Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1993-07-16
1995-05-16
Sikes, William L.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359452, 359449, 359443, 359265, 359267, G02F 113, G02F 115, G03B 2160
Patent
active
054166179
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a diffusing display screen, and more particularly an image projection display screen which can be used in particular in the field of high-definition television.
In fact, in this field, it is currently sought to obtain images whose dimensions are of the order of one square meter, it being possible to satisfy such a constraint by resorting to projection devices comprising cathode ray tubes or liquid crystal matrices in which the observer and the images are on the same side of the display screen.
FIG. 1 illustrates one embodiment of this type of image projector, in which the display screen constitutes an element which independent of the projector, which makes it possible to display an image whose size may be variable. It is composed of a collimated light source, of reflecting mirrors M.sub.R and of dichroic mirrors Md capable of reflecting selectively red, green and blue, as well as lenses (L) coupled with liquid crystal matrices (CL) making it possible to modulate the red, green or blue light intensities. The colour light beams are recombined, then sent to a projection objective (OP) capable of projecting the image thus constituted onto a display screen, the observer being situated between the projector and the display screen, and receiving the images reflected from the display screen. Since the display screen is not integrated with the projector, it is therefore necessary for the user to be equipped with a projector and with an independent display screen. However, the use of a display screen requires either that it be stored and be brought out solely when it is to be used, or that sufficient free space be made available to keep his display screen permanently in operating mode. In order to overcome this problem, the invention provides a device which allows the use of any transparent or non-transparent surface (window or wall) as the diffusing display screen.
For this purpose, a display screen according to the invention is placed on the surface of non-specific nature, which screen is capable of being transparent outside operating mode (allowing light to pass in the case of a window, or the wall decoration, in the case of a wall), and becoming reflecting (an advantage over conventional diffusing display screens) and diffusing like conventional display screens, in operating mode. When this type of display screen according to the invention is fixed to a window, it can advantageously be used as a shutter making it possible to isolate a subject from the outside without thereby creating a darkened zone, since the background light can be backscattered from the window which has become diffusing. The invention thus provides a diffusing display screen characterised in that it is obtained from the combination: which are dispersed microballs laid out parallel to the plane of the film, these microballs containing oblong and birefringent liquid crystal molecules of extraordinary index n.sub.e such that n.sub.e is equal to n.sub.p ; (E.sub.c), both the cells (C.sub.1) and (C.sub.2) being fixed onto a surface (S).
As shown by FIGS. 2a (transparent state) and FIGS. 2b (diffusing state), it is possible with this type of material to obtain the two desired states. In fact, it is possible to manufacture polymer films in which are dispersed balls of liquid crystal. FIG. 2a illustrates a film of polymer with dispersed liquid crystal (PDLC) at rest. The balls dispersed in the polymer may contain particles of liquid crystal, a nematic is preferably chosen which has oblong particles which are oriented parallel to a privileged axis (diagrammatically represented in FIG. 2a by the direction x). The ellipsoid of the indices of such molecules does not have symmetry of revolution, and two optical indices are conventionally defined, the ordinary optical index n.sub.o in a direction perpendicular to the long axis of the molecule, and the extraordinary index n.sub.e in a parallel direction. The manufacture of the films conventionally generates microballs laid-out parallel to the plane of the film, in which the nematic
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Huignard Jean-Pierre
Loiseaux Brigitte
Oppenlander Andreas
Robin Philippe
"Thomson-CSF"
Parker Kenneth
Sikes William L.
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