Despeckling apparatus and method
An apparatus and method that reduces laser speckle by using stimulated Raman scattering in an optical fiber. The fiber core diameter and length are selected to achieve a desired output color. An adjustable despeckler is formed by combining two optical fibers in parallel and adjusting the amount of light in each path.
1. An optical apparatus comprising:
an optical fiber configured to partially convert, via stimulated Raman scattering, a monochromatic input light into an output light having a plurality of output wavelengths that collectively achieve a desired color;
wherein the stimulated Raman scattering in the optical fiber reduces a speckle characteristic of the output light.
2. The apparatus of claim 1 , the optical fiber having a core diameter and a length selected to achieve the desired color of the output light.
3. The apparatus of claim 1 , the optical fiber being a multimode fiber.
4. The apparatus of claim 1 , wherein the desired color is a primary color.
5. The apparatus of claim 4 , wherein the primary color is a green color.
6. The apparatus of claim 5 , further comprising an optical parametric amplifier configured to generate a blue primary color and a red primary color from a portion of the input light.
7. The apparatus of claim 5 , wherein a portion of the output light is red.
8. The apparatus of claim 7 , the green color having a chromaticity of u′=0.099+/−0.01 and v′=0.578+/−0.01.
9. The apparatus of claim 5 wherein a portion of the output light is yellow.
10. The apparatus of claim 9 , the portion of the output light that is yellow being used as a primary color for projecting a digital image with four primary colors.
11. The apparatus of claim 1 , further comprising:
a laser light source; and
a digital projector;
wherein the laser outputs the input light to the optical fiber, and the output light illuminates the digital projector.
12. The apparatus of claim 11 , the laser light source comprising a pulsed laser and a second harmonic generator.
13. The apparatus of claim 12 , the input wavelength being 523.5 nm.
14. The apparatus of claim 12 , the input wavelength being 515 nm.
15. The apparatus of claim 12 , the wavelength being 532 nm.
16. The apparatus of claim 1 wherein a green channel of a six-primary 3D image is created with an unshifted green peak and a third stimulated-Raman-shifted peak.
17. The apparatus of claim 16 wherein a green channel of a six-primary 3D image is created with a first stimulated-Raman-shifted peak and a second stimulated-Raman-shifted peak.
18. The apparatus of claim 1 , further comprising:
a second optical fiber configured to partially convert, via stimulated Raman scattering, a second monochromatic input light into an second output light having a second plurality of output wavelengths that collectively achieve a desired second color;
a first laser light source;
a second laser light source; and
a digital projector;
wherein the first laser light source outputs the monochromatic light into the optical fiber; the second laser light source outputs the second monochromatic light into the second optical fiber; a stimulated Raman scattering in the second optical fiber reduces a second speckle characteristic of the second output light; and the output light and the second output light illuminate the digital projector.
19. A laser projector comprising:
a blue laser light source;
an optical fiber; and
a spatial light modulator;
wherein the blue laser light source illuminates the optical fiber, the optical fiber illuminates the spatial light modulator, and a stimulated Raman scattering in the optical fiber partially converts the blue light into a despeckled green light and a despeckled red light.