Defect Modes in Two-Dimensional Quasiperiodic Photonic Crystal

The defect modes and transmission property of a two-dimensional quasiperiodic photonic crystal (QPC) with defects are studied experimentally and theoretically. It is found that the defects, introduced by removing the dielectric cylinders in the central octagon, may result in various defect modes and resonant frequencies. If the defects possess the same rotational symmetry, the resonant frequencies of the defects are identical. However, the corresponding transmittances can be quite different. This is attributed to the different field distribution leading to various coupling strength between the incident and transmitted waves. When it is symmetrically distributed against the central line which is perpendicular to the incident direction, the transmittance enhances drastically. Based on the wave coupling theory, a simple model is given to explain this phenomenon.