Photonic Band Gap (PBG) materials are artificial, periodic, dielectrics that enable engineering of the most fundamental properties of electromagnetic waves. These properties include the laws of refraction, diffraction, and spontaneous emission of light. Unlike traditional semiconductors that rely on the propagation of electrons through an atomic lattice, PBG materials execute their novel functions through selective trapping or "localization of light" using engineered defects within the dielectric lattice. Unlike traditional wave-guides that confine light in a high refractive index medium using total internal reflection, a PBG micro-chip may consist of air-wave-guides operating using the principle of "light localization" for confinement of light along a low refractive index path. Unlike electronic micro-circuitry, each air-wave-guide path can simultaneously conduct hundreds of wavelength channels of information, throughout a 3D micro-chip. Three dimensional (3D) PBG materials offer a unique opportunity for simultaneously (i) synthesizing micron-scale 3D optical circuits that do not suffer from diffractive losses and (ii) engineering the electromagnetic vacuum density of states in this 3D optical micro-chip. This combined capability opens a new frontier in integrated optics as well as the basic science of radiation-matter interactions. This is of great practical importance for all-optical communications and information processing.
We review recent approaches to micro-fabrication of photonic crystals with a large 3D PBG centered near 1.5 microns. These include self-assembly, glancing angle deposition methods and optical lithography in a polymer photo-resist, followed by replication with silicon. We consider, finally the placement or infiltration of quantum dots within a 3D PBG material for active device applications. The optical micro-chip allows the engineering of very large and abrupt changes in the local electromagnetic density of states as a function of frequency in the vicinity of the quantum dots. This leads to unprecedented frequency selective control of spontaneous emission, novel low threshold nonlinear optical effects, and possibility of all-optical transistor action.