Interference of additional modes in spectra of opal-like photonic crystals in the multiple diffraction regime

The mechanisms of formation of Bragg reflectance and transmittance spectra have been investigated for films of three-dimensional opal-like photonic crystals. Attention has been drawn to the fact that the spectra exhibit an additional short-period interference structure of the novel type due to the multiple Bragg diffraction of light. The spectra have been calculated in the framework of the dynamical three-wave diffraction model taking into account strong spatial modulation of the dielectric function. It has been found that short-period oscillations appear in the spectra due to the spatial quantization of additional modes with a low group velocity.