Anticrossing of polarization modes in liquid-crystal étalons.

Generally when anisotropic materials such as liquid crystals are confined in a Fabry-Perot cavity, the transmission through the device becomes sensitive to the input polarization. While continuous tunability of the refractive index is possible by application of a small electric field across the liquid crystal, it is found that under certain circumstances a forbidden gap in the transmission wavelength is observed. It is shown that this occurs because of mode mixing brought about by a slightly twisted uniaxial structure in between the Fabry-Perot structure. A theoretical model is presented to explain the experimentally observed data, and there is excellent agreement between theory and experiments.