Research On The Magnetic Edge States Of Photonic Crystals And The Coupling Effect

The band gap in photonic crystal has attracted the attention of numerous scientific workers early. If we cut the infinite photonic crystals, the truncated surface is formed. The surface mode in band gap can make photons transfer totally. However, the surface mode of the photonic crystal is normally fixed. In order to obtain tunable surface modes of photonic crystal, we add a magnetic material layer on the truncated surface of a two-dimensional photonic crystal, and the Plane wave expansion method has been modified in this paper. Through calculations of dispersion curve, we obtain the surface defect modes. Through the modulation of applied magnetic field, we can control the frequency, the group velocity and the exciting incidence direction of the surface defect mode. In particular, in the frequency range of surface defect modes, we can all tune the group velocity to zero.On the basis of the above work, we separate the two dimensional photonic crystals made of a triangle lattice, an array of magnetic dielectric column replace the general dielectric rods to form the two magnetic surface defect modes. Through the coupling among the two magnetic surface defect modes, we obtain a new self-trapped mode. The self-trapped mode localized the optical waves along the waveguide direction because of their own features of the coupled modes. The trapping does not rely on the external mechanisms; instead, it comes from band own properties. Then we place an array of finite number of magnetic dielectric column on both sides of the waveguide. Pair of magnetic media columns has become a virtual reflection wall, which forms a micro cavity between the two columns. We call this cavity as the semi-open cavity in this work because it is open in the waveguide direction and it is reflected by the photonic crystal in the vertical waveguide direction. And because the position of the magnetic dielectric column is arbitrarily changed, the cavity may be called a movable cavity. The semi-opening cavity has some unique advantages compared with ordinary cavities, e. g., electromagnetic field in it can be either trapped or released; its position and the field amplification in it are tunable. Our study opens a new research door for the combining of magneto-optical materials and photonic crystals.In addition, we also study the double-frequency filter based on coupling of cavity modes and surface plasmon polaritons. In order to achieve a double-frequency filter, we design a sandwiched structure with a dual-prism total reflection configuration. The sandwiched structure consists of one metal layer and two same media layers. The transmission properties are studied through the standard transfer matrix method. Such system can form two hybrid cavity-surface Plasmon-polariton modes. The coupling of the two hybrid modes results in resonance tunneling effect and mode splitting. Mode splitting leads to the coupled double peaks. The difference of double-peak frequencies can be adjusted through changing the metal thickness, and the position of double peaks can be also tunable through changing incidence direction. Such system can be used in designing double-frequency filters and terahertz emission devices.