Breaking The Diffraction Limitation Of Light Based On 2D Metallic Waveguides

Surface plasmon polaritons(SPPs) has attracted much attention in the areas of subdiffraction and optical lithography since it has large wave-vector and strong localized field. Superlens, which are based on SPPs waveguide, could realize sub-diffraction limit imaging. Multilayered SPPs waveguide could be used to control light at sub-diffraction limit scale. SPPs in metallic waveguide could form sub-diffraction limit interference pattern. Compared to other SPPs structures, SPPs waveguide is more feasible to large scale production due to their simple structures. We investigated the sub-diffraction limit phenomenon in SPPs waveguide structures by using SPPs theory and finite element method.The main researches and achievements of this thesis are summarized as following:We studied the sub-diffraction limit imaging of superlens, which consists of a single metal layer, by using SPPs waveguide theory. We proposed a method to suppress the imaging distortion. We investigated the relations between resolution, imaging distortion and the SPPs modes. The result shows that SPPs mode with high loss could suppresses the imaging distortion and enhances the sub-diffraction limit imaging. We proposed that surrounding the metal layer with high refractive index medium could enlarge the loss of SPPs mode, then improve the imaging resolution and suppress the imaging distortion. It has been demonstrated by numerical simulation based on finite element method. We also analyzed the “index matching condition”.We introduced parity-time symmetric potential into superlens which consists of multilayered metallic waveguide. We could use parity-time potential to control the SPPs mode of this superlens and suppress the distortion of sub-diffraction imaging result. The paritytime symmetric potential could be introduced by adjusting the refractive index of insulator layer. We calculated the eigenspectrum of SPPs mode with different parity-time symmetric potential by using the optical transfer matrix method. The results showed that the real eigenspectrum narrows down, the complex eigenspectrum wides up, and the mode loss became large with the parity-time symmetric potential increasing. The numerical simulation results based on finite element method demonstrated that the sub-diffraction limit imaging results could be improved with the sidelobes and subtle artifacts are suppressed by increasing the parity-time symmetric potential.The multilayered metallic waveguide behaves as anisotrpic metamaterial when it is treated as a whole medium. According to the effective medium theory, we studied the relations between the sub-diffraction limit ability of multilayered metallic waveguide and the structure parameters, the materials, and the working wavelength. When the effective permittivity of multilayered metallic waveguide satisfies it has hyperbolic types dispersion,the sub-diffraction limit ability could be achieved. We studied the sub-diffraction limit focusing of light in the multilayered metallic waveguide by using the effective medium theory. The results showed that the multilayered metallic waveguide with two different kind hyperbolic dispersions behaves opposite chromatic aberration. The result has been demonstrated by numerical simulation based on finite element method. Also, the results showed that the multilayered metallic waveguide could focus light with two different wavelength at a same point.In multilayered metallic waveguide, the excitation and strong coupling of SPPs mode makes it possible that light could be controlled at the sub-diffraction limit scale. According to the coupled-wave equation, we studied the sub-diffraction limit focusing in metallic waveguide array. We derived the coupling coe?cient and spreading angle of SPPs mode as functions of incident light wavelength. The theoretical equation showed that the focal length of sub-diffraction limit focusing in metallic waveguide array increases with the wavelength. Its chromatic aberration is opposite to that of a conventional insulator lens.The numerical simulation based on finite element method agrees well with the theoretical analysis.The SPPs in a metallic waveguide could forms interference pattern with sub-diffraction limit period. By using periodic metallic grating excitation method, we studied the subdiffraction limit interference in three kinds of metallic waveguide. We investigated the influence of the grating slit width and depth on the interference pattern in metallic waveguide. We performed numerical simulations of the sub-diffraction limit interference in two different kinds of metallic waveguide by using finite element method. The simulation results showed that the interference pattern, including the intensity and uniformity, could be improved by adjusting the grating slit width and depth. According to the SPPs waveguide theory, the interference pattern in the metallic waveguide under gratings could be enhanced when the grating slit width and depth satisfy the SPPs cavity resonant condition. The enhancement could be applied to the lithography technique which are based on the sub-diffraction limit in metallic waveguide.