Influence Of The Typical Instruments Of The Non Imaging Optical Path On Laser Speckle In The Laser Projector System

In laser projection system, the speckle will be formed on the surface and detected by human eyes. Speckle will severely reduce image quality, therefore it should be suppressed. However, A single speckle suppression method without considering the system structure of projector can not balance desired speckle reduction effect with light usage well.This paper focuses on the influence of the typical instruments of the non imaging optical path on laser’s properties, such as polarization and coherence, and then laser speckle and laser speckle reduction in the laser projector system are investigated.First, the influence of a light pipe on the polarization properties of linearly polarized light and its polarized speckle is investigated. We propose that the usage of a light pipe does change the polarization properties of the laser light. A simulation model is designed for the propagation of linearly polarized light in three types of light pipes. The polarization properties in three situations are discussed and these results have also been experimentally verified. We can conclude that the hollow light pipe changes the polarization properties of the laser beam by changing the key parameter of the PO(polarization orientation) of the input laser beam. Especially, the best depolarization and speckle suppression characteristics can always be obtained when the PO equals 45°. Furthermore, the influence of other devices on the polarization properties of linearly polarized light is discussed and a laser speckle reduction method based on orthogonal polarization is investigated. We suppose the results of our research may guide the optical designer to consider a light pipe configuration to achieve speckle reduction in the field of laser projection displays.Second, the influence of the structural features of the moving scattering device on speckle suppression in the non imaging optical path is investigated. The experiments verify the speckle suppression effects of the surface appearance of the diffuser and the speckle contrast effects of speckled speckle. A high transmittance and low speckle contrast speckle suppression method by using moving micro lens array in the non imaging optical path is proposed.Third, the limitation of the two-dimensional model for illumination angles producing uncorrelated patterns is discussed. A three-dimensional model of the variation illumination angles in spherical coordinate system is set up for the first time. A scattering vector with a certain illumination direction is expressed by 3 parameters r, θ and △?. A new parameter △? is brought in and the formula of the magnitude of the transverse component of the scattering vector difference Δ qt is derived. The minimal angle difference is discussed theoretically and numerical calculation in the three-dimensional space. The results can be applied to reduce the speckle, especially in digital holography field by diversifying the illumination angle.Finally, based on the new formula, a new expression for the intensity correlation based on the three-dimensional model of the variation illumination angles in spherical coordinate system is derived. Based on the new derivation, the minimal angle difference is investigated by numerical calculation and experiment.