Projection system having low astigmatism

• US 6,786,604 B2
• Filed: 05/29/2002
• Issued: 09/07/2004
• Est. Priority Date: 06/11/2001
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Bruzzone, Charles L., Ma, Jiaying, Aastuen, David J. W.
• Primary Examiner(s): Adams, Russell
• Assistant Examiner(s): SEVER, ANDREW T
• Application Number:
  US10/159,694
• Publication Number:
  US 20030048423A1
• Time in Patent Office: 832 Days
• Field of Search: 353/20, 353/31, 353/33, 353/69, 353/81, 353/84
• US Class Current: 353/20
• CPC Class Codes: G02B 27/1026 for use with reflective spatial light modulators
• CPC Class Codes: G02B 27/1033 having a single light modulator for all colour channels
• CPC Class Codes: G02B 27/126 The splitting element being a prism or prismatic array, including systems based on total internal reflection
• CPC Class Codes: G02B 27/145 having sequential partially reflecting surfaces
• CPC Class Codes: G02B 27/149 using crossed beamsplitting surfaces, e.g. cross-dichroic cubes or X-cubes
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10
• CPC Class Codes: H04N 9/3167 for polarizing the light beam polarizing optical systems per se G02B27/28

Abstract

LCD projection systems that use reflective LCD imager units commonly use one or more polarization beamsplitters to separate the light incident on the imager from the light reflected by one or more respective imagers. The polarizing beamsplitters introduce astigmatism to the image light from the imagers. According to the present invention, the polarization beamsplitters are adapted to reduce the astigmatism.

Claims

1. A projection system, comprising:

a light source to generate light;

an imaging core including at least a first reflecting imager and a first polarizing beamsplitter to impose an image on light received from the light source, the first polarizing beamsplitter being adapted to reduce astigmatism in the image light reflected from the reflecting imager; and

a projection lens system to project the astigmatism-reduced image light from the imaging core.

2. A system as recited in claim 1, wherein the imaging core further includes a second reflecting imager and a second polarizing beamsplitter, the first and second reflective imagers and the first and second polarizing beamsplitters imposing light on respective first and second color bands.

3. A system as recited in claim 2, wherein the imaging core includes a color combiner disposed to combine the image light in the respective color bands received from the at least first and second reflective imagers.

4. A system as recited in claim 3, further comprising a polarization rotation element disposed between one of the first and second polarizing beamsplitters and the color combiner.

5. A system as recited in claim 3, further comprising a third reflective imager and a third polarizing beamsplitter, wherein the color combiner is an x-cube color combiner disposed to combine image light from the first, second and third reflective imagers.

6. A system as recited in claim 5, further comprising a polarization rotating element disposed between the color combiner and at least one of the first, second and third polarizing beamsplitters.

7. A system as recited in claim 3, further comprising color separating optical elements disposed to separate light from the light source into the respective color bands directed to the at least first and second reflective imagers.

8. A system as recited in claim 3, further comprising a temporally modulated color filter disposed in a beam of light directed to at least one of the reflective imagers so as to modulate the color of light directed to the at least one of the reflective imagers.

9. A system as recited in claim 8, wherein the temporally modulated color filter is a color wheel.

10. A system as recited in claim 9, further comprising a controller coupled to synchronize timing of the temporally modulated color wheel with image information directed to the at least one of the reflective imagers.

11. A system as recited in claim 8, wherein the temporally modulated color filter is an electro-optic color switch.

12. A system as recited in claim 11, further comprising a controller coupled to synchronize timing of the temporally modulated electro-optic color switch with image information directed to the at least one of the reflective imagers.

13. A system as recited in claim 1, wherein astigmatism in the image light is reduced to a value less than a depth of field of the projection lens system.

14. A system as recited in claim 1, further comprising light conditioning optics disposed between the light source and the imaging core.

15. A system as recited in claim 1, further comprising a controller coupled to the at least a first reflecting imager to control the image imposed on light incident on the at least a first reflecting imager.

16. A system as recited in claim 1, wherein the first polarizing beamsplitter is a Cartesian polarizing beamsplitter.

17. A system as recited in claim 1, further comprising light conditioning optics disposed between the light source and the imaging core having an f-number equal to or less than 2.5.

18. A system as recited in claim 17, wherein the projection lens system has an f-number matched to the f-number of the conditioning optics.

19. A system as recited in claim 1, wherein the imaging core is designed for telecentric illumination and projection.

20. A system as recited in claim 1, wherein the first polarizing beamsplitter includes a polarization sensitive, reflective multilayer film having refractive indices in a first refractive index range, and covers on either side of the polarization sensitive, reflective multilayer film having a second refractive index higher than the first refractive index range, a sheet of material lying between the multilayer film and one of the covers having a third refractive index higher than the second refractive index.

21. A system as recited in claim 1, wherein the first polarizing beamsplitter includes a multilayer, polarization sensitive reflective film disposed between first and second covers, a wedge of a wedge material being disposed between multilayer film and one of the covers, the wedge material having a refractive index less than the refractive index of the covers.

22. A system as recited in claim 1, wherein the light from the light source is reflected in the first polarizing beamsplitter and the image light reflected from the imager is transmitted through the first polarizing beam splitter.

23. A projection system, comprising:

light generating means for generating light;

imaging core means for imposing an image on light received from the light generating means, the imaging core means including at least first imager means and first polarization beamsplitting means for polarization mode beamsplitting, at least one of the beamsplitting means being adapted to reduce astigmatism in the image light; and

a projection lens unit to project the astigmatism-reduced image light from the imaging core means.

24. A polarizing beamsplitter, comprising:

a multilayer, polarization sensitive film disposed between covers and an astigmatism reducing element disposed between opposing outside faces of the covers to reduce astigmatism introduced by the polarizing film.

25. A beamsplitter as recited in claim 24, wherein multilayer, polarization sensitive film is a multilayer polymer, polarization sensitive film.

26. A beamsplitter as recited in claim 24, wherein the astigmatism reducing element is disposed between the covers.

27. A beamsplitter as recited in claim 24, wherein the covers are formed of a material having a refractive index higher than the refractive index of the multilayer film.

28. A polarizing beamsplitter as recited in claim 24, wherein the astigmatism compensating element is a plate of material disposed between the covers and having a refractive index higher than the refractive index of the first and second covers.

29. A polarizing beamsplitter as recited in claim 24, wherein the astigmatism compensating element is a wedge of material having a refractive index less than the refractive index of the first and second covers.

30. A polarizing beamsplitter as recited in claim 24, wherein the covers are glass prisms.

31. A polarizing beamsplitter as recited in claim 24, wherein the multilayer polarization sensitive film is optimized for polarization sensitivity in one of a red, green or blue projection color band.

32. A projection system, comprising:

a light source to generate light;

an imaging core including at least a first reflecting imager and a first polarizing beamsplitter to impose an image on light received from the light source, the first polarizing beamsplitter including a multilayer polarizing film disposed between covers and an astigmatism reducing element to reduce astigmatism introduced by the polarizing film; and

a projection lens system to project image light received from the imaging core.

33. A system as recited in claim 32, wherein the imaging core further includes a second reflecting imager and a second polarizing beamsplitter, the first and second reflective imagers and the first and second polarizing beamsplitters imposing light on respective first and second color bands.

34. A system as recited in claim 33, wherein the imaging core includes a color combiner disposed to combine the image light in the respective color bands received from the at least first and second reflective imagers.

35. A system as recited in claim 34, further comprising a polarization rotation element disposed between one of the first and second polarizing beamsplitters and the color combiner.

36. A system as recited in claim 34, further comprising a third reflective imager and a third polarizing beamsplitter, wherein the color combiner is an x-cube color combiner disposed to combine image light from the first, second and third reflective imagers.

37. A system as recited in claim 36, further comprising a polarization rotating element disposed between the color combiner and at least one of the first, second and third polarizing beamsplitters.

38. A system as recited in claim 34, further comprising color separating optical elements disposed to separate light from the light source into the respective color bands directed to the at least first and second reflective imagers.

39. A system as recited in claim 34, further comprising a temporally modulated color filter disposed in a beam of light directed to at least one of the reflective imagers so as to modulate the color of light directed to the at least one of the reflective imagers.

40. A system as recited in claim 32, wherein astigmatism in the image light is reduced to a value less than a depth of field of the projection lens system.

41. A system as recited in claim 32, further comprising light conditioning optics disposed between the light source and the imaging core.

42. A system as recited in claim 32, further comprising a controller coupled to the at least a first reflecting imager to control the image imposed on light incident on the at least a first reflecting imager.

43. A system as recited in claim 32, wherein the first polarizing beamsplitter is a Cartesian polarizing beamsplitter.

44. A system as recited in claim 32, further comprising light conditioning optics disposed between the light source and the imaging core having an f-number of no more than 2.5.

45. A system as recited in claim 32, wherein the imaging core is designed for telecentric illumination and projection.

46. A system as recited in claim 32, wherein the multilayer film has refractive indices in a first refractive index range, and the covers have a second refractive index higher than the first refractive index range, the astigmatism reducing element including a sheet of material lying between the multilayer film and one of the covers having a third refractive index higher than the second refractive index.

47. A system as recited in claim 32, wherein the astigmatism reducing element includes a wedge of a wedge material being disposed between multilayer film and one of the covers, the wedge material having a refractive index less than the refractive index of the covers.

48. A system as recited in claim 32, wherein the multilayer, polarization sensitive film is a multilayer polymer, polarization sensitive film.