Systems and methods for speckle reduction

• US 20090244684A1
• Filed: 03/27/2008
• Published: 10/01/2009
• Est. Priority Date: 03/27/2008
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Gollier, Jacques
• Granted Patent: US 7,997,735 B2
• Time in Patent Office: Days
• US Class Current: 359/278
• CPC Class Codes: G02B 13/22 Telecentric objectives or lens systems
• CPC Class Codes: G02B 27/48 Laser speckle optics

Abstract

A laser projection system including a system controller, a visible light source, and a light disrupting element is provided. The visible light source includes at least one laser and the laser projection system is programmed to scan a scanned optical signal of the visible light source across a plurality of image pixels. The scanned optical signal comprises a low spatial frequency beam and a high spatial frequency beam, and the low spatial frequency beam generates a low spatial frequency image having spatial frequencies below a spatial frequency threshold, the high spatial frequency beam generates a high spatial frequency image having spatial frequencies that are above the spatial frequency threshold, and the scanned laser image is a sum of the high spatial frequency image and the low spatial frequency image. The low spatial frequency beam is altered by an out of focus light disrupting element.

Claims

1. A laser projection system comprising a system controller, a visible light source, and a light disrupting element, wherein the visible light source comprises at least one laser, and the laser projection system is programmed to:

generate at least a portion of a scanned laser image by operating the laser for optical emission of encoded image data and controlling a scanning element to scan an optical signal of the visible light source across a plurality of image pixels, wherein the scanned optical signal comprises a low spatial frequency beam and a high spatial frequency beam, and the low spatial frequency beam generates a low spatial frequency image having spatial frequencies below a spatial frequency threshold, the high spatial frequency beam generates a high spatial frequency image having spatial frequencies that are above the spatial frequency threshold, and the scanned laser image is a sum of the high spatial frequency image and the low spatial frequency image; and

alter the low spatial frequency beam by directing and focusing the low spatial frequency beam upon an out of focus light disrupting element, wherein the light disrupting element is out of focus with respect to an intermediate image that is formed by scanning and focusing the low spatial frequency beam.

2. The laser projection system as claimed in claim 1 wherein the light disrupting element comprises a spatial light modulator, a diffusing optical element or a diffracting optical element.

3. The laser projection system as claimed in claim 1 wherein the low spatial frequency beam and the high spatial frequency beam are generated by a single laser and a beam splitting element.

4. The laser projection system as claimed in claim 1 wherein:

a low spatial frequency laser generates the low spatial frequency beam;

a high spatial frequency laser generates the high spatial frequency beam; and

the low spatial frequency laser and the high spatial frequency laser emit wavelengths that are approximately equal.

5. The laser projection system as claimed in claim 1 wherein the scanned optical signal comprises a blue beam, a red beam and a green beam, and only the green beam is split such that the low spatial frequency beam comprises a low frequency portion of the green beam and the high spatial frequency beam comprises the blue beam, the red beam and a high frequency portion of the green beam.

6. The laser projection system as claimed in claim 1 wherein the light disrupting element comprises a passive optical element, and the laser projection system is programmed to direct the low spatial frequency beam toward the passive optical element, and direct the high spatial frequency beam away from the passive optical element.

7. The laser projection system as claimed in claim 6 wherein the passive optical element comprises a diffusing optical element or a diffracting optical element.

8. The laser projection system as claimed in claim 1 wherein:

the light disrupting element comprises a passive optical element;

the laser projection system further comprises a polarization modulator positioned in a path of the optical signal and programmed such that the polarization modulator modulates the polarization of the optical signal between a first polarization state and a second polarization state, wherein the first and second polarization states are orthogonal; and

the laser projection system further comprises a polarizing beam splitter that splits the scanned optical signal into the low spatial frequency beam and the high spatial frequency beam, and directs the low spatial frequency beam toward the passive optical element and the high spatial frequency beam toward a projection surface, wherein the low spatial frequency has the first polarization state and the high spatial frequency has the second polarization state.

9. The laser projection system as claimed in claim 8 wherein:

the polarization modulator comprises a two dimensional polarization modulator positioned in the path of the optical signal after the scanning element;

the two dimensional polarization modulator further comprises a plurality of modulator pixels; and

the two dimensional polarization modulator locally modulates the polarization of the scanned optical signal as the optical signal is scanned across the two dimensional polarization modulator by switching the phase of individual modulator pixels that correspond to the low spatial frequency image.

10. The laser projection system as claimed in claim 8 wherein the polarization modulator comprises a single polarization modulator positioned in the path of the optical signal prior to the scanning element.

11. The laser projection system as claimed in claim 10 wherein:

the high spatial frequency beam comprises a red beam, a blue beam and a portion of a green beam that corresponds to the high spatial frequency image;

the low spatial frequency beam comprises a portion of the green beam that corresponds to the low spatial frequency image; and

the laser projection system further comprises a dichroic beam splitter such that the high spatial frequency beam is reflected by the dichroic beam splitter, and the low spatial frequency beam is reflected by the polarizing beam splitter as a function of polarization.

12. The laser projection system as claimed in claim 8 wherein:

the low spatial frequency beam is transmitted through the polarizing beam splitter and the high spatial frequency beam is reflected by the polarizing beam splitter;

the reflected high spatial frequency beam is reflected toward a projection surface;

the transmitted low spatial frequency beam is imaged by a lens toward the passive optical element; and

the passive optical element disrupts and reflects the transmitted low spatial frequency beam through the lens and toward the polarizing beam splitter.

13. The laser projection system as claimed in claim 8 wherein:

the high spatial frequency beam is transmitted through the polarizing beam splitter and the low spatial frequency beam is reflected by the polarizing beam splitter;

the transmitted high spatial frequency beam is directed toward a projection surface;

the reflected low spatial frequency beam is imaged by a lens toward the passive optical element; and

the passive optical element disrupts and reflects the reflected low spatial frequency beam through the lens and toward the polarizing beam splitter.

14. The laser projection system as claimed in claim 8 wherein:

the low spatial frequency beam is directed toward the passive optical element through a lens such that the passive optical element disrupts and reflects the low spatial frequency beam;

the laser projection system further comprises a first quarter wave plate positioned between the passive optical element and the lens;

the first quarter wave plate rotates the polarization state of the low spatial frequency beam;

the low spatial frequency beam is transmitted through the lens toward the polarizing beam splitter;

the polarizing beam splitter reflects the low spatial frequency beam toward a second quarter plate that rotates the polarization of the low spatial frequency beam and reflects the low spatial frequency beam toward the polarizing beam splitter; and

the low spatial frequency beam is transmitted through the polarizing beam splitter toward the projection surface.

15. The laser projection system as claimed in claim 8 wherein:

the low spatial frequency beam comprises a low spatial frequency power;

the high spatial frequency beam comprises a high spatial frequency power; and

the laser projection system is programmed to adjust a ratio between the low spatial frequency power and the high spatial frequency power by adjusting a level of modulation provided by the polarization modulator.

16. The laser projection system as claimed in claim 1 wherein the light disrupting element comprises a spatial light modulator.

17. The laser projection system as claimed in claim 16 wherein the spatial light modulator is configured to selectively switch the phase of individual ones of the plurality of image pixels generated by the scanned optical signal and the laser projection system is programmed such that the spatial light modulator selectively switches the phase of individual ones of the plurality of image pixels that correspond to the low spatial frequency image.

18. The laser projection system as claimed in claim 16 wherein the spatial light modulator is configured to selectively disrupt individual ones of the plurality of image pixels generated by the scanned optical signal and the laser projection system is programmed such that the spatial light modulator selectively disrupts individual ones of the plurality of image pixels that correspond to the low spatial frequency image.

19. The laser projection system as claimed in claim 18 wherein the scanned optical signal comprises a red beam, a blue beam and a green beam, and the laser projection system further comprises:

a field lens that receives the scanned optical signal from the scanning element and corrects a field curvature associated with the scanned optical signal and the scanned laser image;

a dichroic mirror that reflects the red beam and the blue beam, and transmits the green beam toward the spatial light modulator; and

a projection lens that projects the reflected red beam, the reflected blue beam and the reflected green beam onto a projection surface.

20. The laser projection system as claimed in claim 19 wherein the laser projection system is programmed such that the spatial light modulator disrupts the green beam by switching the phase of the green beam in the portions of the scanned laser image corresponding to the low spatial frequency image.

21. The laser projection system as claimed in claim 19 wherein the laser projection system further comprises a focusing lens that converges the red beam, blue beam and green beam of the scanned optical signal onto the scanning element.

22. The laser projection system as claimed in claim 19 wherein:

the dichroic mirror is positioned adjacent to the spatial light modulator; and

the dichroic mirror and the spatial light modulator are tilted such that the red beam, blue beam and green beam converge at a position near the scanning element.

23. The laser projection system as claimed in claim 18 wherein:

the spatial light modulator comprises a one dimensional spatial light modulator and is configured to generate at least one line image;

the scanned optical signal illuminates the one dimensional spatial light modulator; and

the one dimensional spatial light modulator is programmed such that the one dimensional spatial light modulator reflects and scans the at least one line image across the projection surface to generate the scanned laser image.

24. The laser projection system as claimed in claim 18 wherein the laser projection system further comprises a two dimensional spatial light modulator comprising a plurality of phase modulating pixels.

25. A method of controlling a laser projection system comprising a visible light source and a light disrupting element, wherein the visible light source comprises at least one laser, and the method comprises:

generating at least a portion of a scanned laser image by configuring the at least one laser for optical emission of encoded image data and controlling a scanning element to scan an output beam of the visible light source across a plurality of image pixels, wherein the scanned optical signal comprises a low spatial frequency beam and a high spatial frequency beam, and the low spatial frequency beam generates a low spatial frequency image having spatial frequencies below a spatial frequency threshold and the high spatial frequency beam generates a high spatial frequency image having spatial frequencies that are above the spatial frequency threshold; and

selectively disrupting the low spatial frequency beam by directing the low spatial frequency beam upon an out of focus light disrupting element, wherein the light disrupting element is out of focus with respect to an intermediate image that is formed by scanning and focusing the low spatial frequency beam.