The Analysis Of Speckle Reduction By The Vibrating Fiber And Related Problems

Recently, with the development of laser projection displays technology, the practical technology of suppressing the laser speckle has become an urgent problem to solve in industry. There are many of experimental methods to choose from, but not many practical approaches can be found when the factors such as the conflict of reduced speckle and light utilization, and increasing complexity of the structure are considered.This article describes the practical program to suppress speckle by the vibrating fiber. In order to find a perfect way which can not only effectively suppress the speckle but also reduce the light loss, Generalized van Cittert-Zernike theorem is used in the theoretical analysis of speckle reduction in the laser projection display, where the vibrating fiber is used as speckle reduction approach. The results show that the speckle contrast depends on number of Optical fiber model and the projection system pupil size. For the same size of the image plane, in order to reduce speckle contrast, we should collect more modes of multimode fibers and enlarge pupil diameter of projection system. This method can easily provide a theoretical basic for choosing the fiber and designing the illumination mode, In the projection system, the comparison experiment using two different multimode fibers are done and the results confirm this conclusion qualitatively. And large pupil diameter of projection lens are designed.Due to the spread of coherence in fiber may change, and speckle contrast is closely related to the coherence quality, this paper studied the time coherence and spectrum change after the light spread in multimode fiber and single-mode fiber.The results show that, with the increase of the transmission distance, coherent time all get longer and global coherence are changeless. The multimode fiber narrowing the power spectrum width, but for single-mode optical fiber, power spectrum in transmission process remain unchanged.Finally, this paper presents a method using the correlation of speckle patterns to measure the degree of laser polarization. This method is convenient and feasible, and could be used to study the change of degree of the polarization state changes, when the laser is scattered by the medium.