When circularly polarised light is passed through a chiral
nematic, only one of the two rotating polarisation directions will have
the same 'handedness' as the chiral molecule.
This results in a difference in the liquid crystal's refractive index
for the two components - so one will travel faster than the other.
Once again an optical path difference will be created, and the polarisation
of the light will have rotated upon exiting the sample.