GB1372868A - Optical device - Google Patents

Abstract

1372868 Modulating light F HOFFMANN-LA ROCHE & CO AG 18 Nov 1971 [4 Dec 1970 13 April 1971] 53678/71 Heading H4F The surfaces of plates 14, 15 bounding a liquid crystal layer 16 are prepared, e.g. by rubbing with a cotton plug, so that the immediately adjacent molecules of layer 11 are constrained to lie in a respective single direction parallel to the surface, the respective directions for the two plates being non-parallel, e.g. at 90 degrees, so that layer 16 possesses a helical structure extending between the plates and is optically active. As particularly described, layer 16 may be a pure nematic compound with positive dielectric anisotropy, and plates 14 and 15 are conductive SnO 2 coated glass plates. Application of an A.C. or D.C. electric field above a threshold voltage tends to destroy the helical structure and optical activity, Figs. 3 and 4 (not shown), as may be observed by placing the cell 11 between parallel or crossed polarizers 12, 13, since the molecule axes tend to align with the field. In modifications, (a) the layer 16 may additionally include a cholesteric compound, the mixture naturally tending to have a helical structure; only one plate surface needs preparation to fix the helical structure, (b) liquid crystal 16 may be coloured, (c) analyser 13 may be secured to a mirror for operation in a reflective mode. Different locations in the cell may be activated by X-Y addressing electrodes, for example for use as a write-in matrix for a hologram store (the coherence of the transmitted light being retained). Further references to uses of the shutter are to television, data processing, and in spectacles wherein the absorption is controlled by the incident light intensity.