Electrooptics of the Twist Cell for Oblique Incidence

FIGURE 4.15. The twist cell for oblique light incidence at the angles ie, i ). The angle ie is measured from the normal to the substates, while the angle is from the symmetric plane of the twist structure. 

The most crucial partoieter that affects the uniformity of transmission is the Mauguin number [87]. For low And/ values the anisotropy of transmission is weak [87, 88]. According to this, liquid crystal mixtures with low An values and the first Mauguin minimum And/X = f%j2 as a working point are preferable. We do not consider the influence of the parameters ATaa/ifTii and Aef on the transmission characteristics of the twist cell, as their effect now is very small compared with the case of normal incidence [74, 95]. 

Let us note that coloration, i.e., dependence of the light transmission on the wavelength, and the stronger temperature dependence of 6n make the operation in the first Mauguin s minimum less attractive. Sometimes it seems more convenient to choose y/S/2 And/X a/5/2 (between the first and second minima) even at the cost of the partial loss of the contrast [95]. 

FIGURE 4.17. Isocontrast curves for the normally white mode [98] (twist cell between crossed polarizers in white light). The first polarizer is (a) perpendicular and (b) parallel to the director on the input substrate. 

4 Matrix Addressed Displays and Multiplexing Capability of Twist-Effect Materials 

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