A photonic crystal is a three-dimensional dielectric structure which is opaque to electro-magnetic radiation within a given wavelength irrespective of the direction of incidence. The photonic crystal may include, for instance, a matrix-type arrangement of free-standing dielectric micro-columns or cylinders having small diameters. The micro-columns or cylinders are placed on a substrate whose thermal expansion coefficient between 60.degree. C. and 85.degree. C. is at least 50% lower than the thermal expansion coefficients of quartz glass, enabling the thermal expansion of the substrate to be kept to a minimum even when high temperature variations occur. The distance between the micro-columns supported by the substrate or the microcylinders of the photonic crystal varies only to a small amount. The optical characteristics are essentially more stable than those of photonic crystals with a quartz glass substrate. Glass ceramics or, for example, Zerodur.RTM. may be used as a substrate.