New absorptive mode reflective liquid-crystal display device

A new liquid-crystal alphanumeric display device is described. The device is of the guest-host type and involves the orientational change of a pleochroic dye (guest) in a cholesteric liquid-crystal mixure (host) by the application of an external electric field. The cholesteric nature of the host permits the operation of the device in the reflective mode with excellent brightness since no external polarizers are required. Good contrast ratios have been obtained for new pleochroic dyes (guests) which have higher optical order parameters than those previously employed. The theory of light absorption in a cholesteric liquid crystal having both homogeneous and homeotropic boundary conditions is developed and aspects of contrast ratio and its relation to human perception are described.