Double cell dichroic LCDs

The contrast ratio of the phase change dichroic display is found to decrease with an increase in temperature (see Fig. 22). This decrease is basically caused by the reduced absorption in the quiescent state that results from the decrease in the order parameter and pitch of the dichroic mixture at higher temperatures. The cells show faster switching speed and lower memory at higher temperature. The switching becomes slow at lower temperature due to an increase in the viscosity of the mixture, and a heater is usually required for low temperature operation. 

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The geometry of a double cell nematic dichroic LCD [13-16, 21, 126] is shown in Fig. 21. The liquid crystal mixture generally used is composed of pleochroic dyes in a nematic host of positive dielectric anisotropy. The first cell has a unidirectional homogeneous alignment in one direction, while the second cell has a unidirectional homo-... 

Figure 21. Geometry of a double cell nematic dichroic LCD. (After Seki, et al. [22]).

The geometry is very similar to that of the double cell nematic dichroic LCD, with each cell having a single turn of cholesteric dichroic mixture [23, 24]. 

Figure 22. Temperature variation of the contrast ratio of a double cell phase change dichroic LCD.

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