| The true three-dimensional display is the next goal for modern imaging techniques after the high definition display technology. Holography has been acknowledged as one of the most promising true three-dimensional display techniques because it can supplies all stereoscopic visual stimulations. The classical optical holography uses high-resolution film as the display medium, which can achieve a ghost-like three-dimensional visual impression. However, this technology could not satisfy the demand for real-time, dynamic display, which limits its application as a mainstream display technique.Benton in MIT brings holography from film age to digital age. In1989, the Spatial Imaging Group headed by him created the first practical video holographic display system, which is a remarkably transition. However, there are still many challenges faced with the utility of holographic video display. In principle, the core of video holographic display is an electro-optical apparatus which is called spatial light modulators (SLMs). Recently, available SLMs devices include Acousto-optical spatial light modulator (AO-SLM), Digital micromirror devices (DMD), Liquid crystal spatial light modulator (LC-SLM). Liquid crystal on silicon (LCOS), one of the LC-SLMs, has merits such as high diffraction efficiency, high fill factor and high resolution.By taking advantage of the phase-only modulated LCOS, this thesis has mainly focus on the research for video holographic display method. The main works done and the contributions of this thesis are outlined as follows:1) After the inherent feature of the multi-copy and multi-order diffraction modulation produced by the pixilated SLM is analyzed, the way to improve visual impression of holographic reconstructed image has been presented. Combined with computational and optical method, the two focus planes of multi-order reconstructed image and the multi-order diffraction beam can be separated by using digital blazed grating and numerical spherical wave phase, then low-pass filter in the frequency domain of4f system is used to eliminate the higher order reconstructed images.2) An experimental holographic display system based on LCOS is set up. The system integrates server current methods as well as multiple optical elements to eliminate the high-order beam and zero-order beam. A method adaptive for the reflective LCOS is proposed in which the focal plane is moved forward by adding the phase of the convergent spherical wave to the phase-only hologram. As results, a major disadvantage that the physical length of the holographic display system in propagation direction is too long has been improved. An imaging lens is adopted in the system to adjust the position and the size of reconstructed image. An aperture and a high pass filter are also used to eliminate the influences of higher-order diffraction beam, multi-copy images and zero-order beam on the visual impression of reconstructed image. A dynamic holographic display of360degree field angle pictures is demonstrated by the images sequences method in the system.3) The main principle and methods to achieve color video holographic display are investigated, and the wavelength dependences of the size of reconstructed images involved in color video holographic display with RGB lasers are focused. The method to remove the magnification chromatics is studied. In order to achieve a high optical efficiency, a proof-of-concept color video holographic display system with spatial multiplexing method has been developed. |
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