NEW LIQUID-CRYSTAL POLARIZED COLOR PROJECTION PRINCIPLE

A wide-aperture, color projection principle is presented whose functional parts, namely, polarizers, bandpass filters and electrooptical modulators, consist entirely of liquid crystal elements. The concept ideally enables one hundred percent input-output light conversion. The angular and wavelength dependences of planar cholesteric layers and layer combinations are shown. From them optical filter/polarizer elements result with adjustable center wavelengths and tunable bandwidths. The filters comprise novel cholesteric liquid crystals with a temperature dependence of their center wavelengths as low as 0.06 nm/°C. New, circularly polarized operating modes for twisted nematic (TN-LCDs) and other field effects exhibit not only low threshold voltages, but also voltage-transmission (reflection) characteristics whose slope is adjustable over a wide range. Thus, the new modes are applicable in high-information-content, actively addressed television TN-LCDs requiring gray scale, as well as in displays requiring large time multiplexing rates approaching those of supertwist LCDs. © 1990 IOP Publishing Ltd.