Study On 3-D Digital Dynamic Holographic Display Based On DMD

We live in a three-dimensional world and the visualization technology of 3-dimensional information has become one of the research hotspots both in domestic and abroad. The 3-D display technology has wide demands and good application prosperity in various fields such as military affairs, medicine, industrial design, movie and TV entertainments.The currently developed 3-D display technologies include eye shutters or glasses assisted, volumetric, directed light, time-multiplexed and holographic display, etc., some of them require the viewer to wear the glasses (for example Liquid Crystal shutter glasses and color filter glasses), which restrict the viewers' field of view and make their eyes easily tired. The stereoscope pair synthetic images are just the quasi 3-D images, they usually lost the vertical parallax and only present psychological depth of field other than the physical depth of field. Holographic display technology can reconstruct completely both amplitude and phase information of object, and the reconstructed image has same 3-D characteristics with the original image, so only the holographic images can be called true 3-D images. The holographic display represents the developing direction of the 3-D display technology in the future.The early holography focuses on the optical holographic display based on traditional holographic record material. In order to record optical hologram, one must have real object, laser source, holographic vibration-proof platform, optical elements and holographic record material and the severe record environment. All above requirements bring some problems on the quality and repeatability of hologram, and moreover, the classical optical hologram is not suitable for the dynamic holographic display application.The main work of this paper is to use DMD spatial light modulator as the holographic digital dynamic display device, and conduct the study on dynamic 3-D holographic display technology based on computer generated holography (CGH) and digital holography. Firstly, modified off-axis reference beam CGHs based on Burch, Huang and Lee type coding methods are designed and simulated, then the merit factors of signal-to-noise (SNR) and brightness are introduced to evaluate the quality of reconstructed images of three CGHs. The theoretical simulationresults show that the image quality of Huang's CGH is much better than the two others, so it offers the optimized encoding method for the 3-D holographic display based on CGH. Based on above research work, we use DMD to construct a set of dynamic holographic display system and successfully achieve the dynamic 3-D holographic display based on CGH.Moreover, the factors affecting the reconstructed image quality of digital holograms are analyzed, and a new method is put forward to improve the optically reconstructed image quality by filtering in frequency domain and rebuilding filtered hologram with high fringe visibility. The merit factors of signal-to-noise (SNR) and image brightness are also introduced to evaluate the reconstructed image quality of original and filtered holograms, theoretical simulation results show that the reconstructed image quality of filtered hologram is much better than that of original hologram. The experimental results of optical reconstruction based on DMD holographic display system also agree well with the theoretical results. This method provides a new idea to enhance the reconstruction image's quality of dynamic 3-D holographic display based on digital holography.