Superprism phenomena in photonic crystals

Extraordinary angle-sensitive light propagation, which we call a superprism phenomenon, was demonstrated at optical wavelength in photonic crystals with three-dimensional-periodic structure fabricated on Si substrate. The propagation beam was swung from $\ensuremath{-}90\ifmmode^\circ\else\textdegree\fi{}$ to $+90\ifmmode^\circ\else\textdegree\fi{}$ with a slight change in the incident angle within $\ifmmode\pm\else\textpm\fi{}12\ifmmode^\circ\else\textdegree\fi{}.$ This effect together with wavelength sensitivity is at least two orders of magnitude stronger than that of the conventional prism. The incident-angle dependence including negative refraction and multiple beam branching was interpreted from highly anisotropic dispersion surfaces derived by photonic band calculation. These phenomena will be available to fabricate microscale light circuits on Si with LSI-compatible lithography techniques.