Speckle reduced holographic display system with a jointly-optimized rotating phase mask

Speckle noise degrades image quality in systems with coherent light sources, which must be overcome in holographic displays. In this Letter, we introduce a holographic display system with a rotating phase mask for speckle noise reduction. The rotating phase mask works in a similar way as a conventional rotating diffuser, but its pattern is jointly optimized with the spatial light modulator to maintain the contrast of the reconstructed image. The effectiveness of our system is verified through both numerical simulations and a tabletop prototype, reducing the speckle contrast by 38.8% while preserving the image quality.