Graphene-enabled electrically tunability of metalens in the terahertz range

In general, the functions of most metalenses cannot be adjusted dynamically after being fabricated. Here, we theoretically propose an electrically tunable metalens composed of single-layered and non-structured doped graphene loaded with ribbon-shaped metallic strip arrays with varied widths and gaps. The combination of the different widths and gaps can provide full phase coverage from 0 to 2π, which is necessary for a plane wave to be focused. The metalens exhibits obvious tunability of focal length and focal intensity as we varied the Fermi levels of the doped graphene at 10 THz. The focus is able to be shifted within 90.4 µm (∼3λ), with maximum focusing efficiency up to 61.62%. The tunable metalens can also be expanded to other operation frequencies from mid-infrared to terahertz range by properly designing structural parameters. The metalens consisting of nanostructured metal and non-structured graphene utilizes mature metal nanostructure preparation process and avoids the graphene processing, which consequently facilitates the fabrication and promotes the application.