Optical properties of general double layer twisted and supertwisted nematic liquid crystal displays

Analytic expressions are obtained using the generalized geometrical-optics approximation for the field-off state optical field and transmission of the general double layer twisted nematic and supertwisted nematic liquid crystal displays with arbitrary display parameters. A variety of display characteristics can be obtained from such structures. In particular, the strong interference colors in the field-off state single layer supertwisted nematic displays can be completely removed in a double layer supertwisted nematic display; thus, a black or white off state is possible. For the double layer 90°twisted nematic, besides the complete black or white field-off state, it can also exhibit off state display performance similar to that for either the single layer 180°supertwisted nematic or the optical mode interference display.