Speckle suppression via a polarization-dependent random-phase metasurface without mechanical moving parts

Laser speckle remains a critical limitation in imaging and display systems due to the high spatial coherence of laser sources. In this work, we propose a non-mechanical speckle reduction method based on a polarization-dependent metasurface combined with a liquid crystal (LC) polarizer. The metasurface, composed of randomly arranged GaN nanoresonators on a sapphire substrate, is designed to generate uncorrelated random phase distributions for orthogonal polarization states. Numerical simulations demonstrate that incident speckled sources with varying polarization angles generate highly decorrelated speckle patterns, achieving a speckle contrast reduction ratio of 0.750 relative to the incident speckle through polarization averaging. Experimental validation under realistic conditions further confirmed the effectiveness of the proposed approach, showing a speckle contrast reduction ratio of 0.630 and a final speckle contrast of 0.250. This study demonstrates that polarization diversity introduced by a metasurface can effectively suppress laser speckle, providing a simple, passive, and robust solution for coherent imaging and projection applications.