▎ 摘　　要

Graphene is regarded as the ideal platform for propagating a surface plasmon polariton wave in THz and infrared frequency bands. We proposed a graphene-based planar lens with variable focal length. The proposed lens structure is composed of a single flake of graphene, a set of polysilicon DC gating pads, and a dielectric layer grown over a silicon substrate. The designed lens is realized by applying a gating voltage between the polysilicon DC gating pads and silicon substrate. By dynamically controlling the gating voltage, the lens is capable of focusing and collimating a surface plasmon polariton wave according to different focal lengths, such as 150, 200, 250, and 300 nm. The performance of the proposed lens is evaluated versus different focal lengths and chemical potentials. The correlation filtering system can be simulated by the lenses with different focal lengths. Numerical simulations demonstrated that the results were nearly consistent with our design methodology. The designed planar lens can be used as Micro-Optics elements and opens a new way to achieve plasmonic optics devices.