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

摘要

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.