Method and apparatus for reducing laser speckle

• US 7,719,738 B2
• Filed: 05/24/2008
• Issued: 05/18/2010
• Est. Priority Date: 06/10/2003
• Status: Expired due to Fees

• Current Assignee: Nayef M. Abu-Ageel
• Original Assignee: Nayef M. Abu-Ageel
• Inventors: Abu-Ageel, Nayef M.
• Primary Examiner(s): Wells, Nikita
• Application Number:
  US12/126,867
• Publication Number:
  US 20090128918A1
• Time in Patent Office: 724 Days
• Field of Search: 359/201.2, 359/209.1, 359/602, 356/513, 356/132, 385/31, 385/32, 372/99, 372/103
• US Class Current: 359/201.2
• CPC Class Codes: G02B 21/06 Means for illuminating specimens
• CPC Class Codes: G02B 27/0927 Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
• CPC Class Codes: G02B 27/0994 Fibers, light pipes optical fibers per se G02B6/02
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/4206 Optical features G02B6/4207, G02B6/421 take precedence

Abstract

An apparatus and method for reducing speckle of a laser beam is disclosed. The apparatus includes a light guide, a highly reflective mirror at the input face of the light guide and a partially-transmissive display after the exit face of the light guide. A coherent laser beam is introduced into the light guide through a clear aperture in the highly reflective mirror. Within the light guide, the laser beam gets separated into plural, successive beamlets having different phase shifts, different polarization states and/or path length differences equal to or greater than the coherence length of the laser beam. The beamlets exit through the partially-transmissive display to provide output laser light with reduced speckle. The light guide can be either a solid light pipe of transmissive material or a hollow tunnel with reflective interior sidewalls.

Claims

1. An apparatus, comprising:

a light guide having an entrance face and an exit face;

a first mirror at the entrance face of the light guide, the first mirror having an aperture formed therein for admitting a predetermined input laser beam into the light guide; and

a transmissive display receiving laser light from the exit face of the light guide, the transmissive display being configured to pass a first portion of the laser light incident thereon and to reflect a second portion of the laser light incident thereon back into the light guide toward the first mirror.

2. The apparatus of claim 1, wherein the distance between the first mirror and transmissive display is at least one-half the coherence length of the predetermined input laser beam.

3. The apparatus of claim 1, wherein the transmissive display is a micro-display.

4. The apparatus of claim 1, wherein the transmissive display includes a plurality of pixel apertures configured to pass the first portion of the laser light.

5. The apparatus of claim 1, wherein the transmissive display includes a reflective layer surrounding the pixel apertures.

6. The apparatus of claim 1, wherein each pixel aperture includes a partially reflective coating.

7. The apparatus of claim 1, further comprising a micro-lens array (MLA) aligned with the pixel apertures.

8. The apparatus of claim 1, wherein the transmissive display is located at the exit face of the light guide.

9. The apparatus of claim 1, further comprising a projection lens configured to receive light from the transmissive display.

10. The apparatus of claim 9, further comprising a screen configured to receive light from the projection lens.

11. An apparatus for reducing laser speckle, comprising:

a light guide having an entrance face and an exit face;

a first mirror at the entrance face of the light guide, the first mirror having an aperture formed therein for admitting a predetermined input laser beam into the light guide;

a second, partially-reflective mirror at the exit face of the light guide, wherein the second mirror is capable of passing some of the laser beam incident thereon and reflecting some of the laser beam incident thereon back into the light guide toward the first mirror; and

a transmissive display configured to receive laser light output from the second mirror.

12. The apparatus of claim 11, wherein the distance between the first and second mirrors is at least one-half the coherence length of the predetermined input laser beam.

13. The apparatus of claim 11, wherein the transmissive display is a micro-display.

14. The apparatus of claim 11, wherein the transmissive display includes a plurality of pixel apertures configured to pass some of the laser light incident on the transmissive display.

15. The apparatus of claim 14, wherein the transmissive display includes a reflective layer surrounding the pixel apertures.

16. The apparatus of claim 14, wherein each pixel aperture includes a partially reflective coating.

17. The apparatus of claim 14, further comprising a micro-lens array (MLA) aligned with the pixel apertures.

18. The apparatus of claim 14, further comprising:

a plurality of micro-lenses, each corresponding to a pixel aperture.

19. The apparatus of claim 11, wherein the transmissive display is located at the exit face of the light guide.

20. The apparatus of claim 11, further comprising a projection lens configured to receive light from the transmissive display.

21. The apparatus of claim 20, further comprising a screen configured to receive light from the projection lens.

22. A method for reducing laser speckle, comprising:

providing a light guide having an entrance face and an exit face;

providing a first mirror at the entrance face of the light guide, the first mirror having an aperture formed therein;

providing a transmissive display receiving laser light from the exit face of the light guide, the transmissive display being configured to pass a first portion of the laser light incident thereon and to reflect a second portion of the laser light incident thereon back into the light guide toward the first mirror; and

directing the predetermined input laser beam into the aperture to produce output laser light, with reduced speckle, exiting from the transmissive display.

23. The method of claim 22, wherein the distance between the first mirror and the transmissive display is at least one-half the coherence length of the predetermined input laser beam.

24. The method of claim 22, wherein the transmissive display is a micro-display.