DIFFUSER CONFIGURATION FOR AN IMAGE PROJECTOR

• US 20090185141A1
• Filed: 01/22/2008
• Published: 07/23/2009
• Est. Priority Date: 01/22/2008
• Status: Active Grant

• Current Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Chen, Gang, Ryf, Roland
• Granted Patent: US 8,109,638 B2
• Time in Patent Office: Days
• US Class Current: 353/38
• CPC Class Codes: G02B 13/22 Telecentric objectives or lens systems
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G02B 5/02 Diffusing elements; Afocal elements
• CPC Class Codes: G03B 21/14 Details
• CPC Class Codes: G03B 21/2033 LED or laser light sources
• CPC Class Codes: G03B 21/208 Homogenising, shaping of the illumination light
• CPC Class Codes: H04N 9/3161 using laser light sources using laser beams scanning the display screen H04N9/3129

Abstract

According to one embodiment, an image projector has a spatial light modulator (SLM) adapted to modulate illumination from a laser with a spatial pattern such that the modulated illumination projects an image on a viewing screen. The image projector further has an optical diffuser located on an optical path between the laser and the SLM. The laser is adapted to illuminate the SLM through the optical diffuser to create an illuminated area at the SLM. The optical diffuser is adapted to introduce an angular spread into the light transmitted therethrough. The image projector is adapted to move the illuminated area with respect to the SLM to mitigate speckle in the projected image.

Claims

1. An optical device for projecting an image on a viewing screen, the optical device comprising:

a spatial light modulator (SLM) having a plurality of pixels adapted to modulate a received illumination light beam with a spatial pattern to form said image; and

an optical diffuser located along an optical path between a laser and the SLM and adapted to transmit light generated by the laser to produce said illumination light beam at the SLM so that, at each pixel of the plurality, the illumination light beam has light rays corresponding to a range of incident angles, wherein;

the optical device is adapted to move the illumination light beam across the SLM; and

at each pixel of the plurality, said motion of the illumination light beam changes relative optical phases of the light rays having different incident angles.

2. The invention of claim 1, further comprising a lens located along said optical path and adapted to move to produce said motion of the illumination beam.

3. The invention of claim 2, wherein the lens is configured to image an output aperture of the laser onto the SLM.

4. The invention of claim 2, wherein the lens and the optical diffuser are implemented as a monolithic optical element.

5. The invention of claim 1, further comprising a mirror located along said optical path and adapted to move said motion of the illumination beam.

6. The invention of claim 5, wherein the mirror is adapted to rotate about a rotation axis that is not parallel to a normal to the mirror.

7. The invention of claim 6, further comprising a wedge, wherein the mirror is one surface of the wedge.

8. The invention of claim 1, wherein the SLM is adapted to modulate light transmitted therethrough.

9. The invention of claim 1, wherein the optical device further comprises:

a polarization beam splitter (PBS) located on an optical path between the optical diffuser and the SLM; and

a quarter-wave plate located on an optical path between the PBS and the SLM, wherein;

the PBS is adapted to direct the light transmitted through the optical diffuser to the SLM;

the SLM is adapted to impart said spatial modulation pattern on the light received from the PBS and is further adapted to direct a spatially modulated beam back to the PBS.

10. The invention of claim 1, wherein:

the SLM is further adapted to modulate a light beam from a second laser with a corresponding spatial pattern;

the two lasers are adapted to emit light of different colors; and

the optical device is adapted to time-division multiplex transmission of the light of the two colors to the SLM.

11. The invention of claim 10, further comprising a color combiner adapted to direct the light emitted by each of the two lasers through the optical diffuser.

12. The invention of claim 1, further comprising said laser, wherein the laser is adapted to emit light having different angular spreads along different axes orthogonal to the emission axis of the laser.

13. The invention of claim 1, wherein the optical diffuser is adapted to introduce into the transmitted light different amounts of angular spread along different directions.

14. The invention of claim 1, wherein the optical diffuser is adapted to change a cross section of a light beam applied thereto from substantially circular or oval to substantially rectangular.

15. An optical device for projecting an image on a viewing screen, the optical device comprising:

a spatial light modulator (SLM) adapted to modulate a coherent illumination beam with a spatial pattern; and

an optical diffuser located along an optical path that said coherent illumination beam follows prior to being intercepted by the SLM, wherein;

the optical diffuser is adapted to introduce one angular spread into light transmitted therethrough along a first direction and a different angular spread into said transmitted light along a different second direction; and

the optical diffuser is adapted to move with respect to a surface of the SLM.

16. A method of projecting an image on a viewing screen, the method comprising:

with a laser, illuminating a portion of a surface of a spatial light modulator (SLM) by passing a light beam through an optical diffuser, wherein the optical diffuser is adapted to angularly spread the light beam incident thereon so that, at each pixel of the plurality, the illuminating light beam has light rays corresponding to a range of incident angles;

modulating said illuminating light beam with a spatial pattern displayed by a plurality of pixels of the SLM to form said image; and

moving the illuminating light beam across the SLM, wherein, at each pixel of the plurality, said motion changes relative optical phases of the light rays having different incident angles.

18. The invention of claim 16, wherein the step of moving comprises moving a mirror located on the optical path between the laser and the SLM to produce said motion of the illuminating light beam.

19. The invention of claim 18, wherein the step of moving further comprises rotating the mirror about a rotation axis that is not parallel to a normal to a reflecting surface of the mirror.

20. The invention of claim 16, further comprising:

with a second laser, illuminating a portion of the surface of the SLM by passing a corresponding light beam through the optical diffuser, wherein the two lasers are adapted to emit light of different colors;

modulating said second illuminating light beam with a corresponding spatial pattern displayed by the plurality of pixels of the SLM; and

time-division multiplexing transmission of the light of the two colors to the SLM.

17. The invention of claim 17, wherein the step of moving comprises moving a lens located on an optical path between the laser and the SLM to produce said motion of the illuminating light beam.