基于旋转散射片实现激光散斑抑制的理论分析和实验研究

Theoretical analysis and experimental research on laser specklesuppression based on rotating diffuser

基于光学信息理论分析法,对激光投影显示成像系统中投影光学系统数值孔径尺寸和随机位相片照明光斑大小对散斑衬比度的影响进行了系统分析.分析表明,当投影系统数值孔径较小时,散斑衬比度影响因素主要由投影光学系统自由度数NDOF决定,即此时投影系统数值孔径大小的改变对散斑场衬比度的影响较大;当随机位相片在入射光束光斑直径较小时,散斑衬比度取决于物面光自由度K,此时增大投影系统数值孔径对散斑场衬比度的影响不大.在简化投影系统中,通过系统实验分析了投影镜头孔径大小和位相片上照射光斑大小对散斑抑制的影响.实验结果表明,当投影镜头孔径大小一定时,随着位相片上照射光斑直径的增加,散斑场的衬比度下降率逐渐下降;当位相片入射光斑大小一定时,随着投影系统数值孔径增加散斑衬比度下降率越来越小.实验结果证明了理论分析,位相片出射物面光自由度需要和投影镜头自由度相匹配.该结论可为设计以旋转随机位相片降低激光散斑的投影显示系统提供参考.

Based on the theoretical analysis method of information optics,the influence of the numerical aperture size of the projection optical system and the size of an illumination spot on a random diffuser on the speckle contrast in the laser projection display imaging system is systematically analyzed.The analysis shows that when the numerical aperture of the projection system is small,the influence factor of speckle contrast is mainly determined by the degree of freedom of the projection optical system N DOF.In this case,the change of the numerical aperture of the projection system has a greater impact on the speckle field contrast.When the spot diameter of the incident beam is small,the speckle contrast depends on the optical degree of freedom K of the object surface.In this case,increasing the numerical aperture of the projection system has little effect on the speckle contrast.In the simplified projection system,the effects of the aperture size of the projection lens and the size of the illumination spot on the diffuser on the speckle suppression are analyzed through systematic experiments.The experimental results show that when the aperture size of the projection lens remains unchanged,the speckle contrast gradually decreases with the increase of the diameter of the illuminated spot on the diffuser.When the diameter of the incident light spot on the diffuser remains unchanged,with the increase of the numerical aperture of the projection system,the contrast of the speckle field gradually decreases.The experimental results are consistent with the theoretical analysis,and the degree of freedom of the object surface light emitted from the diffuser needs to match the degree of freedom of the projection lens.This conclusion can provide a reference for the design of projection display system for reducing laser speckle by rotating random diffuser.