Bifurcation in reflection spectra of holographic diffraction grating recorded on dicromated pullulan

Volume diffraction gratings were created holographically on a dichromated pullulan (polysaccharide doped with chromium). Specific and very rare multi-peak structure in the reflection spectra is observed. It was found that multiple peaks are consequence of non-ideal structure of volume diffraction grating. Theoretical analysis and numerical simulations confirm that the observed behavior arise from a slight randomness of grating parameters: refractive index, grating period, film thickness. The results of calculation are in agreement with experimental results.