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Speckle in laser display contains several types of interference wavefront which is originated in different generation mechanism. We found out that subjective speckle can be classified into three types; projected speckle, screen speckle and direct speckle. Some experimental results were shown to see how each type of speckle looks like.

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While laser projection has many advantages, there is a problem with speckle patterns generated as a result of interference of the laser beam and results in bad effects to observers. In 2010, a variable speckle generator, which produces an angular shift of incident light to the screen and generates variable speckle patterns, was suggested. In this study, the performance of a variable speckle generator by using a volume phase holographic beam shaper and scanning mirror was investigated in detail by evaluating both the objective and subjective speckle contrast. The morphology of the speckle pattern was also investigated when the variable speckle generator was activated. With a scanning VPH beam shaper, the objective speckle was effectively reduced because each point of the VPH beam shaper generated different speckle patterns and coherency among each pattern disappeared by using the scan process. On the other hand, subjective speckle was also dramatically reduced by changing the incident angle on the screen, which resulted in generating variable subjective speckle. It was also shown that the speckle reduction rate by using a variable speckle generator did not depend on the coherent length of a laser by evaluating the normalized speckle contrast against the angular shift on the screen. FIGURE 16 -Subjective speckle reduction with increasing scan frequency by one-dimensional scan.FIGURE 17 -Subjective speckle reduction with increasing angular shift by two-dimensional scan.FIGURE 18 -Subjective speckle patterns when the angular shift was 0.22°with two-dimensional scan.