Research On The Properties And Manipulation Of Surface Plasmon Polaritons In Subwavelength Metallic Waveguides

With the development of nanophotonics, the interaction between light andsubwavelength devices has attracted a lot of attention and many novel phenomenaarise, such as super resolution imaging, invisibility cloak, and negative refractiveindex metamaterials. Nowadays, photonic crystals and surface plasmon polaritons(SPPs) are recognized as two important methods to realize integrated optical devices.The properties of SPPs and their interaction with light can be manipulated bychanging the structure of metallic surface. SPPs provide the potential applications fordesigning novel photonic devices, broadband optical communication systems,ultra sensitive optical sensors and integrated optical circuits.The main contents of this dissertation arranged as follows:1. By employing finite difference time domain (FDTD) method, the filteringproperties of subwavelength metallic waveguide coupled with resonators areinvestigated. By introducing nanodisk resonator into metal insulator metal (MIM)waveguide, a nano filter can be realized. It is found that the filtering properties can becontrolled by tuning the radius and the refractive index of the nanodisk resonator, thecoupling distance between the resonator and waveguide. When cascading severalnanodisk resonators into MIM waveguide and appropriately tuning the geometricalparameters, the structure can act as a tunable multi channel wavelength demultiplexer.By optimizing the geometrical parameters, the transmission of each channel can beimproved. A T shaped waveguide coupled with a nanodisk resonator is proposed torealize the unidirectional transmission and manipulation of SPPs. It is found that whencontrolling the optical path difference between the two arms of the T shapedwaveguide, the transmission can be tuned, which is interpreted by the interferencetheory.2. The nonlinear phenomenon in subwavelength metallic waveguide isinvestigated. Kerr third order nonlinear material is filled into the nanodisk resonator.It is found that the refractive index of the Kerr nonlinear material varies for differentincident intensities and then the filtering properties of the nanodisk resonator can bemanipulated. The transmission spectra for different incident intensities areinvestigated by using FDTD method, it is found that the nonlinear metallic waveguidecan act as an optical switch. The resonance properties of the nanodisk resonatorprovide the positive feedback mechanism and the optical bistability can be realized inthe proposed nonlinear structure. In addition, the radius of the nanodisk can also influence the optical bistability. By using transmission line theory, the equivalentcircuit model of the metallic grating structure is investigated. It is found that thefiltering properties of the grating structure can be tuned by changing the grating depth.When incorporating Kerr nonlinear materials, the optical switch can be realized in theproposed quasi periodical grating structure.3. The dispersion equation and characteristics of metallic grating waveguide areinvestigated. It is found that the transmission and dispersion can be tuned by changingthe geometric parameters of the grating waveguide. Especially, obvious slow lighteffect can be observed near the cutoff frequencies of the dispersion curves. Thetraditional slow light devices based on the metal surface own large scattering loss andpoor confinement of light. To solve this problem, a quasi periodical grating structureis introduced into the MIM waveguide. When the grating depth gradually increases,the cutoff frequencies of the dispersion curves decrease. So the incident light withdifferent frequencies can be trapped in different positions of the waveguide and thenthe “rainbow trapping” phenomenon can be realized. The Ohmic loss of metal isinevitable, and its influences on the slow light effect in tapered waveguide areanalyzed by using the eigen equation of waveguide. It is found that the metal loss canaffect the group velocity and destroy the zero group velocity condition. To solve thisproblem, the gain material is introduced into the tapered metallic waveguide tocompensate the metal loss. By appropriately tuning the gain coefficient, the zerogroup velocity condition can be recovered at different positions of the waveguide andthe “rainbow trapping” phenomenon can be realized in the proposed structure. Agraphene plasmonic self focus lens is proposed and the effective mode index canreach to100. Such a lens may find applications on beam collimation, beam focusingand image transfer in subwavelength scale.4. Base on the equivalent circuit model of metallic grating waveguide, theplasmonic analogue of electromagnetically induced transparency (EIT) is investigated.By appropriately tuning the stub depths of each grating unit, the correspondingresonant wavelength can be tuned and the analogue of EIT phenomenon can berealized. The dispersion of the metallic grating waveguide can be attributed to twoparts: the material dispersion and the grating induced dispersion. The grating induceddispersion can be appropriately designed to compensate the material dispersion. It isfound that the dispersionless slow light effect can be observed near the transparencywindow. Based on the transmission line theory, the influences of the geometric parameters on the transmission and dispersion characteristics are investigated. It isfound that difference between the grating depth and the period of the gratingwaveguide can affect the dispersion properties. By optimizing the geometricparameters, a subwavelength slow light waveguide with the group index of35andnormalized delay bandwidth product of0.65can be realized.