Optically active additives in twisted nematic devices

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Abstract
A study has been made of the use of optically active additives in twisted nematic devices to remove areas of reverse twist, the results obtained depending on the chirality of the additives and the director alignment on the two containing surfaces. Under certain conditions degeneracy of the field induced reorientation of the director produces a patched appearance even in the absence of reverse twist. It is shown how to remove the degeneracy to obtain good display uniformity. For particular combinations of chirality and surface alignment it is shown that the application of a sufficiently strong electric field produces a temporary reversal of the chirality of the layer. A calculation of the threshold condition for the field-induced reorientation of twisted nematic layers containing optically active additives is compared with experiment