Investigation On The Plasmonics Of Graphene Microstructures

Graphene plasmons are particular kinds of surface plasmons, they show superior characteristics compared to the noble-metal plasmons, which include the high momenta of the plasmon modes, strong localization of the electromagnetic-field, infrared-terahertz operating frequency, and high tunability via electrostatic doping. Therefore, graphene plasmons are widely believed to have broad application prospects in the field of nanophotonics. Based on the needs of design and research of new photonic devices, we investigated two kinds of graphene microstructures, which are for exciting and guiding the graphene plasrnons respectively, and obtained these achievements:1. We first theoretically investigated the surface plasmons in graphene nanoring structures. We calculated the scattering electromagnetic-fields of the perfect and non-centric nanorings by using the finite element method, and obtained the plasmon modes which were excited by the plane wave. In the perfect nanoring, the ring-type mode and ribbon-type mode can be excited. We analyzed the near-fields of these two modes, and provided the explanation for them. In the non-centric nanorings, besides the ring-type mode and ribbon-type modes, the multipolar modes can also be excited. Then we showed the evolutions of all these modes where the perfect ring was turning into the non-centric ring by introducing the eccentricity, and we proved our explanation for the modes’ origins by these results. Furthermore, we found that the ring-type modes are fairly stable, and they are insensitive to the eccentricity. But for the ring-type modes in the non-centric rings, strong electromagnetic-field concentration is achieved. And this concentration will continue to get stronger when the eccentricity is getting higher. Therefore, much higher near-electric-field amplitude can be achieved in the non-centric nanorings than the perfect nanorings.2. We first theoretically investigated the propagation characteristics of the surface plasmons in graphene wedge and groove waveguides. Also by using the finite element method, we obtained the transverse electromagnetic-fields, propagation momenta, and propagation distances of the plasmon modes in both kinds of the waveguides. Then we analyzed the near-electric-fields of the basic modes in the graphene wedge waveguides, and showed the distributions of the transient charges and the field lines for them. We found that, these plasmon modes could be explained with the plasmon modes in graphene ribbon by folding the ribbon into the shape of the wedge. Moreover, we discussed the brim width and the Fermi energy dependences of the plasmon waveguide modes. We showed how the modes’whole dispersion curves shifted and how the modes’propagation characteristics changed at fixed frequency when the relevant parameters were varying. At last, we analyzed the plasmon modes in graphene groove waveguides. We found that these modes are almost identical to the ones in wedge waveguide, and the momenta gap of relevant modes in the two kinds of waveguides is due to the differences of the distribution of the substrates’permittivities.