The Research On Defect Modes Of Photonic Crystal And Related Application

Photonic crystal, like electronic solid crystal, exhibits such characteristic as optical bandgap and localized optical fields. Propagation of light wave fall within the optical bandgap is forbidden. Micro-optical resonate cavity and 1D optical waveguide could be built by introducing of point or line defects into a photonic crystal. Various new photonic devices could be fabricated utilizing these defects. Therefore the research on the properties of defects mode is of great importance for the design and fabrication of new photonic crystal devices.The theses carried out simulations on the behaviors of point and line defects using finite-difference-time-domain method (FDTD) adopting perfectly matched layers (PML). Firstly the bandgap of a 2D square lattice photonic crystal made of cylindrical media and the transmission characteristics of point and line defects were calculated. As the results shown, the peak value of the mode shifted to lower frequency when the radius of point defects became larger; the center wave length of the pass band of a line defect become larger when the optical crystal lattice constant increased.Secondly, a combination of a line defect and elliptical point defects were introduced into a 2D square lattice photonic crystal. The simulation indicated that central resonate wavelength of an elliptical point defect changed periodically around 2.509～2.673um when the point defects moved around without rotation. The central resonate wavelength remain unchanged only if the elliptical point defect rotated between 30-60 degree. Single and double peak modes might appear alternately when the elliptical point defect rotated outside the range of 30-60 degree.Finally, a photonic crystal, whose lattice constant changed gradually along the propagating direction of a light wave, was proposed. With the introduction of a proper combination of line defect and point defects, the defect mode was made to change continuously and the peaks as narrow as 10nm have nearly equal value. Utilizing these defects modes a six-channel wavelength division demultiplexing system was conceived.