Polarization-independent enhancement of graphene plasmons by coupling with the dipole-like near field of the metallic split-mesh structure.

The localized electric field enhancement of graphene plasmon modes is limited by the duty cycle of graphene, the frequency, the absorption and the scattering rate. To obtain higher detectivity, higher field enhancement is required. While the absorption can be no larger than 100%, the scattering is an intrinsic limitation, and the frequency is designated, the duty cycle is the only parameter that can be designed freely to achieve high field enhancement. By etching graphene into periodic structures, reducing the duty cycle of graphene, the localized electric field can be enhanced as a result of the reduction of the active region. However, too small a duty cycle will weaken the coupling efficiency, which will reduce the absorption, and then the localized electric field can hardly be further enhanced. In this work, we propose to use the metallic split-mesh structure which will focus the incident radiation at the ends of the metallic bars. The absorption and the electric field will be greatly enhanced by placing graphene structures below the small holes formed by the metallic split-mesh structure.