GB1404945A - Data display systems - Google Patents

Abstract

1404945 Modulating light SIEMENS AG 7 Aug 1972 [28 Sept 1971] 36762/72 Heading H4F A controllable optical filter comprises an electrically controlled variably scattering (depolarising) or birefringent liquid crystal layer 4 deposed between a neutral polarizer 3 (i.e. it polarises all visible wavelengths equally) and an arrangement which polarises visible light in a manner dependent on its wavelength, e.g. a linear polarizer 2 which polarizes all colours except red, or the combination of a neutral polarizer and a birefringent plate. Polarizers 2 and 3 may be linear or circular polarizers and they may be interchanged. A ground glass screen 5 increases the angle of view. One electrode 11 may be reflective rather than transparent, Fig. 2 (not shown). In another embodiment, Fig. 3 (not shown), white light is initially filtered via a polarizer, 3#/2 plate and an analyser, and the coloured light passed through a 5#/2 plate, the liquid crystal layer, a further analyser and a ground glass screen. Further passive filter elements may be included, e.g. as a separate element, as a plate of the liquid crystal cell, or by using a coloured liquid crystal material. The electrodes 10 and 11 may cover the centre cell or be segmented to produce a display of white or coloured characters on a differently coloured background for example. When using a variably birefringent liquid crystal layer, electrodes 10 and 11 may undergo prior treatment whereby the liquid crystal molecules align either parallel or perpendicular to their surfaces. When using optical scattering, a mixture of cholesteric and nematic materials may be used to give a memory effect.