Mode Analysis Of Graphene-coated Elliptical Dielectric Nanowire

Graphene,a newly 2D material,consists of monolayer carbon atoms arranged in honeycomb lattice tightly,which has many unique optical properties compared with traditional optical materials,including adjustable surface conductivity,stronger mode confinement and electromagnetic(EM)wave coupling ability in the mid-infrared band.Graphene can be used as the transport carrier of surface plasmon,and is often used to replace traditional noble metal materials,such as gold,silver,copper,etc.Graphene-coated surface plasmon(GSP)waveguides have additional advantages over traditional metal waveguides,for instance,wide adjustable frequency band(infrared to terahertz band),stronger mode confinement and lower ohmic loss.A large number of graphene based surface plasmon waveguides have been designed one after another based on these characteristics.The graphene-based circular nanowires waveguides eliminate edge loss,but still has large propagation loss,resulting in a short propagation length.The graphene-coated elliptical nanowire waveguide can increase the adjustable range of operating wavelength and Fermi energy,enhance the mode confinement,reduce the propagation loss,and increase the propagation length effectively.The specific works of this paper are summarized as follows:(1)In this section,an elliptical dielectric monolayer grapheme-coated nanowire optical waveguide is designed.The influence of the operating wavelength,structure parameters and the Fermi energy of graphene on the real part of the effective refractive indexes((7)(8)Reeffn),propagation lengths propL and the figure of merit(FOM)of the first five modes are investigated in detail with the Mathieu functions by using the separation of variables method(SVM)and the finite element method(FEM).The influence of the operating wavelength and the Fermi energy of graphene on the characteristics of circular dielectric nanowires and that of ellipitcial dielectric nanowires are compared.Then,the advantages of elliptical dielectric nanowire over the circular dielectric nanowire are verified.(2)In this section,a confocal elliptical dielectric nanowire coated with double-layer graphene(CEDNG)surface plasmon waveguide is designed.The influence of the operating wavelength,structure parameters and the Fermi energy of graphene on Re(7)(8)effn,propL and FOM of the first five modes are investigated in detail with the Mathieu functions by using the SVM and FEM.The mode properties of the waveguide can be changed by tuning the operating wavelength,the Fermi energy of graphene,the distance between semi-major axes d and the geometric parameters.Compared with the elliptical dielectric nanowire coated with monolayer graphene(EDNG),the designed waveguide has advantages: wider adjustable range of opraeting wavelength and Fermi energy,stronger mode confinement,lower transmission loss,and larger propagation length.This work can provide a theoretical basis for the work,fabrication and application of optical waveguides based on graphene-coated elliptical dielectric nanowires,and can be used in polarization-maintaining transmission,short distance transmission,memory,plasmon resonances,detectors and microstrip antennas.