A differential method has been developed which determines displacement
from the midpoint of optical transmission (.+-.45.degree.) and utilizes
the coupled nature of the two signals for common mode noise rejection to
enhance the detection of chiral species. A beam of light is modulated,
applied to the chiral mixture, and then split into a first beam and a
related orthogonal beam by a polarizer or prism. The first beam and
orthogonal beam are converted into electrical signals before a
differential comparison of the signals is performed to detect a desired
chiral species within the chiral mixture.