GB1448520A - Stereoscopic display device - Google Patents

Abstract

1448520 Polarization stereoscopy STANDARD TELEPHONES & CABLES Ltd 25 Oct 1974 46259/74 Heading G2J Stero images are displayed alternately and sequentially on a common surface e.g. CRT 10 or cinema screen and are separated for observation by right and left eyes 13, 14 by an optical system including fixed polarizers and one or more liquid crystal cells acting as electrically controllable optically active elements operable at the image alternation frequency. In one embodiment Fig. 1a a linear polarizer 11 is placed in front of, or forms part of a CRT screen 20. In front of polarizer 11 is a twisted nematic liquid crystal cell 12 having a 90 degree twist and the display is observed through linearly polarizing spectacle elements 13, 14. In the absence of an electric field across cell 12 as in Fig. 1a, the cell is optically active and rotates the plane of polarization by 90 degrees; hence the display is seen only by the left eye 15. When an electric field is applied the optical activity of the cell 12 is destroyed so that the display is seen only by the right eye 16. The application of the electric field is synchronized with the presentation of alternate images at a rate such that persistence of vision gives the illusion of a 3-D image. Separate polarizers 11 and cells 12 may be provided for each eye. In another embodiment Fig. 2a CRT 20 is covered with linearly polarizing material 21 in front of which is birefringent #/4 plate 27 oriented with 21 so that a circular polarizer is formed. Between 21 and 27 is placed a 90 degree twisted nematic liquid crystal cell 22 with one of its alignment directions parallel to the plane of polarization of 21. When no field is applied Fig. 2a cell 22 reverses the handedness of the circularly polarized light; when a field is applied the original handedness is unchanged. The display is observed through spectacle elements 23, 24 which are lefthanded and right-handed respectively. Cells 12, 22 comprise a thin layer of a nematic liquid crystal medium (e.g. a mixture of cyanobiphenyl hydrocarbon derivatives) sandwiched between electroded glass plates whose inner surfaces are treated so that the molecules of the liquid crystal medium that are in contact with the surfaces are aligned at right angles to one another. Other liquid crystal devices (cholesteric or smectic) or combinations of them may be used.