the optical wavefront within hundreds of nanometers, can provide a solution for thin and portable photonic devices, for example, as CMOS-compatible modules. While conventional electro-optic modulators are inconvenient to operate in free space configurations, its principle can largely be applied to the development of active metasurfaces with the prospect of modulation speeds up to the GHz region. We extend this principle of the linear electro-optic effect to a metasurface in lithium niobate with an optical resonance in the visible. We exploit the electric and optical field overlap inside the metasurface to enhance the light matter interaction. Hence, the modulation of the transmitted light is increased by 2 orders of magnitude, namely, by a factor of 80, compared to the unstructured substrate. Furthermore, we investigate the influence of the dispersive optical resonance on the wavelength-dependence of the modulation and achieve fast and continuous modulation of light at low voltage and MHz speed. This proof-of-concept work is a first important step toward the use of lithium niobate resonant nanostructures for free space modulation.