Compact passive system for speckle-free uniform illumination in RGB laser projectors based on incoherent focusing

Abstract

A theoretical analysis of the hardware mechanisms for subjective speckle suppression in RGB laser projectors has revealed that achieving a compact speckle-free passive laser illumination system with uniform illumination requires simultaneous reduction of temporal, spatial, and polarization coherence of the illumination laser beam, along with light intensity homogenization. To address this, we propose a compact passive optical scheme based on incoherent focusing of the laser beam using arrays of prisms with varying heights. The system also incorporates depolarization of a portion of the laser beam and an optical diffractive optical element employing a pseudo-random binary sequence to enhance speckle reduction and improve uniform illumination quality. We demonstrate that such a system can be assembled using readily available laser light sources and optical elements, and its operational principle is experimentally validated.