Study On The Key Techniques Of Three-dimensional Display Based On Optoelectronic Holography

The important trend of display technologies is to display real-existing three-dimensional (3D) images. More and more attentions are now paid on 3D electro-holographic display (3D-EHD) because of its capability of reconstructing real-existing 3D images. Some researching works associated with 3D-EHD are described in this paper, including theories and methods of computer holography, algorithms for calculating computer-generated hologram (CGH) of true-color 3D object, characteristics analysis of the spatial light modulator (SLM), establishment of 3D-EHD system and experiment for displaying true-color 3D images. They are described in detail as follows:Basic theories and typical methods of computer holography are described, and comprehensive analysis is carried out for some typical coding methods in computer holography. Analytical result shows that, kinoform is an important coding method in electro-holographic display for its advantages such as high diffraction efficiency, without twin image in image-plane. Genetic simulated annealing algorithm (GA-SA) is introduced to CGH calculation. Typical optimization algorithms for CGH calculation are compared by considering convergence, efficiency and adaptability.Typical algorithms for calculating the CGH of 3D object are introduced. A novel algorithm is proposed and named as dynamic-pseudorandom-phase tomographic computer holography (DPP-TCH), in order to reduce speckle noise, improve diffraction efficiency and eliminate twin image. The qualities of digital reconstructed images are evaluated with peak signal-noise ratio (PSNR) and correlation coefficient (CC). Two strategies, named as"Equidistant Strategy"and"Pixel Number Equalized Strategy", are proposed for calculating CGHs of true-color object, and their characteristics are also analyzed. Multi-angle kinoforms of the true-color 3D objects are calculated and digital reconstructed RGB true-color 3D images are obtained by use of DPP-TCH and the calculation strategies.Phase-only or approximately phase-only modulation is needed to realize correct reconstruction of phase hologram. The amplitude and phase modulation properties of digital micro-mirror device (DMD) and LC-R2500 (LCoS-SLM) are measured. Analytical results show that, LC-R2500 can realize phase-only modulation under special system configurations and settings, and it can be used for phase hologram reconstruction. The modulation curves of LCoS-SLM are measured under different situations, such as different wavelengths used for RGB true-color holographic display, different incident angles and polarizing angles of laser beams. Phase-only modulation (POM) mode is then realized in order to meet the requirement of phase hologram reconstruction. The effects of phase modulation curves on the reconstructed images are also analyzed under POM mode. Gray level mapping (GLP) is proposed to adjust the gray level of each pixel in phase holograms, and the factors influencing the error between theoretical calculation and experiment result are analyzed, which can guide further optimization of optoelectronic reconstruction for phase holograms. The effects of aperture ratio and pixel pitch on the diffraction pattern are analyzed theoretically, and approaches are discussed for improving the intensity uniformity of image, enlarging the size of image and improving the utilization ratio of light power.A novel method is proposed to improve the intensity of reconstructed image by superposing digital blazed grating (DBG) with phase hologram in optoelectronic reconstruction system based on LCoS-SLM. The effects of superposing DBG with different grating periods and orientations on the position and intensity of reconstructed image are also analyzed. Experimental results also verify that, by the proposed method, the intensity of reconstructed image is increased and the utilization efficiency of light power is improved. Theoretical analysis is carried out for the differences of position and size between optoelectronic reconstruction and digital reconstruction, which can guide the design of optoelectronic display system. Experiments are carried out for true-color 3D holographic display with the system and kinoforms calculated by DPP-TCH. The results also show that the speckle noise of reconstructed images can be reduced significantly by use of DPP-TCH. Factors influencing the position deviations of the reconstructed RGB section images are analyzed. A novel method is proposed to correct the deviations by superposing DBG with proper grating period and orientation, and digital Fresnel lens (DFL) with proper focal length in the kinoforms. Theoretical calculation method is described, and experimental results verify that the proposed method is feasible.