Polarization converting device and polarized-light illuminating system using the device and image display unit using the device

• US 5,387,991 A
• Filed: 12/09/1992
• Issued: 02/07/1995
• Est. Priority Date: 05/18/1990
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Mitsutake, Hideaki, Kawasaki, Shigeru
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/988,018
• Time in Patent Office: 790 Days
• Field of Search: 359/93, 359/73, 359/40, 359/49, 359/66, 359/70, 359/490, 359/495, 359/496, 359/499, 359/831, 359/833, 359/834, 359/837, 359/487
• US Class Current: 349/1
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/13355 Polarising beam splitters [PBS]
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A polarization converting device for converting a light from a light source into a polarized light comprises a first prism having a first slant plane for receiving the light from the light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which the first light exits, and a second emergent surface from which the second light exits, a second prism having an incident surface opposed to the second emergent surface of the first prism, a second slant plane for reflecting and deflecting the second light from the incident surface so as to direct it to an optical path almost parallel to that of the first light, and a third emergent surface from which the second light reflected from the second slant plane exits, and a transparent layer carried between the second emergent surface of the first prism and the incident surface of the second prism, the transparent layer having a smaller refractive index than the first prism.

Claims

1. A device for converting a light from a light source into a polarized light, comprising:

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and a second emergent surface from which said second light exits;

a second prism having an incident surface opposed to said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path almost parallel to that of said first light, and a third emergent surface from which said second light reflected from said second slant plane exits; and

a transparent layer provided between said second emergent surface of said first prism and said incident surface of said second prism, said transparent layer having a smaller refractive index than said first prism.

2. A device according to claim 1, wherein said transparent layer includes a thin air layer.

3. A device according to claim 1, wherein said transparent layer includes an optical thin film.

4. A device according to claim 3, wherein said optical thin film has a multi-layer film structure.

5. A device according to claim 1, further comprising a polarized plane modulation member on at least one optical path of said first light and said second light to make polarized planes for said first light and said second light almost coincident.

6. A device according to claim 5, wherein said modulation member comprises a 1/2 wavelength plate, said 1/2 wavelength plate being provided on one optical path of said first light and said second light, and allowing a polarized direction of one of said first light and said second light to be rotated approximately 90°

.

7. A device according to claim 6, wherein said 1/2 wavelength plate comprises a 1/4 wavelength plate and a mirror to rotate a polarized direction while reflecting said one light.

8. A device according to claim 6, wherein said 1/2 wavelength plate comprises a birefringent crystal.

9. A device according to claim 6, wherein said 1/2 wavelength plate comprises a liquid crystal element.

10. A device for converting a light from a light source into a polarized light, comprising:

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and a second emergent surface from which said second light exits;

a second prism having an incident surface substantially in contact with said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path almost parallel to that of said first light, and a third emergent surface from which said second light reflected from said second slant plane exits, and wherein said second prism has a smaller refractive index than said first prism.

11. A device according to claim 10, further comprising a polarized plane modulation member on at least one optical path of said first light and said second light to make polarized planes for said first light and said second light almost coincident.

12. A device according to claim 11, wherein said modulation member comprises a 1/2 wavelength plate, said 1/2 wavelength plate being provided on one optical path of said first light and said second light, and allowing a polarized direction of one of said first light and said second light to be rotated approximately 90°

.

13. A device according to claim 12, wherein said 1/2 wavelength plate comprises a 1/4 wavelength plate and a mirror to rotate a polarized direction while reflecting said one light.

14. A device according to claim 12, wherein said 1/2 wavelength plate comprises a birefringent crystal.

15. A device according to claim 12, wherein said 1/2 wavelength plate comprises a liquid crystal element.

16. A device for converting a light from a light source into a polarized light, comprising:

a light source;

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and a second emergent surface from which said second light exits;

a second prism having an incident surface opposed to said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path almost parallel to that of said first light, and a third emergent surface from which said second light reflected from said second slant plane exits;

modulation means for modulating at least one polarized plane of said first light and said second light to make the polarized plane of said first light and said second light almost coincident; and

a transparent layer provided between said second emergent surface of said first prism and said incident surface of said second prism, said transparent layer having a smaller refractive index than said first prism.

17. A device according to claim 16, wherein said transparent layer includes a thin air layer.

18. A device according to claim 16, wherein said transparent layer includes an optical thin film.

19. A device according to claim 18, wherein said optical thin film has a multi-layer film structure.

20. A device according to claim 16, wherein said modulation member comprises a 1/2 wavelength plate, said 1/2 wavelength plate being provided on one optical path of said first light and said second light, and allowing a polarized direction of one of said first light and said second light to be rotated approximately 90°

.

21. A device according to claim 20, wherein said 1/2 wavelength plate comprises a 1/4 wavelength plate and a mirror to rotate a polarized direction while reflecting said one light.

22. A device according to claim 20, wherein said 1/2 wavelength plate comprises a birefringent crystal.

23. A device according to claim 20, wherein said 1/2 wavelength plate comprises a liquid crystal element.

24. A device according to claim 16, further comprising an extinction filter provided on one optical path of said first light and said second light to make the intensity of said first light and said second light almost coincident with each other.

25. A device according to claim 16, further comprising a light absorption material mixed into one of said first prism and said second prism to make the intensity of said first light and said second light almost coincident with each other.

26. A polarized light illuminating system, comprising:

a light source;

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and second emergent surface from which said second light exits;

a second prism having an incident surface substantially in contact with said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path almost parallel to that of said first light, and a third emergent surface from which said second light reflected from said second slant plant exits, wherein said second prism has a smaller refractive index than said first prism; and

modulation means for modulating at least one polarized plane of said first light and said second light to make the polarized plane of said first light and said second light almost coincident.

27. A device according to claim 26, wherein said modulation member comprises a 1/2 wavelength plate, said 1/2 wavelength plate being provided on one optical path of said first light and said second light, and allowing a polarized direction of one of said first light and said second light to be rotated approximately 90°

.

28. A device according to claim 27, wherein said 1/2 wavelength plate comprises a 1/4 wavelength plate and a mirror to rotate a polarized direction while reflecting said one light.

29. A device according to claim 27, wherein said 1/2 wavelength plate comprises a birefringent crystal.

30. A device according to claim 27, wherein said 1/2 wavelength plate comprises a liquid crystal element.

31. A device according to claim 26, further comprising a light attenuation filter provided on one optical path of said first light and said second light to make the intensity of said first light and said second light almost coincident with each other.

32. A device according to claim 26, further comprising a light absorption material mixed into one of said first prism and said second prism to make the intensity of said first light and said second light almost coincident with each other.

33. An image display unit comprising:

a light source;

an illumination optical system including,

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and a second emergent surface from which said second light exits; and

a second prism having an incident surface opposed to said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path almost parallel to that of said first light, and a third emergent surface from which said second light reflected from said second slant plane exits;

modulation means for modulating at least one polarized plane of said first light and said second light to make the polarized plane of said first light and said second light almost coincident;

a transparent layer provided between said second emergent surface of said first prism and said incident surface of said second prism, said transparent layer having a smaller refractive index than said first prism; and

means for producing an image by modulating said first light and said second light from said illuminating optical system.

34. A unit according to claim 33, further comprising a projecting optical system for projecting said image on to a screen.

35. A unit according to claim 33, wherein said transparent layer includes a thin air layer.

36. A unit according to claim 33, wherein said transparent layer includes an optical thin film.

37. A unit according to claim 36, wherein said optical thin film has a multi-layer film structure.

38. A unit according to claim 33, wherein said modulation member comprises a 1/2 wavelength plate, said 1/2 wavelength plate being provided on one optical path of said first light and said second light, and allowing a polarized direction of one of said first light and said second light to be rotated approximately 90°

.

39. A unit according to claim 38, wherein said 1/2 wavelength plate comprises a 1/4 wavelength plate and a mirror to rotate a polarized direction while reflecting said one light.

40. A unit according to claim 38, wherein said 1/2 wavelength plate comprises a birefringent crystal.

41. A unit according to claim 38, wherein said 1/2 wavelength plate comprises a liquid crystal element.

42. A unit according to claim 38, further comprising an extinction filter provided on one optical path of said first light and said second light to make the intensity of said first light and said second light almost coincident with each other.

43. A unit according to claim 38, further comprising a light absorption material mixed into one of said first prism and said second prism to make the intensity of said first light and said second light almost coincident with each other.

44. An image display unit comprising:

a light source;

an illumination optical system including,

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and a second emergent surface from which said second light exits; and

a second prism having an incident surface substantially in contact with said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path almost parallel to that of said first light, and a third emergent surface from which said second light reflected at said second slant plane exits, and wherein said second prism has a smaller refractive index than said first prism;

modulation means for modulating at least one polarized plane of said first light and said second light to make the .polarized plane of said first light and said second light almost coincident; and

means for producing an image by modulating said first light and said second light from said illuminating optical system.

45. A unit according to claim 44, further comprising a projecting optical system for projecting said image on to a screen.

46. A unit according to claim 44, wherein said modulation member comprises a 1/2 wavelength plate, said 1/2 wavelength plate being provided on one optical path of said first light and said second light, and allowing a polarized direction of one of said first light and said second light to be rotated approximately 90°

.

47. A unit according to claim 46, wherein said 1/2 wavelength plate comprises a 1/4 wavelength plate and a mirror to rotate a polarized direction while reflecting said one light.

48. A unit according to claim 46, wherein said 1/2 wavelength plate comprises a birefringent crystal.

49. A unit according to claim 46, wherein said 1/2 wavelength plate comprises a liquid crystal element.

50. A unit according to claim 45, further comprising an extinction filter provided on one optical path of said first light and said second light to make the intensity of said first light and said second light almost coincident with each other.

51. A unit according to claim 45, further comprising a light absorption material mixed into one of said first prism and said second prism to make the intensity of said first light and said second light almost coincident with each other.

52. A device for converting a light from a light source into a polarized light, comprising:

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits and a second emergent surface from which said second light exits;

a second prism having an incident surface substantially in contact with said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path substantially parallel to that of said first light, and a third emergent surface from which said second light reflected from said second slant plane exits, wherein said second prism has a refractive index which is different from that of said first prism.

53. An image display unit comprising:

a light source;

an illuminating optical system including,

a first prism having a first slant plane for receiving light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and a second emergent surface from which said second light exits;

a second prism having an incident surface substantially in contact with said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface so as to direct it to an optical path substantially parallel to that of said first light, and a third emergent surface from which said second light reflected as said second slant plane exits, said second prism having a refractive index which is different from that of said first prism;

modulation means for modulating at least one polarized plane of said first light and said second light to make the polarized planes of said first light and said second light substantially coincident; and

means for producing an image by modulating said first light and said second light from said illuminating optical system.

54. A polarized light illuminating system, comprising:

a light source;

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and a second emergent surface from which said second light exits;

a second prism having an incident surface opposed to said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface, and a third emergent surface from which said second light reflected from said second slant plane exits;

modulation means for modulating at least one polarized plane of said first light and said second light to make the polarized plane of said first light and said second light almost coincident; and

a transparent layer provided between said second emergent surface of said first prism and said incident surface of said second prism, said transparent layer having a smaller refractive index than said first prism.

55. A polarized light illuminating system, comprising:

a light source;

a first prism having a first slant plane for receiving the light from said light source and dividing it into first and second lights with their polarized planes orthogonal, a first emergent surface from which said first light exits, and second emergent surface from which said second light exits;

a second prism having an incident surface substantially in contact with said second emergent surface of said first prism, a second slant plane for reflecting said second light from said incident surface, and a third emergent surface from which said second light reflected from said second slant plane exits;

wherein said second prism has a refractive index which is different from that of said first prism; and

modulation means for modulating at least one polarized plane of said first light and said second light to make the polarized plane of said first light and said second light almost coincident.

56. A polarized light illuminating system, comprising:

a light source;

a polarization converting unit provided with a first prism at said light source side and a second prism at a illuminated object side on an optical path shaped by said light source wherein said polarization converting unit divides a light from said light source into a first polarized light and a second polarized light which lie in different polarized states to each other, makes a polarized state of said first polarized condition coincide with a polarized state of said second polarized condition and illuminates said illuminated object with said second polarized light; and

a transparent layer provided on a surface of said second prism, said transparent layer having a smaller refractive index than said second prism.