The Study Of Three-dimensional Displaying By Computer-generated Hologram

Computer-generated hologram is a new holographic imaging technique that use computer to make the hologram. As hologram can reconstruct the real three-dimensional image of the object, people naturally want to use the CGH technique to calculate the wavefront of three-dimensional object and to display three-dimensional image. In some branches of the information processing, the three-dimensional object expressed as the form of math are often hoped to display in 3D. Therefore, the three-dimensional displaying occupied an important position in the application of computer-generated hologram. The paper introduced a new method of three-dimensional displaying by computer-generated hologram.The whole paper includes the following parts:At first the history and the main developments of the computer-generated holography are reviewed, the history and the main developments of the three-dimensional displaying are reviewed, the present states of three-dimensional displaying by computer-generated hologram are also reviewed.Secondly we introduce the basic theory which is the foundation of the computer-generated holography, some conventional encoding method of the computer-generated hologram (CGH) are also described.Thirdly, we simulated the encoding algorithms of the CGH with the help of software named Matlab. After we got the CGHs, we also use computer to simulate the reconstruction of the CGHs and present the simulated results. At the same time, The hologram drawn by the method of LomanⅢand two-channel are shown separately on the computer screen, then microfilm separately to 4mm×4mm by camera directly, and films of computer-generated holograms are made. When these films were illuminated with a collimated monochromatic light, the optical reconstruction images can be obtained experimentally. We also use the Burch coding to make the fourier and fresnel hologram and good reconstructed images are obtained by filting methods.Lastly, a new method of displaying 3-D object by computer-generated hologram is proposed. A few experiments are done to validate it. In the experiment a three-dimensional object is created by the software of 3Dmax. The 3D object includs three cuboids. The center coordinates of these cuboids are not in the same plane and there is a different letter in each cuboid's front face. Several continuous projection images of the three-dimensional object of different perspectives in two orthogonal directions are recorded, In accordance with the principle of computer tomography, the three-dimensional Fourier spectrum of the object is calculated by use of these projection images, a character 2-D Fourier spectrum is extracted from the 3-D Fourier spectrum. The Fresnel diffraction distribution in a spectral distance is calculated with the convolution method. Then a Fresnel CGH is generated through the method of Burch coding, the CGH is also reconstructed by computer simulation, the results of the reconstruction in different distance are presented.