Selective manipulation of stop-bands in multi-component photonic crystals: Opals as an example

We report on a comprehensive theoretical and experimental study of stop-band switching in photonic crystals. The suggested principles of light control are based on new Bragg diffraction effects discovered in multi-component periodic structures. The described analytical approach allows a detailed study of selective switching of $(hkl)$ stop-bands by varying the permittivity of the components or the lattice parameters. For two-component photonic crystals, we showed two possible switching-off regimes. In the first regime, all of the stop-bands may only be simultaneously switched off if the certain matching conditions for permittivities are satisfied. In contrast, in the second regime, one can selectively switch off a preferred stop-band by adjusting the structural parameters irrespective of the permittivity values. For multi-component crystals, the on/off switching of stop-bands has a quasiperiodic resonant character. In the absence of resonance conditions, an $(hkl)$ stop-band can be selectively switched by tuning the permittivity of the structural components, whereas at the resonance, a photonic stop-band cannot be switched off by changing the permittivity. A proper choice of the structural and dielectric parameters can create a resonance photonic band determining the Bragg wavelengths, to which a photonic crystal can never be transparent. The theoretical results were experimentally tested on classical photonic crystals, opals. Selective switching of stop-bands was studied by immersion-resolved and polarization-resolved spectroscopy. We found that opals possess all predictable properties of multi-component structures due to inhomogeneity of the constituent a-SiO₂ spheres.