Superprism effect in opal-based photonic crystals

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Abstract
This paper investigates the superprism effect in opal-based three-dimensional photonic crystals which consist of an face-centered cubic (fcc) array of close-packed dielectric spheres embedded in a host. The light propagation angle inside the opals is determined by the group velocity vector of the bulk eigenmodes having the strongest coupling with the incident light at the boundary of the opal. It is found that the superprism effect takes place quite generally in the frequency range where many flat bands exist owing to the zone folding. The numerical simulations of the superprism effect in bare opal systems indicate that the effect can be used as frequency selector devices as well as beam splitters.