Electro-Optically Tunable Transmissive Metasurfaces Based on Lithium Niobate

Tunable metasurfaces offer a compact and efficient solution for shaping and controlling light wavefronts with a wide range of applications, including beam steering, holography, imaging systems, and wireless optical communication [1]. The ability to manipulate optical signals via the electro-optic (Pockels) effect — rather than relying on slower thermo-optic or mechano-optic effects — is crucial for maintaining high-speed, high-fidelity device operation [2]. Here, we report on the design, fabrication, and characterization of nanophotonic silicon-on-lithium-niobate (Si-on-LN) metasurfaces that exhibit reconfigurable optical properties.
We numerically design and experimentally demonstrate tunable metasurfaces using nanostructured amorphous silicon (a-Si) deposited on lithium niobate (LN), integrating driving electrodes to locally modulate the refractive index through an externally applied electric field. This platform allows for free-space near-infrared light (λ = 1550 nm) to couple into localized guided-mode resonance (GMR) modes within the silicon metasurface elements. These localized guided mode resonances exhibit quality factors (Q) of approximately 10,000, while maintaining subwavelength element spacing, enabling enhanced electro-optic response for optical phase control within each resonator element. Electrostatic simulations are conducted to estimate the electro-optic effect, offering insights into the local modification of the refractive index in the LN substrate. By integrating both optical and electrostatic simulations into a multi-physics framework, we accurately predict the electro-optic tuning behavior, including the phase and amplitude of the transmitted optical signal through the active metasurface. We furthermore performed a comprehensive sensitivity analysis of the proposed device to assess its robustness against potential nanofabrication and material imperfections. Our proposed Si-on-LN active metasurface features nearly 2π electro-optic phase tuning using an applied voltage of less than ±30 V, with fast tuning speeds exceeding the MHz range, significantly outperforming conventional phase-tunable spatial light modulators. The design and experimental realization of high-Q, electro-optically tunable lithium niobate metasurfaces is discussed, showcasing their ability to enable dynamic phase-gradient beam steering with a field of view greater than ± 20°, and optical efficiency exceeding 40%. Our study represents a transformative approach to manipulating light at high speeds and subwavelength scales, facilitating novel functionalities such as dynamic beam shaping, holography, and lensing with flat optics.

[1] Kuznetsov, et al., ACS Photonics 11.3, 816-865, (2024)
[2] Thomaschewski, et al., Applied Physics Reviews, 9,2, (2022)