Multi-peak structure of photonic band gaps on dichromated pullulan

Fabrication of wide-bandwidth and highly reflective volume holograms is presented. Using holographic recording method, photonics structure as volume (Bragg) grating was created. Dichromated pullulan (exocellular homopolysaccharide) was used as a recording medium. A peculiar multi-peak structure in the reflection spectra is observed. It was found that appearance of a multi-peak phenomena leads to a wider band gap (i.e., if the diffraction spectra in the range of the band gap is more or less flat), the band gap is typically much narrower then in usual structure of the refection volume holograms, with only one main Bragg peak. We investigate the procedures which lead to more frequent appearance of the multi-peaks within the bandgap.