Color display using supertwisted nematic liquid crystal material

• US 5,050,965 A
• Filed: 11/22/1989
• Issued: 09/24/1991
• Est. Priority Date: 09/01/1989
• Status: Expired

• Current Assignee: InFocus Corporation (Lap-Shun Hui, MBA)
• Original Assignee: InFocus Corporation (Lap-Shun Hui, MBA)
• Inventors: Conner, Arlie R., Gulick, Paul E.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/445,769
• Time in Patent Office: 671 Days
• Field of Search: 350/335, 350/337, 350/334, 350/339 F, 350/347 E, 350/347 V, 350/339 R
• US Class Current: 349/6
• CPC Class Codes: G02F 1/133524 Light-guides, e.g. fibre-optic bundles, louvered or jalousie light-guides
• CPC Class Codes: G02F 1/133526 Lenses, e.g. microlenses or Fresnel lenses
• CPC Class Codes: G02F 1/133533 Colour selective polarisers G02F1/1347 takes precedence
• CPC Class Codes: G02F 1/134336 Matrix
• CPC Class Codes: G02F 1/13473 for wavelength filtering or for colour display without the use of colour mosaic filters
• CPC Class Codes: G06F 1/1601 Constructional details related to the housing of computer displays, e.g. of CRT monitors, of flat displays constructional details related to flat displays integrated in a portable computer, e.g. laptop, handheld computer G06F1/1637; constructional details related to television receivers H04N5/64
• CPC Class Codes: G06F 1/1613 for portable computers cooling arrangements therefor G06F1/203; constructional details or arrangements for pocket calculators, electronic agendas or books G06F15/0216; constructional details of portable telephone sets: with several bodies H04M1/0202
• CPC Class Codes: G06F 1/1615 with several enclosures having relative motions, each enclosure supporting at least one I/O or computing function constructional details of portable telephones comprising a plurality of mechanically joined movable body parts H04M1/0206
• CPC Class Codes: G06F 1/1616 with folding flat displays, e.g. laptop computers or notebooks having a clamshell configuration, with body parts pivoting to an open position around an axis parallel to the plane they define in closed position
• CPC Class Codes: G06F 1/1639 the display being based on projection
• CPC Class Codes: G06F 1/1645 the display being suitable to be used in combination with an external overhead projector
• CPC Class Codes: G06F 1/203 for portable computers, e.g. for laptops
• CPC Class Codes: G06F 2200/1612 Flat panel monitor

Abstract

A color display is formed by stacking two or more birefringent elements that are tuned to provide different spectral characteristics, and operating each of the elements independently.

Claims

1. A method of producing a color display comprising:

providing first and second optical assemblies, each assembly including a plurality of independently operable pixels, each of said pixels exhibiting a birefringent effect that varies in response to a signal applied thereto;

stacking said assemblies with a pixel in the first assembly linearly aligned with a corresponding pixel in the second assembly;

interposing a first polarizer between the assemblies and sandwiching the stack between a second and a third polarizer wherein said second and third polarizers are colored complementary colors; and

applying a first dynamic signal to the pixels in the first assembly and applying a second dynamic signal to the pixels in the second assembly so as to selectively change the birefringent effect.

2. The method of claim 1 which includes providing a supertwisted nematic liquid crystal panel in each of said first and second optical assemblies.

3. The method of claim 1 which further includes enhancing display brightness by interposing a polarizer dyed a color other than black between the assemblies.

4. The method of claim 1 further comprising:

applying said first dynamic signal to said pixels in the first assembly wherein said first dynamic signal changes selectively and periodically between more than two values so that said second dynamic signal differs from said first signal thereby producing more than two distinct birefringent effects.

5. The method of claim 1 wherein each assembly has a value of Δ

nd greater than 0.05 μ

m and is individually tuned to produce a different plurality of colors in cooperation with additional layers of birefringent material and said polarizers to produce a wider voltage variable coloration effect.

6. A display subassembly comprising:

first, second and third supertwisted nematic birefringent liquid crystal display panels;

first, second, third and fourth polarizers;

the first panel being positioned between the first and second polarizers, the second panel being positioned between the second and third polarizers and the third panel being positioned between the third and fourth polarizers;

the birefringence of the first, second and third panels, together with the polarizers adjacent thereto, cooperating to pass light of first, second and third colors, respectively, when the panels are in first states, and to pass substantially all colors of light when the panels are in second states;

each of said panels having a plurality of independently electronically operable pixels, said panels being stacked so that corresponding pixels in each of said panels are aligned; and

at least said first or said fourth polarizers is a color other than black so as to increase display brightness.

7. The display subassembly of claim 6 wherein said second polarizer colored a color common to said first and second colors of light passed by said first and second panels in the first state.

8. The display subassembly of claim 6 wherein said third polarizer is colored a color common to said second and third colors of light passed by said second and third panels in the first state.

9. The display subassembly of claim 6 in which the first, second and third colors are each subtractive primary colors.

10. A color display that can be operated to yield at least the colors black, white, red, green, blue, cyan, yellow and magenta comprising:

an entrance and exit polarizer, each polarizer dyed a color other than black and at least a first and second birefringent subassembly disposed between said polarizers in a stacked relationship, each of said subassemblies defining a plurality of pixels, each of said pixels being independently operable to birefringently control passage of a portion of a spectrum of light passing therethrough, and wherein at least two of said subassemblies each includes a supertwisted nematic panel.

11. The display of claim 10 wherein said supertwisted nematic panels have substantially equal values of Δ

nd and a third neutral polarizer disposed between said firs and second subassemblies.

12. The display of claim 11 in which the first and second subassemblies are stacked without an intervening polarizer.

13. The display of claim 11 in which the first and second subassemblies are stacked with an intervening polarizer therebetween.

14. The display of claim 13 in which the intervening polarizer is dyed a color other than black.

15. The display of claim 10 in which a supertwisted nematic panel in a first of the subassemblies has a different value of Δ

nd than a supertwisted panel in a second of the subassemblies.

16. The display of claim 15 in which the first and second subassemblies are stacked without an intervening polarizer.

17. The display of claim 15 in which the first and second subassemblies are stacked with an intervening polarizer therebetween.

18. The display of claim 17 in which said intervening polarizer is dyed a color other than black.

19. The display of claim 10 further comprising a third subassembly wherein, at least two of said three subassemblies include supertwisted nematic panels each with a substantially equal value of Δ

nd.

20. The display of claim 10 further comprising a third subassembly wherein, each of said subassemblies includes a supertwisted nematic panel and each of said panels has a substantially equal value of Δ

nd.

21. The display of claim 20 in which at least two of said subassemblies comprise a birefringent LCD panel and at least a passive compensation layer.

22. The display of claim 21 further comprising means for grey scaling said display to yield more than eight colors.

23. The display of claim 10 in which at least one of the subassemblies includes a passive compensation layer.

24. The display of claim 10 further comprising means for grey scaling said display to yield more than eight colors.

26. The method of claim 23 in which:

the providing step includes providing a third display subassembly, said third subassembly including a supertwisted nematic birefringent panel and a fourth polarizer;

the stacking step includes stacking said third subassembly with the first and second subassemblies whereby said third display subassembly is disposed between said third and fourth polarizers;

the operating step including operating pixels in the third panel to birefringently control passage of a portion of a spectrum of light passing therethrough in cooperation with said third and fourth polarizers; and

the grey scaling step including grey scaling each of the three supertwisted nematic panels.

27. The method of claim 26 in which the providing step includes providing first, second and third display subassemblies, each of said subassemblies including supertwisted nematic birefringent panels with the same values of Δ

nd, and at least two of said subassemblies each including a passive compensation layer.

25. A color display method comprising the steps:

providing first and second display subassemblies, each of said assemblies including a supertwisted nematic birefringent panel, each of said panels defining a plurality of independently operable pixels, at least one of said display subassemblies additionally including a passive compensation layer to tune the color response thereof;

stacking said subassemblies with a first polarizer therebetween, said first polarizer being dyed a color other than a color intended to be blocked by said first subassembly;

sandwiching the stacked subassemblies between second and third polarizers;

operating pixels in each of the panels independently to birefringently control passage of a portion of a spectrum of light passing therethrough in cooperation with said first, second and third polarizers, wherein at least the eight colors black, white, red, green, blue, cyan, yellow and magenta may thereby be displayed; and

controllably grey scaling at least one of the supertwisted nematic panels to yield colors in addition to the aforesaid eight colors.

28. An accessory for use with a conventional overhead projector to project electronically generated color images therefrom, the projector having a bulb, a projection lens, and a projection surface having a Fresnel lens thereunder, the Fresnel lens focusing light from the bulb into the projection lens, the accessory being adapted to rest on the projection surface and comprising:

first lens means for receiving converging white light from the projection surface of the projector and collimating said light;

second lens means for receiving collimated light and focusing said light into the projection lens;

a display subassembly positioned between the first and second lens means and illuminated by the collimated light, said subassembly including first, second, third and fourth polarizers and further including first, second and third transmissive liquid crystal birefringent display panels, the birefringence of said panels being tuned, respectively, to first, second and third subtractive complementary colors, each of said panels having a plurality of electronically operable pixels, said panels being stacked so that corresponding pixels in each of said panels are aligned with the direction of the collimated light, the first panel being positioned between the first and second polarizers, the second panel being positioned between the second and third polarizers and the third panel being positioned between the third and fourth polarizers.

29. The accessory of claim 28 in which the first polarizer is colored the first color.

30. The accessory of claim 29 in which the fourth polarizer is colored the third color.

31. The accessory of claim 28 in which the second polarizer is colored a color other than the first or second color or black.

32. The accessory of claim 28 in which:

the first polarizer is colored the first color;

the fourth polarizer is colored the third color;

the second polarizer is colored a color passed by both the first and second panels; and

the third polarizer is colored a color passed by both the second and third panels.

33. The accessory of claim 28 in which:

one of the panels is yellow;

one of the panels is cyan;

one of the panels is magenta;

the colors of the first and fourth polarizers are selected from the list;

yellow, cyan, magenta and black; and

the colors of the second and third polarizers are selected from the list;

red, green, blue and black;

wherein each of the polarizers is colored differently.

34. A method of projecting a colored image, comprising the steps:

providing first, second and third birefringent liquid crystal panels that include a plurality of independently selectable pixels, said panels being tuned to selectively pass first, second and third subtractive color primaries, respectively, when a signal is applied to each panel;

stacking said first, second and third panels so that corresponding pixels in each of said panels are aligned along an axis orthogonal thereto, said stacked panels forming a subassembly;

providing a first polarizer between the first and second panels;

providing a second polarizer between the second and third panels; and

sandwiching said subassembly and said first and second polarizers between a third polarizer, colored the first subtractive primary color, and a fourth polarizer, colored the third subtractive primary color;

passing light through the subassembly in a direction parallel to the axis of alignment and selectively controlling spectral portions of said light when a signal is applied to pixels on at least one of said panels;

focusing the light exiting the subassembly parallel to the axis of alignment into a projection lens; and

projecting the light exiting the projection lens onto a display screen.

35. The method of claim 34 which further includes the step of collimating the light parallel to the axis of alignment of the panels prior to passage into the subassembly.

36. A color display comprising:

first and second optics;

first, second and third display subassemblies disposed between said optics;

each of said display subassemblies including a liquid crystal panel defining a plurality of independently operable pixels wherein at least two of said three liquid crystal panels control color through use of a birefringence effect and wherein at least two of said display subassemblies have different values of Δ

nd;

first, second, third and fourth polarizers, at least one of said four polarizers dyed a color other than black;

said first display subassembly disposed between the first and second polarizers;

said second display subassembly disposed between the second and third polarizers; and

said third display subassembly disposed between the third and fourth polarizers.

37. The color display of claim 36 in which the liquid crystal panels each comprises supertwisted nematic liquid crystal panels.

38. The color display of claim 36 in which at least one of the display subassemblies includes:

a birefringent liquid crystal panel;

a first passive layer that minimizes the birefringent effect exhibited by the birefringent liquid crystal panel; and

a second passive layer that introduces a birefringent effect.

39. The color display of claim 36 in which at least one of said four polarizers is colored a color other than black.

40. The color display of claim 36 in which one of said display subassemblies operates, in conjunction with the polarizers adjacent thereto, to pass all colors of light in a first state and to pass all colors of light except blue in a second state.

41. The color display of claim 36 in which:

at least one of said four polarizers is colored a color other than black;

one of said display subassemblies operates, in conjunction with the polarizers adjacent thereto, to pass all colors of light in a first state and to pass all colors of light except blue in a second state.

42. The color display system of claim 41 in which said first optic comprises a Fresnel lens adapted to collimate converging light introduced thereto, and the second optic comprises a Fresnel lens adapted to cause said collimated light exiting therefrom to substantially converge.

43. A color display according to claim 42 that is operable to produce at least the colors black, white, red, green, blue, cyan, yellow and magenta.

44. The color display of claim 36 in which the first optic includes a mirror, and the second optic includes a translucent screen having a back surface on which an image can be displayed and a front surface from which the image can be viewed, said screen being disposed about a spring loaded roller from which it can be unrolled for use and rolled for storage.

45. A method of producing a color display comprising the steps:

collimating illuminating light;

linearly polarizing said collimated light with a first polarizer;

passing said collimated polarized light through a first display subassembly that includes a liquid crystal panel with a plurality of independently operable pixels;

said passing step including elliptically polarizing the linearly polarized light so that different wavelengths of light are rotated to different angular orientations;

analyzing light exiting the first display subassembly with a second polarizer to attenuate therefrom wavelengths of light cross polarized relative to the second polarizer, said analyzing step thereby yielding linearly re-polarized light from which certain wavelengths have been attenuated;

passing said linearly re-polarized light through a second display subassembly that includes a liquid crystal panel with a plurality of independently operable pixels;

said second passing step including elliptically polarizing the linearly re-polarized light so that different wavelengths of light are rotated to different angular orientations;

analyzing light exiting the second display subassembly with a third polarizer to attenuate therefrom wavelengths of light cross polarized relative to the third polarizer, this analyzing step thereby yielding linearly polarized light from which additional wavelengths have been attenuated; and

converging the linearly polarized light from the third polarizer;

wherein;

the elliptical polarization effected during the first passing step differs from elliptical polarization effected during the second passing step due to different values of Δ

nd exhibited by the first and second display subassemblies; and

at least one of said first, second or third polarizers is dyed a color other than black;

and the method further includes;

applying a first dynamic signal to a pixel in the first liquid crystal panel; and

applying a second dynamic signal different from the first dynamic signal to a pixel in the second liquid crystal panel.

46. The method of claim 45 which further includes independently varying the first and second dynamic signals among more than two values.

47. The method of claim 45 in which the passing steps each further includes passing light through a supertwisted nematic liquid crystal panel.

48. The method of claim 45 in which at least one of the passing steps includes passing light through:

a birefringent liquid crystal panel;

a first passive layer that minimizes the birefringent effect exhibited by the birefringent liquid crystal panel; and

a second passive layer that introduces a birefringent effect.

49. A color display comprising, in combination:

first and second display subassemblies each having a net Δ

nd value greater than 0.5 μ

m, each including a liquid crystal panel defining a plurality of independently operable pixels, which exhibit a birefringent effect that varies in response to a signal applied thereto, said first subassembly having a net Δ

nd value at least 0.05 μ

m greater than the net Δ

nd value of the second subassembly;

a first polarizer interposed between the two display subassemblies; and

a second and a third polarizer sandwiched about the two display subassemblies wherein at least one of the first, second or third polarizers is colored a color other than black.

50. The color display of claim 49 in which the first and second liquid crystal panels are each supertwisted nematic liquid crystal panels.

51. The color display of claim 49 in which at least one of the first and second liquid crystal panels comprise:

a birefringent liquid crystal panel;

a first passive layer that minimizes the birefringent effect exhibited by the birefringent liquid crystal panel; and

a second passive layer that introduces a birefringent effect.

52. The color display of claim 49 which further comprises:

a third display subassembly having a net Δ

nd value at least 0.05 μ

m greater than the net Δ

nd values of the first and second panels;

said third display subassembly including a liquid crystal panel and defining a plurality of independently operable pixels;

a fourth polarizer; and

said third display subassembly interposed between the third and fourth polarizers;

wherein;

all three of the subassemblies have Δ

nd values greater than 0.5 μ

m.

53. A subtractive color display method that includes the steps:

providing a birefringent display subassembly that includes a nematic liquid crystal cell and that defines a plurality of independently operable pixels, wherein a birefringent effect exhibited by one of said pixels varies in response to an electrical signal applied thereto;

operating the display subassembly in conjunction with entrance and exit polarizers;

linearly polarizing light entering the pixel by passing it through the entrance polarizer;

elliptically polarizing said linearly polarized light as it passes through the pixel, whereby different wavelengths of light are oriented at different angular orientations when they exit the pixel, the elliptical polarization when a first electrical signal is applied to said pixel differing from the elliptical polarization when a second electrical signal is applied to said pixel;

analyzing the elliptically polarized light exiting the pixel so that light oriented orthogonally to an axis of the exit polarizer is attenuated by the exit polarizer;

wherein;

when the first electrical signal is applied to the pixel, the birefringence of the pixel orients a first wavelength of light orthogonally to the axis of the exit polarizer, thereby causing its attenuation by the exit polarizer; and

when the second electrical signal is applied to the pixel, the different birefringence of the pixel orients the first wavelength of light so that it is no longer oriented orthogonally to the axis of the exit polarizer, thereby permitting it to pass through the exit polarizer relatively less attenuated;

wherein the exit polarizer is dyed to pass wavelengths of light, other than the first wavelength, relatively unattenuated regardless of their orientation, thereby improving the transmission of said wavelengths of light and optimizing the resulting display brightness of the subtractive color display.

54. A subtractive color display method that includes the steps:

providing a birefringent display subassembly that includes a nematic liquid crystal cell and that defines a plurality of independently operable pixels, wherein a birefringent effect exhibited by one of said pixels varies in response to an electrical signal applied thereto;

operating the display subassembly in conjunction with entrance and exit polarizers;

linearly polarizing light of a first wavelength entering the pixel by passing it through the entrance polarizer;

elliptically polarizing light as it passes through the pixel, whereby different wavelengths of light are oriented at different angular orientations when they exit the pixel, the elliptical polarization when a first electrical signal is applied to said pixel differing from the elliptical polarization when a second electrical signal is applied to said pixel;

analyzing the elliptically polarized light exiting the pixel so that light oriented orthogonally to an axis of the exit polarizer is attenuated by the exit polarizer;

wherein;

when the first electrical signal is applied to the pixel, the birefringence of the pixel orients the first wavelength of light orthogonally to the axis of the exit polarizer, thereby causing its attenuation by the exit polarizer; and

when the second electrical signal is applied to the pixel, the different birefringence of the pixel orients the first wavelength of light so that it is no longer oriented orthogonally to the axis of the exit polarizer, thereby permitting it to pass through the exit polarizer relatively less attenuated;

wherein the entrance polarizer is dyed to pass wavelengths of light, other than the first wavelength, relatively unattenuated regardless of their orientation, thereby improving the transmission of said wavelengths of light and optimizing the resulting display brightness of the subtractive color display.

55. In a color display system comprising:

a first, second and third polarizer;

first and second cells comprising supertwisted nematic type liquid crystal material, said cells exhibiting a birefringent effect and having different values of Δ

nd, said cells having a plurality of independently operable pixels and disposed in a stacked arrangement with said polarizers;

said first polarizer interposed between said first and second cells and said second and third polarizers disposed outside the stacked arrangement adjacent to said first and second cells, respectively, whereby said first cell in cooperation with said first and second polarizers provides spectral response different from said second cell in cooperation with said first and third polarizers.

56. The color display system of claim 55 further comprising a passive compensation layer adjacent to one of said cells.

57. The color display system of claim 55 which further includes at least two polarizers adjacent different surfaces of the first and second portions, each of said two polarizers being dyed a color other than black.

58. A color display system comprising:

a first and second portion in stacked arrangement;

each portion including an optical element defining a plurality of independently operable pixels and exhibiting a birefringent effect that varies in response to an applied signal;

a first polarizer interposed between said first and second portion;

a second and third polarizer sandwiched about said stacked portions, said second and third polarizers colored a color other than black so that the leakage characteristics of said second and third polarizers do not overlap;

the first portion, in combination with said first and second polarizers, exhibits a first spectral response when driven with a first signal; and

the second portion, in combination with said first and third polarizers, exhibits a second spectral response when driven with the first signal.

59. The color display system of claim 58 in which the portions exhibit different spectral responses and different values of Δ

nd, each of which is greater than 0.50 μ

m;

60. The color display system of claim 58 in which the different spectral responses are achieved by inclusion of a passive optical element in one of said portions.

61. The color display system of claim 60 in which the passive element is a retardation film.

62. A color display comprising:

first and second stacked birefringent display subassemblies, each having a supertwisted nematic liquid crystal panel defining a plurality of independently operable pixels, said first and second display subassemblies stacked so that corresponding pixels in each of said subassemblies are linearly aligned, at least one of said display subassemblies having a value of Δ

nd greater than 1.05 micrometers;

a first polarizer disposed between said first and second subassemblies;

second and third polarizers sandwiched about said first and second subassemblies, said second and third polarizers colored different primary colors selected from the list;

red, green and blue whereby each pair of corresponding pixels in the first and second display subassemblies can be cooperatively operated to produce all the colors comprising red, green, blue, yellow, magenta, cyan, black and white.

63. The color display of claim 62 wherein:

the first and second display subassemblies each includes a supertwisted nematic panel;

at least one of said display subassemblies exhibits a value of Δ

nd greater than 1.05 micrometers; and

each pair of corresponding pixels in the first and second display subassemblies can be cooperatively operated to produce all the primary and secondary colors (red, green, blue, yellow, magenta and cyan), together with black and white;

wherein a true, eight color display can be produced with a stack of just two liquid crystal panels.

64. The color display of claim 63 wherein:

at least one of the display subassemblies exhibits a value of Δ

nd greater than 1.15 micrometers.