Different regimes of light localization in a disordered photonic crystal

It is known that photonic Bloch states can become strongly localized near t he band edges in a disordered photonic crystal. We show that Bloch states a re disrupted and another localization regime establishes when local fluctua tions of the band-edge frequency caused by randomization of refractive inde x profile becomes as large as the band-gap width. Transmission experiments performed on opal photonic crystal have shown the exponential decay of ligh t throughout the gap region, which is ascribed to building up of the second regime of light localization.