Microwave Applications of Photonic Crystals

Abstract

This paper reviews three applications we have investigated using conventional (i.e., all dielectric) photonic crystals at frequencies up to about 30 GHz: (1) microwave mirrors, (2) substrates for planar antennas, and (3) photonic-crystal heterostructures. In each case, an important characteristic of the photonic crystal is that the reflection at frequencies in the stop band is distributed over at least one lattice constant in depth. Thus, the heat generated by residual dielectric absorption is distributed over a much larger volume than the heat generated by surface losses in a metal mirror, enabling a lower operating temperature. An additional characteristic of the photonic crystal, essential to the antenna application, is that its stop band is three-dimensional and thus rejects the majority of power radiated by an antenna mounted on its surface. This makes the planar antenna much more efficient than the same antenna placed on a homogeneous substrate made from the same dielectric material as the photonic crystal. A key factor in the ultimate practicality of these applications is the development of new types of photonic crystals that are superior structurally to conventional crystals or that display enhanced stop-band characteristics. To widen the stop band, we have studied a photonic-crystal heterostructure consisting of a stack of monoperiodic sections having different lattice constants. The resulting structure is shown to have a stop band of nearly one octave.