A Basic Research On Nonlinear Control Of Surface Plasmons

Recently, much interest in surface plasmons has been excited in subwavelength metallic structures. the advancements in research methods and experimental techniques have triggered the rapid developments in plasmonics. Nonlinear optical devices based on subwavelength metallic structures have been proposed to actively control plasmonic signals by nonlinear material, and open up a new avenue for designing new types of nano-optic devices. Optical bistability in nonlinear surface plasmon polaritonic crystals has been observed. Full numerical simulations of the nonlinear surface plasmon crystals in various geometries have been performed, such as, optical bistability, beam deflection and focusing, all-optical switching.In this dissertation, the dispersion relation of surface plasmon at the interface between metal and nonlinear medium are analyzed. The transmission of transverse-electric polarization through one-dimensional metallic grating with subwavelength slits at the wavelength range from visible to near-infrared light is investigated. The main research works are as following:1. The dispersion relation of surface plasmon at a metal-Kerr nonlinear medium interface is analyzed based on the Maxwell equations and the boundary conditions. In this model, the Maxwell equations allow two sets of self-consistent solutions with different polarization properties of the propagating waves, e.g., the transverse magnetic (TM or p) modes and the transverse electric (TE or s) modes. Due to the nonlinear dielectric, the dispersion relation of TM wave is complex. The changes in surface plasmons dispersion relations depending on film thicknesses and nonlinearity are studied. The damping of metal is considered using Drude model. TE wave does not exist at this interface.2. The analytic surface plasmons dispersion relation in a system consisting of a thin metallic film bounded by two sides media of nonlinear dielectric is studied by applying a generalized first integral approach. At first, Kerr nonlinear-metal-Kerr nonlinear structure is analyzed. Both asymmetric and symmetric structures are considered. Especially, in the symmetric system, two possible modes can exist:the odd mode and the even mode. The dispersion relations of the two modes are obtained, the dispersion relations depending on film thicknesses and nonlinearity are studied. Numerical results are compared to those from a certain approximate treatment. The reason is that in the approximation model, the Kerr media is taken to behave as a homogenous medium with a dielectric constant; whereas in our approach, the graduate decrease in the nonlinear term away from the interface is taken into account. Furthermore, the arbitrary nonlinearity is considered.3. Based on finite-difference-time-domain method, we have shown that the transmission of TE polarization is affected with the geometrical parameters of one-dimensional metallic grating with subwavelength slits at the wavelength range from visible to near-infrared light. The increase of the dielectric refractive index of slits and the slit width leads to the redshift of the position of the peaks in transmission spectra, but the change of the grating period does not affect that. This points out that the grating openings can be regarded as an ensemble of independent emitters. Additionally, due to the decrease of the density of openings as the grating period increased, the overall values of the transmission coefficient are decreased. By tuning the structural geometry, the polarization independent element can be achieved at Communication wavelength.Highlights of the dissertation are as following: 1. The analytic expression of the dispersion relation of surface plasmons at a metal-Kerr nonlinear medium interface is obtained, and the damping of metal is considered. The role of nonlinearity on dispersion relation can be determined by the analytic expression. This can provides the basis for design subwavelength nonlinear metal structure.2. The analytic expression of the dispersion relation of surface plasmons in nonlinear-metal-nonlinear structure is obtained. Both asymmetric and symmetric structures are analyzed. The graduate decrease in the nonlinear term away from the interface is taken into account. The model is extended to arbitrary nonlinearity.3. In the study of the transmission of TE polarization, no extra dielectric filler is necessary for the EOT of TE polarization, and the periodicity is smaller. The investigated wavelength range is from visible to near-infrared light. The possible application of this structure in the polarization independent element at communication wavelength is indicated.