Abstract
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.
Highlights
Lasers have been widely used in various imaging systems, such as in projection displays and medical imaging, due to their advantages of high brightness, a wide color gamut, high directionality, and a long lifetime [1]–[3]
The speckle patterns and their 1D intensity distributions are shown in Table 1 when the laser light passes through the static multimode fiber and the laser light passes through the vibrating multimode fiber for the green and the red lasers
When a multimode fiber is vibrated, the speckle pattern changes due to phase modulation and mode coupling, and the speckle contrast can be reduced by angle diversity and the time averaging of the speckle patterns
Summary
Lasers have been widely used in various imaging systems, such as in projection displays and medical imaging, due to their advantages of high brightness, a wide color gamut, high directionality, and a long lifetime [1]–[3]. The propagation or reflection of a highly coherent laser through an optically rough object causes interference for the scattered light, which results in a random light intensity distribution, known as granular speckles [4], [5]. Speckles degrade the quality of images; reducing laser speckle has become an urgent task
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