  A liquid crystal optical device made of an optically anisotropic
heterostructure is considered. The device consists of a cholesteric liquid
crystal (CLC) layer sandwiched by two phase-shifting anisotropic layers of a
nematic liquid crystal (NLC). In this structure each of the NLC layers is a
quarterwave plate. The problem is solved both by Ambartsumian method of layer
addition and Muller matrix method. The peculiarities of reflection spectra,
eigen polarizations, rotation of polarization plane and polarization
ellipticity are studied. It is shown that this device can work as a light
modulator or a system for obtaining linearly polarized light with electrically
tunable rotation of the polarization plane (which is especially important for
optical communication), as well as a device for obtaining the linearly
polarized light from a non-polarized one.
