Reduced-speckle display system

• US 5,272,473 A
• Filed: 08/17/1992
• Issued: 12/21/1993
• Est. Priority Date: 02/27/1989
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Thompson, E. Earle, DeMond, Thomas W.
• Primary Examiner(s): BRIER, JEFFERY A
• Application Number:
  US07/931,130
• Time in Patent Office: 491 Days
• Field of Search: 340/702, 340/716, 340/763, 340/764, 340/783, 340/794, 340/795, 350/19, 350/269, 358/60, 358/61, 358/62, 358/201, 358/230, 358/233, 358/236, 358/235, 353/31, 353/34, 353/122
• US Class Current: 345/7
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G09F 19/18 involving the use of optical projection means, e.g. projection of images on clouds projection apparatus per se G03B

Abstract

A digitized video system with an increased viewing angle having a light projector and a display screen. The light projector generating a plurality of narrow light beams to impinge on the display screen at a plurality of associated points. The display screen has a transducer generating surface acoustic waves which traverse the associated points. This results in reduced laser speckle.

Claims

1. A coherent light projection system having reduced speckle comprising:

a coherent light source;

a display screen;

said coherent light source for generating a light beam to impinge on said display screen at a point; and

said display screen having a transducer coupled thereto operative to generate surface acoustic waves wherein said surface acoustic waves traverse said point.

2. The projection system as claimed in claim 1 wherein said surface acoustic waves have an ultrasonic frequency.

3. The projection system as claimed in claim 1 wherein said display screen is of a back projection configuration.

4. The projection system as claimed in claim 1 wherein said coherent light source is a laser.

5. The projection system as claimed in claim 1 wherein said surface acoustic waves have an amplitude greater than one wavelength of said light beam.

6. The projection system as claimed in claim 1 wherein said display system further comprises a spatial light modulator operative to direct said light beam to impinge on said display screen.

7. The projection system as claimed in claim 1 wherein said surface acoustic waves are substantially parallel.

8. A method of reducing speckle in a coherent light source projection system having a display screen comprising:

generating a surface acoustic wave that traverses said display screen;

generating a coherent light beam;

directing said coherent light beam toward said display screen; and

said coherent light beam impinging said display screen at a point where said surface acoustic wave traverses said display screen.

9. The method as claimed in claim 8 wherein said light beam substantially passes through said display screen.

10. The method as claimed in claim 8 wherein said directing step is performed by modulating at least one element of a spatial light modulator.

11. A coherent light projection system having reduced speckle comprising:

a coherent light source;

said coherent light source for generating a first light beam;

a spatial light separator for dividing said first light beam into a plurality of second light beams, wherein said separator comprises an array of separately controlled, discrete elements;

a display screen for receiving predetermined ones of said second light beams; and

selected ones of said predetermined ones of said second light beams have different phases when received by said display screen.

12. The projection system as claimed in claim 11 wherein said display screen is of a back projection configuration.

13. The projection system as claimed in claim 11 wherein said coherent light source is a laser.

14. The projection system as claimed in claim 11 wherein said spatial light separator is a spatial light modulator.

15. The projection system as claimed in claim 11 wherein said different phases of said selected ones of said predetermined ones of said second light beams are the result of differing optical path lengths.

16. The projection system as claimed in claim 11 wherein said said selected ones of said predetermined ones of said second light beams have differing optical path lengths to said display screen.

17. A method for reducing speckle in a coherent light projection system comprising:

generating a first coherent light beam;

dividing said first coherent light beam into a plurality of second coherent light beams, with the use of a spatial light separator comprising an array of individually controlled discrete elements; and

directing predetermined ones of said second coherent light beams toward a display screen wherein selected ones of said predetermined ones of said second coherent light beams are in differing phase when they impinge said display screen.

18. The method as claimed in claim 17 wherein said predetermined light beams substantially pass through said display screen.

19. The method as claimed in claim 17 including the step of varying the optical path length of different ones of said coherent light beams.

20. The method as claimed in claim 17 wherein said dividing step and said directing step are substantially simultaneously performed by said spatial light separator.

21. A projection system having increased viewing angle comprising:

a light projector;

a display screen;

said light projector for generating a plurality of narrow light beams to impinge on said display screen at a plurality of associated points; and

said display screen having a transducer coupled thereto operative to generate surface acoustic waves wherein said surface acoustic waves traverse said associated points.

22. The projection system as claimed in claim 21 wherein said surface acoustic waves have an ultrasonic frequency.

23. The projection system as claimed in claim 21 wherein said display screen is of a back projection configuration.

24. The projection system as claimed in claim 21 wherein said light projector includes a laser light source.

25. The projection system as claimed in claim 21 wherein said surface acoustic waves have an amplitude greater than one wavelength of the longest visible light.

26. The projection system as claimed in claim 21 wherein said light projector includes a spatial light modulator operative to direct said light beams to impinge on said display screen.

27. The projection system as claimed in claim 26 wherein said spatial modulator includes:

an array of individual display cells;

at least two memory cells associated with each display cell;

a first decoder for addressing a plurality of memory cells for storing information therein; and

a second decoder for addressing substantially all of said display cells to display an image.

28. The projection system as claimed in claim 21 wherein said surface acoustic waves are substantially parallel.

29. A method of varying the dispersion of light from a surface comprising the steps of:

generating surface acoustic waves to traverse a surface;

generating a beam of light; and

impinging said beam on said surface for a time period at least sufficient to allow one of said surface acoustic waves to traverse the area of said surface impinged by said beam.

30. The method as claimed in claim 29 including the step of reflecting portions of said beam at varying angles in response to said one of said surface acoustic waves traversing said area.

31. The method as claimed in claim 29 including the step of diffracting portions of said beam at varying angles in response to said one of said surface acoustic waves traversing said area.