20 - Omnidirectional Bandgaps and Selective Transmission in Layered Photonic Crystals
Résumé
It has been shown that a one-dimensional periodic structure such as a layered photonic crystal can exhibit the property of omnidirectional reflection, which means that any incident wave launched from the vacuum (or from a substrate) will undergo a total reflection at the layered photonic crystal boundary, whatever the incident angle or the polarization of light. In this chapter, we show that large omnidirectional bandgaps can be obtained by associating two or several layered photonic crystals in tandem. We discuss the existence conditions for these gaps compared to the usual case of a binary layered photonic crystal. By introducing a defect layer in the finite layered structure, one can obtain localized modes inside these omnidirectional bandgaps, giving rise to the selective transmission through the structure. These modes appear as peaks in the transmission spectrum with a very high quality factor, and therefore may have useful applications in the frame of photonic bandgap materials. We also know that the property of the omnidirectional reflection requires that the incident wave is launched from vacuum or from a low refractive index material. In the second part of this chapter, we show that the limitation about the choice of the substrate can be removed by adding a clad layer of low refractive index at one boundary of the superlattice. The additional layer acts like a barrier for the propagation of the light. An alternative solution based on a combination of two multilayer structures is also mentioned.