Effect of incidence/observation angles and angular diversity on speckle reduction by wavelength diversity in laser projection systems

Abstract

The speckle reduction for laser projectors has been vigorously studied because speckle causes a serious deterioration in image quality. Most speckle reduction methods can be categorized into wavelength diversity, angular diversity and polarization diversity, which are usually treated independently. In this paper, it is shown that the effect of wavelength diversity and angular diversity on speckle reduction is not independent, and that the effect of wavelength also depends on incidence and observation angles on screen. The speckle reduction effect by wavelength diversity is smaller when the angular diversity is larger. Also, the speckle reduction effect is investigated on various screens including matte and silver screens, and it is shown that the effect of wavelength diversity is larger on matte screen than on silver screen.

Dependency of speckle reduction by wavelength diversity on angular diversity in laser projection system

“…Assuming that the speckle reduction by each effect is independent, the speckle contrast is given by where C λ , C Ω , and C σ are the speckle reduction factors by wavelength diversity, angular diversity, and polarization diversity, respectively. However, as shown in Yamada et al ., speckle reduction by angular diversity and wavelength diversity is not independent. Thus, instead of Eq.…”

“…Both the center angles of the incidence direction and observation direction have only ξ‐components, α i and α o , and the η‐components are zero ( β i = β o = 0). The detailed description of the experimental setup can be found in Yamada et al …”

“…On the other hand, wavelength diversity and angular diversity are treated independently in many cases. 6,7 However, Yamada et al 8 showed that wavelength diversity is dependent on angular diversity, as well as incidence and observation angles in laser projection systems. In this paper, the theoretical model to express the dependency of wavelength and angular diversity is derived.…”

P‐15.4: Dynamic Measuring Method of Speckle Contrast

“…Dynamic speckle contrast has been reported in motion sensing, medicine, biology, industry, and food quality evaluation [8,9] . With the expansion of dynamic speckle measurement range, the main goal of these fields is to develop efficient algorithms that can provide robust results under various environments [10] , In laser projection display, one of the most serious problems of a laser projector is speckle, which will seriously reduce the image quality [11] , Speckle often obscures the information of the image, so it is necessary to measure speckle in detecting and evaluating the quality of laser display.…”

Light source optimization for partially coherent holographic displays with consideration of speckle contrast, resolution, and depth of field

“…The partially coherent light source includes a bundle of mutually incoherent light sources 26 , 27 , an optical fiber 28 , 29 , and spectrally-broadband light source (e.g. a light-emitting diode, LED) 25 , 30 – 34 . The temporal superposition is to update speckle patterns at a fast frame rate.…”