Photonic crystals (PCs) as it is often called photonic band gap materials (PBGs), are artificial composite materials, micro/nanostructured on an optical length scale (e.g. few hundreds of nm). The resulting periodicity in the dielectric constant is responsible for inhibiting light from propagating through the material as a result of Bragg diffraction. The forbidden frequency range is called a stop band. In PCs the electromagnetic waves within the band gap are completely reflected by the crystal, while spontaneous emission (within the band gap) are totally concealed.
This chapter introduces the physical concepts behind PC structures, along with bottomup fabrication methods, properties, and applications.
Keywords: opal, photonic bandgap glasses (PBGs), photonic crystals (PC), sol-gel.