Micromachined Photonic Band Gap Crystals: From Microwave to the Far-Infrared

In May 1992, I accepted a position at Iowa State University (ISU) and started working on photonic band gap materials with Gary Tuttle, assistant professor of electrical engineering. By that time, the classical papers in the field had already been published [1, 2]. Concepts like conduction and valence bands, acceptor and donor defects [3], had been introduced and widely used. There were series of articles in Physical Review Letters, about physical mechanisms around these materials [4,5]. People were excited about possible “photonic” applications and experiments, where the spontaneous emission would be reduced to nil at optical frequencies. To my surprise, all of the experimental work was limited by the original work done by Eli Yablonovitch [2] which was only performed at 15 GHz!! There had been some work by the IBM group to test two-dimensional alumina rods which showed a band gap around 70 GHz, but only for one of the polarizations[6]. I could not find any other experimental work which showed a full band gap in all directions. Besides, there were no published efforts to push the frequency performance to a frequency higher than the original 15 GHz.