Plasmonic coupling in separated graphene sheets

In this work, we investigate the coupling of surface plasmon polaritons (SPPs) in spatially separated monolayer graphene sheets. Differing from conventional coupled dielectric waveguides, SPPs experience negative coupling in between neighboring graphene sheets. Thanks to the extremely large mode index of SPPs, the optical devices taking advantage of SPP coupling in graphene are able to work deeply below the diffraction limit. In addition, monolayer graphene sheet arrays (MGSAs) show new features of SPP propagation that are quite unique by comparing with the dielectric and metallic waveguide arrays. We observe beam self-splitting and negative coupling of SPPs in the MGSA and the effects can be easily controlled considering the electronic tunability of graphene. Our study provides a promising platform as a discrete optical system for exploring the diffraction activities of light in deep sub-diffraction-limit scale. The proposed structures may find applications in high performance optoelectronic devices.