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Xu M.,North University of China | Wang H.,North University of China | Gao W.,North University of China | Gao W.,Shanxi Ovision Optronics LTD | Yan J.,Shanxi Ovision Optronics LTD
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2015

Base on speckle formation mechanism in laser projection display system, two key parameters that influence speckle suppression are theoretically analyzed, namely the number N of statistically independent speckle images and the number M of projection-lens resolution elements within a single imaging-lens resolution element on the screen. The increasing value of the parameter M or N can effectively reduce the contrast of the speckle image. However, although the number N of independent speckle images projected on the screen tends to infinity, the contrast of the speckle image can only be reduced to 1/√M. By using a rotating small diffuser to generate independent speckle image, the degrees of speckle suppression are experimentally compared without projectionlens and with projection-lens in simplified projection system. And the effects of the change of the F-number of the projection-lens or the F-number of the imaging-lens on the parameter M and the speckle suppression are experimentally analyzed. The results demonstrate that for the same value of N and under the same test conditions, the contrast of the speckle image increases from 0.146 to 0.427 and the speckle is more serious due to the presence of the projection-lens, and the increase of the F-numbers of the projection-lens can further deteriorate the speckle image, which will be a challenge for the miniaturization of laser projection system. ©, 2015, Science Press. All right reserved.


Xu M.-F.,North University of China | Wang W.-B.,Shanxi Ovision Optronics Ltd. Co. | Gao W.-H.,North University of China | Gao W.-H.,Shanxi Ovision Optronics Ltd. Co. | Shi Y.-B.,North University of China
Guangxue Jingmi Gongcheng/Optics and Precision Engineering | Year: 2013

The optical system which produces speckles in a laser projection display system was simplified. By combining theories and practices, the simplified system was used to analyze the formation mechanism of a compound speckle and its effective characterization. Based on the speckle contrast analysis method, four important factors affecting the contrast of the compound speckles were analyzed by the experiments, namely, the spot diameter of an incident light beam, the distance between diffuser and screen, the coarse speckle granule on the screen and the fine speckle granule above the screen. Then, the contrasts of the compound speckles as a function of these parameters were determined by the experimental data. After researching the constitute of the compound speckle, a relational model based on contribution of the coarse granule and the fine granule on the compound speckle was presented by statistical analysis method and confirmed by an experiment. Obtained results provide an effective experimental basis for the speckle suppression in the laser projection display.


Xu M.,North University of China | Shi Y.,North University of China | Gao W.,North University of China | Gao W.,Shanxi Ovision Optronics LTD | And 2 more authors.
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2014

Display screen is an integral part of laser projection system. The surface roughness of screen directly affects speckle suppression based on angle diversity. The relation between speckle correlation and the surface roughness of measured screen is established by analyzing the speckle suppression method based on angle diversity. In the experiment, the incident angle is fixed to 1° and the angle increment is set to 0.0038°, which is a compromise between the sensitivities of surface roughness of the measured screen to those two factors. To avoid the effects of external perturbation and surface flatness on measured results, nine sub-regions are chosen in 5 cm × 5 cm measured screen areas and measured results from these sub-regions are averaged, which effectively improves the measurement accuracy. The surface roughness for four screens determined by the proposed method are 235.80, 209.57, 132.24 and 137.60 μm, respectively, which provides a basis to design a projection display screen applied to effectively reduce laser speckle.


Xu M.,North China University of Technology | Gao W.,North China University of Technology | Gao W.,Shanxi Ovision Optronics Ltd. | Shi Y.,North China University of Technology | Li J.,North China University of Technology
Guangxue Xuebao/Acta Optica Sinica | Year: 2014

Speckle suppression is a technical bottleneck hampering the development of laser display technology. The effects of the scattering angle of the diffuser, the number of cascade diffusers and the separations between them on the width of the scattering beam coherence area are analyzed by the experiments. On the base of the scatterer composed of cascade diffusers and lightpipe, the laser decoherence phenomena achieved by applying cascade diffusers is explained according to the multiple scattering theory. Based on statistics of integrated speckle, the relationship between the autocovariance function of the intensity and the speckle contrast is derived from the speckle pattern within the integration time T of CCD, and the influence of cascade diffusers on the displacement of the moving diffuser is determined, which contributes speckle suppression. The experimental results show that the combination of the scatterer with the moving diffuser not only improves optical energy utilization, but also reduces the speckle contrast from 0.753 to 0.069 within the integration time 1/30 s of the detector.


Xu M.,North University of China | Gao W.,North University of China | Gao W.,Shanxi Ovision Optronics Ltd. | Shi Y.,North University of China | And 4 more authors.
Optik | Year: 2016

The speckle characteristics of a broad-area edge-emitting semiconductor laser diode (BAEELD) in continuous wave emission regime are investigated experimentally. Performed measurements aim to assess the dependence of the speckle characteristics on spatial region of emitted light field, driving current and case temperature of BAEELD. When BAEELD operates at operating current of 550 mA and at 24 °C, the speckle in different regions from the broad-area field are measured by three different experimental configurations, including direct measurement, rotating the BAEELD, and gathering all emission by the collimating lens or two mirrors. The correlations between the speckle patterns of different regions of the broad-area field are analyzed. The results demonstrate that the speckle images measured are correlated although the BAEELD operates at different operating currents and case temperatures. © 2015 Elsevier GmbH. All rights reserved.

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