LCD device including an illumination device having a polarized light separating sheet between a light guide and the display

• US RE38,305 E1
• Filed: 02/24/2000
• Issued: 11/11/2003
• Est. Priority Date: 10/09/1992
• Status: Expired due to Term

• Current Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Original Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Inventors: Matsumoto, Tetsuro, Hasebe, Hiroshi, Ito, Hiroaki, Gunjima, Tomoki, Ozeki, Masao, Nakagawa, Yutaka, Ooi, Yoshiharu
• Primary Examiner(s): Spikes, William L.
• Assistant Examiner(s): TON, MINH TOAN T
• Application Number:
  US09/512,735
• Time in Patent Office: 1,356 Days
• Field of Search: 349/9, 349/62, 349/64, 349/96, 349/115, 359/487, 359/490
• US Class Current: 349/9
• CPC Class Codes: F21V 9/14 for producing polarised light
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G02F 2001/13355 Polarising beam splitters [PBS]

Abstract

An illumination device for a direct viewing type display element comprising a flat light guide; a light source set such that light is incident on a side portion of said flat light guide; a polarized light separating flat set on a first side of a light emitting side of the flat light guide for transmitting a p polarized light component and reflecting at least a portion of an a polarized light component with respect to a light ray substantially having a predetermined direction of incidence; and a light reflecting sheet disposed on a second side opposite to said light emitting side of the flat light guide in parallel with the light emitting site.

Claims

1. An illumination device for a direct viewing type display element, comprising:

a flat light guide;

a light source set such that light is incident on a side portion of said flat light guide;

a polarized light separating sheet set on a light emitting side of the flat light guide for transmitting a p polarized light component and reflecting at least a portion of an s polarized light component with respect to a light ray substantially having a predetermined direction of incidence; and

a light reflecting sheet disposed on another side opposite to and facing said light emitting side of the flat light guide in parallel with the emitting side, said light reflecting sheet converting said portion of s polarized light component reflected by said polarized light separating sheet into p polarized light and reflecting the converted p polarized light to said polarized light separating sheet for transmission of the converted p polarized light through said polarized light separating sheet in overlapping relationship with the p polarized light component.

2. The illumination device for a direct viewing type display element according to claim 1, wherein the polarized light separating sheet is comprising a multi-layered structure wherein light transmitting media having a relatively large refractive index and light transmitting media having a relatively small refractive index are laminated.

3. The illumination device for a direct viewing type display element according to claim 1, wherein the polarized light separating sheet comprises a transparent supporter and at least one dielectric thin film laminated on said transparent supporter having a thickness which is equal to or smaller than a wavelength of visible light.

4. The illumination device for a direct viewing type display element according to claim 1, wherein the polarized light separating sheet comprises a plurality of laminated transparent polymer layers having different refractive indices.

5. A liquid crystal display device, wherein the illumination device according to claim 1 is disposed on a rear side of a direct viewing type liquid crystal display element such that a principle polarization direction of emitted light from the illumination device substantially agrees with a direction of an optical axis of polarization of a polarizing sheet on a light-incident side of a liquid crystal display element.

6. The liquid crystal display device according to claim 5 further comprising:

a light deflecting means disposed between the polarized light separating sheet and the liquid crystal display element for deflecting a direction of a light ray maximizing a light intensity among light distributing directions to a direction substantially perpendicular to a display face of the liquid crystal display element.

7. The liquid crystal display device according to claim 5, further comprising:

a means for rotating polarization direction disposed between the illumination device and the liquid crystal display element for rotating the principle direction of emitted light.

8. An illumination device for a direct viewing type display element, comprising:

a flat light emitting means for emitting a diffused light including a first polarized light component having a first direction of polarization and a second polarized light component having a second direction of polarization perpendicular to the first direction of polarization; and

a polarized light converting and emitting means disposed in an optical path of a light emitted from said flat light emitting means for emitting said first polarized light component and for emitting, in overlapping relationship with the emitted first polarized light component, at least a portion of said second polarized light component after selectively converting said portion of said second polarized light component into the first polarized light component.

9. An illumination device for a direct viewing type display element, comprising:

a flat light guide;

a light source set such that light is incident on a side portion of said flat light guide;

a polarized light separating sheet set on a light emitting side of the flat light guide for transmitting a p polarized light component and reflecting at least a portion of an s polarized light component with respect to light rays substantially having a predetermined direction of incidence; and

a light reflecting sheet disposed on another side opposite to and facing said light emitting side of the flat light guide in parallel with the emitting side, said light reflecting sheet converting said portion of s polarized light component reflected by said polarized light separating sheet into p polarized light and reflecting the converted p polarized light to said polarized light separating sheet for transmission of the converted p polarized light trough said polarized light separating sheet in overlapping relationship with the p polarized light component.

10. The illumination device for a direct viewing type display element according to claim 9, wherein the polarized light separating sheet comprises a transparent supporter and at least one dielectric thin film laminated on said transparent supporter having a thickness which is equal to or smaller than a wavelength of visible light.

11. The illumination device for a direct viewing type display element according to claim 9, wherein the polarized light separating sheet is composed of a multi-layer structure including alternately laminated light transmitting media, having a refractive index, n₀, and other transmitting media, having a refractive index, n₁, smaller than the refractive index n₀.

12. The illumination device for a direct viewing type display element according to claim 9, wherein a λ

/4 phase interference plate is provided on the back face of the light guide and a side face of the light guide opposing the light source.

13. The illumination device for a direct viewing type display element according to claim 10, wherein a λ

/4 phase interference plate is provided on the back face of the light guide and a side face of the light guide opposing the light source.

14. The illumination device for a direct viewing type display element according to claim 9, wherein a prism shape is formed on a surface of the light guide.

15. The illumination device for a direct viewing type display element according to claim 14, wherein the prism shape is a lenticular lens array.

16. The illumination device for a direct viewing type display element according to claim 9, further comprising a light deflector.

17. The illumination device for a direct viewing type display element according to claim 16, wherein a micro lens array or prism array having a lenticular shape or Fresnel shape is employed as the light deflector.

18. An illumination device for a direct viewing type display element, comprising:

a flat light guide;

a light source set such that light is incident on a side portion of said flat light guide;

a polarized light separating sheet set on a light emitting side of the flat light guide for transmitting a p polarized light component and reflecting at least a portion of an s polarized light component with respect to a light ray substantially having a predetermined direction of incidence; and

a light reflecting sheet disposed on another side opposite to and facing said light emitting side of the flat light guide in parallel with the emitting side, wherein said polarized light separating sheet is planar and parallel to the light emitting side of the flat light guide and is set in proximity to the flat light guide in the light emitting direction.

19. In an illumination device for a direct viewing type display element including a display face, the improvement comprising:

a planar polarized light separating sheet comprising at least two opposed planar layers with different refractive properties, said planar polarized light separating sheet separating incident light into a first polarized light component which is transmitted through the display face and a second polarized light component which is at least partially reflected; and

a reflecting element disposed opposite said planar polarized light separating sheet to produce phase-interference of the second polarized light component and reflect light resulting from said phase-interference to said planar polarized light separating sheet.

20. The illumination device according to claim 19, wherein said polarized light separating sheet comprises at least one planar plastic layer.

21. The illumination device according to claim 20, wherein said at least one planar plastic layer is obtained by extrusion.

22. The illumination device of claim 21, wherein said polarized light separating sheet comprises plural planar layers including said at least one plastic layer obtained by multi-layer extrusion.

23. The illumination device according to claim 22, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

24. The illumination device according to claim 23, wherein the direction of light distribution of light for said display element is substantially perpendicular to said display element.

25. The illumination device according to claim 21, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

26. The illumination device according to claim 20, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

27. The illumination device according to claim 26, wherein said polarized light separating sheet comprises at least one planar polymer layer.

28. The illumination device according to claim 27, wherein said at least one planar polymer layer is obtained by extrusion.

29. The illumination device of claim 28, wherein said polarized light separating sheet comprises plural planar layers including said at least one polymer obtained by multi-layer extrusion.

30. The illumination device according to claim 29, wherein said polarized light separating sheet comprises plural planar polymer layers having a thickness not less than 0.05 μ

m and not more than 0.45 μ

m.

31. The illumination device according to claim 30, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

32. The illumination device according to claim 31, wherein the direction of light distribution of light for said display element is substantially perpendicular to said display element.

33. The illumination device according to claim 29, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

34. The illumination device according to claim 33, wherein the direction of light distribution of light for said display element is substantially perpendicular to said display element.

35. The illumination device according to claim 28, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

36. The illumination device according to claim 27, wherein said polarized light separating sheet comprises plural planar polymer layers having a thickness not less than 0.05 μ

m and not more than 0.45 μ

m.

37. The illumination device according to claim 27, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

38. The illumination device according to claim 36, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.

39. The illumination device according to claim 36, wherein the direction of light distribution of light for said display element is substantially perpendicular to said display element.

40. The illumination device according to claim 19, further comprising:

a microlens array or a prism array which converts a direction of light distribution of the light for a display element.