Photonic band-gap formation, light diffusion, and localization in photonic amorphous diamond structures

We report experimental and numerical studies on photonic band-gap (PBG) formation and light propagation in a recently proposed unique photonic structure, photonic amorphous diamond (PAD). PADs have been fabricated in a microwave regime, and the formation of a full three-dimensional (3D) PBG has been substantiated experimentally. This proves unambiguously that periodicity is not essential to the realization of a 3D-PBG, contrary to the common belief. The 3D-PBG has been demonstrated to be completely isotropic, regardless of the light polarization direction, which, in principle, cannot be realized in conventional photonic crystals. In passbands, the PAD has exhibited diffusive light propagation, where the scattering strength increases significantly as the frequency approaches the band edge, indicating a precursor of light localization. Localized states have indeed been identified at the band edges by a numerical calculation. Numerical studies have also indicated that the picture of dielectric and air bands in conventional photonic crystals can be applied to the PBG formation in PAD as well. These findings provide different insights into the physical origin of PBGs and issues such as light diffusion and localization in photonic materials.