الفهرس 
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Abstract
In this study, a method to encrypt and decrypt three-dimensional scene using computer generated holograms (CGH) and phase mask encoding is proposed which provide a full understanding to the factors that affect the encryption system. The amplitude and phase information of a three dimensional scene is obtained computationally using phase shifting interferometer and stored on digital computer. Encryption performed using a random phase mask at a plane located in the Fresnel diffraction region. The principle of off-axis digital holography is used with single and multiple phases encoding to encrypt the 3D scene. The proposed optical encryption system is based on Mach-Zehender interferometer. This interferometer is applying the principle of Fresnel diffraction, free-space propagation and CGH. The Fresnel CGH is generated from a scene located within a Fresnel region in which the Fresnel diffraction formula is satisfactory valid. For this case, a digital construction of a 3D test scene is performed by slicing the 3D object image into a number of 2D images; each of these images describes the 3D object at different distance from the CCD camera. The encrypted hologram and the decryption key are recorded as a digital hologram. Only, the authorized users that have the proper decryption key parameters can restore the scene images. Different images of the three dimensional scene at different planes can be restored after the decryption. The encryption system is tested for the decryption parameters and its effect on the encryption performance is conducted for the single and multiple phase encoding. These parameters are propagation distance between the 3D scene and the hologram plane, the propagation distance between the phase mask encoding and the hologram plane, the phase mask encoding function, and the order of multiple phases makes to the hologram plane. A comparison between single and multiple phases encoding for binary and gray scale scene is performed. Bit error rate and mean square error are reported to measure the quality of the decryption process. The encryption system is very sensitive to the decryption parameters, phase mask function, and the order of the phase masks in case of multiple phase encoding and less sensitive to the object propagation distance where the user can scan for the exact object distance. In addition, results show that the multiple phase encoding is more secure than single phase encoding. Also, multiple phase encoding increases the mean square error for the gray scale images.