In this study, the optical activity of cholesteric liquid crystal and common-path heterodyne interferometry are used in a
simple measurement technique that was developed to measure small wavelength differences. A circularly polarized
heterodyne light passes through a cholesteric liquid crystal cell and an analyzer. Consequently, an interference signal is
generated. When the cholesteric liquid crystal cell is properly chosen at circular regime, it owns strongly optical activity.
Accordingly, the phase difference between the s- and p-polarized components of the interference signal depends strongly
on the wavelength. As the wavelength changed, a variation of the phase difference can be accurately detected by
heterodyne interferometry. Substituting the variation of phase difference into specially derived equations, the wavelength
variations can be estimated accurately. The feasibility of this method was demonstrated and this method provides the
advantages of a simple structure, easy operations, rapid measurement, high stability, and high sensitivity.