Illumination system to eliminate laser speckle and a single-panel projection system employing the same

• US 20060092515A1
• Filed: 09/26/2005
• Published: 05/04/2006
• Est. Priority Date: 10/28/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Sung-ha, Dho, Sang-whoe
• Granted Patent: US 7,433,124 B2
• Time in Patent Office: Days
• US Class Current: 359/566
• CPC Class Codes: G02B 27/0933 Systems for active beam shaping by rapid movement of an element
• CPC Class Codes: G02B 27/0944 Diffractive optical elements, e.g. gratings, holograms gratings per se G02B5/18; holograms used as optical elements per se G02B5/32
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G02B 5/0252 using holographic or diffractive means
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G03H 1/32 Systems for obtaining speckle elimination
• CPC Class Codes: H04N 9/3152 for shaping the light beam beam shaping per se G02B27/09
• CPC Class Codes: H04N 9/3161 using laser light sources using laser beams scanning the display screen H04N9/3129

Abstract

An illumination system designed to eliminate laser speckle and a single-panel projection system employing the same. The illumination system includes a laser light source to sequentially emit a plurality of laser beams, and a first diffractive optical element that is partitioned into a plurality of segments having diffractive patterns that correspond to the plurality of laser beams to move synchronously with the sequential emission of the plurality of laser beams. The laser speckle is removed by moving the first diffractive optical element in such a manner as to temporally average the plurality of laser beams. The illumination system efficiently removes the laser speckle, and the projection system having the illumination system provides improved image quality.

Claims

1. An illumination system, comprising:

a laser light source to sequentially emit a plurality of laser beams; and

a first diffractive optical element that is partitioned into a plurality of segments having diffractive patterns that correspond to the plurality of laser beams and to move synchronously with the sequential emission of the plurality of laser beams,

wherein the first diffractive optical element removes laser speckle by temporally averaging the plurality of laser beams.

2. The illumination system of claim 1, wherein the first diffractive optical element has a wheel-like shape and is rotatable.

3. The illumination system of claim 1, wherein the first diffractive optical element has a rectangular shape and is linearly reciprocatable.

4. The illumination system of claim 1, wherein the first diffractive optical element converts an incident beam emitted by the laser light source into a plurality of beamlets and superimposes and focuses the plurality of beamlets so as to spatially average the incident beam.

5. The illumination system of claim 1, further comprising:

a second diffractive optical element to shape a beam that passes through the first diffractive optical element to match an aspect ratio of a display device that produces an image from the shaped beam.

6. The illumination system of claim 5, wherein the second diffractive optical element controls a divergence angle of an incident beam to increase an F-number.

7. The illumination system of claim 1, wherein each of the plurality of segments of the first diffractive optical element comprises a plurality of diffractive unit cells to modify a plurality of partial beams of an incident beam, and each of the plurality of partial beams includes a plurality of beamlets.

8. The illumination system of claim 1, wherein each of the plurality of segments of the first diffractive optical element include a plurality of unit cells to modify partial beams of an incident beam, and each of the plurality of segments of the first diffractive optical element is designed to reduce a laser speckle according to:

$C=\frac{\sqrt{\langle <br><br>I_i^2\rangle <br><br>-{\langle <br><br>I_i\rangle <br><br>}^2}}{\langle <br><br>I_i\rangle <br><br>}=\frac{\mathrm{\sigma <br><br>}}{\mathrm{\mu <br><br>}}\times <br><br>100<br><br>\left(\%\right)$

where C represents a contrast of the laser speckle, I_i represents an intensity of an i-th unit cell of a corresponding segment of the first diffractive optical element, σ

represents a standard deviation of the intensity values I_i of the plurality of unit cells of the corresponding segment, and μ

represents a mean intensity value.

9. The illumination system of claim 1, wherein each of the plurality of segments of the first diffractive optical element is designed to have an optimal diffraction efficiency according to:

$D_{\mathrm{eff}}={\left\{\frac{\mathrm{Sin}<br><br>\left[\mathrm{\pi <br><br>}\times <br><br>\left({\mathrm{\lambda <br><br>}}_D/\mathrm{\lambda <br><br>}-1\right)\right]}{\mathrm{\pi <br><br>}\times <br><br>\left({\mathrm{\lambda <br><br>}}_D/\mathrm{\lambda <br><br>}-1\right)}\right\}}^2$

where λ

_D and λ

represent a design wavelength of a predetermined segment of the first diffractive optical element and an actual wavelength used in the predetermined segment, respectively.

10. An illumination unit usable in an optical projection system, comprising:

a laser unit to emit a light beam;

a laser speckle removal unit to receive the light beam from the laser unit and to remove a laser speckle therefrom by averaging intensities of the light beam spatially and temporally to produce a uniform light beam; and

an image creation unit to receive the uniform light beam from the laser speckle removal unit and to create an image from the uniform light beam.

11. The illumination unit of claim 10, wherein the laser speckle removal unit comprises a plurality of segments having unit cells, and the unit cells of the segments have corresponding patterns.

12. The illumination unit of claim 11, wherein the pattern of each unit cell comprises a translucent cell including a transparent portion.

14. The illumination unit of claim 10, further comprising:

a shaping unit disposed between the laser speckle removal unit and the image creation unit to shape the uniform light beam according to a geometry of the image creation unit.

15. The illumination unit of claim 14, wherein the image creation unit comprises a rectangular display panel to sequentially modulate pixels of the uniform light beam according to an image signal, and the shaping unit modifies the uniform light beam to correspond to an aspect ratio of the rectangular display panel.

16. The illumination unit of claim 14, wherein the shaping unit converts the uniform light beam from having a circular cross section to a rectangular cross section by controlling a divergence angle of the uniform light beam.

17. The illumination unit of claim 10, wherein the light beam emitted by the laser unit comprises a plurality of sequentially alternating wavelengths and the laser speckle removal unit comprises a diffractive optical element having a plurality of segments having diffraction patterns that correspond to the plurality of sequentially alternated wavelengths, and the diffractive optical element switches a current segment through which the light beam passes according to a current wavelength of the light beam to temporally average the intensities of the light beam.

18. The illumination unit of claim 17, wherein each of the plurality of segments of the diffractive optical element comprises a plurality of unit elements to divide the light beam into a plurality of partial beams having different phases, to superimpose the plurality of partial beams on one another, and to focus the plurality of superimposed partial beams to spatially average the intensities of the light beam.

19. The illumination unit of claim 17, wherein the diffractive optical element emits the light beam having the current wavelength that is equal to a design wavelength of the diffraction pattern of the current segment so as to obtain substantially a 100% diffraction efficiency.

20. The illumination unit of claim 17, wherein the diffractive optical element has one of a wheel shape having the plurality segments in a radial arrangement and a rectangular shape having the plurality of segments arranged adjacent to one another.

21. The illumination unit of claim 20, wherein the laser speckle removal unit further comprises an actuator to switch the current segment through which the light beam passes.

22. The illumination unit of claim 20, wherein the diffractive optical element includes a first segment having a diffraction pattern that corresponds to a blue light wavelength, a second segment having a diffraction pattern that corresponds to a red light wavelength, and a third segment having a diffraction pattern that corresponds to a green light wavelength, and the diffractive optical element is moved in synch with the sequential alternation of the wavelengths, and the laser unit comprises a first laser to emit a light beam of the blue light wavelength, a second laser to emit a light beam of the red light wavelength, and a third laser to emit a light beam of the green light wavelength.

23. The illumination unit of claim 10, wherein the laser speckle removal unit comprises a diffractive optical element having a plurality of unit elements to divide the light beam into a plurality of partial beams having different phases, to superimpose the plurality of partial beams on one another, and to focus the plurality of superimposed partial beams to spatially average the intensity of the light beam.

13. The illumination unit of claim 13, wherein the pattern comprises first areas and second areas dividing the first areas.

24. A projection system, comprising:

a laser light source to sequentially emit a plurality of laser beams;

a first diffractive optical element that is partitioned into a plurality of segments having diffractive patterns that correspond to the plurality of laser beams to remove laser speckle by moving synchronously with the sequential emission of the laser beams in such a manner as to temporally average the plurality of laser beams;

a second diffractive optical element to shape a beam that passes through the first diffractive optical element to match a geometry of a display device that produces an image from the shaped beam;

a display device to produce the image using the shaped beam that passes through the second diffractive optical element; and

a projection lens unit to enlarge and project the produced image onto a screen.

25. The projection system of claim 24, wherein the first diffractive optical element has a wheel-like shape and is rotatable.

26. The projection system of claim 24, wherein the first diffractive optical element has a rectangular shape and is linearly reciprocatable.

27. The projection system of claim 24, wherein the first diffractive optical element converts an incident beam emitted by the laser light source into a plurality of beamlets and superimposes and focuses the plurality of beamlets, thereby spatially averaging the incident beam.

28. The projection system of claim 24, wherein the second diffractive optical element shapes the beam that passes through the first diffractive optical element to match an aspect ratio of the display device.

29. The projection system of claim 28, wherein the second diffractive optical element controls a divergence angle of an incident beam to increase an F-number.

30. The projection system of claim 24, wherein the display device comprises one of a transmissive liquid crystal display (LCD), a Liquid Crystal on Silicon (LCoS) display, a Deformable Micromirror Device (DMD), and a Grating Light Valve (GLV).

31. An optical projection system, comprising:

a screen;

an illumination unit including a movable diffractor having at least two wavelength dependent diffraction patterns to create a uniform beam substantially without laser speckle by averaging intensities of an incident light beam;

an image creation unit to create an image from the uniform beam; and

at least one projection lens to enlarge and project the created image onto the screen.

32. The system of claim 31, wherein the illumination unit further includes:

a laser unit to emit a light beam having a wavelength that alternates between a plurality of color wavelengths, and

the movable diffractor includes a plurality of segments having a plurality of diffraction patterns that correspond to the plurality of color wavelengths to average the light beam temporally by alternating among the plurality of segments in synch with the alternation between the color wavelengths, to average the light beam spatially by dividing the light beam into a plurality of partial light beams and superimposing the partial light beams on one another, and to create the uniform beam accordingly; and

a second diffractive optical element to convert the uniform beam to have a shape that corresponds to the image creation unit.

33. An optical projection system, comprising:

a screen;

an illumination unit including a laser light source to produce a light beam and a diffraction unit to produce a uniform beam substantially without laser speckle from the light beam by performing a first intensity averaging operation and a second intensity averaging operation on the light beam;

an image creation unit to create an image from the uniform beam; and

at least one projection lens to enlarge and project the created image onto the screen.

34. A method of producing a uniform beam in an illumination unit usable with an optical projection system, the method comprising:

creating a light beam having sequentially alternating wavelengths;

converting the light beam to a uniform beam by spatially and temporally averaging the light beam; and

providing the uniform beam to an image creation device.

35. The method of claim 34, wherein the temporal averaging of the light beam comprises:

controlling a diffraction optical element including a plurality of segments having a plurality of wavelength dependent diffraction patterns that correspond to the sequentially alternating wavelengths to switch between the plurality of segments in synch with the sequentially alternating wavelengths.