Speckle Reduction Using Multiple Starting Wavelengths
A method and apparatus for despeckling light that includes combining a first starting wavelength, stimulated Raman scattering light from the first starting wavelength, a second starting wavelength, and stimulated Raman scattering light from the second starting wavelength. The method and apparatus may include a first laser with a first infrared wavelength of 1047 nm and a second laser with a second infrared wavelength of 1053 nm.
1 . A method of despeckling light comprising:
generating a first laser light with a first starting wavelength;
generating a first stimulated Raman scattering light and a residual first laser light from the first laser light;
generating a second laser light with a second starting wavelength that is distinct from the first starting wavelength;
generating a second stimulated Raman scattering light and a residual second laser light from the second laser light; and
forming a first combination of laser light by combining the first stimulated Raman scattering light, the residual first laser light, the second stimulated Raman scattering light, and the residual second laser light.
2 . The method of claim 1 wherein an amount of the first laser light and an amount of the second laser light are selected so that the first combination of laser light achieves a desired color point.
3 . The method of claim 1 wherein the first combination of laser light has a lower speckle characteristic than a second combination of laser light formed by combining the first stimulated Raman scattering light and the residual first laser light.
4 . The method of claim 1 wherein the first stimulated Raman scattering light is formed in an optical fiber.
5 . The method of claim 4 wherein the optical fiber comprises a multimode fiber.
6 . The method of claim 1 wherein the first starting wavelength is between 514 nm and 550 nm.
7 . The method of claim 1 further comprising:
illuminating a digital projector with the first combination of laser light; and
forming a digital image with the digital projector and the first combination of laser light.
8 . The method of claim 1 wherein the first starting wavelength is 523.5 nm.
9 . The method of claim 8 wherein the first laser light is generated by frequency doubling of a laser operating at 1047 nm.
10 . The method of claim 8 wherein the second starting wavelength is 526.5 nm.
11 . The method of claim 10 wherein the second laser light is generated by frequency doubling of a laser operating at 1053 nm.
12 . An optical apparatus comprising:
a first laser that generates a first infrared light operating at a first infrared wavelength;
a first frequency doubler that generates a first visible laser light at a first starting wavelength from the first infrared light;
a first optical fiber that generates a first stimulated Raman scattering light and a residual first laser light from the first visible laser light;
a second laser that generates a second infrared light operating at a second infrared wavelength that is distinct from the first infrared wavelength;
a second frequency doubler that generates a second visible laser light at a second starting wavelength from the second infrared light; and
a second optical fiber that generates a second stimulated Raman scattering light and a residual second laser light from the second visible laser light.
13 . The optical apparatus of claim 12 wherein the first infrared wavelength is 1047 nm.
14 . The optical apparatus of claim 13 wherein the second infrared wavelength is 1053 nm.
15 . The optical apparatus of claim 14 wherein the first laser comprises a neodymium-doped yttrium-lithium-fluoride gain crystal.
16 . The optical apparatus of claim 15 wherein the second laser comprises a neodymium-doped yttrium-lithium-fluoride lasing crystal, a polarizing element, and a half-wave plate, wherein the polarizing element and half-wave plate are arranged to make the polarization state of the second laser match the polarization state of the first laser.
17 . The optical apparatus of claim 16 wherein the second laser comprises a cylindrical lens element.
18 . The optical apparatus of claim 17 wherein the first laser and the second laser have the same configuration except for the polarizing element, the half-wave plate, and the cylindrical lens element in the second laser.