Analysis of Fabry-Perot interference effects on the modulation properties of liquid crystal displays

In this paper, we present the analysis of Fabry-Perot interferences in a twisted nematic liquid crystal display (LCD), and its influence on the modulation properties of the device. We develop a theoretical analysis based on the Jones matrix formalism and compare the results with the experimental response of a commercial display. The developed theory considers multiple reflections to derive a new Jones matrix for the display, which accounts for both polarization and Fabry-Perot interference effects. The validity of this treatment is limited to normal incidence illumination, but it is much simpler than other 4 × 4 matrix treatments developed for a general oblique incidence. It is shown that the existence of multiple reflections can be added to previously existing simplified models for the display, resulting in a modified Jones matrix with two new parameters: the Fresnel reflection coefficient r and the voltage independent phase Φ. In addition, a calibration procedure is proposed where the calculation of these two new parameters related with the multiple reflections, can be uncoupled from the calculation of the rest of the parameters, related with the modulation properties. We remark the good agreement between the theoretical results and the experimental measurements.