Although light propagation in weakly modulated photonic crystals is basically similar to propagation in a diffraction grating in which conventional refractive index loses its meaning, we demonstrate that light propagation in strongly modulated two-dimensional (2D)/3D photonic crystals becomes refractionlike in the vicinity of the photonic bandgap. Such a crystal behaves as a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. By utilizing this phenomenon, negatively refractive material can be realized, which has interesting optical properties such as mirror-image refraction.

• Received 7 April 2000

DOI:https://doi.org/10.1103/PhysRevB.62.10696