| Holographic3D display is able to show picture as same as the real one, so it is called as ultimate tool for true three-dimensional display. In conventional holographic display, holographic plate is used to recording amplitude and phase information of which to be photographed. It will present the reconstructed3D image when using the same source as the original recording light source.However, the conventional holographic technology is not able to show dynamic three-dimensional reconstructed image of the object. Researchers from MIT Media Lab make holographic into the digital age by using acousto-optic modulator to replace the holographic plate. As a kind of LC-SLM, Liquid crystal on silicon (LCOS) is the core part of today’s video holographic display system as combine of display technology and silicon chip technology with many potential advantages. The pixel pitch of LCOS is as small as6～8um, but it still can not exhibit a large diffraction angle to meet the needs of the human eyes in holographic display. How to achieve larger angle field-of-view is a great challenge in this area.The smaller size of pixel, the larger angle of diffraction can be achieved. While the fringing-field effect caused by adjacent two pixels with the reduced size of the edge pixel, which affect the amount of phase modulation and diffraction efficiency seriously. In this paper, the author try to find the way how to achieve larger diffraction angle with the high diffraction efficiency by studying the size and shape of the electrodes in liquid crystal device including the interdigital electrode which has been widely used in LCD. The pixel size of LCD is much lager than pixel size of LCOS, and their operating modes are different. Whether the drive mode in LCD can be used in LCOS is need to be focused explore in the paper.The paper including the following research contents:1) The background of the study is investigated and the challenges of current commercialized LCOS in video holographic display is pointed out.2) The conventional matrix method is limited to calculating the LC director distribution in1D condition,but it is not applicable to the LCOS with interdigitated electrodes or smaller pixel pitch. The method which is more complex and be able to calculate the optical properties in multi-dimensional condition is needed. As more rigorous method, FDTD method is used to calculate the optical properties of liquid crystals accurately. For the simulation of desired LCOS used in holographic video display, Techwiz LCD and FDTD Solutions are selected as simulation tools. They construct the experimental platform for this paper and the future research in our group.3) The influences on optical properties of LCOS which pixel size is6.4um with different inter-pixel gap, pre-tilt angle and thickness are studied. The results show that diffraction efficiency is almost no change as pre-tilt angle within5°or inter-pixel gap is below0.5um. While diffraction efficiency is greatly affected by the thickness of cell.4) By changing the electrode width and the gap width, the optical properties of the liquid crystal device driven by the interdigitated electrodes is studied. The result shows that nearly11.5°diffraction angle and up to14%～15%diffraction efficiency can be achieved by varying the electrode width and the gap width. The phase modulation can be up to1～1.725π for a certain range of thickness. It’s significant and offer reference for applying the interdigitated electrodes to LCOS which can achieve large diffraction angle and high diffraction efficiency in holographic reconstruction. |
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