Research On Optical Transmission Characteristics Of Subwavelength Metallic Gratings And Plasmonic Waveguedes

Surface plasmon polaritons (SPPs) are electromagnetic surface modes by interaction of free electrons of metallic surface with environmental photons. In recent years, the researchs on the physical characteristics of the SPPs in subwavelength metallic structures becomes a hot spot of the modern nano-optics. In this dissertation, based on finite-difference time-domain (FDTD) code developed independently by ourselves, which can calculate dispersive metallic material, in the visible and near infrared regions, we investigate the optical transmission through some subwavelength metallic gratings (periodical structures) and the transmission characteristics of coupled waveguide mode in plasmonic waveguides with ring resonator (nonperiodical structures), and theoretically analyse the characteristics of excitation and propagation of SPPs in these structures.The main research works and conclusions are as following:(1) A novel metal/dielectric multilayer-film grating structure, in which both metal layers and dielectric layers are in fact air slit arrays with the same grating period and the same slit width and a metal/dielectric/metal sandwich stack is being viewed as a functional layer, is proposed. The transmission response of the multilayer-film grating structure is investigated in the visible and near infrared regions. The results show that the optical transmission property is mediated by the interference among the propagating coupled-SPP modes along the lateral direction inside the dielectric layers and the conditions of Fabry-Perot-like resonance along the longitudinal direction together. When some geometric parameters are suitably initialized, the high transmission peaks can split into more peaks as the functional layer number increases, and the wavelength of the same-order transmission peak exhibits a red shift as the grating period increases and a blue shift as the slit width or dielectric layer thickness increases.(2) A novel compound metallic grating with two subwavelength slits filled with different dielectrics inside each period is proposed, and the transmission resonances of the compound metallic grating are investigated in the visible and near infrared regions. The results show that the transmission spectrum is almost a compound of that of two corresponding simple gratings expect for the transmisson feature at a certain resonant wavelength, where the Fabry-Perot-like phenomena have been found both inside the two slits, but the orders of the FP-like modes are different. If the order of the FP-like mode inside one slit is one bigger than inside the other, the intensity of the transmission will be significantly weakened. We attribute this phenomenon to the phase resonance because the phases at the exits of the two slits are opposite to each other. On the contrary, when the order of the FP-like mode inside the one slit is two bigger than inside the other, the intensity of the transmission will be enhanced because the light waves at the exits of the two slits are in-phase.(3) Optical transmission through double-layer compound metallic gratings composed of two identical compound metallic gratings with two subwavelength slits inside each period is investigated. The results show that the transmission properties of the double-layer gratings are dependent on both the coupling effect of electromagnetic fields between the two metallic layers and the phase configurations of the electromagnetic waves at the exits of adjacent slits of each layer. Then the transmission response of the double-layer compound metallic gratings is very different from that of corresponding single-layer compound metallic gratings and double-layer simple metallic gratings. For example, when a suitable layer separation is chosen, for the double-layer compound metallic gratings a notable transmission peak emerges at a certain wavelength, at which phase resonance appears for the corresponding single-layer compound metallic gratings, while the transmission spectra of the corresponding double-layer simple metallic gratings with the separation exhibit unexpected transmission suppressions in a broad spectral region nearby the wavelength.(4) The transmission characteristics of the electromagnetic wave are investigated in two-dimensional compound plasmonic structures composed of two straight subwavelength metal-insulator-metal (MIM) waveguides and a ring resonator. The two straight MIM waveguides situate on both sides of the ring resonator, and the MIM waveguide of the outgoing side has a positional angular deviation9relative to the MIM waveguide of the incoming side. The results show that the filtering performances of the asymmetric structures (θ>0°) are greatly improved by comparison with the symmetric structure (θ>0°). For the most of the asymmetric structures, there is a transmission minimum at the slightly bigger wavelength than one where the transmission peak appears for the symmetric structures, and there is still a transmission peak at the wavelength of the transmission peak of the symmetric structures. Then the difference between the transmission maximum and transmission minimum is increased, and the breadth of the transmission peak becomes narrow. For these transmission minima of the asymmetric structures, it is found that the parts of coupling the MIM waveguide of the outgoing side with the ring resonator locate at the magnetic nodes of the standing waves in the ring resonator.