Compound Speckle Reduction in Laser Imaging Systems by Using a Vibrating Multimode Fiber and a Tracked Moving Flexible DOE Loop

The speckle phenomenon produced by coherent waves interfering with each other is undesirable in laser imaging systems. For each of the laser speckle reduction methods in the literature, it is difficult to reduce speckle to an extremely low level (< 3%) and also ensure good image quality. Therefore, a compound speckle reduction method based on the combination of a vibrating multimode fiber and a tracked moving flexible DOE loop is proposed and demonstrated for the first time. We have experimentally demonstrated the effectiveness of the proposed compound method, which can reduce the speckle contrast to 1.96% and obtain good spot quality. The relationship between the time-averaging effect of the speckle patterns from a vibrating multimode fiber and from a tracked moving DOE loop is discussed thoroughly. Our experimental results are in good agreement with Goodman's speckle theory. We expect that the compound speckle reduction method we proposed will have promising potential for applications in laser imaging systems.