Speckle reduction using a motionless diffractive optical element

Speckle reduction by moving diffuser has been previously studied in display systems with coherent light sources, such as lasers. In this Letter, we propose a motionless diffractive optical element (DOE) for speckle reduction. The DOE was designed based on finite-element method simulations, fabricated using micromachining technology, and characterized for despeckle efficiency. Experiments using a DOE with two gratings have indicated that the speckle was suppressed to 50%, which shows fair agreement with theoretical analysis. With some modification of this DOE, the speckle noise can be reduced to 10% according to the theory.