Optical devices having reflective and transmissive modes for display

• US 20030090804A1
• Filed: 10/28/2002
• Published: 05/15/2003
• Est. Priority Date: 11/09/2001
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Kotchick, Keith M.
• Granted Patent: US 6,894,821 B2
• Time in Patent Office: Days
• US Class Current: 359/619
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G02F 2201/343 cholesteric liquid crystal reflector
• CPC Class Codes: G02F 2203/09 transflective

Abstract

Display apparatuses are shown capable of displaying information in a reflective mode using only ambient light and in a transmissive mode using a light source. In one embodiment, the display apparatus includes a reflecting polarizer disposed between a light modulating layer and an isotropic light cavity. The light cavity reflects incident light with a first degree of depolarization. The reflecting polarizer reflects light with a second degree of depolarization for at least one polarization that is greater than the first degree of depolarization. In another embodiment of the display apparatus, a microstructured film is included above a light cavity and below a light modulating system where the microstructured film includes sawtooth formations having at least a tilted surface. In another embodiment of a dual-mode display device, the display includes a cholesteric reflecting polarizer disposed between a light modulating layer and a light cavity where the light cavity causes a polarization phase shift upon reflectance.

Claims

1. A display apparatus capable of displaying information in a reflective mode using only ambient light and in a transmissive mode using a light source, comprising:

a light modulating system comprising a light modulating layer between a first polarizing layer and a second polarizing layer;

an isotropic light cavity comprising a light source and a reflector, the light cavity adapted to selectively provide light to the light modulating layer, the light cavity reflecting incident light with a first degree of depolarization of the incident light, the reflector configured to reflect ambient light toward the light modulating layer to illuminate the display using only ambient light in the reflective mode; and

a reflecting polarizer disposed between the light modulating layer and the light cavity, adapted to transmit a component of incident light having a first polarization and reflect a component of the incident light having a second polarization, the polarizer reflecting the light of the second polarization with a second degree of depolarization greater than the first degree of depolarization to provide light of the first polarization.

2. The display apparatus of claim 1 wherein the reflecting polarizer is a diffusely reflecting polarizer.

4. The display apparatus of claim 1 wherein the reflector of the light cavity is a planar mirror.

5. The display apparatus of claim 4 wherein the planar mirror includes an opaque metal coating.

9. The display apparatus of claim 1 wherein the reflector of the light cavity comprises a reflective polarizer and a mirror layer, wherein the reflective polarizer of the light cavity substantially maintains a polarization state in at least one of reflection and transmission.

10. The display apparatus of claim 1 wherein the reflector of the light cavity comprises a diffuse polarized mirror comprising a reflective polarizer, wherein the reflective polarizer of the light cavity substantially maintains a polarization state in at least one of reflection and transmission.

11. The display apparatus of claim 1 wherein the reflector of the light cavity includes a beam steering layer that provides a shift in the reflectance propagation direction toward an optimal viewing angle, wherein the reflector substantially preserves polarization upon reflection.

12. The display apparatus of claim 11 wherein the beam steering layer includes mirror surfaces tilted from the horizontal.

13. The display apparatus of claim 1 further comprising a first microstructured film located above the light cavity and below the light modulating system, the first microstructured film comprising sawtooth formations, wherein the sawtooth formations each include a tilted surface;

wherein ambient light strikes the first microstructured film and a first portion of incident energy of the ambient light is refracted in a first angular direction and a second portion of the incident energy of the ambient light is refracted in a second angular direction different than the first angular direction.

14. The display apparatus of claim 13 wherein the sawtooth formations are on a side of the first microstructured film facing the light modulating system.

15. The display apparatus of claim 13 wherein the first microstructured film is configured to provide an increase in a brightness of light in a range of viewing directions leaving the light cavity.

16. The display apparatus of claim 13 wherein the display apparatus does not include a transflector layer that is partially reflective and partially transmissive between the light source and the light modulating layer.

17. The display apparatus of claim 13 wherein the reflective polarizer is the first microstructured film.

18. The display apparatus of claim 13 wherein the first microstructured film is above the reflective polarizer.

19. The display apparatus of claim 13 wherein the reflective polarizer is above the first microstructured film.

20. The display apparatus of claim 1 wherein the light source comprises an organic light emitting diode.

21. The display apparatus of claim 1 wherein the light source comprises an edge-illuminated light guide configured to direct light below the edge-illuminated light guide to the reflector.

3. The display apparatus of claim I wherein the display apparatus does not include a transflector layer that is partially transmissive and partially reflective.

6. The display apparatus of claim I wherein the reflector of the light cavity is a diffuse mirror.

7. The display apparatus of claim 6 wherein the diffuse mirror comprises a textured surface.

8. The display apparatus of claim 6 wherein the diffuse mirror comprises a planar mirror layer and a diffuse layer.

22. A display apparatus capable of displaying information in a reflective mode using only ambient light and in a transmissive mode using a light source, comprising:

a light modulating system comprising a light modulating layer and a first polarizing layer;

a light cavity for providing light to the light modulating layer;

a reflector located below the light cavity and disposed to receive light from the light cavity and direct light toward the light modulating layer to illuminate the display using only ambient light in the reflective mode; and

a first microstructured film located above the light cavity and below the light modulating system, the first microstructured film comprising sawtooth formations, wherein the sawtooth formations each include a tilted surface;

wherein ambient light strikes the first microstructured film and a first portion of incident energy of the ambient light is refracted in a first angular direction and a second portion of the incident energy of the ambient light is refracted in a second angular direction different than the first angular direction.

23. The display apparatus of claim 22 wherein the sawtooth formations are on a side of the first microstructured film facing the light modulating system.

24. The display apparatus of claim 22 wherein each sawtooth formation comprises a prism.

25. The display apparatus of claim 24 further comprising a second microstructured film disposed below the first microstructured film, the second microstructured film comprising sawtooth formations wherein each sawtooth formation includes prism having a tilted surface, wherein the sawtooth formations of the first microstructured film are perpendicular to the sawtooth formations of the second microstructured film;

and

wherein incident light that has passed through the first microstructured film strikes the second microstructured film and a first portion of incident energy of the incident light is refracted in a third angular direction and a second portion of the incident energy of the incident light is refracted in a fourth angular direction that is different than the third angular direction.

26. The display apparatus of claim 22 wherein the first microstructured film is configured to provide an increase in a brightness of light in a range of viewing directions leaving the light cavity.

27. The display apparatus of claim 22 wherein the display apparatus does not include a transflector layer that is partially reflective and partially transmissive between the light source and the light modulating layer.

28. The display apparatus of claim 22 wherein the sawtooth formations of the first microstructured film include pyramid structures.

29. The display apparatus of claim 28 wherein the pyramids are square-based pyramids.

30. The display apparatus of claim 22 wherein the reflector of the light cavity is a planar mirror.

31. The display apparatus of claim 30 wherein the planar mirror includes an opaque metal coating.

32. The display apparatus of claim 22 wherein the reflector of the light cavity is a diffuse mirror.

33. The display apparatus of claim 32 wherein the diffuse mirror comprises a textured surface.

34. The display apparatus of claim 32 wherein the diffuse mirror comprises a planar mirror layer and a diffuse layer.

35. The display apparatus of claim 32 wherein the reflector of the light cavity comprises a reflective polarizer and a mirror layer, wherein the reflective polarizer substantially maintains a polarization state in at least one of reflection and transmission.

36. The display apparatus of claim 22 wherein the reflector of the light cavity comprises a diffuse polarized mirror comprising a reflective polarizer, wherein the reflective polarizer substantially maintains a polarization state in at least one of reflection and transmission.

37. The display apparatus of claim 22 wherein the reflector of the light cavity includes a beam steering layer that provides a shift in the reflectance propagation direction toward an optimal viewing angle, wherein the reflector substantially preserves polarization upon reflection.

38. The display apparatus of claim 37 wherein the beam steering layer includes mirror surfaces tilted from the horizontal.

39. The display apparatus of claim 22 wherein the light cavity is isotropic and reflects incident light with a first degree of depolarization of the incident light, the reflector being configured to reflect ambient light toward the light modulating layer to illuminate the display using only ambient light in the reflective mode, the display apparatus further comprising:

a reflecting polarizer disposed between the light modulating layer and the light cavity, adapted to transmit a component of incident light having a first polarization and reflect a component of the incident light having a second polarization, the polarizer reflecting the light of the second polarization with a second degree of depolarization greater than the first degree of depolarization to provide light of the first polarization.

40. The display apparatus of claim 39 wherein the reflecting polarizer is a diffusely reflecting polarizer.

41. The display apparatus of claim 39 wherein the display apparatus does not include a transflector layer that is partially transmissive and partially reflective.

42. The display apparatus of claim 39 wherein the first microstructured film is above the reflective polarizer.

43. The display apparatus of claim 39 wherein the reflective polarizer is above the first microstructured film.

44. The display apparatus of claim 22 wherein the light source comprises an organic light emitting diode.

45. The display apparatus of claim 22 wherein the light source comprises an edge-illuminated light guide configured to direct light below the edge-illuminated light guide to the reflector.

46. A display apparatus capable of displaying information in a reflective mode using only ambient light and in a transmissive mode using a light source, comprising:

a light modulating system comprising a light modulating layer between a first polarizing layer and a second polarizing layer;

a light cavity comprising a light source and a reflector, the light cavity adapted to selectively provide light to the light modulating layer, the reflector configured to reflect ambient light toward the light modulating layer to illuminate the display using only ambient light in the reflective mode, wherein the reflector of the light cavity causes a polarization phase shift upon reflectance; and

a cholesteric reflecting polarizer disposed between the light modulating layer and the light cavity, adapted to transmit a component of incident light having a first polarization and reflect a component of the incident light having a second polarization.

47. The display apparatus of claim 46 wherein the display apparatus does not include a transflector layer that is partially reflective and partially transmissive between the light source and the light modulating layer.

48. The display apparatus of claim 46 wherein the light source comprises an organic light emitting diode.

49. The display apparatus of claim 46 wherein the light source comprises an edge-illuminated light guide configured to direct light below the edge-illuminated light guide to the reflector.

50. The display apparatus of claim 46 further comprising a quarter wave film disposed between the light modulating system and the cholesteric reflecting polarizer.