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Projection system having low astigmatism

Imported: 24 Feb '17 | Published: 06 Jan '04

David J. W. Aastuen, Charles L. Bruzzone, Stephen K. Eckhardt, Jiaying Ma

USPTO - Utility Patents

Abstract

Generally, the present invention relates to an apparatus for reducing astigmatism in a projection system that is particularly well suited to reducing astigmatism in LCD projection systems. A projection system includes a light source to generate light, conditioning optics to condition the light from the light source and an imaging core to impose on image on conditioned light from the conditioning optics to form image light. The imaging core includes a polarizing beamsplitter and at least one imager, and at least one element in the imaging core is adapted to reduce astigmatism in the image light. The astigmatism may arise in the polarizing beamsplitter. A projection lens system projects the astigmatism-reduced image light from the imaging core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates an embodiment of a projection unit based on a single reflective imager;

FIG. 2 schematically illustrates another embodiment of a projection unit based on multiple reflective imagers;

FIGS. 3A and 3B illustrates different orientations of a color prism relative to a polarizing beamsplitter;

FIG. 4 schematically illustrates a first approach to reducing astigmatism in a projector system, based on a gap in a color prism, according to an embodiment of the present invention;

FIG. 5 schematically illustrates another approach to reducing astigmatism in a projector system, based on gaps in a color prism, according to another embodiment of the present invention;

FIG. 6 schematically illustrates another approach to reducing astigmatism in a projector system, based on a gap between a wedge prism and a color prism, according to another embodiment of the present invention;

FIG. 7 schematically illustrates another approach to reducing astigmatism in a projector system, based on a plate positioned between elements of a color prism, according to another embodiment of the present invention;

FIG. 8 schematically illustrates another approach to reducing astigmatism in a projector system, based on plates positioned between and within elements of a color prism, according to another embodiment of the present invention;

FIG. 9 schematically illustrates another approach to reducing astigmatism in a projector system having an x-cube color combiner, according to another embodiment of the present invention

FIGS. 10A and 10B illustrate different orientations of x-cube color combiner relative to polarization beamsplitter, according to embodiments of the present invention;

FIG. 11 schematically illustrates another approach to reducing astigmatism in a projector system, based on a plate positioned within a polarization beamsplitter, according to another embodiment of the present invention;

FIG. 12 schematically illustrates another approach to reducing astigmatism in a projector system, based on a second, low index film, according to an embodiment of the present invention;

FIG. 13 schematically illustrates an approach to reducing astigmatism in a two imager projection engine, according to an embodiment of the present invention;

FIG. 14 schematically illustrates another approach to reducing astigmatism in a two imager projection engine, according to another embodiment of the present invention; and

FIG. 15 schematically illustrates another approach to reducing astigmatism in a projector system, based on a wedged component within a polarizing beamsplitter, according to another embodiment of the present invention.

Claims

1. An optical device, comprising:

2. A device as recited in claim 1, further comprising a light source to generate the light and light conditioning optics to condition the light before reaching the polarizing beamsplitter.

3. A device as recited in claim 1, further comprising a projection lens system to project image light from the at least one imager.

4. A device as recited in claim 3, wherein the astigmatism compensating element reduces the astigmatism to a value less than a depth of field of the projection lens system.

5. A device as recited in claim 1, further comprising a controller coupled to the at least one imager to control an image imposed on the light incident on the at least one imager.

6. A device as recited in claim 1, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and further comprising imager illumination optics having an f-number equal to or less than 2.5, the device having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

7. A device as recited in claim 1, wherein the multilayer, polarization sensitive reflective film lies in an x-y plane and has a thickness in a z-direction, and the film has a z-refractive index substantially matched to one of the x- and y-refractive indices.

8. A device as recited in claim 1, wherein the astigmatism compensating element includes a plate of high index material having a refractive index higher than a refractive index of material on at least one side of the plate of high index material.

9. A device as recited in claim 8, wherein the plate of high index material has a refractive index higher than a refractive index of the covers, the plate of high index material being disposed between the polarization sensitive reflective film and one of the covers.

10. A device as recited in claim 1, wherein the wedged element has a refractive index lower than the refractive index of the covers.

11. A device as recited in claim 1, wherein the wedged element is a wedged adhesive layer attaching the one of the covers to the polarization sensitive reflective film.

12. A device as recited in claim 1, wherein at least one of the covers has non-parallel optical surfaces.

13. A projection system, comprising:

14. A device as recited in claim 13, wherein the at least one element in the astigmatism imaging core adapted to reduce astigmatism reduces the astigmatism to a value less than a depth of field of the projection lens system.

15. A system as recited in claim 13, further comprising a controller coupled to the at least one imager to control the image imposed on light incident on the at least one imager.

16. A system as recited in claim 13, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and the light conditioning optics have an f-number equal to or less than 2.5, the system having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

17. A system as recited in claim 13, wherein the polarizing beamsplitter includes a wedge disposed between the multilayer, polarization sensitive reflective film and one of the covers, the wedge having a refractive index less than the refractive index of the covers.

18. A system as recited in claim 13, wherein the polarizing beamsplitter includes a plate disposed between the multilayer, polarization sensitive reflective film and one of the covers, the plate having a refractive index higher than the refractive index of the covers.

19. A system as recited in claim 13, wherein the imager core includes an astigmatism-reducing cube disposed between the polarizing beamsplitter and the projection lens system, the astigmatism-reducing cube including a layer having a layer refractive index disposed between covers having a cover refractive index different from the layer refractive index, the layer being tilted relative to a propagation direction of the image light.

20. A system as recited in claim 19, wherein the layer is a polarizing layer.

21. A system as recited in claim 13, further comprising a color separator disposed between the polarization beamsplitter and the at least one imager.

22. A system as recited in claim 21, wherein the color separator is a color separating prism having at least first and second color separating elements separated by a gap layer of material having a refractive index different from a refractive index of the first and second color separating elements, a thickness of the gap layer being selected to reduce astigmatism in the image light.

23. A system as recited in claim 22, wherein the gap layer has a refractive index lower than the refractive index of the first and second color separating elements.

24. A system as recited in claim 22, wherein the gap layer has a refractive index higher than the refractive index of the first and second color separating elements.

25. A system as recited in claim 22, wherein the first color separating element is made of two parts separated by a second gap layer having a refractive index different from the refractive index of the first color separating element, and having a thickness selected to reduce astigmatism in the image light.

26. A system as recited in claim 25, wherein the second gap layer has a refractive index lower than the refractive index of the first color separating element.

27. A system as recited in claim 25, wherein the second gap layer has a refractive index higher than the refractive index of the first color separating element.

28. A system as recited in claim 22, further comprising a wedge prism disposed between the color separating prism and the polarizing beamsplitter, a third gap layer between the wedge prism and the color separating prism, having a refractive index different from wedge prism, having a thickness selected to reduce astigmatism.

29. A system as recited in claim 22, wherein the color separating prism separates light into different colors in a plane approximately perpendicular to a reflection plane of the polarizing beamsplitter.

30. A system as recited in claim 22, wherein the color separating prism separates light into different colors in a plane approximately parallel to a reflection plane of the polarizing beamsplitter.

31. A system as recited in claim 13, wherein the imaging core further comprises an x-cube to combine light in at least two color bands, the x-cube combiner including astigmatism-reducing slabs of material having a refractive index different from a refractive-index of x-cube prisms forming the x-cube.

32. A system as recited in claim 31, wherein the astigmatism-reducing slabs are formed of material having a refractive index lower than the refractive index of the x-cube prisms.

33. A device as recited in claim 13, wherein at least one of the covers has non-parallel optical surfaces.

34. An optical device, comprising:

35. A device as recited in claim 34, further comprising a light source to generate the light and light conditioning optics to condition the light before reaching the polarizing beamsplitter.

36. A device as recited in claim 34, further comprising a projection lens system to project image light from the at least one imager.

37. A device as recited in claim 36, wherein the astigmatism compensating element reduces the astigmatism to a value less than a depth of field of the projection lens system.

38. A device as recited in claim 34, further comprising a controller coupled to the at least one imager to control an image imposed on the light incident on the at least one imager.

39. A device as recited in claim 34, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and further comprising imager illumination optics having an f-number equal to or less than 2.5, the device having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

40. A device as recited in claim 34, wherein the multilayer, polarization sensitive reflective film lies in an x-y plane and has a thickness in a z-direction, and the film has a z-refractive index substantially matched to one of the x-and y-refractive indices.

41. An optical device, comprising:

42. A device as recited in claim 41, further comprising a light source to generate the light and light conditioning optics to condition the light before reaching the polarizing beamsplitter.

43. A device as recited in claim 41, further comprising a projection lens system to project image light from the at least one imager.

44. A device as recited in claim 41, wherein astigmatism of the device is reduced to a value less than a depth of field of the projection lens system.

45. A device as recited in claim 41, further comprising a controller coupled to the at least one imager to control an image imposed on the light incident on the at least one imager.

46. A device as recited in claim 41, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and further comprising imager illumination optics having an f-number equal to or less than 2.5, the device having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

47. A device as recited in claim 41, wherein the multilayer, polarization sensitive reflective film lies in an x-y plane and has a thickness in a z-direction, and the film has a z-refractive index substantially matched to one of the x-and y-refractive indices.

48. A device as recited in claim 41, wherein the first gap layer is an air gap having a thickness of at least at 50 m.

49. A device as recited in claim 41, wherein the first color separating element is made of two parts separated by a second gap layer, the second gap layer positioned so as to be outside a path traveled through the first color separating element by light not separated by the first color separating element, the second gap layer having a thickness selected to reduce astigmatism arising in the polarizing beamsplitter for light in a wavelength range separated by the first light separating element.

50. A device as recited in claim 41, wherein the second gap layer is an air gap.

51. An optical device, comprising:

52. A device as recited in claim 51, further comprising a light source to generate the light and light conditioning optics to condition the light before reaching the polarizing beamsplitter.

53. A device as recited in claim 51, further comprising a projection lens system to project image light from the at least one imager.

54. A device as recited in claim 53, wherein the wedge prism reduces the astigmatism to a value less than a depth of field of the projection lens system.

55. A device as recited in claim 51, further comprising a controller coupled to the at least one imager to control an image imposed on the light incident on the at least one imager.

56. A device as recited in claim 51, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and further comprising imager illumination optics having an f-number equal to or less than 2.5, the device having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

57. A device as recited in claim 51, wherein the multilayer, polarization sensitive reflective film lies in an x-y plane and has a thickness in a z-direction, and the film has a z-refractive index substantially matched to one of the x-and y-refractive indices.

58. A device as recited in claim 51, wherein the thickness of the third gap layer is selected to substantially correct the astigmatism arising in the polarizing beamsplitter.

59. A device as recited in claim 51, wherein the color separating prism includes a first color separating element and at least a second color separating element, the first color separating element being closer to the wedge prism than the at least a second color separating element, the first and second color separating elements being separated by a first gap layer, thicknesses of the first and third gap layers being selected to substantially correct astigmatism arising in the polarizing beamsplitter.

60. An optical device, comprising:

61. A device as recited in claim 60, further comprising a light source to generate the light and light conditioning optics to condition the light before reaching the polarizing beamsplitter.

62. A device as recited in claim 60, further comprising a projection lens system to project image light from the at least one imager.

63. A device as recited in claim 62, wherein the plate reduces the astigmatism to a value less than a depth of field of the projection lens system.

64. A device as recited in claim 60, further comprising a controller coupled to the at least one imager to control an image imposed on the light incident on the at least one imager.

65. A device as recited in claim 60, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and further comprising imager illumination optics having an f-number equal to or less than 2.5, the device having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

66. A device as recited in claim 60, wherein the multilayer, polarization sensitive reflective film lies in an x-y plane and has a thickness in a z-direction, and the film has a z-refractive index substantially matched to one of the x-and y-refractive indices.

67. A device as recited in claim 60, wherein the plate of the first material has a thickness selected to reduce astigmatism arising in the polarizing beamsplitter.

68. A device as recited in claim 60, wherein the first color separating element is made of two parts separated by a plate of a second material different from a material of the first color separating element, the plate of second material being positioned so as to be outside a path traveled by light not separated by the first color separating element.

69. A device as recited in claim 68, a width of the plate of second material being selected to reduce astigmatism arising in the polarizing beamsplitter for light in a wavelength range separated by the first light separating element.

70. A device as recited in claim 68, wherein the second material is the same as the first material.

71. An optical device, comprising:

72. A device as recited in claim 71, wherein the astigmatism-reducing slabs are formed of material having a refractive index lower than the refractive index of the x-cube prisms.

73. A device as recited in claim 71, further comprising a light source to generate the light and light conditioning optics to condition the light before reaching the polarizing beamsplitter.

74. A device as recited in claim 71, further comprising a projection lens system to project image light from the at least one imager.

75. A device as recited in claim 74, wherein the astigmatism reducing slabs reduce the astigmatism to a value less than a depth of field of the projection lens system.

76. A device as recited in claim 71, further comprising a controller coupled to the at least one imager to control an image imposed on the light incident on the at least one imager.

77. A device as recited in claim 71, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and further comprising imager illumination optics having an f-number equal to or less than 2.5, the device having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

78. A device as recited in claim 71, wherein the multilayer, polarization sensitive reflective film lies in an x-y plane and has a thickness in a z-direction, and the film has a z-refractive index substantially matched to one of the x-and y-refractive indices.

79. A device as recited in claim 78, wherein a rotation axis of the first film relative to the second path is perpendicular to a rotation axis of a polarization sensitive reflection film in the polarizing beamsplitter.

80. A device as recited in claim 79, wherein the first film is a multilayer, polarization sensitive, reflective film.

81. A device as recited in claim 78, further comprising a light source to generate the light and light conditioning optics to condition the light before reaching the polarizing beamsplitter.

82. A device as recited in claim 78, further comprising a projection lens system to project image light from the at least one imager.

83. A device as recited in claim 82, wherein the first film reduces the astigmatism to a value less than a depth of field of the projection lens system.

84. A device as recited in claim 78, further comprising a controller coupled to the at least one imager to control an image imposed on the light incident on the at least one imager.

85. A device as recited in claim 78, wherein the polarizing beamsplitter is a Cartesian polarizing beamsplitter having a structural orientation defining fixed axes of polarization and further comprising imager illumination optics having an f-number equal to or less than 2.5, the device having a dynamic range of at least 100 to 1 over projected color bands in the visible light range.

86. A device as recited in claim 78, wherein the multilayer, polarization sensitive reflective film lies in an x-y plane and has a thickness in a z-direction, and the film has a z-refractive index substantially matched to one of the x-and y-refractive indices.

87. An optical device, comprising:

88. A projection system, comprising:

89. A projection system, comprising:

90. A projection system, comprising:

91. A system as recited in claim 90, wherein the layer is a polarizing layer.

92. A projection system, comprising:

93. A system as recited in claim 92, wherein the gap layer has a refractive index lower than the refractive index of the first and second color separating elements.

94. A system as recited in claim 92, wherein the gap layer has a refractive index higher than the refractive index of the first and second color separating elements.

95. A system as recited in claim 92, wherein the first color separating element is made of two parts separated by a second gap layer having a refractive index different from the refractive index of the first color separating element, and having a thickness selected to reduce astigmatism in the image light.

96. A system as recited in claim 95, wherein the second gap layer has a refractive index lower than the refractive index of the first color separating element.

97. A system as recited in claim 95, wherein the second gap layer has a refractive index higher than the refractive index of the first color separating element.

98. A system as recited in claim 92, further comprising a wedge prism disposed between the color separating prism and the polarizing beamsplitter, a third gap layer between the wedge prism and the color separating prism, having a refractive index different from wedge prism, having a thickness selected to reduce astigmatism.

99. A system as recited in claim 92, wherein the color separating prism separates light into different colors in a plane approximately perpendicular to a reflection plane of the polarizing beamsplitter.

100. A system as recited in claim 92, wherein the color separating prism separates light into different colors in a plane approximately parallel to a reflection plane of the polarizing beamsplitter.

101. A projection system, comprising:

102. A system as recited in claim 101, wherein the astigmatism-reducing slabs are formed of material having a refractive index lower than the refractive index of the x-cube prisms.