Equivalent retarder-rotator approach to on-state twisted nematic liquid crystal displays

Polarization properties of a twisted nematic liquid crystal cell are fully characterized by an equivalent optical system that consists of a retarder wave plate and a rotator. In this paper we show that this result is of interest to optimize the light-modulation capabilities of a voltage-addressed liquid crystal display (LCD). We provide two examples. First, we demonstrate a calibration method that can be carried out by a standard polarimetric technique with a high degree of precision. Second, we propose an optical device to generate a family of equiazimuth polarization states by adding a quarter-wave plate to the LCD. We find that the design procedure is best described in geometrical terms on the Poincaré sphere by use of the equivalent model. Finally, laboratory results corresponding to a commercial LCD are presented.