Manipulating Metal And Graphene Surface Plasmon At Nanoscale And Its Device Designing

In this thesis, We investigate the manipulation of the behavior of surface plasmonpolaritons in various configuration using numerical methods of finite difference time do-main. Generally, there are several main ways to manipulate or control Surface PlasmonPolaritons(SPPs): adopting various material and changing the shape of structures whichsupport SPPs, or both of them together. According to the physical mechanism of excitingSPP, the optical properties of material are very important. Noble metal of Ag or Au areadopted by many researchers whose complex relative permittivity is characterized well byDrude model or Lorenta-Drude model due to its negative real part of permittivity at opticalspectrum. The insulating material include uniform dielectric or anisotropic material forfilling the gap, various gain medium to overcome the intrinsic loss of plasmonic waveg-uide, Kerr nonlinear material for all-optical controlling SPP and so on. In this thesis, wehave study on the mechanism of manipulating surface plasmon in various nano systems,in which related novel physical phenomena and effects, including extraordinary opticaltransmission (EOT) through single nanoslit, nonlocal response in super nanosystem, res-onant effect in2D plasmonic modulator and plasmonic induced transparency (PIT)in2Dmetamateria, are pilot discussed. The results and conclusions will give some guidance intheory for designing useful plasmonic devices.We have numerically studied the transmission properties of a composite structureconsisting of a de-focusing tapered slit and nano-strip by using the finite difference timedomain (FDTD) method. For a fixed wavelength, the dependence of transmission efficien-cy of light on the structure parameters is demonstrated in detail. we have found that theextraordinary optical transmission through a single tapered metallic nano-slit is enhancedby placing a metallic nano-strip over it, in which tapered slit with large taper angle is usedfor de-focusing of light and be avoid of Fabry-Perot resonance in straight metallic nano-slit. It is shown that a suitable tapered slit assisted by nano-cavity-antenna can enhancethe transmission by about50%(compared with that in straight slit case). Furthermore,the parameters of the tapered slit (the taper angle and the taper length) hardly change theresonance in the horizontal nano-cavity. The transmission spectrum of the tapered slit canalso be tuned by adjusting the taper angle. Such striking characteristic tapered slit haspromising applications in designing optical nano-scale device.We simulate and analyze the influence of nonlocal effects on optical properties of metal-coated hollow nanowire by finite element method. We prove that surface plasmonresonance (SPR) split into two plasmonic mode due to the strong optical coupling betweeninner and outer wall of the hollow nanowire. Nonlocal-response effects modifies theplasmonic modes of the hollow nanowire with a tiny metal layer, which are considerablefor extinction cross area but more for field enhancements. The modification by nonlocaleffects is dependent on the property of resonant mode. Then, we show the dependence ofextinction effect of the investigated nonlocal model on its parameters, including thicknessof the hollow nanowire, the average radius and the optical constant of the hollow core. Wefind that high frequency plasmonic mode has great stability as increasing the size of thehollow nanowire or changing the hollow core. Furthermore, the eccentricity of the hollownanowire bring out other new physic phenomena, such as nanofocusing and multimodesetc. Maximum electric enhancement factor of27000is achieved in the nonconcentrichollow nanowire, which promises a great of applications in nanoscale, such as designingnanoplasmonic antenna, nanoscale sensing and nanoscale nonlinear optics etc.We simulate and analyze the influence of the short graphene nanoribbon on transport-ing of graphene plasmonic waves (GPWs) on an infinite graphene monolayer by finiteelement method (FEM). We find that plasmonic waves transporting along one atomic-thick graphene are sensitive to short nanoribbons which are arranged near the infinitegraphene sheet. There are two main different mechanisms for modulating GPWs transporton graphene sheet: One is that Fabry-Perot resonance of plasmonic waves on graphenenanoribbons, which function as the resonant line cavity; Another is the forming of s-tanding waves on the infinite graphene sheet based on GPWs reflecting at the end ofgraphene nanoribbon. Owing to tunablity of the chemical potential μcof the dopedgraphene nanoribbon, we are also able to actively control plasmonic waves by gate volt-age or chemical doping. The optical properties are also sensitive to the structural detailsof the system, namely width and distance modulation. It provides an additional handle tocontrol plasmonic waves transferring and could find its application in designing infraredand THz plasmonic devices.We have designed several plasmonic modulators based on graphene nanoribbonwaveguide using3D finite element method. The plasmonic waveguide mode in graphenenanoribbon is controlled by several kind of resonant cavities with different geometricalshape including tooth, disk and ring. For these nanocavities, the transmission of grapheneplasmonic wave is periodically manipulated by the tooth length, the disk radius and theouter radius of the ring. Due to the tunability of graphene conductivity by gate volt-age, the graphene nanoribbon waveguide mode could be dynamically turned on and off. During these modulators, plasmonic resonance in the nanocavity dominate the main con-tribution to the behavior of the GPWs transferring in graphene nanoribbon. The proposedstructures could find its application in constructing2D plasmonic integrated circuit.We have studied the electromagnetic response of2D metamateria based on singlepatterned of doped graphene for the mid-infrared region. Each cell of periodically pat-terned graphene consist of three graphene nanostrips. By breaking the symmetric config-uration, Plasmonically induced transparency (PIT) effect can be achieved for a fixed fermienergy. In addition, we find that the polarization direction of the light is very importantfor maintaining PIT modulation strength,transmission peaks, and spectral line width. Thiswork may offer a further step in the development infrared metamateria.