Abstract

Photonic crystals are formed of periodically structured dielectric material, the pitch or period of the structure being of the order of the optical wavelength. A novel property of photonic crystal materials is they can be designed so as to exhibit photonic bandgaps. i.e. frequency ranges in which there are no propagating modes in the material.¹ Some interesting consequences of such photonic band gaps occur for waves propagating out-of-plane in two-dimensionally periodic materials. One possibility is to fabricate low-loss waveguides which guide solely by Bragg reflection.² This could be done by using a 2-D structure which is effectively infinite in the third dimension, and which exhibits a bandgap in its transmission characteristics for waves which have a certain wavevector component β=k. along the structure. By purposefully introducing some kind of defect which is embedded in the crystal structure we can create a spatially localized region where such a wave can exist - a "defect stale" appears in the band structure of the material. Light in this defect state would be unable to leak away from the defect through the crystal material, but would travel along the defect with propagation constant β.

© 1996 IEEE