REDUCTION OF SPECKLE AND INTERFERENCE PATTERNS FOR LASER PROJECTORS

• US 20060221429A1
• Filed: 03/31/2005
• Published: 10/05/2006
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Tanner, Allen H., Christensen, Robert R., Williams, Forrest L.
• Granted Patent: US 7,193,765 B2
• Time in Patent Office: Days
• US Class Current: 359/279
• CPC Class Codes: G02B 27/48 Laser speckle optics
• 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

Abstract

The invention provides a system and method for reducing laser speckle and interference patterns in a laser projector display when using a laser projector having a spatial light modulator (SLM) with a defined pixel rate. The method can include the operation of polarizing a laser output of a continuous wave laser such that the laser output is s-polarized with respect to a beam combiner. The s-polarized laser output can be divided into a first laser beam and a second laser beam. A phase of the second laser beam can be modulated with an amplitude sufficient to create a phase delay of approximately half a wavelength of the laser output and at a frequency at least twice that of the SLM'"'"'s pixel rate.

Claims

1. An apparatus for reducing laser speckle and interference patterns in a laser projector display, when using a laser projector having a spatial light modulator (SLM) with a defined pixel rate, comprising:

a continuous wave laser having a laser output defining an optical path to be split into multiple optical paths;

a beam combiner positioned optically down field from the continuous wave laser for recombining the multiple optical paths;

a first half wave plate placed in an optical path incident to the laser output and configured to polarize the laser output to be s-polarized with respect to the beam combiner;

a first polarization-independent beam splitter optically positioned and configured to divide the laser output of the continuous wave laser into a first laser beam and a second laser beam;

a phase modulator optically positioned and configured to oscillate a phase of the second laser beam with an amplitude sufficient to create a phase delay of an odd integer multiple of approximately half a wavelength of the laser output and at a frequency at least twice that of the pixel rate of the SLM;

a second polarization-independent beam splitter optically positioned and configured to reflect approximately half of the first laser beam and half of a phase modulated second laser beam and to transmit approximately half of the first laser beam and half of the phase modulated second laser beam to produce third and fourth laser beams, each of the third and fourth laser beams comprising approximately half of the first laser beam and approximately half of the phase modulated second laser beam;

a second half wave plate optically positioned and configured to polarize the fourth laser beam to be p-polarized with respect to the beam combiner; and

the beam combiner configured to combine an s-polarized third laser beam and a p-polarized fourth laser beam into a fifth laser beam.

2. An apparatus as in claim 1, wherein the s-polarized third laser beam and the p-polarized fourth laser beam are combined to form a linearly polarized fifth laser beam.

3. An apparatus as in claim 1, wherein the s-polarized third laser beam and the p-polarized fourth laser beam are combined to form an elliptically polarized fifth laser beam.

4. An apparatus as in claim 1, further comprising a first substantially fully reflective mirror configured to redirect the first laser beam output from the first polarization-independent beam splitter onto the second polarization-independent beam splitter.

5. An apparatus as in claim 1, further comprising a second substantially fully reflective mirror configured to redirect the second laser beam as output from the phase modulator onto the second polarization-independent beam splitter.

6. An apparatus as in claim 1, wherein the first polarization-independent beam splitter is a partially reflective mirror configured to transmit approximately half of the laser output and reflect approximately half of the laser output.

7. An apparatus as in claim 6, wherein the first laser beam comprises the approximately half of the laser output that is transmitted.

8. An apparatus as in claim 6, wherein the second laser beam comprises the approximately half of the laser output that is reflected.

9. An apparatus as in claim 1, wherein the second polarization-independent beam splitter is a partially reflective mirror that transmits approximately half of the first laser beam and reflects approximately half of the first laser beam and transmits approximately half of the phase modulated second laser beam and reflects approximately half of the phase modulated second laser beam.

10. An apparatus as in claim 9, wherein the third laser beam comprises the approximately half of the reflected first laser beam and the approximately half of the transmitted phase modulated second laser beam.

11. An apparatus as in claim 9, wherein the fourth laser beam comprises the approximately half of the transmitted first laser beam and the approximately half of the reflected phase modulated second laser beam.

12. An apparatus as in claim 1, further comprising a third substantially fully reflective mirror configured to redirect the third laser beam from the second polarization-independent beam splitter onto the beam combiner.

13. An apparatus as in claim 1, further comprising a fourth substantially fully reflective mirror configured to redirect the fourth laser beam from the second polarization-independent beam splitter through the second half wave plate and onto the beam combiner.

14. An apparatus as in claim 1, wherein the phase modulator is an electro-optic phase modulator.

15. An apparatus as in claim 1, wherein the phase modulator is configured to oscillate the second laser beam at an amplitude of at least a half wavelength of the laser output.

16. An apparatus as in claim 1, wherein the phase modulator is configured to oscillate the second laser beam with a frequency of at least 4 times the pixel rate.

17. An apparatus as in claim 1, further comprising a scanning mirror configured to substantially reflect the fifth laser beam onto a viewing screen.

18. An apparatus for reducing laser speckle and interference fringes, comprising:

a continuous wave laser having a laser output defining an optical path to be split into multiple optical paths;

a spatial light modulator (SLM) optically coupled to the continuous wave laser, wherein the SLM has a defined pixel rate;

a beam combiner positioned optically down field from the continuous wave laser for recombining the multiple optical paths;

a first half wave plate placed in an optical path incident to the laser output and configured to polarize the laser output to be s-polarized with respect to the beam combiner;

a first polarization-independent beam splitter optically positioned and configured to divide the laser output of the continuous wave laser into a first laser beam and a second laser beam;

a phase modulator optically positioned and configured to oscillate a phase of the second laser beam with an amplitude sufficient to create a phase delay of an odd integer multiple of approximately half a wavelength of the laser output and at a frequency at least twice that of the pixel rate of the SLM;

a second polarization-independent beam splitter optically positioned and configured to reflect approximately half of the first laser beam and half of a phase modulated second laser beam and to transmit approximately half of the first laser beam and half of the phase modulated second laser beam to produce third and fourth laser beams, each of the third and fourth laser beams comprising approximately half of the first laser beam and approximately half of the phase modulated second laser beam;

a second half wave plate optically positioned and configured to polarize the fourth laser beam to be p-polarized with respect to the beam combiner;

the beam combiner configured to combine an s-polarized third laser beam and a p-polarized fourth laser beam into a fifth laser beam;

a quarter wave plate optically positioned and configured to substantially linearly polarize the fifth laser beam; and

a polarization rotator optically positioned and configured to rotate a polarization of the substantially linearly polarized fifth laser beam.

19. An apparatus as in claim 18, wherein the SLM is selected from the group of spatial light modulators consisting of electro-optic;

photoconductor-liquid crystal, and photoconductor-deformable mirror.

20. An apparatus as in claim 18, wherein the polarization rotator is an electro-optic polarization rotator.

21. An apparatus as in claim 18, wherein the polarization rotator is configured to rotate the polarization of the fifth laser beam at a frequency of at least twice a rate of the phase modulator.

22. An apparatus as in claim 18, further comprising a scanning mirror configured to substantially reflect a polarization rotated beam onto a screen.

23. An apparatus as in claim 22, wherein the screen is a depolarizing screen.

24. A method for reducing laser speckle and interference patterns in a laser projector display, when using a laser projector having a spatial light modulator (SLM) with a defined pixel rate, comprising:

polarizing a laser output of a continuous wave laser such that the laser output is s-polarized with respect to a beam combiner;

dividing the s-polarized laser output into a first laser beam and a second laser beam;

modulating a phase of the second laser beam with an amplitude sufficient to create a phase delay of approximately half a wavelength of the laser output and at a frequency at least twice that of the SLM'"'"'s pixel rate;

mixing the first and second laser beams to create third and fourth laser beams, each of the third and fourth laser beams comprising approximately half of the first laser beam and approximately half of a phase modulated second laser beam;

polarizing the fourth laser beam to be approximately p-polarized with respect to the beam combiner; and

combining the third and fourth laser beams with the beam combiner to create a fifth laser beam.

25. A means for reducing laser speckle and interference patterns in a laser projector display, when using a laser projector having a spatial light modulator (SLM) with a defined pixel rate, comprising:

a means for polarizing a laser output of a continuous wave laser such that the laser output is s-polarized with respect to a beam combiner;

a means for dividing the s-polarized laser output into a first laser beam and a second laser beam;

a means for modulating a phase of the second laser beam with an amplitude sufficient to create a phase delay of approximately half a wavelength of the laser output and at a frequency at least twice that of the SLM'"'"'s pixel rate;

a means for mixing the first and second laser beams to create third and fourth laser beams, each of the third and fourth laser beams comprising approximately half of the first laser beam and approximately half of a phase modulated second laser beam;

a means for polarizing the fourth laser beam to be approximately p-polarized with respect to the beam combiner; and

a means for combining the third and fourth laser beams with the beam combiner to create a fifth laser beam.