Compound Speckle Characterization Method and Reduction by Optical Design

Speckle and the compound speckle can be reduced by angle diversity. In laser projection displays, simple, low cost and efficient speckle reduction techniques require smart optical design . Using a MEMS scanner together with a condenser lens, laser beams with different illumination angles are obtained on the diffuser surface with low speckle contrast ratio (CR). After homogenizing within a rod integrator, the speckle field illuminates a display panel, and is projected onto the screen which forms the compound speckle. Characterization method to evaluate the compound speckle reduction efficiency is analyzed and discussed in a simplified optical system. The preliminary speckle reduction is demonstrated in a commercial projector where a 600 mW green laser has been used as the illumination source, and the compound speckle CR is brought down from 0.38 to 0.14.