The evaluation of speckle contrast with variable speckle generator

Abstract

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.

Evaluation of speckle of light-diffusion-fiber using laser light source

“…(1), and Cs is determined by the ratio of the average Ī of the pixel values in the measurement area to the standard deviation σ. [7][8][9][11][12][13][14][15][16][18][19][20][21][22][23][24] As can be seen from this, Cs has a statistical property, and a large amount of pixel data of a speckle pattern (Glen) image is required to obtain a highly accurate Cs value.…”

“…Also, color mixing using different wavelengths is possible. [7][8][9][10] And, this application is also effective as an emergency guide light as shown in the Fig. 3.…”

Theoretical calculation and experimental investigation of speckle reduction by multiple wavelength lasers in laser projector with different angular diversities

“…Speckle reduction by wavelength diversity can be achieved by broadening spectral bandwidth of a light source [9,10] or using multiple wavelength lasers [11][12][13]. Speckle reduction by angular diversity is achieved when a screen is illuminated by light with substantial angular divergence [14,15]. Polarization diversity depends on the polarization state of illumination light and depolarization on screen, which reduces speckle contrast by at most a factor of 2 [1].…”

31.3: Classification of Subjective Speckle for Evaluation of Laser Display

“…While laser display has many advantages such as long life-time span, high energy efficiency, and wide color gamut [1], there are still several issues to be solved. Speckle problem is one of main topic in laser display, so its measurement and reduction methods have been proposed in many articles [2], [3], [4]. However, especially for measuring method, its measuring conditions and measurement setup have not been standardized [5].…”