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

Abstract

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.

Spatially entangled photon pairs from lithium niobate nonlocal metasurfaces

“…We develop a nonlocal metasurface based on the LiNbO 3 -on-insulator platform, which was recently used for various applications including electro-optic modulation (24,25) and classical optical frequency conversion (26). The LiNbO 3 material features large second-order susceptibility, low fluorescence, and high optical transmission in a broad wavelength range (27,28), which are essential for the quality of generated photon pairs.…”

Spatially entangled photon-pairs from lithium niobate nonlocal metasurfaces

“…We develop a nonlocal metasurface based on the LiNbO 3 -on-insulator platform, which was recently employed for various applications including electro-optic modulation [22,23] and classical optical frequency conversion [24]. The LiNbO 3 material features large secondorder susceptibility, low fluorescence, and high optical transmission in a broad wavelength range [25,26], which is essential for the quality of generated photon pairs.…”

Electro-optic metasurface-based free-space modulators

“…39 Use of resonance configurations, for example, Fabry–Perot resonators (FPR), would allow one to increase the effective interaction length, thereby increasing the modulation at the expense of the decreased operating wavelength range. 12,40…”

“…39 Use of resonance configurations, for example, Fabry-Perot resonators (FPR), would allow one to increase the effective interaction length, thereby increasing the modulation at the expense of the decreased operating wavelength range. 12,40 In this paper, we build on our previous work on an electrooptically controlled dynamic Fresnel lens, which consisted of connected concentric FPR rings (covering Fresnel zones) representing a continuous semitransparent top gold electrode atop a LN thin film supported by an optically thick gold bottom electrode. 12 The use of a continuous top electrode for completing an efficient FPR imposed a severe restriction on the gold thickness, requiring it to be ∼12 nm for the operating wavelength of ∼850 nm.…”

“…The modulation depth of ∼20% at the modulation voltage of ± 10 V is demonstrated within the bandwidth of 8.0 MHz, offering characteristics that are favorable compared to those achieved previously. 12,40 Furthermore, we fabricate and demonstrate space-variant control of the reflectance by means of a 2 × 2 array of individually addressable modulators opening the way towards ultrafast and ultrathin SLMs.…”