Visual resolution of raster-scan laser mobile projectors under effects of color speckle

Abstract

Visual resolution of raster-scan, laser mobile projectors using red, green, blue (RGB) laser diodes was measured using a high-speed 2D speckle measurement equipment, considering the effects of color speckle. Blind evaluation of three laser mobile projectors was carried out. Photometric visual resolution of white point was obtained by calculating contrast modulation CM using a grille pattern of narrowing line-pairs. The color speckle distribution was plotted in CIE 1931 chromaticity diagram and in CIELab color space. The color speckle was found to degrade photometric visual resolution, as well as the color speckle distribution spreading in the color spaces. Color shifts at the edge of the line image were obviously observed by the color speckle plots in the color spaces. The color shifts are found to be generated due to RGB LD switch timing mismatches. As a result, one of them achieved better performance than the others. This 2D color speckle measurement method is indispensable for measuring visual resolution of laser displays, reproducing speckle grain sizes on human retina.