Title: High-directivity multi-level beam switching with single-gate tunable metasurfaces based on graphene Show Chinese title

Title: 基于石墨烯的单栅可调超表面的高定向多级波束切换

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 device with active beam switching capability is a potential candidate for realizing those applications, there have been only a few works to realize beam switching in reconfigurable metasurfaces with active tuning materials. In this paper, we theoretically present a multi-level beam-switching dielectric metasurface 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 were near 50% at the operation wavelength ${\lambda}_0$ = 8 ${\mu}$m. Through quasi-normal mode expansion, we illustrate the physics of the beam switching metasurface inverse-designed by the adjoint method, highlighting the role of resonant modes and their response to charge carrier tuning. Under the same design scheme, we design and report characteristics of a three-level and four-level beam switching device, suggesting a possibility of generalizing to multi-level beam switching. Show Chinese abstract

Abstract: 超快电信、自动驾驶和未来技术的日益增长的需求突显了纳米尺度主动光束转向的关键作用。 这对于诸如激光雷达、波束成形和全息显示等应用至关重要，尤其是在设备尺寸缩小的情况下。 尽管具备主动光束切换能力的器件是实现这些应用的一个潜在候选方案，但利用有源调谐材料在可重构超表面中实现光束切换的工作却寥寥无几。 本文理论上提出了一种带有石墨烯层用于主动调谐的多级光束切换介电超表面，解决了实现高方向性和衍射效率的相关挑战，并且是在单一栅极设置下完成的。 对于两级切换，方向性超过95%，在操作波长${\lambda}_0$= 8${\mu}$m 处衍射效率接近50%。通过准正则模式展开，我们阐明了由伴随法逆向设计的光束切换超表面的物理原理，强调了共振模式及其对载流子调谐的响应。 在相同的设计方案下，我们设计并报告了三级和四级光束切换装置的特性，表明可以推广到多级光束切换的可能性。