▎ 摘　　要

Graphene is a one-atom-thick planar sheet of sp(2)-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Graphene has been found to support plasmons in a wide range from infrared to terahertz. The confinement of plasmons in graphene is stronger than that on metallic surface. Moreover, the plasmon properties can be dynamically adjusted by doping or grating graphene. In this study, a composite structure comprised of graphene and subwavelength grating is proposed. Highly confined plasmons in graphene are excited by using a diffraction grating with guided mode resonance effect. The wave vector of plasmonic wave in graphene is far larger than that of light in vacuum. To excite plasmons in graphene with a freespace optical wave, their large difference in wave vector must be overcome. Optical gratings are widely used to compensate for wave vector mismatches. A diffraction wave generated by the grating structure can overcome the large wave vector difference and excite surface plasmons. The guided-mode resonance can greatly enhance the intensity of the diffraction field and the coupling efficiency between graphene and incident light. When the phase matching between illuminating wave and a guide mode supported by grating is achieved, guided-mode resonance effect occurs. A nearly 100% diffraction efficiency peak in the reflection or transmission spectrum occurs at a certain wavelength. In this study, the influences of graphene and grating structure on the local characteristics (the surface electric field E-x/E-in, quality factor Q, and effective mode area S-eff) of surface plasmons are investigated. The effects of the structural parameters (the thickness of the buffer layer T-2, the grating period p, the carrier mobility mu, and the Fermi level E-F) on localization properties are analyzed by the finite element method (COMSOL). The results reveal that the localizations of the surface plasmons in the graphene surface is significantly improved at the certain parameters. 1) The increase of T-2 will reduce the intensity of electric field on graphene (E-x/E-in), but the quality factor will obtain a certain increase. The excition of highly confined SPPs needs to improve Q and keep the intensity of E-x/E-in, so in this study T-2 = 10 nm. 2) By adjusting mu the quality factor of SPPs can be improved significantly without changing the resonance frequency (mu = 0.7 m(2) (V.s), Q(max) = 1793). 3) Small changes in p and E-F will make the resonance peak shift obviously, and the electric field on graphene is greatly enhanced (p = 235 nm, E-x/E-in = 3154; E-F = 0.72 eV, and E-x/E-in = 3968). Strong localization leads to strong light-matter interaction, and thus the proposed structure has the potential to be used as sensors with high sensitivity and high-efficiency nonlinear optical devices, greatly expanding the application of graphene in nano optics.