Frequency Control of Despeckling
A method and apparatus that reduces laser speckle by using stimulated Raman scattering in an optical fiber. The pulse repetition frequency of the laser is adjusted to control aspects of the laser light such as color or despeckling. In DLP projection systems, an optical monitor may be used to send information to a bit sequence, and the bit sequence may control the pulse repetition frequency of the laser based on the optical monitor signal.
1 . A method of despeckling comprising:
generating a laser beam;
focusing the laser beam into an optical fiber;
generating stimulated Raman scattering light in the optical fiber;
using the stimulated Raman scattering light to form a projected digital image; and
adjusting a frequency of the laser beam to control a first aspect of the projected digital image.
2 . The method of claim 1 wherein the first aspect of the projected digital image is a primary color of the projected digital image.
3 . The method of claim 2 wherein the primary color of the projected digital image is green.
4 . The method of claim 1 further comprising:
adjusting a power of the laser beam to control a second aspect of the projected digital image.
5 . The method of claim 4 wherein the second aspect of the projected digital image is a brightness of the projected digital image.
6 . The method of claim 1 wherein the first aspect of the projected digital image is a speckle characteristic of the projected digital image.
7 . The method of claim 1 wherein the first aspect of the projected digital image is a brightness of the projected digital image.
8 . The method of claim 1 wherein the projected digital image is formed by using a liquid crystal on silicon (LCOS) light valve.
9 . The method of claim 1 wherein the projected digital image is formed by using a digital light processing (DLP) light valve.
10 . The method of claim 9 wherein the DLP light valve is operated with a bit sequence; and the bit sequence is adapted for use with the adjustable frequency of the laser beam.
11 . The method of claim 10 further comprising:
generating an optical monitor signal that measures the first aspect of the projected digital image.
12 . The method of claim 11 further comprising:
sending the optical monitor signal to the bit sequence; and
using the bit sequence to control the frequency of the laser beam.
13 . An optical apparatus comprising:
An optical fiber;
wherein a stimulated Raman scattering in the optical fiber reduces a speckle characteristic of a light output from the optical fiber; and a frequency of the light output from the optical fiber is adjusted to control a first aspect of the light output from the optical fiber.
14 . The apparatus of claim 13 wherein the first aspect of the light output from the optical fiber is the color of the light output from the optical fiber.
15 . The apparatus of claim 14 wherein the color of the light output from the optical fiber is green.
16 . The apparatus of claim 13 further comprising:
a laser light source that illuminates the optical fiber;
wherein the laser light source has an adjustable power output; and the adjustable power output is adjusted to control a second aspect of the light output from the optical fiber.
17 . The apparatus of claim 16 wherein the second aspect of the light output from the optical fiber is a brightness of the light output from the optical fiber.
18 . The apparatus of claim 13 wherein the first aspect of the light output from the optical fiber is a speckle characteristic of the light output from the optical fiber.
19 . The apparatus of claim 131 wherein the first aspect of the light output from the optical fiber is a brightness of the light output from the optical fiber.
20 . The apparatus of claim 13 further comprising:
a digital projection system that forms a digital projected image.
21 . The apparatus of claim 20 wherein the digital projection system comprises a liquid crystal on silicon (LCOS) light valve.
22 . The apparatus of claim 20 wherein the digital projection system comprises a digital light processing (DLP) light valve.
23 . The apparatus of claim 22 wherein the DLP light valve is operated with a bit sequence; and the bit sequence is adapted for use with the adjustable frequency of the light output from the optical fiber.
24 . The apparatus of claim 23 further comprising:
an optical monitor that measures the first aspect of the light output from the optical fiber.
25 . The apparatus of claim 24 wherein the optical monitor sends a signal to the bit sequence and the bit sequence controls the frequency of the light output from the optical fiber.