Experimental Probe of Gaps in Photonic Crystals

Photonic crystals are 3D periodic composites of dielectric materials with lattice spacings of the order of wavelengths of light. Such crystals show stop gaps in the dispersion relations, that are revealed as optical Bragg reflections. If light interacts strongly with photonic crystals, stop gaps broaden and may merge to form photonic band gaps. In anticipation of band gaps, it is thus important what is a useful experimental probe of stop gaps, especially the widths. Previously, transmission measurements were done, and analyzed in terms of the width or the attenuation of the stop gaps. The interpretation of transmission experiments is severely hampered, however, by polycrystallinity or crystal imperfections, that are difficult to avoid.