Simulation and Experiment of Speckle Reduction by the Beam Splitting Method on a Pico-Projection System

Abstract

An optical scheme using two correlationless beams to suppress the speckle of the pico-projection system is proposed. By using two broadband beam splitters (BBS) and two high reflection mirrors, the originally incident laser beam is split into two beams. The mutual correlation coefficient between two split beams is very close to zero. We use the haze reflection based on the random scattering model to simulate light reflected from the rough surface. In simulations, light is respectively reflected from the same size flat and rough surfaces and both recorded images are compared with each other. The image from flat surface is very clear on the detector plane. On the contrary, the image from rough surface is very fuzzy and the edge is hard to figure out. The simulations show that the speckle contrast ratio (CR) is reduced from 1.0 to 0.707. We find out a solution of the speckleCRless than 0.71 when the distance between two BBSs is 2.4 mm and the thickness of each BBS is 0.4 mm. Finally, we carry out an experiment and verify the simulating results. By our analysis from the experimental data, the speckleCRcan be reduced about 25% which is close to the theoretical value of 29.3%.

A Large-Size MEMS Scanning Mirror for Speckle Reduction Application

“…The scanning area can be changed with different driving currents, however, we need to control the total reflected light entering into the light pipe. According to speckle suppression theory [ 20 , 21 ], once the speckle images at different times and different positions are uncorrelated, then these irrelevant speckle figures are finally superimposed on each other during a frame image formed on the screen. If N independent speckle patterns are overlapped on an intensity basis, and we assume that each pattern has an equal mean intensity, the speckle contrast C in the integrated image is reduced to [ 4 ]: where N is the number of independent speckle patterns.…”

A large size MEMS scanning mirror for speckle reduction application

“…The scanning area can be changed with different driving currents, however, we need to control the total reflected light entering into the light pipe. According to speckle suppression theory [20,21], once the speckle images at different times and different positions are uncorrelated, then these irrelevant speckle figures are finally superimposed on each other during a frame image formed on the screen. If N independent speckle patterns are overlapped on an intensity basis, and we assume that each pattern has an equal mean intensity, the speckle contrast C in the integrated image is reduced to [4]:…”

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

“…To reduce the speckle for laser displays, various methods are used to decrease the spatial and temporal coherences of laser light 8,9) using a broadband green light source, 10) a moving or rotating optical element, [11][12][13][14][15][16] a fast scanning micromirror, 17,18) a binary diffuser, [19][20][21][22] and other reduction methods. [23][24][25][26][27][28][29] Although previous research studies have obtained efficient results for the speckle reduction, they generally require complex bulky optics or moving components with enough space to store speckle reduction elements. However, it is required to realize the entire system in a compact space with various optics, light sources, and MEMS scanning mirrors, which indicates the miniaturized speckle reduction element, as shown in Fig.…”