Mode Characteristics Analysis Of Nested Waveguides Coated With Graphene

Graphene is a single-layer thin film material composed of carbon atoms.Its structure and properties are quite different from those of conventional materials,such as the ability to excite surface plasmons at terahertz frequencies,adjustable electromagnetic properties and good ductility.Compared with metal-based surface plasmons,graphene-based surface plasmons have higher electromagnetic confinement and lower ohms loss.Therefore,the research focus of many scholars is gradually inclined to graphene surface plasmons and related devices,which also accelerates the research and development progress of graphene-coated nanowire waveguides.In this paper,two kinds of nested eccentric hollow waveguides based on graphene-coated cylindrical and elliptical cylindrical dielectric nanowires are designed,and the mode characteristics of the structures are studied by using the multipole method and the finite element method.The detailed work is as follows:(1)A graphene-coated elliptical cylinder dielectric nanowire waveguide with a nested eccentric hollow cylinder is designed.The transmission characteristics of the first three lowest order modes supported by the waveguide are analyzed by using the multipole method.The optimal waveguide is determined by changing the working wavelength,the Fermi energy of graphene,the dielectric constant of the elliptic cylindrical dielectric nanowire and the structural parameters of the waveguide.It is found that the transmission characteristics of the three lowest order modes are significantly improved by increasing the working wavelength and Fermi energy or decreasing the dielectric constant of the elliptic dielectric nanowire.By changing the structural parameters of the waveguide,the transmission performance of the modes can be adjusted to some extent.Compared with a graphene-coated cylindrical dielectric nanowire waveguide with a nested eccentric hollow cylinder,it is found that this structure has better transmission performance.These results are verified by the finite element method.(2)A graphene-coated cylindrical dielectric nanowire waveguide with a nested eccentric hollow elliptical cylinder is designed.The transmission characteristics of the first three lowest order modes supported by the waveguide are analyzed by using the multipole method.It is found that the transmission performance of the waveguide is the best when the symmetric center of the internal elliptic cylinder is located on the longitudinal axis of the cylindrical dielectric nanowire.When the working wavelength,the Fermi energy and the dielectric constant of the cylindrical dielectric nanowires are changed,the transmission performance of the waveguide changes greatly.However,when the semi-major axis,the semi-minor axis,the cylindrical radius and the minimum distance between the two rods are changed,the transmission performance of the waveguide changes little.Compared with the graphene-coated cylindrical dielectric nanowire waveguide with a nested eccentric hollow cylinder and graphene-coated elliptical cylinder dielectric nanowire waveguide with a nested eccentric hollow cylinder,it is found that this structure has better transmission performance.These results are verified by the finite element method.The waveguides designed in this paper are expected to be applied in the fields of graphene photonic devices,high density integrated chips and micro-nano sensors.