PHOTONIC BAND-GAP CRYSTALS

The analogy between electromagnetic wave propagation in multidimension ally periodic structures and electron wave propagation in real crystal s has proven to be a very fruitful one. Initial efforts were motivated by the prospect of a photonic band gap, a frequency band in three-dim ensional dielectric structures in which electromagnetic waves are forb idden, irrespective of propagation direction in space. Today many new ideas and applications are being persued in two and three dimensions, and in metallic, dielectric and acoustic structures, etc. In this pape r, we review the early motivations for this work, which were derived f rom the need for a photonic band gap in quantum optics. This led to a series of experimental and theoretical searches for the elusive photon ic band-gap structures, those three-dimensionally periodic dielectric structures which are to photon waves what semiconductor crystals are t o electron waves, Then we describe how the photonic semiconductor can be 'doped', producing tiny electromagnetic cavities. Finally, we will summarize some of the anticipated implications of photonic band struct ure for quantum electronics and the prospects for the creation of phot onic crystals in the optical domain.