The stop-band characteristics of waves in cholesteric-liquid-crystal half-space are investigated using the exact wave solution, the Floquet theorem, and the corresponding Brillouin diagram. The other half-space is filled with a uniform dielectric medium. By appropriate choice of the dielectric constant of the uniform medium and the angle of incidence of the incoming plane wave, the stop band may split into two or three stop bands.
C. Elachi and C. Yeh, "Stop bands for optical wave propagation in cholesteric liquid crystals," J. Opt. Soc. Am. 63, 840-842 (1973)