RGB laser projector with uniform speckle-free illumination based on a compact passive system of incoherent focusing

• Main Authors: Лапчук, А. С., Пригун, О. В., Горбов, І. В., Морозов, Є. М., Бородін, Ю. О.
• Format: Article
• Language: Ukrainian
• Published: Інститут проблем реєстрації інформації НАН України 2024
• Subjects: спекли; зменшення спеклів; лазерний проектор; некогерентність; некогерентні системи фокусування; фокусуюча призма; мультиретардерна призма; : speckle; speckle reduction; laser projector; incoherence; incoherent focusing systems; focusing prism; multi-retarder prism
• Online Access: http://drsp.ipri.kiev.ua/article/view/308600

An analysis of properties of laser projectors has shown that in spite of large advantageous of laser illumination like high optical efficiency, high optical gamut and images saturation, an interference phenomenon that demonstrates himself through interference fringes in illumination spot and in strong granular modulation of image by subjective speckle are main obstacles to wider application of laser illumination for compact optical projectors. Till now, in spite of large effort for suppression of interference effects in laser illumination system the known solutions are not sufficiently simple, efficient and compact for small optical projectors. An analysis of the mechanisms for subjective speckle suppression in RGB laser projectors has shown that for obtaining 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. In addition, a simplest illumination system should not have active optical element. A compact passive optical scheme based on incoherent focusing of the laser beam using two 1D arrays of prisms with varying heights that focused a laser beam in one rectangular shaped homogeneous laser spot is proposed. In proposed optical scheme a decrease of time coherence of laser illumination is achieved by using two wideband lasers with orthogonal polarization. The system also has depolarization module of laser beam to use polarization for speckle suppression. An additional passive optical diffractive element (DOE) employing a pseudo-random binary sequence is used to enhance speckle reduction and improve uniform illumination quality. It is demonstrated that such a system can be assembled using readily available laser light sources and optical elements, and its operational principle is experimentally validated. Fig.: 12. Refs: 57 titles.