Stacked color photodisplay
First Claim
1. A stacked photodisplay comprising:
- at least first and second liquid crystal layers of cholesteric liquid crystal material stacked in a fixed relation to each other including a first and a second photosensitive chiral additive, respectively;
wherein said first liquid crystal layer comprises exposed regions that have been exposed to electromagnetic radiation including said first photosensitive chiral additive of a twisting power, and unexposed regions that have not been exposed to said electromagnetic radiation, said unexposed regions including said first photosensitive chiral additive of a different twisting power than in said exposed regions;
wherein said second liquid crystal layer comprises exposed regions that have been exposed to electromagnetic radiation including said second photosensitive chiral additive of a twisting power, and unexposed regions that have not been exposed to said electromagnetic radiation, said unexposed regions including said second photosensitive chiral additive of a different twisting power than in said exposed regions;
electrically conductive layers disposed on both sides of each of said first and second liquid crystal layers;
a light absorbing layer positioned to absorb light passing through said first and second liquid crystal layers;
wherein said first liquid crystal layer includes a first fixed image portion and said second liquid crystal layer includes a second fixed image portion that is different than said first fixed image portion, wherein each of said first fixed image portion and said second fixed image portion comprises one of said exposed regions and said unexposed regions in a planar texture and the other one of said exposed regions and said unexposed regions in a focal conic texture so as to resist degradation over time, wherein said first and second fixed image portions combine to form an image on said photodisplay.
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Abstract
The invention comprises a stacked color photodisplay apparatus using a photosensitive cholesteric liquid crystalline material on which an image can be optically addressed, retained without degradation for an indefinite period of time, electrically erased and a new image addressed. This is similar to a photographic film except that the photodisplay film can be used over and over again similar to digital display but without the cost of addressing electronics. Included is a device for enhancing the brightness of the image and electrooptical devices for optically writing digital images on the photodisplay. Each cell in the stack can be selectively addressed with a different optical image such as the red, green and blue components of a color digital image.
150 Citations
38 Claims
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1. A stacked photodisplay comprising:
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at least first and second liquid crystal layers of cholesteric liquid crystal material stacked in a fixed relation to each other including a first and a second photosensitive chiral additive, respectively; wherein said first liquid crystal layer comprises exposed regions that have been exposed to electromagnetic radiation including said first photosensitive chiral additive of a twisting power, and unexposed regions that have not been exposed to said electromagnetic radiation, said unexposed regions including said first photosensitive chiral additive of a different twisting power than in said exposed regions; wherein said second liquid crystal layer comprises exposed regions that have been exposed to electromagnetic radiation including said second photosensitive chiral additive of a twisting power, and unexposed regions that have not been exposed to said electromagnetic radiation, said unexposed regions including said second photosensitive chiral additive of a different twisting power than in said exposed regions; electrically conductive layers disposed on both sides of each of said first and second liquid crystal layers; a light absorbing layer positioned to absorb light passing through said first and second liquid crystal layers; wherein said first liquid crystal layer includes a first fixed image portion and said second liquid crystal layer includes a second fixed image portion that is different than said first fixed image portion, wherein each of said first fixed image portion and said second fixed image portion comprises one of said exposed regions and said unexposed regions in a planar texture and the other one of said exposed regions and said unexposed regions in a focal conic texture so as to resist degradation over time, wherein said first and second fixed image portions combine to form an image on said photodisplay. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. An apparatus for writing on a photodisplay, the photodisplay including two or three layers of cholesteric liquid crystal material stacked relative to each other each including a photosensitive chiral additive, electrically conductive layers flanking each of said liquid crystal layers and a light absorbing layer positioned to absorb light passing through said liquid crystal layers, said apparatus comprising:
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a controller adapted to provide electronic image data signals corresponding to image data and to provide electronic light source signals; an electronic display device including a plurality of pixels adapted to form images when said pixels are in ON or OFF states; a display driver adapted to supply voltage pulses to said display device in response to said image data signals from said controller effective to independently place said pixels of said display device in said ON or OFF states; a light source adapted to be energized or de-energized in response to said light source signals from said controller effective to project ultraviolet light through said display device onto said photodisplay; wherein when said light source is energized to produce ultraviolet light and said display driver applies said voltage pulses forming the image on said display device the ultraviolet light passing through the image of said display device addresses said photodisplay with an image portion formed of optically addressed regions at a first twisting power and optically unaddressed regions at a second twisting power; and a pulse driver adapted to apply fixing voltage pulses to said electrically conductive layers flanking a selected one of said liquid crystal layers effective to form a fixed image portion by placing one of said optically addressed or optically unaddressed regions of said selected layer in a focal conic texture that is stable in an absence of an electric field and the other of said optically addressed or optically unaddressed regions of said selected layer in a planar texture, said pulse driver being further adapted to apply erasing pulses that erase each said fixed image portion from said photodisplay. - View Dependent Claims (21, 22, 23, 24)
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25. A method of optically writing on a stacked color photodisplay comprising
a) providing a photodisplay including two or three layers of cholesteric liquid crystal material stacked on each other, said liquid crystal layers each comprising nematic liquid crystal and a photosensitive chiral additive that is adapted to be reversibly changed between a first twisting power and a second twisting power, said liquid crystal material of said liquid crystal layers having a pitch length effective to reflect light of different predetermined colors in ambient light, electrically conductive layers disposed on both sides of each of said liquid crystal layers, and a light absorbing layer that absorbs light passing through said liquid crystal layers; -
b) projecting electromagnetic radiation to address said photodisplay with an image portion formed of optically addressed regions where said photosensitive additives are at said first twisting power and optically unaddressed regions where said photosensitive additives are at said second twisting power, said first twisting power being different from said second twisting power; c) applying fixing voltage pulses to said electrically conductive layers disposed on both sides of a selected one of said liquid crystal layers effective to form a fixed image portion that resists degradation over time by placing one of said optically addressed or optically unaddressed regions of said selected layer in a focal conic texture that is stable in an absence of an electric field and the other of said optically addressed or optically unaddressed regions of said selected layer in a planar texture; d) erasing all images from said photodisplay except for said fixed image portions; and e) repeating steps c) and d) until said photodisplay reflects a fixed image comprising an additive mixture of two or three different said fixed image portions each being at said predetermined colors. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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Specification