Abstract
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 0.01° and 0.013
µm in the measurement of twist angle and cell
thickness, respectively, have been obtained. The average deviation of 0.23° in the measurement of director angle has also been achieved.
© 2007 IEEE
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