Abstract
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.
Highlights
In 1987, Yablonovitch1 and John2 proposed the idea that a three-dimensional3Dphotonic band gapPBG, in which electromagnetic wave propagation is forbidden in all directions, can be realized in artificial 3D periodic dielectric structures
Numerical studies have indicated that the picture of dielectric and air bands in conventional photonic crystals can be applied to the PBG formation in PAD as well
Because Bragg scattering due to lattice periodicity has been considered to be the main origin of gap formation, it was commonly believed that lattice periodicity is indispensable for the realization of 3D-PBGs
Summary
In 1987, Yablonovitch and John proposed the idea that a three-dimensional3Dphotonic band gapPBG, in which electromagnetic wave propagation is forbidden in all directions, can be realized in artificial 3D periodic dielectric structures. Since these “photonic crystals” have attracted considerable attention and have been studied extensively because of their great potential for applications to strong light confinement and manipulation of light propagation, which might enable us to realize novel optic devices. This PCD structure is known to be the best 3D-PBG structure; it exhibits the largest 3D-PBG among all the photonic crystals studied far. PAD and PCD can be regarded as the photonic versions of amorphous and crystalline Si, respectively, in electronic systems
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