Tunable Metasurface Using Thin-Film Lithium Niobate in the Telecom Regime

Metasurfaces have seen a great evolution over the last few years, demonstrating a high degree of control over the amplitude, phase, polarization, and spectral properties of reflected or transmitted electromagnetic waves. Nevertheless, the inherent limitation of static metasurface realizations, which cannot be controlled after their fabrication, engages an ongoing pursuit for reconfigurable metasurfaces with profound tunability. In this paper, we mitigate this grand challenge by demonstrating a new method for free-space rapid optical tunability and modulation, utilizing a planar aluminum nanodisk metasurface coated with indium tin oxide (ITO) on a thin film of lithium niobate (LiNbO) with a chromium/gold (Cr/Au) substrate. Resonance coupling gives rise to an enhanced, confined electromagnetic field residing in the thin film, leading to a narrow and high contrast dip in reflectance of around 1.55 μm. The precise spectral position of this resonance is tuned using the electro-optic Pockels effect by applying an electric bias voltage across the thin film of LiNbO. By doing so, we show that we can likewise modulate the optical reflectance from the metasurface around a wavelength of 1.54 μm. Following that, we experimentally demonstrate a free-space, planar optical modulator with a modulation depth of 40%. The device paves the way for the integration of metasurfaces in applications requiring tunable optical components such as tunable displays, spatial light modulators for advanced imaging, free-space communication, beam scanning LIDARs with no moving parts, and more.