System and method for despeckling an image illuminated by a coherent light source
View Patent ↗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.
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 propogated 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.