Research On Speckle Suppression In Laser Display And Speckle Tracking In The Image Plane

Laser display is predicted to have broad market owing to its advantages in wide color gamut, high saturated color, high image contrast and lower energy consumption. But there is a major problem in this system for high coherence of laser beam, which is a phenomena called speckle. Speckle reduces the contrast and resolution of images seriously and hinders the practical use of this system. Some methods should be found to resolve the problem. The model of speckle formation in laser scanning display system has been established, based on which the affect of system parameters on speckle contrast has been analyzed. For the laser projection display, a new apparatus with fiber vibrating combining with spatial polarized modulation has been proposed. It has been researched that the effect of fiber vibrating on speckle reduction and the parameters for the spatial polarized modulation device.Laser speckle sensing technology has significant advantages in simplicity, non-contract testing, high precision and real-time testing. It is widely used in computer mouse design and material testing. But there is little research employing image speckle and non-Gauss speckle. In this paper, the parameters for tracking with image speckle are researched. The speckle contrast and tracking range are improved for speckle tracking on the glass surface.The main research works are as following:1. The statistical properties of speckle are described in detail. The affect of the structure and dimension of laser spot, the diameter of lens on speckle temporal correlation properties is researched by simulation and experiment. It is analyzed that speckle suppression from the average effect of the temporal speckle sequence.2. The mechanisms for speckle arising in laser scanning display system are analyzed and the model is established, based on which the affect of system parameters on speckle suppression is researched. The results show that: speckle contrast is not sensitive to the standard deviation of surface height and decreases as the correlation length gets smaller, from which the speckle contrast can be reduced to 50%; speckle contrast reduces as the decreasing of the pupil aperture, which is nearly proportional. But there are slight differences of speckle vision for people with different pupil aperture; speckle contrast has great changes as observing distance increases, it gets smaller; speckle contrast is reduced by 1/5, when laser spot is narrowed in scanning direction. For the results with circular laser spot, some experimental results are given.3. The apparatus and mechanism for laser projection display are described in detail and the reasons for speckle arising in this system are analyzed. The methods for speckle suppression are reviewed. A new laser projection system with speckle reduction employing fiber vibrating and spatial polarized modulation is designed. The affection from system parameters on speckle contrast and image quality is researched. The parameters for spatial polarized modulation device are given from simulation research.4. The theory for speckle tracking and the method for image processing are described in detail. The affection on tracking precise and range for tracking with image speckle from rough surfaces is researched. For glass surface as a relative smooth surface, with non-Gauss speckle tracking generating by imaging system speckle contrast rises from 0.25 to 1.25 and the tracking range increases from 200μm to 400μm compared with tracking employing free propagation speckle.Highlights of the dissertation are as follows1. It is the first time to analyze mechanisms of the speckle arising in the laser scanning display system and to establish the speckle physical model. Based on the model, the affection of system parameters on speckle contrast is researched, proper explanations for the results are given. The results show that speckle vision can be suppressed by choosing suitable optical parameters in laser scanning display system, which can give an instruction to speckle reduction.2. A new laser projection system with speckle reduction employing fiber vibrating and spatial polarized modulation is designed. The affection from system parameters on speckle contrast and image quality is researched by experimentally and the effect for speckle suppression with fiber vibrating is given. It is the first time to design a spatial polarized modulation device for speckle reduction and the parameters for the device are given by simulation research. 3. It is the first time to track with non-gauss speckle and to conquer the problem of low speckle contrast upon glass surface. With non-Gauss speckle tracking generating by imaging system speckle contrast rises from 0.25 to 1.25 and the tracking range increases from 200μm to 400μm compared with tracking employing free propagation speckle.