ELECTRO-OPTICAL DISPLAY DEVICE EMPLOYING LIQUID CRYSTALS

• US 3,666,881 A
• Filed: 12/28/1970
• Issued: 05/30/1972
• Est. Priority Date: 12/28/1970
• Status: Expired due to Term

• Current Assignee: Richard J. Stein
• Original Assignee: Richard J. Stein
• Inventors: Stein, Richard J.
• Primary Examiner(s): Richardson, Robert L.
• Assistant Examiner(s): Stellar, George G.
• Application Number:
  US05/101,602
• Time in Patent Office: 519 Days
• Field of Search: 178/5.4R,5.4BD,7.3D,7.5D,DIG.8 350/16LC 250/213R,199 313/89,91
• US Class Current: 348/791
• CPC Class Codes: G02F 1/1347 Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
• CPC Class Codes: G02F 1/13475 in which at least one liquid crystal cell or layer is doped with a pleochroic dye, e.g. GH-LC cell G02F1/13476 takes precedence
• CPC Class Codes: G02F 1/135 Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied G02F1/133348 takes precedence
• CPC Class Codes: G02F 1/13725 based on guest-host interaction G02F1/13762, G02F1/13737, take precedence

Abstract

An electro-optical display system comprises a display screen including one or more juxtaposed sets of nematic liquid crystal and photoconductive layers bounded by transparent electrodes. The screen is scanned by scanning light while modulated bias voltages are applied across the liquid crystal and photoconductive layers. Images appearing on the screen are viewable by reflected ambient light to which the photoconductive layers are transparent. Colored dyes mixed with the nematic liquid crystals result in colored images on the screen. Cholesteric liquid crystal mixed with the nematic liquid crystal retains the images on the screen for predetermined periods of time. The images are viewable at either side of the screen. The screen can be internally illuminated.

Claims

2. An electro-optical display system as defined in claim 1, wherein said screen is exposed to exciting illumination, the wavelength at which the photoconductive layer is responsive lying outside the range of wavelengths of said exciting illumination, so that said images become detectable in the presence of the exciting illumination and are undetectable in the absence of said exciting illumination.

3. An electro-optical display system as defined in claim 2, wherein said photoconductive layer is transparent to said exciting illumination so that said images are viewable at either side of said screen.

4. An electro-optical display system as defined in claim 2, wherein said liquid crystal layer comprises a cholesteric liquid crystal compound mixed with a nematic liquid crystal compound so that said images are retained by the liquid crystal layer for predetermined periods of time.

5. An electro-optical display system as defined in claim 1, wherein said screen further comprises a second photoconductive layer juxtaposed to said first electrically conductive layer, a second nematic liquid crystal layer juxtaposed to said second photoconductive layer, and a third transparent electrically conductive layer juxtaposed to said second liquid crystal layer;

and means for applying other modulated video signal bias voltages the first and third electrically conductive layers, both nematic liquid crystal layers containing respectively pleochroic dyes of different colors so that composite colored images corresponding to the bias voltages applied across the liquid crystal layers are formed in both liquid crystal layers at points scanned by the unmodulated scanning light.

6. An electro-optical display system as defined in claim 5, wherein both liquid crystal layers are exposed to ambient light, the wavelengths at which the photoconductive layers are responsive lying outside the range of wavelengths of said ambient light, so that the colored images become detectable in the presence of ambient light and are undetectable in the absence of ambient light.

7. An electro-optical display system as defined in claim 5, further comprising a cholesteric liquid crystal compound mixed with the nematic liquid crystal in at least one nematic liquid crystal layer so that the colored images are retained for predetermined periods of time.

8. An electro-optical display system as defined in claim 6, wherein said photoconductive layers are transparent to ambient light, so that the colored images are viewable at either side of said screen.

9. An electro-optical display system as defined in claim 1, wherein said screen further comprises a second photoconductive layer juxtaposed to said first electrically conductive layer, a second nematic liquid crystal layer juxtaposed to said second photoconductive layer, a third transparent electrically conductive layer juxtaposed to said second liquid crystal layer, a third photoconductive layer juxtaposed to the third electrically conductive layer, a third nematic liquid crystal layer juxtaposed to the third electrically conductive layer, and a fourth transparent electrically conductive layer juxtaposed to the third liquid crystal layer;

and means for applying further modulated video signal bias voltages across the first and third electrically conductive layers and across the third and fourth electrically conductive layers, all of the three liquid layers containing pleochroic dyes different in color from each other, so that composite colored images corresponding to the bias voltages applied across the liquid crystal layers are formed in the liquid crystal layers at points scanned by the scanning light.

10. An electro-optical display system as defined in claim 9, wherein the screen is exposed to ambieNt light, the wavelengths at which the photoconductive layers are responsive lying outside the range of wavelengths of said ambient light, so that the colored images become detectable in the presence of the ambient light and are undetectable in the absence of ambient light.

11. An electro-optical display system as defined in claim 9, wherein the photoconductive layers are transparent to ambient light so that the colored images are viewable at either side of said screen.

12. An electro-optical display system as defined in claim 9, further comprising a cholesteric liquid crystal compound mixed with the nematic liquid crystal of at least one of the liquid crystal layers so that the colored images are retained for predetermined periods of time.