Laser illuminated projection displays

• US 20060126022A1
• Filed: 12/14/2004
• Published: 06/15/2006
• Est. Priority Date: 12/14/2004
• Status: Active Grant

• Current Assignee: Coherent Inc (Coherent Corp.)
• Original Assignee: Coherent Inc (Coherent Corp.)
• Inventors: Caprara, Andrea, Reed, Murray K., Chilla, Juan L., Govorkov, Sergei V., Spinelli, Luis A.
• Granted Patent: US 7,244,028 B2
• Time in Patent Office: Days
• US Class Current: 353/31
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G03B 21/10 Projectors with built-in or built-on screen
• CPC Class Codes: G03B 21/56 Projection screens
• CPC Class Codes: G03B 21/62 Translucent screens
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161
• CPC Class Codes: H04N 9/3152 for shaping the light beam beam shaping per se G02B27/09
• CPC Class Codes: H04N 9/3161 using laser light sources using laser beams scanning the display screen H04N9/3129

Abstract

A projection video display includes at least one laser for delivering a light beam. The display includes a beam homogenizer and a condenser lens. A scanning arrangement is provided for scanning the light in beam in a particular pattern over the condenser lens in a manner that effectively increases the beam divergence. The scanned beam is homogenized by a beam homogenizer and a spatial light modulator is arranged to receive the homogenized scanned light beam and spatially modulate the beam in accordance with a component of an image to be displayed. Projection optics are projecting the homogenized scanned light beam onto a screen. The scanning provides that the homogenized scanned light beam at the screen has a coherence radius less than the original coherence radius of the beam. The reduced coherence radius contributes to minimizing speckle contrast in the image displayed on the screen. The screen includes one or more features providing a further contribution to minimizing speckle contrast in the displayed image. In one example, the screen includes a transparent cell containing a liquid having light scattering particles in suspension.

Claims

1. A projection display, comprising:

at least one laser for delivering a light beam, said light beam of having an original beam divergence and an original coherence radius, and propagating along a beam path;

a beam homogenizer;

a first lens;

a scanning arrangement for scanning said light in beam in a particular pattern over said first lens, such that, averaged over a time less than about the response time of a human eye, said light beam has an effective beam divergence greater than said original divergence thereof, said scanned beam being delivered from said first lens into said beam homogenizer to be homogenized thereby;

a spatial light modulator, said spatial light modulator arranged to receive said scanned light beam homogenized by said beam homogenizer and spatially modulate said homogenized scanned light beam in accordance with a component of an image to be displayed;

a screen for displaying said image;

projection optics for projecting said homogenized scanned light beam onto said screen, said homogenized scanned light beam at said screen having a reduced coherence radius less than said original coherence radius thereof as a result of said scanning thereof, said reduced coherence radius providing a first contribution to minimizing speckle contrast in said image displayed on said screen; and

wherein, said screen includes one or more features for providing a second contribution to minimizing speckle contrast in said image displayed thereon.

2. The display of claim 1, wherein said scanning arrangement includes a rotatable prism disposed in said beam path in a manner such that when said prism is rotated said light beam is scanned in an annular pattern over said first lens.

3. The display of claim 1, wherein said scanning arrangement includes a fixed mirror disposed in said beam path, and directing said common path onto a rotatable mirror arranged at an angle to a rotation axis thereof in a manner such that when said rotatable mirror is rotated said light beam is scanned in an annular pattern over said first lens.

4. The display of claim 1, wherein said scanning arrangement includes first and second rotatable mirrors, each thereof inclined to a rotation axis thereof and having a second lens therebetween, said first rotatable mirror being disposed on said beam path in a manner such that when said first mirror is rotated said light beam is scanned over said second lens in a first annular pattern, said second lens being arranged to focus said first annular pattern onto said second rotatable mirror, and said second rotatable mirror being arranged such that rotation thereof, while said first mirror is rotating causes said first annular pattern to be scanned over said first lens in a second annular pattern.

5. The display of claim 1, wherein said scanning arrangement includes first and second rotatable faceted scanning wheels having a second lens therebetween, said facets of said first rotatable scanning wheel being disposed on said beampath in a manner such that when said first scanning wheel is rotated said light beam is scanned over said second lens in a first transverse axis, said second lens being arranged to focus said scanned beam onto facets of said second rotatable scanning wheel, and said second scanning wheel being arranged such that rotation thereof, while said first scanning wheel is rotating, causes said focused scanned beam be scanned over said first lens in a second axis perpendicular to said first axis, whereby said light beam is scanned in a raster pattern over said first lens.

6. The display of claim 1, wherein said scanning arrangement includes first and second reciprocally rotatable galvanometer mirrors having a second lens therebetween, said first galvanometer mirror being disposed on said beam path in a manner such that when said first galvanometer mirror is rotated said light beam is scanned over said second lens in a first axis, said second lens being arranged to focus said scanned beam onto said second galvanometer mirror, and said second galvanometer mirror being arranged such that rotation thereof causes said focused scanned beam to be scanned over said first lens in a second axis perpendicular to said first axis, whereby said red, green blue beams are scanned in a raster pattern over said first lens.

7. The display of claim 1, wherein said scanning arrangement includes a rotatable faceted scanning wheel rotatable about a rotation axis, facets of said scanning wheel being inclined at a plurality of different angles to said rotation axis thereof, and said scanning wheel being disposed on said beam path in a manner such that when said scanning wheel is rotated said light beam is scanned by said facets in mutually perpendicular axes in a raster pattern over said first lens.

8. The display of claim 1, wherein said original coherence radius is about equal to the radius of said light beam at said laser, said effective beam divergence is equal to about Θ

_A, where Θ

_A is the acceptance angle of said projection optics, and said reduced coherence radius r_c has a value about equal to λ

/Θ

_S, where λ

is the wavelength of said light beam and Θ

_S is is the angle subtended by said projection optics at said screen.

9. The display of claim 1, wherein said laser is one of first, second, and third lasers included in the display for generating and delivering respectively a red light beam, a green light beam and a blue light beam.

10. The display of claim 9, wherein said display further includes an optical arrangement for combining said red, blue, and green, light beams along said beam path.

11. The display of claim 9, wherein said laser is an optically pumped semiconductor laser (OPS-laser).

12. The display of claim 11, wherein said light beam delivered by said OPS-laser is delivered in a plurality of transverse modes.

13. The display of claim 12, wherein said light beam has a divergence M² between about 2 and 20.

14. The display of claim 1, wherein said screen includes a first transparent sheet having a plurality of raised features distributed over a surface thereof, each of said features having a dimension greater than said reduced coherence radius of said light beam, but less than a dimension that would be resolvable by a normal human eye at a normal viewing distance from said screen.

15. The display of claim 14, wherein said surface features include a first parallel array of cylindrical microlenses.

16. The display of claim 15, wherein said surface features further include a second parallel array of cylindrical microlenses on an opposite surface of said transparent sheet, said second parallel array of cylindrical microlenses being oriented perpendicular to said first parallel array of cylindrical microlenses.

17. The display of claim 15, further includes a second transparent sheet, and wherein said surface features further include a second parallel array of cylindrical microlenses on a surface of said second transparent sheet, said second parallel array of cylindrical microlenses being oriented perpendicular to said first array of cylindrical microlenses.

18. The display of claim 14, wherein said surface features include a regular two-dimensional array of convex spherical microlenses.

19. The display of claim 18, wherein said microlenses are contiguous.

20. The display of claim 18, wherein said microlenses are spaced apart and are separated by a distance greater than said reduced coherence radius of said light beam, but less than a dimension that would be resolvable by a normal human eye at a normal viewing distance from said screen.

21. The display of claim 1, wherein said screen includes a transparent cell containing a transparent fluid having particles therein, said particles having a dimension sufficiently small to scatter light.

22. The display of claim 21, wherein said particles have a dimension less than about 10 micrometers.

23. The display of claim 21, wherein said transparent cell includes an agitating arrangement operable for causing said particles to be in random motion with each other.

24. The display of claim 23, wherein said agitating arrangement includes at least one rotatable blade located in said cell.

25. The display of claim 24, wherein said agitating arrangement includes at least a plurality of said rotatable blades located along a periphery of said cell.

26. The display of claim 25, wherein each of said blades is rotated magnetically by a drive a drive unit located outside of said cell.

27. The display of claim 21, wherein said particles include particles of one of silicon dioxide, aluminum oxide, and titanium oxide.

28. The display of claim 21, wherein said transparent fluid is water.

29. The display of claim 21, wherein said cell has an RF transducer therein operable for discouraging said particles from coagulating.

30. The display of claim 1, wherein said screen includes a transparent cell containing a transparent fluid having particles therein, said particles having a dimension sufficiently small to scatter light and sufficiently small that said particles are suspended in said fluid in Brownian motion with respect to each other.

31. The display of claim 30, wherein said particles have a dimension less than about one micrometer.

32. A projection display, comprising:

at least one laser for delivering a light beam, said light beam of having an original beam divergence and an original coherence radius, and propagating along a beam path;

a beam homogenizer;

a first lens;

a scanning arrangement for scanning said light in beam in a particular pattern over said first lens, such that, averaged over a time less than about the response time of a human eye, said light beam has an effective beam divergence greater than said original divergence thereof, said scanned beam being delivered from said first lens into said beam homogenizer to be homogenized thereby;

a spatial light modulator, said spatial light modulator arranged to receive said scanned light beam homogenized by said beam homogenizer and spatially modulate said homogenized scanned light beam in accordance with a component of an image to be displayed;

a screen for displaying said image;

projection optics for projecting said homogenized scanned light beam onto said screen, said homogenized scanned light beam at said screen having a reduced coherence radius less than said original coherence radius thereof as a result of said scanning thereof; and

wherein, said screen includes a first transparent sheet having a plurality of raised features distributed over a surface thereof, each of said features having a dimension greater than said reduced coherence radius of said light beam, but less than a dimension that would be resolvable by a normal human eye at a normal viewing distance from said screen.

33. The display of claim 32, wherein said surface features include a first parallel array of cylindrical microlenses.

34. The display of claim 33, wherein said surface features further include a second parallel array of cylindrical microlenses on an opposite surface of said transparent sheet, said second parallel array of cylindrical microlenses being oriented perpendicular to said first parallel array of cylindrical microlenses.

35. The display of claim 33, further includes a second transparent sheet, and wherein said surface features further include a second parallel array of cylindrical microlenses on a surface of said second transparent sheet, said second parallel array of cylindrical microlenses being oriented perpendicular to said first array of cylindrical microlenses.

36. The display of claim 32, wherein said surface features include a regular two-dimensional array of convex spherical microlenses.

37. The display of claim 36, wherein said microlenses are contiguous.

38. The display of claim 36, wherein said microlenses are spaced apart by a distance greater than said reduced coherence radius of said light beam, but less than a dimension that would be resolvable by a normal human eye at a normal viewing distance from said screen.

39. A projection display, comprising:

at least one laser for delivering a light beam, said light beam of having an original beam divergence and an original coherence radius, and propagating along a beam path;

an arrangement for homogenizing said light beam delivered by said laser;

a spatial light modulator, said spatial light modulator arranged to receive said homogenized light beam and spatially modulate said homogenized light beam in accordance with a component of an image to be displayed;

a screen for displaying said image;

projection optics for projecting said homogenized light beam onto said screen; and

wherein, said screen includes a transparent cell containing a transparent fluid having particles therein, said particles having a dimension sufficiently small to scatter light.

40. The display of claim 39, wherein said particles have a dimension less than about 10 micrometers.

41. The display of claim 39, wherein said transparent cell includes an agitating arrangement operable for causing said particles to be in random motion with each other.

42. The display of claim 41, wherein said agitating arrangement includes at least one rotatable blade located in said cell.

43. The display of claim 42, wherein said agitating arrangement includes at least a plurality of said rotatable blades located along a periphery of said cell.

44. The display of claim 43, wherein each of said blades is rotated magnetically by a drive a drive unit located outside of said cell.

45. The display of claim 39, wherein said particles include particles of one of silicon dioxide, aluminum oxide, and titanium oxide.

46. The display of claim 39, wherein said transparent fluid is one of water or an organic fluid.

47. The display of claim 39, wherein said cell has an RF transducer therein operable for discouraging said particles from coagulating.

48. The display of claim 39, wherein said particles also have a dimension sufficiently small that said particles are suspended in said fluid in Brownian motion with respect to each other.

49. The display of claim 48, wherein said particles have a dimension less than about one micrometer.

50. A screen for a projection display, comprising:

a transparent cell containing a transparent fluid having particles therein, said particles having a dimension sufficiently small to scatter light.

51. The screen of claim 50, wherein said particles have a dimension less than about 10 micrometers.

52. The display of claim 50, wherein said transparent cell includes an agitating arrangement operable for causing said particles to be in random motion with each other.

53. The display of claim 50, wherein said particles also have a dimension sufficiently small that said particles are suspended in said fluid in Brownian motion with respect to each other.

54. The screen of claim 53, wherein said particles have a dimension less than about 1 micrometer.