Researchers in Canada and Spain have overcome the obstacles to develop a three-dimensional photonic crystal that can be easily manufactured on a large scale at a low cost. Fabricated with silicon, it meets the criteria needed for complete photonic bandgap formation. Such advances could ultimately help optical circuitry replace slower electronic circuits in chips. "The advantage of silicon is that the [photonic bandgap] can be centered at 1.5 µm, the wavelength of choice for telecommunications," said Sajeev John, a physics professor at the University of Toronto. "And it integrates readily with existing silicon-based microelectronics." Silicon's surface properties also behave well, he added. John and his colleagues at the University of Toronto, the Universidad Politécnica in Valencia, Spain, and the Instituto de Ciencia de Materiales de Madrid described their achievement in the May 25 issue of Nature. Starting with an artificial opal crystal, they infiltrated silicon into the crystal's air gaps and etched out the opal, leaving the silicon structure. The only drawbacks to their technology, John said, are that the silicon inverse opal photonic bandgap is limited in size to about 5 to 9 percent of the gap center frequency, and that the structure is sensitive to disorder. John said the group's goal for the technology is to couple light from an optical fiber into the photonic crystal and to create light circuits inside it. "The material can also be doped to make it active for light emission (microlasers) and nonlinear optical effects," he said.