The Optical Properties Of Several Subwavelength Metal Structures

Recently, the sub-wavelength optics holds people a lot of interest as the related scientific problems and its broad application potential, for instance, used in near-field optics, magneto-optic data storage, sub-wavelength photolithography, as well as the sensors for detecting biologically interesting molecules.In this thesis, the following problems deal with the sub-wavelength optics are researched by use of the finite-difference time-domain (FDTD) method and theoretical method:1. The characteristics of the subwavelength self-focus and transmission properties of light in a set of nanoscale Ag-waveguide array (Ag-WGA) are investigated by using the FDTD method. The simulated results show that the self-focus can be tuned by the distance between the light source and the incident facet of the Ag-WGA, the shape of the incident entrance of Ag-WGA, and the wavelength of the incident wave. The extraordinary optical transmissions (high transmissions) are also obtained.2. The process of light passing through a single subwavelength slit cut into metal (Au) film is simulated by the FDTD method. The magnetic and electric fields observed at the exits and entrance display that the multi-reflection of light occurs in the metal slit. Considering that the absorbency of Au can not be ignored, the attenuation constant is introduced into the theoretical formula describing the multi-reflection process occurring in the plated dielectric slab (PDS) model. The data obtained from FDTD simulation fit the theoretical formula well. Thus, this work verifies the PDS model in a high absorbing metal slit.3. The refractive indexes of ferromagnetic wire lattice (FWL) composed of ferromagnetic wires made of Fe, Co, Ni, and Gd, respectively, arranged in a two-dimensional square lattice under external magnetic field are investigated theoretically. In proper frequency regions, thenegative refractive indexes may be acquired and adjusted by the external field. The frequencyregions in which the negative refractive indexes appear are influenced by the geometryparameters. As the frequency region of the negative refr ctive index is the intersection ofboth frequency regions corresponding to the negativeε(dielectric constant)(ENG) andnegativeμ(permeability)(MNG), we investigated respectively the both regions and foundthat it is easy to increase the ENG frequency region and hard to increase the MNG frequencyregion. The MNG frequency is limited by the saturation magnetization of the ferromagneticmaterial, so the key factor for a FWL to increase the frequency of negative refractive index isthe saturation magnetism of the material that constitutes the FWL.