Regular paper

Polychromatic speckle reduction in laser pico-projectors using stationary dual Hadamard diffusers

Electrical and Computer Engineering Department, Michigan Technological University, Houghton, MI 49931, United States of America

^* whthomas@mtu.edu
^** ctmiddle@mtu.edu

Received: 17 October 2014
Revised: 16 December 2014

Abstract

Speckle from coherent light sources continues to be a limiting factor in the design and manufacturing of laser projectors. Utilizing diffractive diffusers has been an effective method for reducing monochromatic speckle contrast. Color laser projection devices require the use of red, green, and blue laser sources therefore; using a monochromatic diffractive diffuser may not be optimal for color speckle contrast reduction. A new static dual-diffuser system utilizing Hadamard matrices has been designed to reduce full color speckle. This paper analyzes the effectiveness of the new Hadamard diffusers in reducing speckle using three separate RGB laser diodes. A simulation of the Hadamard diffusers is conducted to determine the optimum spacing between the two diffusers for polychromatic speckle reduction. Experimental measured results are presented using the optimal spacing of Hadamard diffusers for RGB color speckle reduction showing 60% reduction in contrast.