Some Studies On Properties And Applications Of Photonic Crystals And Metamaterials

Scientists have long been seeking effective approaches to control and manipulate the light. In the past two decades, two kinds of man-made materials, namely, photonic crystals and metamaterials, have become hot research topics in multidisciplinary community of optics, electromagnetics, physics and material science, since they have remarkable capability of localizing and guiding radiation and provide unprecedented electromagnetic properties and functionalities unattainable from naturally occurring materials.Photonic crystals are composed of periodic dielectric or metallo-dielectric nanostructures that are designed to affect the propagation of electromagnetic waves. The electromagnetic properties of photonic crystals, e.g. phtonic band gap, result from the periodicity of the whole structure. Due to their great ability of controlling the flow of light, photonic crystals have already been used for e.g. high-Q nanocavities, narrow waveguides and microlasers. The dispersive properties of photonic crystals can also be exploited for manipulating the group velocity of light, shaping and compressing optical pulses, and realizing negative refraction and superprism effects.In contrast, metamaterials are usually composed of metallic elements whose size is much smaller than the resonant wavelength. Therefore, the electromagnetic properties of metamaterials depend on the response of each subwavelength element. By properly designing the resonant elements, metamaterial can be an effective medium with desired permittivity and permeability, which has been used to achieve some interesting phenomena, such as negative reflective index, invisibility cloaking, perfect absorption, super lenses and polarization conversion.In this thesis, we study some properties and applications of photonic crystals and metamaterials. Our original works are listed as follow:1. We design a composite dielectric waveguide for the realization of a localized "light wheel", which is numerically demonstrated and explained physically in detail. A delocalized "light wheel" is found at the band gap edge caused by contra-directional coupling between the two waveguides. The delocalized "light wheel" can be used to trap light as a cavity.2. We study on the band structures and equifrequency contours of one-dimensional photonic crystals (PCs), which consist of an electromagnetically induced transparency (EIT) medium and a common dilectric medium,when the coupling Rabi frequency (CRF) of the EIT medium is tuned. It is found that for a probe light at a fixed frequency, either positive or negative refraction in the EIT PC can be realized with a proper CRF. This tunable optical response enables manipulating light flow.3. We design a nearly omni-directional THz absorber for both TE and TM polarizations. The perfect absorption in a thin thickness about 25 times smaller than the resonance wavelength is numerically demonstrated to be caused by the excitation of magnetic polariton. More importantly, by simply stacking the proposed layer structure, the bandwidth of the absorption can be effectively increased due to the hybridization of magnetic polaritons in different layers, which pave a way for broad bandwidth absorber in THz frequency.4.We design a bilayered chiral metamaterial to realize a 90°polarization rotator, whose giant optical activity is due to the transverse magnetic dipole coupling among the metallic wire pairs of enantiomeric patterns. It is demonstrated that it is the chirality in the propagation direction that makes this efficient cross-polarization conversion possible. The optical activity of the present structure is about 2700°/λ, which is the largest optical activity that can be found in literature.5. We report the enhanced transmission of TE waves through an array of subwavelength slits in a thin metallic film at microwave frequencies. By adding a dielectric layer with a metallization of cut wire array, we obtain an 800 fold enhanced transmission through the slits. We numerically demonstrate that the resonant transmission is to due to the excitation of the electric dipole-like resonances of cut wires in close proximity to the apertures of the slits. which effectively coupled the incident wave into the subwavelength slits.