Research On THz Device Based On Graphene Surface Plasmons

In recent years,graphene has got more and more attention due to its outstanding electronic,mechanical,optical character,and etc.Especially,graphene can support surface plasmons in the THz region,which has been verified both in theory and experiment.Compared with the other noble metals,graphene surface plasmons(GSP)has stronger confinement and lower loss.The most important advantage of graphene is the tunability of properties by electrical gating.This paper will start from the following three parts.First of all,we introduce the properties of graphene,which is mainly the discussion of the conductivity and relative permittivity of graphene.We also introduce the method for realizing electric tunability and two kinds of excitation ways of GSP in the THz region.Based on the above theory basis,we firstly introduce a graphene surface plasmon waveguide working in the THz region.The waveguide is composed of metal/Silica/graphene.According to finite element method,the fundamental mode of the waveguide is strongly confined in the middle Silica layer,indicating strong confinement and controllable transmission loss.The realization of the proposed waveguide does not need to pattern or deform the graphene layer,thus retaining the superior properties of the bulk graphene material.We analyze the dependence of the mode effective index Re(neff)and normalized attenuation constant Im(neff)on the structure parameters and chemical potential,which shows the properties of the waveguide can be not only tuned by structure parameters but also by voltage,reflecting the tunability of graphene.Besides surface plasmon waveguide in the THz region,graphene can be used to realize metamaterial structure.Therefore we introduce four graphene metamaterial structures at the end of the paper.Firstly,we propose different graphene metamaterial patterns,which are microribbon,cross structure,and disc structure respectively.From the results of simulation,graphene microribbon is just like resonator and we can use Fabry-Perot model to forecast peak position.The properties of graphene cross structure and disc structure is independent on polarization direction,which provides a good idea for the design of switch,modulator and tunable absorber in the future.Finally,we propose a tunable perfect absorber based on graphene.The structure is composed of metal/dielectric/graphene/dielectric/metal(MIGIM).The absorption efficiency can be achieved above 98% in the THz region,and the absorption performance is not only affected by geometrical parameters but also by voltage.