The CLC helix pitch and location of

The CLC helix pitch and location of the bandgap can be essentially changed by varying temperature and pressure and applying electromagnetic fields or mechanical stress. The qualitative difference of CLC from any other type of PC lies in their polarization selectivity by diffractive reflection. In CLCs there are PBGs for light propagating along the CLC helix with a circular polarization coinciding with the twist of the CLC helix. When reflected from CLC, a light wave of such polarization does not change the sign of its polarization.