Adjustment And Research On The Electromagnetically Induced Transparency (EIT)-like In Multi-cavity Coupled Waveguide System

Surface plasmons (SPs) are a transverse magnetic wave which is caused by the electric field perpendicular to the metal surface of the metal. The wave is spread along the surface of the metal and medium by the interaction of free-electrons and photos. We can arouse the Surface plasmons in the surface of the metal and medium by making use of the auxiliary structures or changing the surface structure of the metal, so that we can control the light and we can get some particular optical properties. In our paper, we investigate the physical properties of electromagnetically induced transparency and the basic physical mechanism in plasmonic waveguide system by using the Finite-Difference Time Domain method(FDTD).Our main work is listed as follows:1. We investigated a plasmonic waveguide system composed of a straight waveguide, with rectangular and U-shaped (split-ring resonator) cavities. It is demonstrated that an EIT-like transparency window occurs in the transmitting spectrum and the magnetic field is dramatically changed by varying the coupling strength and tailoring the degree of asymmetry of the structure due to the destructive interference between two resonance pathways. Meanwhile, a cascaded structure which consists of two rectangular and U-shaped structures has been studied and it is found that the strong couplings between them can lead to EIT-like transmission. We thought that the EIT phenomena appear due to the destructive interference between two resonance pathways and the two pathways are the direct excitation of the bright mode by the external light field and the excitation of the dark mode by coupling with the bright mode. We can explain the phenomena using magnetic coupling, electric coupling and inductive coupling2. We studied two resonators side-coupled to a bus waveguide. It is found that the EIT is achieved due to the two resonances of different length coupled to a bus waveguide. The resonant frequency of individual structure and cavity-cavity separation of two resonators and different detuning of the two resonator cavities have great influence on the transparency peak. The transmission features can be investigated by coupled-mode theory.3. We demonstrate a π-shaped waveguide system that exhibits plasmonic analogue of electromagnetically induced transparency.π-shaped waveguide system possesses the same photometric characteristics as the Metamaterials, so we call the single rectangular cavity as dipole and two parallel rectangular cavities as quadrupole. When the dipole and quadrupole of the π-shaped structure are uniquely coupled, an EIT-like transparency window occurs in the transmitting spectrum of the waveguide system and transmission spectra can be modified by changing the coupling strength between them. Finally, we investigated a cascaded structure which consists of two π-shaped system and the coupling strength between them has great influence on the transparency peak.