Based on the theory of dielectric film, the structure of 1-D photonic crystal with symmetrical defect layer is designed. The method of transfer matrix was used to analyze the band structure.The result shows that the peak of the defect mode will increase, but its width will narrow as the number of defect layers increases; and the defect mode will shift to the longwave direction as the thickness of the defect layer increases, and multi-defect mode will appear under a certain thickness. The bandgap becomes significantly wider as the periodic unit thickness increases. The defect mode number will reduce as the periodic unit number increases, and a narrow-band defect mode will be formed eventually. These results will play an important role in designing novel photonic crystal devices, such as realizing selectable frequency and scaleable frequency band.
