31.3: Classification of Subjective Speckle for Evaluation of Laser Display

Abstract

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.

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.…”

Speckle reduction in laser picoprojector by combining optical phase matrix with twin green lasers and oscillating MEMS mirror for coherence suppression

“…6. 6) Green laser diodes (OSRAM PL 520B) with collimating lenses are aligned through a polarization beam splitter (Thorlabs BS16) to be combined as a single laser spot. They are modulated with the scanning frequency of the MEMS mirror to realize the WVGA resolution (800 × 480).…”

“…In the case of laser projectors, however, the deterioration of image quality, the so-called speckle phenomenon, is induced by reflecting highly coherent characteristics of lasers with single wavelengths on random rough surfaces, resulting in a random spatial intensity distribution. 4,5) In general, a speckle is quantified by the speckle contrast ratio (SCR), which is expressed as [5][6][7])…”

“…Speckles are classified into the following two types on the basis of the origin of speckle generation: 1) the projected speckle originating from the display unit before the screen and 2) the screen speckle originating from the screen characteristics based on the scattering or diffusing effect. 6,7) Since the laser display is related to the speckles generated by both optical engines of laser sources and optical components and the screen characteristics, both types of speckles must be suppressed to enhance the image quality. We think that there are many candidate screens under real application conditions for laser picoprojectors.…”