Effect of defect states on photonic dispersion in colloidal crystals

Summary form only given. A colloidal crystal of submicron-sized polystyrene spheres in water may serve as a photonic crystal owing to the dielectric contrast between the constituent materials. Such photonic crystals exhibit strong attenuation in regions of the transmission spectrum (stop bands) arising from Bragg diffraction of light by the crystal planes. Stop bands in polystyrene colloidal crystals have been observed and studied extensively for both FCC and BCC crystal phases. Photonic crystals also modify the photonic dispersion relation near the stop band. In addition, defect states can be introduced into the stop band of a colloidal photonic crystal by substitutional doping with microspheres of different size or dielectric strength. We have significantly improved the Mach-Zehnder interferometer used in a previous dispersion study. We report the application of the improved instrument to the study of dispersion in a colloidal crystal with defect states present.