The almost magical world of photonic crystals

An innovative and exciting new class of materials has emerged called photonic band gap materials, or photonic crystals. The specific applications, needed performance, and overall fabrication costs will dictate the gap properties of the photonic crystal. In this regard a very significant and attractive difference between photonic crystals and electronic semiconductor crystals is the former's inherent ability to provide complete tunability to the desired performance specifications. In recent years, work in the field of photonic crystals has focused primarily on designing and fabricating crystals with 2D and 3D omnidirectional band gaps and on studying the properties of defects in these crystals. Given a photonic crystal with a complete band gap, light with a frequency inside the gap is forbidden to exist within the material unless there is a defect (or a break in the periodic dielectric function) in the otherwise perfect photonic crystal. Such a defect will act like an internal surface within which a photon is confined or localized. A point-like defect will act like a cavity, a line-defect will act like a waveguide, and a planar-defect or surface will act like a perfectly reflecting mirror. Moreover, the structural and material properties of these defects (unlike electronic defects in semiconductors) can be completely and continuously tuned to provide whatever photon properties are desired. Using this great flexibility, researchers could design photonic crystal structures to control and mold the properties of light in new and important ways.