Tunable reflectance spectra of multilayered cholesteric photonic structures with anisotropic defect layers

In this paper, we investigate the spectral characteristics of normal incident light reflected by a multilayered structure composed of an alternated sequence of single-pitch cholesteric liquid-crystal (ChLC) and anisotropic layers. Using the Berreman 4 x 4 matrix formalism, we numerically obtain the reflection spectrum and the chromaticity diagram as a function of the anisotropic layers thickness d. For d --> 0, the structure behaves like a single ChLC layer, showing a single reflection band. As the anisotropic layer thickness increases, the reflection band shifts toward high-wavelength spectral regions, while new reflection bands appear. As a consequence, the reflection chromaticity continuously changes with d. It is observed that a suitable choice of the anisotropic layer thickness can produce a threefold reflection band with a red-green-blue associated color for both polarized and unpolarized incident lights.