Laser speckle contrast reduction measurement using diffractive diffusers

Document Type

Conference Proceeding

Publication Date

4-6-2009

Abstract

In order to produce future generation micro-projection systems that can function independently or in conjunction with small personal communication devices lasers are the preferred source of illumination over LEDs. Lasers are much brighter and require less power than LEDs allowing for larger screen sizes and smaller battery requirements. In order to illuminate the spatial light modulator used in the micro-projection system micro-optical elements are used within the illumination path of a projector system to shape the RGB laser sources. Due to the diffractive nature of the optical elements and the high coherence of the lasers a speckle pattern is produced in the final image reducing the overall image quality. Diffractive diffusers are typically used in combination with micro-lens arrays in a time varying fashion in an attempt to reduce the spatial coherence of the laser sources and hence reduce the speckle. Previous reduction techniques have successfully used pseudo-random hadamard matrix diffusers to greatly minimize the contrast of the pattern. This paper examines new reduction methods involving diffractive diffusing elements and presents measurements in the reduction of speckle contrast for each technique. © 2009 SPIE.

Publication Title

Proceedings of SPIE - The International Society for Optical Engineering

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