A Novel Heterodyne Polarimeter for the Multiple-Parameter Measurements of Twisted Nematic Liquid Crystal Cell Using a Genetic Algorithm Approach

A new method for measuring the multiple parameters of a twisted nematic liquid crystal (TNLC) by applying a genetic algorithm is presented. This paper adopts an electrooptic modulator to modulate the linear polarized light which passed through a TNLC cell in a heterodyne polarimetric setup. The intensity ratio and the phase of the detected heterodyne signal are used for the inverse calculation in the LC cell parameters by applying a genetic algorithm approach. As a result, the multiparameter measurements in the entrance director angle of TNLC, twist angle, and cell thickness are achieved. The advantage of the heterodyne polarimeter introduces high sensitivity on intensity and phase detections, and the multiple parameters could be easily extracted through the genetic algorithm. Also, the ambiguity in the angle extraction could be uniquely solved in this paper. The experimental results show that the average deviation of 0.01deg and 0.013 mum in the measurement of twist angle and cell thickness, respectively, have been obtained. The average deviation of 0.23deg in the measurement of director angle has also been achieved