Yunbo Shi

Speckle characterization in free space and imaging space

There have two ways to observe speckle, free space and image space. We introduced the factors impact speckle contrast in a speckle characterization system and established an equivalent relation between image space speckle characterization and free space speckle characterization, validating the equivalent relation through experiments. The experimental results show that if the equivalent relation come into existence, the speckle contrast measured in image space match well with it in free space. At last we have discussed the speckle in a projection system with a rough surface inside and given the compound speckle measuring method.

Speckle characteristics of a broad-area laser diode

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.

Effect of the projection lens on speckle contrast measurement in laser projection displays

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.