Method and apparatus utilizing waveguide and polarized light for display of dynamic images

• US 4,822,145 A
• Filed: 05/14/1986
• Issued: 04/18/1989
• Est. Priority Date: 05/14/1986
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Staelin, David H.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Mai, Huy Kim
• Application Number:
  US06/863,122
• Time in Patent Office: 1,070 Days
• Field of Search: 350/345, 350/338, 350/334, 350/345, 350/339 R, 362/31
• US Class Current: 349/63
• CPC Class Codes: G02F 1/1326 Liquid crystal optical waveguides or liquid crystal cells specially adapted for gating or modulating between optical waveguides
• CPC Class Codes: G02F 1/133616 Front illuminating devices
• CPC Class Codes: G09F 13/0472 Traffic signs
• CPC Class Codes: G09F 9/35 being liquid crystals G09F9/302 takes precedence; liquid crystal materials C09K19/00; liquid crystal panels comprising a number of electrodes in a single cell per se G02F1/13

Abstract

A visual display device is disclosed in which a liquid crystal cell is adjacent a light waveguide. Electrodes in the liquid crystal cell alter the dielectric constant therein to change the critical angle defined by the two media of the cell and the waveguide to regulate the amount and location of light which may escape from the waveguide. Color display can be obtained with visible light by providing a dyed layer and with ultraviolet light by providing colored ultraviolet phosphors. A shaped mirror or contoured reflective layer is provided with a visible light device to cause the displayed light to scatter in desired directions.

Claims

1. A visual display device having a viewing side, said device comprising:

a light waveguide having a viewing face adjacent to the viewing side of said display device, and an oppositely located rear face;

an array of liquid crystal cells adjacent to the rear face of said waveguide, each cell including a dielectric layer and a pair of electrodes on opposite faces of said layer, said dielectric layer having a dielectric constant to define a critical angle relative to the normal to said rear face such that above said critical angle light will remain trapped within said light waveguide; and

means for changing the voltage level across any of said pairs of electrodes to change said critical angle so that light may escape from said light waveguide and through the liquid crystal cell between said pair of electrodes so as to be visible on the viewing side of said display device.

2. The visual display device of claim 1 further comprising means, located behind each of said liquid crystal cells, for dispersing said escaped light.

3. The display device of claim 2 wherein said dispersing means comprises a shaped mirror.

4. The display device of claim 3, further comprising a layer of dye adjacent said mirror for providing a color display.

5. The display device of claim 2 wherein said dispersing means comprises ultraviolet phosphors and said light trapped within said light waveguide is ultraviolet.

6. The display device of claim 1 further comprising a light source for supplying said light waveguide with light at an angle greater than a minimum critical angle.

7. The display device of claim 6 wherein said light source comprises means for directing ambient light into said light waveguide.

8. The display device of claim 7 wherein said directing means is a cylindrical lens.

9. The display device of claim 6 wherein said light source comprises a fluorescent bulb.

10. The display device of claim 6 wherein said light source includes means for supplying polarized light to said light waveguide.

11. The display device of claim 1 further comprising an antireflection sheet overlying the viewing face of said light waveguide.

12. A visual display device comprising:

a light waveguide having a front face and a rear face;

an array of liquid crystal cells overlying the front face of said waveguide, each cell including a dielectric layer and a pair of transparent electrodes on opposite faces of said layer, said dielectric layer having a dielectric constant to define a critical angle relative to the normal to said front face, said critical angle being the angle above which light will remain trapped within said waveguide;

means for changing the voltage level across any of said pairs of electrodes to change said critical angle so that previously trapped light may escape said light waveguide through the liquid crystal layer between said pair of electrodes; and

a grooved surface overlying said array of liquid crystal cells for directing said escaped light, said grooved surface having a plurality of transparent surfaces facing in one direction alternately positioned with a plurality or mirror surfaces facing in a second direction.

13. The display device of claim 12 wherein said mirror surfaces have a light absorbing layer on their rear side facing the light waveguide.

14. The display device of claim 12 wherein said plurality of transparent surfaces comprise anti-reflection transformer plates.

15. The display device of claim 12 further comprising a light absorbing layer separated by a gap from said rear face of said light waveguide.

16. The display device of claim 12 further comprising means for supplying polarized light to said light waveguide.

17. A visual display device comprising:

a light source of ultraviolet light;

a waveguide having a front face and a rear face, for guiding ultraviolet light from said light source,

an array of liquid crystal cells overlying the front face of said waveguide, each cell including a dielectric layer and a pair of transparent electrodes on opposite faces of said layer, said dielectric layer having a dielectric constant to define a critical angle relative to the normal to said front face, said critical angle being the angle above which light will remain trapped within said light waveguide;

means for changing the voltage level across energizing any of said pairs of electrodes to change said critical angle so that previously trapped light may escape said light waveguide through the liquid crystal layer between said pair of electrodes; and

a layer of ultraviolet phosphors overlying said array of liquid crystal cells for producing visible light in response to said escaped ultraviolet light.

18. The display device of claim 17 further comprising a light absorbing layer separated by a gap from said rear face of said light waveguide.

19. A method for illuminating a visual display device comprising the steps of;

providing a light waveguide and an array of liquid crystal cells adjacent said waveguide;

directing polarized light through said waveguide at an angle such that said polarized light remains trapped within said light waveguide; and

changing the voltage level across a pair of electrodes in at least one of said liquid crystal cells to change the dielectric constant of said at least one liquid crystal cells so as to release polarized light from said light waveguide so that it is visible through said at least one liquid crystal cells.

20. A visual display device comprising:

a light waveguide;

means for supplying polarized light to said light waveguide;

an array off liquid crystal cells adjacent to said light waveguide, each cell including a dielectric layer and a pair of transparent electrodes on opposite faces of said layer, said dielectric layer having a dielectric constant to define a critical angle relative to the normal to a face of said layer, said critical angle being the angle above which said polarized light remains trapped within said light waveguide; and

means for changing the voltage level across any of said pairs of electrodes to change said critical angle so that previously trapped polarized light may escape said light waveguide through the liquid crystal layer between said pair of electrodes.

21. The visual display device of claim 20 further comprising means for directing said escaped light.

22. The visual display device of claim 21 wherein said means for directing said escaped light comprises a grooved surface, adjacent to said array of liquid crystal cells opposite from said light waveguide.

23. The visual display device of claim 22 wherein said grooved surface comprises a plurality of transparent surfaces facing in one direction alternately positioned with a plurality of mirror surfaces facing in a second direction.

24. The visual display device of claim 23 wherein said mirror surfaces have a light absorbing layer on their rear side facing the light waveguide.

25. The visual display device of claim 23 wherein said plurality of transparent surfaces comprise anti-reflection transformer plates.

26. The visual display device of claim 21 further comprising a light absorbing layer separated by a gap from said rear face of said light waveguide.

27. The visual display device of claim 20 further comprising a light source for limiting the supply of light to said light waveguide to light having an angle greater than a minimum critical angle.

28. The visual display device of claim 27 wherein said light source comprises means for directing ambient light into said light waveguide.

29. The display device of claim 28 wherein said means for directing ambient light comprises a cylindrical lens.

30. A visual display device comprising:

a light waveguide;

an array of liquid crystal cells adjacent to said light waveguide, each cell including a dielectric layer and a pair of transparent electrodes on opposite faces of said layer, said dielectric layer having a dielectric constant to define a critical angle relative to the normal to a face of said layer, said critical angle being the angle above which light remains trapped within said light waveguide;

means for directing ambient light into said light waveguide and limiting the supply of said ambient light to light having an angle greater than a minimum critical angle;

means for changing the voltage level across any of said pairs of electrodes to change said critical angle so that previously trapped light may escape said light waveguide through the liquid crystal layer between said pair of electrodes; and

means for directing said escaped light.

31. The visual display device of claim 30 wherein said means for directing said escaped light comprises a grooved surface, adjacent to said array of liquid crystal cells opposite from said light waveguide.