Speckle reduction II: Laser projection without speckle noise? Experimental investigation

Scanning laser projectors offer several useful features, most stunningly the small size, not much bigger than a cigarette pack. The laser beam is modulated and scanned across the projection screen by a small MEMS mirror. There is no imaging optics, the depth of field is virtually infinite. The major drawback is an image quality degraded by speckle noise. To avoid this, we experimentally investigate different options to narrow the width of the spatial coherence function within the projected laser spot on the screen. This can be achieved by a large illumination aperture which is filled with temporally incoherent modes. The temporal incoherence is generated by a stack of glass plates in the pupil or by sending the laser light through a multimode optical fiber. The experiments will illustrate the theoretical considerations of our first contribution (Speckle reduction I).