Researches On Extraordinary Optical Transmission And Its Manipulation In Subwavelength Periodic Structures

In the field of the subwavelength optics, it is an important and long-term concerned issue that modulating the transmission of electromagnetic wave in metal nano-structures in academe and technology and application domain. Surface plasmon polaritons (SPP) present a new vision for controlling and transmitting light. The extraordinary optical transmission (EOT) of light impinging on metallic films perforated with periodic subwavelength hole arrays is one of the most striking phenomena discovered in nano-structure studies based on SPP. The study of EOT is helpful for the design of subwavelength optics device and the implementation of photonic circuit. By using the finite difference time domain method (FDTD), in combination with plasmonics and electromagnetic field theory, we investigate EOT of the subwavelength periodic metal structures with different types in this thesis on the foundation of existing research. New structure factors are introduced, which lead to many novel optical phenomena. The results enrich the adjustment measures of the transmission progress of the metal structure in subwavelength dimension. Corresponding physical mechanisms are analyzed, and potential optical applications are explored.The main contents of this thesis are listed as follows:1. The EOT of the double-layer subwavelength periodic metal structure is studied, and it is attributed to the surface plasmon resonance mode collaborated with the localized waveguide resonance mode. The influences of structure parameters such as distance between layers, slit width, lateral displacement of the structure on the EOT are analyzed in detail, in cases of structure with identical or different, coaxial or non-coaxial, and touching or un-touching layers. It is found that both resonance modes change in separated ways with structure parameters varying in different cases. Many interesting physical phenomena are discovered, such as the red-shift, blue-shift, splitting, degeneration, enhancement, broadening, narrowing of the high transmission peaks, and so on. It is presented that the filter characteristic is better of the double-layer subwavelength periodic metal structure than that of a single layer one, and the transmission of the double-layer structure can be modulated in more ways. The results may be useful for the design of related nano-photonic devices.2. The EOT of the nonlinear medium-metal slit arrays are researched in cases of nonlinear medium filled in the metal slits and metal slit array embedded in the nonlinear medium. It is found that the center peak wavelength and peak value of the transmission resonance modes are strongly dependent on the intensity of the incident light, the thickness of the nonlinear medium and the metal film, the third-order nonlinear susceptibility, and nonlinear refractive index. Interesting optical phenomena appear, such as the red-shift of the transmission resonance modes and the skipping of the transmission peak values. The results can be helpful for the design of the optical devices such as an optical switch.3. The EOT is presented of the subwavelength periodic metal slit arrays and slit-groove arrays with converging-diverging, diverging-converging, only converging, and Z shaped channels. Resonance modes of both types exhibit red-shift, blue-shift, splitting, merging, degeneration, and enhance, respectively, with the variation of the shape, size and unit number inside the slit channel. Especially, it is proved that the transmission of a thinner metal film perforated with Z-shaped slit array behaves nearly the same as that of a thicker metal film perforated with straight slit array with the same central slit length, which is useful for the miniaturization of the optical device. The structures with shaped channel slit arrays are novel which introduce more ways to control the transmission resonance modes.4. The investigation of a special continuous periodic metallic structure composed of parallel touching metal nano-cylinder and film demonstrates that the structure without light passing through straightly can also raise EOT, and the transmission resonance modes are tunable sensitively by the cylinder radius, cylinder array layers, the dielectric constant of the dielectric around the cylinders, and the distance between the cylinders and film. With altering these structure factors, the transmission resonance peaks split, shift and degenerate. The EOT of the continuous structure is associated with the surface plasmon tunneling resonance.