PHOTONIC CRYSTALS

The invention relates to photonic crystals, i.e. three-dimensional dielectri c structures which are opaque to electromagnetic radiation within a given wavelength irrespective of the direction of incidence. An inventive photonic crystal comprises, for instance, a matrix-type arrangement of free-standing dielectric micro-columns or cylinders having small diameters. Said micro- columns or cylinders are placed on a substrate whose thermal expansion coefficient between 60 ~C and 85 ~C is at least 50 % lower than the thermal expansion coefficients of quartz glass, thereby enabling the thermal expansi on of the substrate to be kept to a minimum even when high temperature variatio ns occur; whereby the distance between the micro-columns supported by the substrate or the microcyinders of the photonic crystal varies only to a smal l amount, whereby the optical characteristics are essentially more stable than those of photonic crystals with a quartz glass substrate. Preferably, glass ceramics or, for example, Zerodur.RTM. are used as a substrate.