Projection system and mirror elements for improved contrast ratio in spatial light modulators

• US 20020024641A1
• Filed: 12/07/2000
• Published: 02/28/2002
• Est. Priority Date: 08/30/2000
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Ilkov, Fedor A., Stockton, John K., Patel, Satyadev R., Richards, Peter W.
• Granted Patent: US 6,523,961 B2
• Time in Patent Office: Days
• US Class Current: 353/99
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means

Abstract

In order to minimize light diffraction along the direction of switching and more particularly light diffraction into the acceptance cone of the projection optics, in the present invention, mirrors are provided which are not rectangular. Also, in order to minimize the cost of the illumination optics and the size of the display unit of the present invention, the light source is placed orthogonal to the rows (or columns) of the array, and/or the light source is placed orthogonal to a side of the frame defining the active area of the array. The incident light beam, though orthogonal to the sides of the active area, are not however, orthogonal to any substantial portion of sides of the individual mirrors in the array. Orthogonal sides cause incident light to diffract along the direction of mirror switching, and result in light ‘leakage’ into the on-state even if the mirror is in the off-state. This light diffraction decreases the contrast ratio of the mirror. The mirrors of the present invention result in an improved contrast ratio, and the arrangement of the light source to mirror array in the present invention results in a more compact system.

Claims

1. A projection or direct-view light system, comprising:

an array of active micromirrors disposed in a rectangular shape, the micromirrors capable of rotation around a switching axis between an off-state and an on-state, the micromirrors corresponding to pixels in a viewed image;

a light source for directing light to the array of micromirrors, the light source disposed so as to direct light non-perpendicular to at least two sides of each micromirror, and parallel, when viewed as a top view of each micromirror, to at least two other sides of each micromirror;

projection or viewing optics disposed to receive light from micromirrors in an on-state.

2. The system of claim 1, wherein the light source directs light at an angle substantially perpendicular to the switching axes of the micromirrors.

3. The system of claim 1, further comprising a color separating element provided between the light source and the micromirror array.

4. The system of claim 1, wherein the light source is disposed to direct light at the micromirrors such that the light impinges on a leading side of each micromirror at an angle of from 100 to 150 degrees.

5. The system of claim 1, wherein the micromirrors comprise metal and a dielectric material.

6. The system of claim 5, wherein the dielectric material is a nitride, carbide or oxide of silicon.

7. The system of claim 1, wherein the micromirrors are disposed above a circuit substrate.

8. The system of claim 7, wherein the circuit substrate is a CMOS substrate.

9. The system of claim 1, wherein the micromirrors are attached to an upper glass substrate which is bonded to a lower silicon substrate.

10. The system of claim 9, wherein the upper and lower substrates are held together via UV and/or IR epoxy.

11. The system of claim 1, wherein from 64,000 to about 6,000,000 micromirrors are provided in an area of from about 1 cm² to about 1 in².

12. The system of claim 11, further comprising a rectangular mask disposed on or above the micromirror array.

13. The system of claim 1, wherein the micromirror array comprises four corner active micromirrors which define a rectangle with four sides.

14. The system of claim 13, wherein the micromirrors comprise at least four elongated mirror sides, one or more of the mirror sides being neither parallel nor perpendicular to any side of the rectangle defined by the four corner active micromirrors.

15. The system of claim 14, wherein no mirror side is parallel or perpendicular to any side of the micromirror rectangle array.

16. The system of claim 14, wherein at least two mirror sides are neither parallel or perpendicular to the sides of the micromirror array rectangle, and wherein at least two mirror sides are parallel to sides of the micromirror array rectangle.

17. The system of claim 1, wherein each micromirror comprises one or more hinges that extend in a direction at an angle between 0 and 90 degrees from the axis of rotation of the micromirror.

18. The system of claim 17, wherein the one or more hinges extend at an angle of about 45 degrees to the direction of the axis of rotation.

19. The system of claim 1, wherein each micromirror has a shape of a parallelogram or an assembly of parallelograms.

20. The system of claim 19, wherein each micromirror has a shape of an assembly of from 2 to 7 parallelograms.

21. The system of claim 20, wherein each micromirror has a shape of an assembly of from 2 to 4 parallelograms.

22. The system of claim 20, wherein the shape as an assembly of parallelograms appears as a series of parallelograms each a mirror image of an adjacent parallelogram.

23. The system of claim 20, wherein the shape as an assembly of parallelograms appears as a series of identical parallelograms.

24. The system of claim 1, wherein said at least two sides are on the leading and/or trailing sides of the micromirrors.

25. The system of claim 24, wherein the leading and trailing sides are jagged or saw-tooth sides.

26. The system of claim 20, wherein the width of each parallelogram in the assembly has a width substantially greater than the wavelength of light directed at the micromirrors.

27. The system of claim 19, wherein the number of parallelograms is less than M/λ

, where M is the width of the micromirror and λ

is the wavelength of incident light.

28. The system of claim 27, wherein the number of parallelograms is less than 0.5M/λ

.

29. The system of claim 28, wherein the number of parallelograms is less than 0.1M/λ

.

30. The system of claim 1, wherein the micromirrors comprises 5 or more elongated straight sides.

31. The system of claim 30, wherein the 6 or more sides form a shape with at least one projection and cut-out.

32. The system of claim 30, wherein the micromirrors comprise 8 or more sides.

33. The system of claim 31, wherein the projection and cut-out are in the form of a triangle.

34. The system of claim 31, wherein the projection forms an exterior angle of from 70 to 120 degrees, and the cut-out forms a corresponding interior angle of from 70 to 120 degrees.

35. The system of claim 1, wherein the micromirrors have shapes other than substantially rectangular.

36. The system of claim 1, wherein the micromirrors have at least two exterior angles of between 35 and 60 degrees.

37. The system of claim 1, wherein the micromirrors have straight sides that are neither parallel nor perpendicular to the sides of the rectangular active area.

39. The system of claim 38, wherein each micromirror has a shape of a non-rectangular parallelogram or an assembly of non-rectangular parallelograms side by side.

40. The system of claim 39, wherein each micromirror has a shape of an assembly of from 2 to 7 parallelograms.

41. The system of claim 40, wherein each micromirror has a shape of an assembly of from 2 to 4 parallelograms.

42. The system of claim 40, wherein the shape as an assembly of parallelograms appears as a series of parallelograms each a mirror image of an adjacent parallelogram.

43. The system of claim 40, wherein the shape is a concave polygon having six or more sides and at least one concave portion.

44. The system of claim 38, wherein said at least two sides are on the leading and/or trailing sides of the micromirrors.

45. The system of claim 44, wherein the leading and trailing sides are jagged or saw-tooth sides.

46. The system of claim 40, wherein the width of each parallelogram in the assembly has a width substantially greater than the wavelength of light directed at the micromirrors.

47. The system of claim 39, wherein the number of parallelograms is less than M/λ

, where M is the width of the micromirror and λ

is the wavelength of incident light.

48. The system of claim 47, wherein the number of parallelograms is less than 0.5M/μ

.

49. The system of claim 48, wherein the number of parallelograms is less than 0.1M/μ

.

50. The system of claim 38, wherein the micromirrors comprise 6 or more elongated straight sides.

51. The system of claim 50, wherein the 6 or more sides form a shape with at least one projection and cut-out.

52. The system of claim 50, wherein the micromirrors comprise 8 or more sides.

53. The system of claim 51, wherein the projection and cut-out are in the form of a triangle.

54. The system of claim 51, wherein the projection forms an exterior angle of from 70 to 120 degrees, and the cut-out forms a corresponding interior angle of from 70 to 120 degrees.

55. The system of claim 38, wherein the micromirrors have shapes that are substantially different from a square shape.

56. The system of claim 38, wherein the micromirrors have at least two exterior angles of between 35 and 60 degrees.

57. The system of claim 38, wherein the micromirrors have straight sides that are neither parallel nor perpendicular to the sides of the rectangular active area.

58. The system of claim 38, wherein each micromirror has the shape of a concave polygon having more than 4 sides and 4 angles.

38. A projection or direct view light system, comprising:

an array of micromirrors, each micromirror corresponding to a pixel in a viewed image and having a shape of a concave polygon or one or more non-rectangular parallelograms;

a light source for directing light to the array of micromirrors

projection or viewing optics disposed to receive light reflected from the micromirrors.

59. An array of movable mirrors, each mirror having a shape substantially the same as that illustrated in any of FIGS. 14A to F, 15A to F, 17 to 19, and 20A to L.

60. An array of movable micromirrors, the array having a substantially rectangular shape and comprising at least 1,000 micromirrors, wherein the micromirrors are in the shape of a concave or convex polygon and wherein no sides of the polygonal micromirrors are parallel to the sides of the substantially rectangular active area.

61. The array of claim 60, wherein the mirrors have at least 4 substantially straight sides, none of which are parallel to leading or trailing sides of the rectangular active area.

62. The array of claim 61, wherein the array comprises four corner micromirrors which, when connected together, form the rectangular shape of the array.

63. The array of claim 60, wherein the micromirrors have switching axes parallel to at least two sides of the rectangular array.

64. The array of claim 60, wherein each micromirror has a shape of a parallelogram or an assembly of parallelograms.

65. The array of claim 64, wherein each micromirror has a shape of an assembly of from 2 to 7 parallelograms.

66. The array of claim 65, wherein each micromirror has a shape of an assembly of from 2 to 4 parallelograms.

67. The array of claim 65, wherein the shape as an assembly of parallelograms appears as a series of parallelograms each a mirror image of an adjacent parallelogram.

68. The array of claim 65, wherein the shape as an assembly of parallelograms appears as a series of identical parallelograms.

69. The array of claim of claim 60, wherein the micromirrors comprises 5 or more elongated straight sides.

70. The array of claim 69, wherein the micromirrors comprise 6 or more sides form a shape with at least one projection and cut-out.

71. The array of claim 69, wherein the micromirrors comprise 8 or more sides.

72. The array of claim 70, wherein the projection and cut-out are in the form of a triangle.

73. The array of claim 70, wherein the projection forms an exterior angle of from 70 to 120 degrees, and the cut-out forms a corresponding interior angle of from 70 to 120 degrees.

74. The array of claim 60, wherein the micromirrors have at least two polygon sides that form an angle therebetween of less than 90 degrees.

75. The array of claim 74, wherein the micromirrors have at least two polygon sides that form an angle therebetween of from 35 to 60 degrees.

76. The array of claim 60, wherein the micromirrors each have a shape of an assembly of from 1 to 10 parallelograms.

77. The array of claim 60, wherein the micromirrors have sides that are about 35 to 55 degrees to the sides of the active area.

79. The projection system of claim 78, wherein each pixel in the projected image is a concave polygon having more than 4 sides and 4 angles.

80. The projection system of claim 79, wherein each pixel has a shape substantially the same as any of those illustrated in FIGS. 14-19.

81. The projection system of claim 78, where no pixel sides are parallel to at least two of the sides of the rectangular projected image.

82. The projection system of claim 78, wherein at least two pixel sides are non-parallel and non-perpendicular to the projected image sides, and wherein at least two pixel sides are parallel and perpendicular to projected image sides.

83. The projection system of claim 78, wherein at least one pixel side extends in a direction at an angle of from 35 to 85 degrees from one of the projected image sides.

84. The projection system of claim 83, wherein at least two pixel sides extend in a direction at an angle of from 40 to 55 degrees from at least one of the projected image sides.

78. A projection system comprising a light source for providing an incident light beam, an array of movable reflective elements, and projection optics for projecting light from the array, wherein an image projected from the projection system will appear on a target as a rectangular image, with the image being formed of from thousands to millions of pixels, each pixel being in the shape of a concave polygon, a single non-rectangular parallelogram, or an assembly of non-rectangular parallelograms.

85. A projection system comprising a light source, an array of movable mirror elements, and projection optics, wherein each mirror element in the array has a switching axis substantially parallel to at least one side of the active area of the array, and at an angle of from 35 to 60 degrees to one or more sides of the mirror element.

86. A projection system comprising a light source and an array of movable mirror elements, each mirror element having a leading side that is non-perpendicular to the incident light beam, and non-perpendicular to any side of the active area, so as to achieve an increase of 2 to 10 times the contrast ratio compared to mirror elements having perpendicular sides to the incident light beam.

87. A projection system comprising a light source, projection optics, and an array of movable mirror elements, the projection system having a diffraction pattern substantially the same as that illustrated in FIG. 21C.

88. A projection system comprising a light source and a rectangular array of movable mirrors, the mirrors capable of moving between an on-state and an off-state and capable of reflecting light in the on-state to a predetermined spatial area, wherein the light source is disposed to direct light at a substantially 90 degree angle to at least one side of the rectangle defined by the array, and wherein substantially no diffracted light enters the predetermined spatial area when the mirrors are in the off-state.

90. The method of claim 89, wherein the light beam is incident on the leading side of the rectangular array substantially perpendicularly.

89. A method for projecting an image on a target comprising:

directing a light beam onto a rectangular array of mirrors, the light beam directed to the leading side of the rectangular array at an angle within a range of 90 degrees plus or minus 40 degrees, and wherein the mirrors in the array are shaped as polygons and positioned such that the light beam is incident on all of the polygonal sides at angles other than 90 degrees; and

projecting the light from the mirrors onto a target so as to form an image thereon.

91. An array of pivotable mirrors, each mirror having a pivot axis, and each mirror having one or more elongated sides that extend at an angle of less than 45 degrees to the pivot axis.

92. The array of claim 91, wherein the angle is from 30 to 42.5 degrees.

93. An array of movable mirrors, each mirror having four or more sides, wherein two of the sides come together at an angle of less than 90 degrees.

94. The array of claim 93, wherein the angle is from 45 to 85 degrees.