System and Method for Despeckling an Image Illuminated by a Coherent Light Source

• US 20100053729A1
• Filed: 12/17/2008
• Published: 03/04/2010
• Est. Priority Date: 09/02/2008
• Status: Active Grant

• Current Assignee: Elbit Systems of America LLC (Elbit Systems Limited)
• Original Assignee: EFW Incorporated (Elbit Systems Limited)
• Inventors: Tilleman, Michael M., Traynor, Joseph Thomas
• Granted Patent: US 7,969,644 B2
• Time in Patent Office: Days
• US Class Current: 359/298
• CPC Class Codes: G02B 2027/0118 comprising devices for improving the contrast of the display / brillance control visibility
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G02B 3/0006 Arrays G02B3/02, G02B5/188 take precedence
• CPC Class Codes: G02B 6/02 Optical fibres with cladding with or without a coating
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H04N 9/3161 using laser light sources using laser beams scanning the display screen H04N9/3129

Abstract

A method and system for reducing speckle in an image produced from a coherent source of radiation is provided. The method includes coupling a source beam received from a coherent optical source into an optical fiber. A position of at least a portion of the fiber may be modulated using a ditherer. The source beam may be refracted by a lens after it is decoupled from the optical fiber, such that the source beam is aimed at a microlens diffuser. In accordance with a particular embodiment, the source beam may be projected from the microlens diffuser onto a spatial modulator. The spatial modulator may be positioned to project the source beam via an imaging lens, to a target.

Claims

1. An image generation system, comprising:

an optical fiber positioned to receive a source beam from a coherent optical source;

a ditherer being coupled with the optical fiber and operable to modulate a position of at least a portion of the optical fiber;

a lens configured to refract the source beam, such that the source beam is aimed at a microlens diffuser;

the microlens diffuser being positioned to project the source beam onto a spatial modulator; and

the spatial modulator positioned to project the source beam via an imaging lens, to a target.

2. The system of claim 1, wherein the coherent optical source comprises a laser.

3. The system of claim 1, wherein the microlens diffuser comprises an ENGINEERED DIFFUSER™

.

4. The system of claim 1, wherein the optical fiber comprises an optical multimode fiber.

5. The system of claim 1, wherein the multimode fiber comprises a step index fiber having a core diameter of between 105 micrometers and 500 micrometers.

6. The system of claim 4, wherein the multimode fiber comprises a step index fiber having a core diameter greater than approximately 105 micrometers.

7. The system of claim 4, wherein the optical multimode fiber comprises a step index fiber having a core diameter of approximately 200 micrometers.

8. The system of claim 4, wherein the multimode fiber is a step index fiber having a core diameter less than approximately 400 micrometers.

9. The system of claim 1, wherein the ditherer comprises a mechanical vibration stage.

10. The system of claim 1, wherein the ditherer is modulated at 30 Hz or more.

11. The system of claim 1, wherein the target comprises a screen.

12. The system of claim 1, wherein the target comprises a diffuser.

13. The system of claim 1, wherein the target comprises a camera.

14. The system of claim 1, wherein the microlens diffuser is disposed within a headup display unit.

15. The system of claim 14, wherein the headup display comprises a projector including a spatial modulator disposed therein.

16. The system of claim 1, wherein the target comprises an optical surface transmitting nearly all of the visible spectrum except for a narrowband wavelength band of the coherent optical source, and having a reflection of at least 60% in the narrowband wavelength band.

17. The system of claim 15, wherein the microlens diffuser is positioned before the spatial modulator.

18. The system of claim 17, wherein the microlens diffuser comprises an ENGINEERED DIFFUSER™

.

19. A method for generating an image, comprising:

coupling a source beam received from a coherent optical source into an optical fiber;

modulating a position of at least a portion of the fiber using a ditherer;

refracting the source beam at a lens after it is decoupled from the optical fiber, such that the source beam is aimed at a microlens diffuser; and

projecting the source beam from the microlens diffuser onto a spatial modulator; and

positioning the spatial modulator to project the source beam via an imaging lens, to a target.

20. The method of claim 19, further comprising displaying an image formed by the projected source beam onto the target, the image appearing with a speckle contrast of at least 20%.

21. The method of claim 19, wherein the coherent optical source comprises a laser, and further comprising propagating the source at a wavelength range of 510-550 nanometers.

22. The method of claim 19, wherein the coherent optical source comprises lasers having wavelength ranges of 400-500 nanometers, 510-550 nanometers, and 590-700 nanometers, respectively.

23. A Head-up Display (HUD) system, comprising:

an optical fiber positioned to receive a source beam from a coherent optical source;

a ditherer being coupled with the optical fiber and operable to modulate a position of at least a portion of the optical fiber;

a lens configured to refract the source beam, such that the source beam is aimed at a microlens array;

the microlens array being positioned to project the source beam onto a spatial modulator;

the spatial modulator positioned to project the source beam via an imaging lens, to a diffuser;

a relay lens group being positioned to relay optical rays propagated from the diffuser; and

a prism being configured to bend the relayed optical rays and direct the relayed rays toward a combiner.

24. A Head Mounted Display (HMD) system, comprising:

an optical fiber embedded in a cable, the optical fiber being positioned to receive a source beam from a coherent optical source and guide the source beam to a plurality of image generation units that are coupled to head gear; and

a ditherer being coupled with the optical fiber and operable to modulate a position of at least a portion of the optical fiber;

each image generation unit comprising;

a lens configured to refract the source beam, such that the source beam is aimed at a microlens diffuser;

the microlens diffuser being positioned to project the source beam onto a spatial modulator; and

the spatial modulator positioned to project the source beam via an imaging lens, to a visor combiner that is coupled with the head gear.