Transflective displays with reflective polarizing transflector

• US 6,124,971 A
• Filed: 10/17/1997
• Issued: 09/26/2000
• Est. Priority Date: 06/26/1995
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Cobb, Sanford Jr., Weber, Michael F., Ouderkirk, Andrew J., Wortman, David L., Cull, Brian D.
• Primary Examiner(s): CHANG, AUDREY Y
• Application Number:
  US08/953,779
• Time in Patent Office: 1,075 Days
• Field of Search: 359/63, 359/70, 359/71, 359/68, 359/487, 359/490, 359/494, 359/498, 359/580, 359/584, 359/488, 359/493, 359/495, 359/496, 359/583, 349/114, 349/117, 349/62, 349/64, 349/96
• US Class Current: 359/485.03
• CPC Class Codes: B32B 27/36 comprising polyesters
• CPC Class Codes: G02B 5/3025 Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state G02B5/3008, G02B5/3016 take precedence
• CPC Class Codes: G02B 5/3033 in the form of a thin sheet or foil, e.g. Polaroid
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133545 Dielectric stack polarisers
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A transflector is described which increases efficiency and brightness under both ambient and supplemental lighting conditions in visual display applications. In one embodiment, the transflector includes a reflective polarizing element that reflects one polarization of light and transmits the other. In an alternate embodiment, the transflector includes a reflective polarizing element and a diffusing element such that the transflector diffusely reflects light of one polarization and transmits the other. The transflector is useful for both reflective and transflective liquid crystal displays.

Claims

1. A reflective display, comprising:

a light modulator provided to selectively alter a polarization state of polarized light passing through the light modulator;

a reflective polarizer positioned to receive light passing through the light modulator from a viewer side of the light modulator, the reflective polarizer reflecting light having

a first polarization state back through the light modulator and transmitting light having a second polarization state; and

a diffuser disposed between the light modulator and the reflective polarizer, the diffuser diffusing the light having the first polarization state reflected by the reflective polarizer prior to transmission back through the light modulator while substantially maintaining the first polarization state of the reflected light.

2. The reflective display of claim 1 further including a front dichroic polarizer positioned on a side of the light modulator opposite the reflective polarizer.

3. The reflective display of claim 2 wherein the transmission axis of the reflective polarizer is effectively aligned with a transmission axis of the front dichroic polarizer.

4. The reflective display of claim 3 further including a rear dichroic polarizer positioned between the light modulator and the diffuser.

5. The reflective display of claim 4 wherein the transmission axis of the reflective polarizer is effectively aligned with an extinction axis of the rear dichroic polarizer.

6. The reflective display of claim 5, wherein light of the second polarization state incident on the front dichroic polarizer which is transmitted through the light modulator such that its polarization state is rotated to the first polarization state is transmitted by the rear dichroic polarizer and reflected by the reflective polarizer,

and further wherein light of the second polarization state incident on the front dichroic polarizer which is transmitted through the light modulator such that its polarization is not rotated to the first polarization state is absorbed by the rear dichroic polarizer.

7. The reflective display of claim 3, wherein light of the second polarization state incident on the front dichroic polarizer which is transmitted through the light modulator such that its polarization state is rotated to the first polarization state is reflected by the reflective polarizer.

8. The reflective display of claim 7 further including an absorber positioned on a side of the reflective polarizer opposite the diffuser.

9. The reflective display of claim 8 wherein the absorber is a black absorber.

10. The reflective display of claim 8 wherein the absorber is an absorbing black ink.

11. The reflective display of claim 1 wherein the reflective polarizer further has an average relectance of at least 80% for light of the first polarization state incident normal to the reflective polarizer and an average reflectance of at least 80% for light of the first polarization state incident 60°

from normal to the reflective polarizer.

12. The reflective display of claim 1 wherein the reflective polarizer further has an average reflectance of at least 90% for light of the first polarization state incident normal to the reflective polarizer and an average reflectance of at least 90% for light of the first polarization state incident 60°

from normal to the reflective polarizer.

13. The reflective display of claim 1 wherein the reflective polarizer further has an average reflectance of at least 95% for light of the first polarization state incident normal to the reflective polarizer and an average reflectance of at least 90% for light of the first polarization state incident 60°

from normal to the reflective polarizer.

14. The reflective display of claim 1 wherein the reflective polarizer further has an average transmittance of at least 80% for light of the second polarization state incident normal to the reflective polarizer and an average transmittance of at least 80% for light of the second polarization state incident 60°

from normal to the reflective polarizer.

15. The reflective display of claim 1 wherein the reflective polarizer further has an average transmittance of at least 90% for light of the second polarization state incident normal to the reflective polarizer and an average transmittance of at least 90% for light of the second polarization state incident 60°

from normal to the reflective polarizer.

16. The reflective display of claim 1 wherein the reflective polarizer further has an average transmittance of at least 70% for light of the second polarization state incident normal to the reflective polarizer and an average transmittance of at least 70% for light of the second polarization state incident 60°

from normal to the reflective polarizer.

17. The reflective display of claim 1 wherein the reflective polarizer comprises a pluraity of layers.

18. The reflective display of claim 17 wherein a refractive index difference between at least two adjacent layers in a first in-plane direction of the reflective polarizer is greater than a refractive index difference between the at least two adjacent layers in a second in-plane direction.

19. The display of claim 1 further including a front dichroic polarizer disposed on the viewer side of the light modulator, and a supplemental light source disposed on a side of the light modulator opposing the viewer side, the display capable of generating an image under supplemental lighting conditions.

20. The display of claim 19 wherein the reflective polarizer and the front dichroic polarizer are aligned for optimal viewing under ambient lighting conditions.

21. The display of claim 19 wherein the reflective polarizer and the front dichroic polarizer are aligned for optimal viewing under supplemental lighting conditions.

22. The display of claim 19 wherein the transmission axis of the reflective polarizer is effectively aligned with a transmission axis of the front dichroic polarizer.

23. The display of claim 22 wherein the display has an appearance of dark pixels on a diffusely lit background under ambient lighting conditions.

24. The display of claim 22 wherein the display reverses image between ambient and supplemental lighting conditions.

25. The display of claim 24 wherein the display has an appearance of illuminated pixels on a dark background under supplemental lighting conditions.

26. The display of claim 22 and further including an absorbing element positioned between the reflective polarizer and the supplemental light source.

27. The display of claim 26 wherein the display has an appearance of dark pixels on a diffusely lit background under ambient lighting conditions.

28. The display of claim 26 wherein the display reverses image between ambient and supplemental lighting conditions.

29. The display of claim 28 wherein the display has an appearance of illuminated pixels on a dark background under supplemental lighting conditions.

30. The display of claim 26 wherein the absorbing element is a dichroic polarizer.

31. The display of claim 19 further including a rear dichroic polarizer positioned between the light modulator and the reflective polarizer.

32. The display of claim 31 wherein the reflective polarizer, the front dichroic polarizer and the rear dichroic polarizer are aligned for optimal viewing under ambient lighting conditions.

33. The display of claim 31 wherein the reflective polarizer, the front dichroic polarizer and the rear dichroic polarizer are aligned for optimal viewing under supplemental lighting conditions.

34. The display of claim 31 wherein the transmission axis of the reflective polarizer is effectively aligned with an extinction axis of the rear dichroic polarizer.

35. The transflective display of claim 34 wherein the display has an appearance of dark pixels on a diffusely lit background under both ambient lighting conditions and supplemental lighting conditions.

36. The display of claim 31 wherein the transmission axis of the reflective polarizer is effectively aligned with a transmission axis of the rear dichroic polarizer.

37. The display of claim 36 wherein the display has an appearance of dark pixels on a diffusely lit background under both ambient lighting conditions and supplemental lighting conditions.

38. The display of claim 19 wherein the transmission axis of the reflective polarizer is effectively aligned with an extinction axis of the front dichroic polarizer.

39. The display of claim 38 wherein the display has an appearance of dark pixels on a diffusely lit background under ambient lighting conditions.

40. The display of claim 38 wherein the display reverses image between ambient and supplemental lighting conditions.

41. The display of claim 40 wherein the display has an appearance of illuminated pixels on a dark background under supplemental lighting conditions.

42. A reflective display as recited in claim 1, wherein the reflective polarizer specularly reflects the light having the first polarization state.

43. A reflective display as recited in claim 1, wherein the reflective polarizer comprises a stack of alternating layers of at least two materials, a refractive index difference between the at least two materials being greater for light polarized along a first in-plane axis of the stack than for light polarized along a second in-plane axis of the stack.

44. A reflective display as recited in claim 1, further comprising a light absorbing material disposed adjacent a side of the reflective polarizer opposite the diffuser, the light absorbing material absorbing light transmitted through the reflective polarizer.

45. A reflective display as recited in claim 1, further comprising a supplemental light source disposed behind the reflective polarizer.

46. A reflective display as recited in claim 45, wherein the reflective polarizer transmits a portion of light generated by the light source having the first polarization state, the portion of the light transmitted through the light modulator generating an image for viewing.

47. A reflective display as recited in claim 45, wherein the reflective polarizer transmits light generated by the light source having the second polarization state, at least a portion of the light being transmitted through the light modulator to generate an image for viewing.

48. A reflective display as recited in claim 1, wherein the light modulator, the diffuser and the reflective polarizer comprise a laminated structure.

52. The display of claim 1 wherein the reflective polarizer comprises a plurality of layers.

53. The display of claim 52 wherein a refractive index difference between at least two adjacent layers in a first in-plane direction of the reflective polarizer is greater than a reflective index difference between the at least two adjacent layers in a second in-plane direction.

49. A transflective display, comprising:

a transmissive light modulator, having a front and back side, provided to selectively alter a polarization state of polarized light passing through the light modulator;

a supplemental light source disposed on the back side of the light modulator;

a reflective polarizer disposed between the light source and the light modulator, the reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having a second polarization state; and

a transmissive diffuser disposed between the light modulator and the reflective polarizer to diffuse light passing between the light modulator and the reflective polarizer while substantially maintaining a polarization state of the light transmitted through the diffuser,

wherein an image is generated by the light modulator when either ambient light is incident on the front side of the light modulator or when light is generated by the supplemental light source.

50. The display of claim 49 wherein the reflective polarizer further has an average reflectance of at least 80% for light of the first polarization state incident normal to the reflective polarizer and an average reflectance of at least 80% for light of the first polarization state incident 60°

from normal to the reflective polarizer.

51. The display of claim 49 wherein the reflective polarizer further has an average transmittance of at least 70% for light of the second polarization state incident normal to the reflective polarizer and an average transmittance of at least 80% for light of the second polarization state incident 60°

from normal to the reflective polarizer.

54. The display of claim 49 wherein the display has an appearance of dark pixels on a diffusely lit background under ambient lighting conditions.

55. The transflective display of claim 49 wherein the display reverses image between ambient and supplemental lighting conditions.

56. The display of claim 49 wherein the display has an appearance of diffusely lit pixels on a dark background under supplemental lighting conditions.