A flexible design for one-dimensional photonic crystals with controllable photonic bandgap width

We propose a flexible design for one-dimensional photonic crystals (1D-PCs) with controllable bandgap width which based on the two refractive index mediums. In this structure, each of the low index layers replaced by equivalent three-layers which consist of the same applicable and compatible materials of the basic structure but different fractional optical thicknesses. When decreasing the effective optical contrast ratio of the medium (the ratio of the high refractive to effective refractive index) less than its ordinary value, the relative bandwidth of the 1D-PCs can be changed continuously to any desired value. As an example, for the medium made of TiO2 and SiO2 as the high and low refractive index, and using the concept of symmetric three-layers structure, the results demonstrate that when the effective optical contrast ratio adjusted from 1.61 to less than 1.07, the relative bandwidth (Δωω0) of the photonic bandgap (PBG) can be varied continuously (from 0.30 to less than 0.04).