Analysis of the peculiar shift of the low-frequency end of a variable photonic band gap

The effect of the variation of a rod’s dielectric constant on the photonic band gap in a two-dimensional square lattice structure photonic crystal is studied in this paper. The effects were calculated by FDTD algorithm and some peculiar variation properties were obtained. By consecutively changing the dielectric constant of the rod over certain wide ranges and fixing that of the background, the low-frequency end of the TM band gap in low frequency regions reveals very tiny shifts which to some extent can be treated as fixed. This is primarily due to the fact that the high-e region in the crystal is nearly unchanged, hence, the concentrated energy of the low frequency mode changes only slightly. This effect does not exist for materials whose dielectrics are varied over wide ranges. We propose an alternative method using 2D core-shell photonic crystals. The final results of the band calculation show that the gap maps of the core-shell cases closely match those of the ideal case. Such peculiar changes in the photonic band gap have wide application prospects. PACS 42.70.Qs; 78.20.Bh