In this paper, far field speckle contrast from a broad area laser diode is measured. The intensity of the incident
laser light onto a diffuser is controlled by using polarizer or adjusting input current. A rectangular aperture
close to diffuser is used to select different parts of laser light field as illumination spot. The speckle contrast
measured for different illuminationspots has no significant change. When the laser diode operates at its typical
power output condition, the speckle contrast measured approximately equals 1, while the speckle contrast is
depressed tremendously when the laser diode operates with low driving current.
Laser speckle degrades image quality in laser displays. The speckle contrast needs to be correctly evaluated in designing laser displays. In this paper, a moving small diffuser for speckle reduction is set up for laser projection display system. We demonstrate the effect of the projection lens on speckle contrast under the scenarios of free-space and image geometry measurement with different configurations. The results show the speckle contrast in free-space geometry is measured as about 74.16% without projection lens and 60.74% with projection lens for the static diffuser, which are reduced to 2.75% when the diffuser moves for both with and without projection lens. In the imaging geometry, the moving diffuser reduces the speckle contrast from 83.22% to 9.61% without projection lens, and from 98.7% to 36.59% with projection lens.
An optical system model has been built up for evaluating de-coherence performance of Mie scattering by using ZEMAX software. The optical system consists of a linearly polarized laser source of the wavelength 0.6328 micrometer, the interferometer configuration with a double-arm beam path, the light pipe with the particles solution of variable parameters including the refractive index, the particle size and the particle concentration, and the detectors. Seven types of particles with different refractive index have been used as scattering medium. The de-coherence performance and the light energy loss have been calculated for solutions with different particle concentration and dimension. The calculated results indicate that the de-coherence performance can be improved by increasing the particle concentration in solution and the particle size. The improvement of the performance is more notable as the particle refractive index becomes higher. The dependence of the light energy loss caused by Mie scattering on the refractive index and size of the particle, and the particle concentration in solution is obtained.
In this work, a multilayered dielectric film and metallic film are used as reflecting surface to fabricate light
pipe. Linearly polarized laser beam with wave length of 532nm enters into the light pipe. After
multi-reflection process, laser beam come out from the light pipe. We have found that the polarization state of
linearly polarized incident light after reflection are different for the light pipe coated with metal and
multilayered dielectric film. We also found a distributed polarization characteristic in the output optical field.
The polarization degree has been simulated by using ZEMAX software. Laser speckle contrast from a glass
diffuser is measured to exam the simulated result.