IMAGE PROJECTOR EMPLOYING A SPECKLE-REDUCING LASER SOURCE

• US 20100290009A1
• Filed: 05/15/2009
• Published: 11/18/2010
• Est. Priority Date: 05/15/2009
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Inventors: Chen, Gang, Ryf, Roland
• Granted Patent: US 8,226,241 B2
• Time in Patent Office: Days
• US Class Current: 353/31
• CPC Class Codes: G03B 21/006 using LCD's
• CPC Class Codes: H01S 2301/02 ASE (amplified spontaneous emission), noise; Reduction thereof
• CPC Class Codes: H01S 3/0085 Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 3/08086 Multiple-wavelength emission
• CPC Class Codes: H01S 3/1022 by controlling the optical pumping
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 3/1611 neodymium
• CPC Class Codes: H01S 3/17 amorphous, e.g. glass
• CPC Class Codes: H04N 9/3161 using laser light sources using laser beams scanning the display screen H04N9/3129

Abstract

An image projector having one or more broadband lasers designed to reduce the appearance of speckle in the projected image via wavelength diversification. In one embodiment, a broadband laser has an active optical element and a nonlinear optical element, both located inside a laser cavity. The broadband laser generates an output spectrum characterized by a spectral spread of about 10 nm and having a plurality of spectral lines corresponding to different spatial modes of the cavity. Different individual spectral lines effectively produce independent speckle configurations, which become intensity-superimposed in the projected image, thereby causing a corresponding speckle-contrast reduction.

Claims

1. An optical device for projecting an image, comprising:

a first laser comprising a laser cavity and adapted to generate a first light beam; and

a spatial light modulator (SLM) configured to be illuminated using the first light beam, wherein;

the SLM is adapted to modulate received illuminating light using a spatial pattern generated by a plurality of pixels to form the image;

the first light beam has a spectrum comprising a plurality of spectral lines corresponding to a plurality of different spatial modes of said laser cavity; and

the optical device projects the image using light having said spectrum.

2. The invention of claim 1, wherein the first light beam is characterized by a spectral spread greater than about 2 nm, but is smaller than about 20 nm.

3. The invention of claim 1, wherein the spectrum is characterized by a spectral envelope having a median wavelength corresponding to red, green, or blue color of light.

4. The invention of claim 1, wherein the plurality of spectral lines comprises more than about 100 spectral lines.

5. The invention of claim 1, wherein the first laser further comprises a controller adapted to actively induce mode hopping in the laser cavity to cause temporal changes in the spectrum of the first light beam.

6. The invention of claim 1, wherein:

the first laser further comprises an optical pump adapted to optically pump the laser cavity;

the laser cavity comprises an active optical element and a nonlinear optical (NLO) element;

the active optical element is adapted to absorb light supplied by the optical pump and emit light forming an emission band; and

the NLO element is adapted to multiply frequencies corresponding to a sub-band of the emission band to cause the first laser to generate the first light beam.

7. The invention of claim 6, wherein the NLO element is adapted to double or triple said frequencies.

8. The invention of claim 6, wherein the sub-band has a spectral width of at least about 10 nm.

9. The invention of claim 6, wherein the active optical element comprises a glass material doped with rare-earth ions.

10. The invention of claim 6, wherein the first laser further comprises a controller circuit adapted to configure the optical pump to actively cause temporal changes in the spectrum of the first light beam.

11. The invention of claim 1, wherein at least some of the spectral lines are broadened, which causes different spectral lines to at least partially overlap and coalesce.

12. The invention of claim 11, wherein the spectrum of the first light beam is a continuous spectrum.

13. The invention of claim 1, further comprising:

a second laser adapted to generate a second light beam; and

a third laser adapted to generate a third light beam, wherein;

the SLM is configured to be illuminated using the second and third light beams;

the first, second, and third light beams have light of respective different colors to cause said image to be perceived as being multi-colored; and

at least one of the second and third light beams is characterized by a spectral spread greater than about 2 nm, but is smaller than about 20 nm.

14. The invention of claim 1, wherein the first laser further comprises a pulse carver adapted to temporally gate the first light beam.

15. A method of projecting an image, the method comprising:

generating with a first laser a first light beam;

directing the first light beam to illuminate a spatial light modulator (SLM);

modulating illuminating light received by the SLM with a spatial pattern generated by a plurality of pixels to form the image, wherein;

the first laser comprises a laser cavity; and

the first light beam has a spectrum comprising a plurality of spectral lines corresponding to a plurality of different spatial modes of said laser cavity; and

projecting the image using light having said spectrum.

16. The invention of claim 15, wherein:

the plurality of spectral lines comprises more than about 100 spectral lines; and

the method further comprises actively inducing mode hopping in the laser cavity to produce temporal changes in the spectrum.

17. The invention of claim 16, wherein the step of inducing comprises:

optically pumping the laser cavity with pump light; and

changing one or more characteristics of the pump light to induce said mode hopping.

18. An optical device for projecting an image, comprising:

a first laser adapted to generate a first light beam characterized by a spectrum having a spectral spread greater than about 2 nm, but smaller than about 20 nm; and

a spatial light modulator (SLM) configured to be illuminated using the first light beam, wherein;

the SLM is adapted to modulate received illuminating light using a spatial pattern generated by a plurality of pixels to form the image; and

the optical device projects the image using light having said spectrum.

19. The invention of claim 18, wherein:

the first laser comprises a laser cavity and an optical pump adapted to optically pump the laser cavity;

the laser cavity comprises an active optical element and a nonlinear optical (NLO) element;

the active optical element is adapted to absorb light supplied by the optical pump and emit light forming an emission band; and

the NLO element is adapted to multiply frequencies corresponding to a sub-band of the emission band to cause the first laser to generate the first light beam.

20. A laser, comprising:

a laser cavity; and

an optical pump adapted to optically pump the laser cavity, wherein;

the laser is adapted to generate a light beam characterized by a broadband spectrum; and

the spectrum comprises a plurality of spectral lines corresponding to a plurality of different spatial modes of said laser cavity.

21. The laser of claim 20, wherein:

the laser cavity comprises an active optical element and a nonlinear optical (NLO) element;

the active optical element is adapted to absorb light supplied by the optical pump and emit light forming an emission band; and

the NLO element is adapted to multiply frequencies corresponding to a sub-band of the emission band to cause the first laser to generate the light beam.