WAVELENGTH CHARACTERISTICS OF BIREFRINGENT FILM REFRACTIVE-INDEX ANISOTROPY FOR A BLACK-AND-WHITE FILM SUPERTWISTED NEMATIC LIQUID-CRYSTAL DISPLAY WITH A HIGH-CONTRAST RATIO

Film supertwisted nematic liquid crystal displays (F-STN-LCDs) with a single birefringent plastic film can be used for monochromatic black a nd white (B/W) LCDs, but their contrast ratio is inferior to that of d ouble-layered (D-) STN-LCDs. We optimized the wavelength characteristi cs of the birefringent film refractive index anisotropy (Delta n) thro ugh calculations and experiments to increase the contrast ratio of F-S TN-LCDs. It was found that the wavelength characteristics of the Delta n should be large at shorter wavelength regions and small at longer w avelengths. Moreover, the main axis in exit elliptical polarized light of the film must be crossed perpendicular to that of the STN-LC cell in all wavelength regions to obtain a high contrast ratio of the B/W F -STN-LCD.