Research On Electromagnetically Induced Transparency Of Metamaterials At Optical Frequency Range

In the last decade, metamaterials have attracted great attention from scientists and engineers and had many novel physical phenomena, which are unavailable or hard to realize using conventional materials. In recent years, the research of electromagnetically-induced transparency (EIT) has also received much attention in metamaterials, which it can realize the high Q value, low-loss and large group index resonance due to destructive interference of the subwavelength two-dimensional planar structure. Therefore, the EIT phenomenon is of great importance for slow light, sensing, nonlinear and optical switching. The classical analogue of EIT in metamaterials can be realized in a wide range from microwave to the optical domain,which avoids many problems and complicated experimental conditions of achieving EIT in quantum systems. In this dissertation, we mainly investigate EIT in metamaterials at optical frequency range based on numerical simulations from the software CST. We design several different metamaterial structures, and study in details these structures' design method, the electromagnetic characteristics and coupling mechanism. Our research shows significant importance for achieving the EIT's application in practical. The main innovative points are as follows:(1) Based on the coupling of a "bright" and "dark" mode, we design a planar metamaterials structure, and investigate its optical properties by use of electromagnetic simulations. The proposed structure can achieve the low loss and high EIT transmission peak.Further, we study the coupling mechanism of bright and dark modes utilizing current density and electromagnetic field distribution at these resonances.(2) Based on trapped-mode resonance mechanism, we design a planar metamaterial structure. The structure can realize EIT phenomenon due to the coupling of bright and bright modes, and further study the coupling mechanism by current density and electric field distribution at the corresponding resonances. We can also tune the structure' resonant characteristics and resonant frequencies by changing the asymmetric degree of the structure,and realize the tunability of the EIT phenomenon in optical metamaterial.(3) we propose a single-layer planar metamaterial consisting of an array of two coupled resonators. The proposed structure can achieve a classical analog of EIT with a high Q in the metamaterial at optical frequencies, which originates from destructive interference between dark and bright elements. In addition to the enhanced transmission in the case of the EIT effect, the constructive interference of near-field coupling of the bright mode to the dark mode results in a narrow peak of enhanced absorbance. We study the dependence of transmission and absorption spectra of the metamaterial on the structural parameters, and the transition between the EIT and EIA is achieved easily.(4) we propose a bilayered metamaterial structure. The structure can achieve the multi-band transmission windows based on mutually coupling between two twisted resonators that contributes to the resonance hybridization at normal incidence in the optical range. We also analyze the impacts of the structural parameters on the transmission of the bilayered metamaterial. The transmission properties can be controlled efficiently by adjusting structural geometric parameters and dielectric constant of the substrate.