High-Efficiency Multi-Level Beam Switching with Single-Gate Tunable Metasurfaces Based on Graphene

Abstract

The growing demand for ultra-fast telecommunications, autonomous driving, and futuristic technologies highlights the crucial role of active beam steering at the nanoscale. This is essential for applications like LiDAR, beam-forming, and holographic displays, especially as devices reduce in form factor. Although a device with active beam-switching capability is a potential candidate for realizing those applications, there are only a few works to realize beam switching in reconfigurable metasurfaces with active tuning materials. In this paper, a multi-level beam-switching dielectric metasurface is theoretically presented with a graphene layer for active tuning, addressing challenges associated with achieving high directivity and diffraction efficiency, and doing so while using a single-gate setup. For two-level switching, the directivities reached above 95%, and the diffraction efficiencies are ≈50% at the operation wavelength λ₀ = 8 µm. Through quasi-normal mode expansion, the physics of the beam-switching metasurface inverse-designed by the adjoint method is illustrated, highlighting the role of resonant modes and their response to charge carrier tuning. Under the same design scheme, characteristics of a three-level and four-level beam-switching device is designed and reported, suggesting a possibility of generalizing to multi-level beam switching.