Theory of speckle suppression in a laser projector based on a long multimode fiber

We analyzed the speckle suppression efficiency of a multimode fiber in a practical laser projector, and developed a theoretical model. Theoretical analysis and simulations indicate that the speckle suppression coefficient can be approximated as a linear function of the square root of the ratio of the numerical aperture of the objective lens and the eye. To suppress the speckle below human eye sensitivity, the objective lens should have a large numerical aperture. The decorrelation uses only the radial direction of the objective lens aperture for speckle suppression and does not consider the azimuthal direction, which can be the focus of future studies. The speckle contrast data obtained in the experiments are consistent with the theoretical results.