Photonic Crystals and Acoustic Crystals
The periodic dielectric structures are called photonic crystals and the periodic elastic stuctures are acoustic crystals , Such artificial crystals can exhibit frequency regions where the waves cannot propagate in any directions. These regions are named as photonic band gaps(PBG's) and acoustic band gaps(ABG's), analogous to electronic band gaps due to the spatial of defet in semiconductors, which gives rise to an isolated energy level within the energy band gap, can be applicable to the artificial periodic structures, too. Since defect states in PBG's and ABG's can be created by breaking locally the periodicity of the stuctures, it is possible to tune the defect the shape of the local defect. In application, photonic crystals can be used in high-efficiency semiconductor lasers, light-emitting-diodes, solar cells, optical switches, filters, and high-Qresonant cavities. Acoustic crystals can lead to improvements in the design of transducers and acoustric filters