| Surface plasmon polaritons(SPPs)is a surface wave that can be transmitted at the metal-dielectric interface.SPPs can confine light waves to sub-wavelength scales and break the diffraction limit,and are expected to be used in highly integrated optoelectronic devices and next-generation optical interconnection technologies.The successful preparation of graphene provides a new physical platform for the development of SPPs.Graphene has excellent optical and electrical properties and a controllable electronic structure,making it a surface plasmon waveguide material with a wide range of applications in the terahertz and mid-infrared bands.Compared with the traditional SPPs in the metal-dielectric interface,graphene plasmons(GPs)not only have stronge optical field confinement and low loss characteristics,but also tunable.GPs have not only become an important part of the field of SPPs,but also provide new possibilities for the realization of miniaturized,highly integrated and actively tunable optoelectronic devices.On the basis of in-depth study of the formation mechanism,physical properties and practical applications of conventional SPPs and GPs,the mode characteristics and transmission of plasmons in graphene-dielectric hybrid plasmonic waveguides are mainly analyzed.On one hand,using the the properties of strong optical confinement of graphene in terahertz wavelength,several hybrid plasmonic waveguides with ultra-deep subwavelength confinement,low loss and ultra-low crosstalk in terahertz wavelength are proposed.On the other hand,using the tunability of graphene,the actively tunable plasmonics are theoretically realized,and the structural parameters of the hybrid plasmonic waveguides are optimized.The research in this thesis not only enriches and extends the traditional study of plasmonic waveguides,but also is expected to be used in optical transmission and optical interconnection at subwavelength scale.The main research results and innovative achievements are as follows:1.A graphene-microwire hybrid plasmonic waveguide is designed.The fundamental hybrid mode characteristics supported by this hybrid structure are studied and analyzed.The results indicate that the mode size of the fundamental hybrid mode can be effectively compressed by changing the diameter of the microwire and the gap distance,and then the deep subwavelength confinement can be achieved and the normalized mode area reached ~1.8×10-3 when the frequency is 3THz and the chemical potential ofgraphene is 0.5e V.In addition,the crosstalk of graphene-microwire hybrid plasmonic waveguide is analyzed.The parallel adjacent graphene-microwire hybrid plasmonic waveguides with a distance of 32μm still have low crosstalk.2.A hollow structure graphene-microwire hybrid plasmonic waveguide,i.e.,graphene-microtube hybrid plasmonic waveguide,is designed.The results show that the mode size of the fundamental hybrid mode can be effectively compressed by changing the inside and outside diameters of the microtube,the gap distance,and the chemical potential of graphene,resulting in tunable hybrid plasmonic modes.The hybrid plasmonic waveguide with deep subwavelength confinement can be realized at 3THz and the normalized mode area reached ~6.4×10-4.In addition,when the chemical potential of graphene is less than 0.5e V,the distance between two graphene-microtube hybrid plasmonic waveguides with low crosstalk is less than 32μm.3.A graphene-elliptical microwire hybrid plasmonic waveguide is designed.The influences of the geometry and size of the microwire as well as the chemical potential of graphene on the mode characteristics of the fundamental hybrid modes supported by the hybrid structure are investigated and analyzed.The results indicate that when the semi-axis of the elliptical microwire satisfied a=10μm and b=6μm,the normalized mode area is as small as ~4.6×10-4,the propagation length is 36.81μm and the figure of merit is up to ~60.91.Compared with graphene-microwire hybrid plasmonic waveguide,this graphene-elliptical microwire hybrid structure has richer mode characteristics and also has the properties of deep subwavelength confinement.In addition,compared with the case of b>a,the case of b<a is more favorable to achieve low crosstalk.4.A graphene-rectangular groove hybrid plasmonic waveguide is designed,and the influence of the system structural parameters and the chemical potential of graphene on the mode characteristics of the fundamental hybrid modes supported by the hybrid structure are studied and analyzed.The results show that the hybrid modes can be effectively compressed by changing the size of rectangular grooves,the gap distance,and chemical potential of graphene.The hybrid plasmonic waveguide with ultra-deep subwavelength confinement and relatively low loss can be realized at 3THz.The corresponding normalized mode area is as small as ~1.56×10-4,the propagation length is 21.26μm andthe figure of merit is up to ~60.13.Compared with the conventional hybrid structure without groove,the mode area is reduced by two orders of magnitude.In addition,crosstalk can be effectively reduced by decreasing the height of Ga As rectangular waveguide and increasing the width of groove.Moreover,the distance between two graphene-rectangular groove hybrid plasmonic waveguides without crosstalk can be reduced to 22μm when the height h is 15μm and the groove width wr is 10μm.5.A graphene-semi-circle groove hybrid plasmonic waveguide is designed.The influence of the system structural parameters and the chemical potential of graphene on the mode characteristics of the fundamental hybrid modes supported by the hybrid structure are studied and analyzed.The results show that the hybrid modes can be effectively tuned by changing the size of semi-circle groove,the gap distance,and chemical potential of graphene.When the frequency is 3THz and the chemical potential of graphene is tuned to 0.2e V,the hybrid plasmonic waveguide with ultra-deep subwavelength confinement and relatively low loss can be realized.The normalized mode area is as small as ~2.67×10-4,the propagation length is 24.91μm and the figure of merit is up to ~54.07.Compared with the conventional hybrid structure without groove,the mode area is reduced by two orders of magnitude.In addition,crosstalk can be effectively reduced by increasing the groove radius.Moreover,the distance between two graphene-semi-circle groove hybrid plasmonic waveguides without crosstalk can be reduced to 26μm when the groove radius r is 4.5μm.6.The propagation characteristics of the Cosine-Gauss plasmons in graphene-dielectric hybrid waveguide are studied.The transmission characteristics of Cosine-Gauss plasmons in the symmetrical and asymmetric dielectric-graphene-dielectric planar waveguides are analyzed by tuning the chemical potential of graphene,and the dynamically adjustable Cosine-Gauss plasmons are realized for the first time.In addition,the influences of the asymmetry of the waveguide structures on the propagation characteristics of Cosine-Gauss plasmons are analyzed.The results show that the larger the refractive index difference of dielectric,the smaller the transverse oscillation period and longitudinal propagation distance of Cosine-Gauss plasmons. |
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