Speckle reduction with fast electrically tunable lens and holographic diffusers in a laser projector

We proposed a speckle reduction system in the laser pico-projector. The holographic diffusers and the fast electrically tunable lens (FET lens) were adopted in the method of the speckle reduction. This research focuses on speckle reduction by the different divergence angle of the holographic diffusers. Moreover, the speckle contrast value can be further reduced by the fast electrically tunable lens. Different divergence angle of the holographic diffuser provides the different angular diversity to compare the speckle reduction ability. We propose three experimental methods to explore speckle reduction. In experiment 1, we use a holographic diffuser and the FET lens. The speckle contrast value can be reduced to 0.08353. In experiment 2, the speckle contrast value can be reduced to 0.06403 under the balance between power consumption and speckle reduction. In experiment 3, we adjust different waveforms to get lower speckle contrast value. Finally, the speckle contrast value is 0.048 at 400Hz. That is lower than 0.05 successfully. That caused the speckle phenomenon is undetectable by human eye.