Abstract
Speckle reduction by angular, wavelength, and polarization diversities is widely used to suppress speckle
in laser projectors. Although several methods achieve these three diversities, few have shown a
quantitative comparison among these methods. Thus, in this study, we summarize the speckle reduction
effect by the wavelength, angular, and polarization diversities introduced by several different methods.
Angular diversity is altered by changing either the angular distribution of the illumination light or the
speckle measurement condition. Wavelength diversity is introduced using the continuous spectrum of a
Xe lamp with bandpass filters or multiple wavelength lasers. We also discussed the dependency between
angular and wavelength diversities. Polarization diversity is introduced with an optical fiber to
depolarize the laser light and rotating a half-wave plate to temporally change the polarization state. We
also investigated the effect of depolarization on a matte screen.
