Theoretical investigations in active control of plasmon induced nanofocusing based on graphene monolayer on substrate

A compact graphene monolayer on substrate nano-structure to realize nanofocusing and slow light effect is analytically and numerically investigated in this letter. By creating a chemical potential well in the desired positions via chemical doping or external gating, the normalized electric field enhancement factor here reaches over 300 where the mid-infrared (MIR) light is slowed down to over as high as 1/7000 times the speed in vacuum at the same time. The spot size is in 1 nm magnitude. Furthermore, when the chemical potential along the graphene sheet is properly designed, multi-focusing can be successfully controlled. The incident wave can also be trapped at the corresponding positions if it contains multiple frequency components. This structure may find applications for energy focusing on nano chips or lenses in the MIR regime beyond the diffraction limit.