Information Encryption And Phase Object Detection Through Digital Holography

Digital holography is a technology which combines conventional optic holography with computer technology. Besides the advantages of conventional holography, it avoids the wet chemic process and obtains the object wave field easily through numerical calculation. So it is attracting the attention of researchers around the world.Optical information processing combines the characteristics of having large capability, high speed and parallelism. It can provide a great degree-of-freedom to hide the information such as phase, wavelength, spacial frequency, and light state of polarization. Therefore, the research of optical encryption technology has important academic significance and application prospects in exploiting the application area of optical technology and providing the new technological means for the information security.Conventional optical information encryption system can be divided into three kinds: double random phase encryption, iterative phase retrieve algorithm and digital holography. The random phase mask is needed in all of the methods above. Encryption and decryption processes are realized through the optical method. These encryption systems are used only for two-dimensional image encryption.This paper studies the digital holographic recording and reconstruction process. In view of two-dimensional image and three-dimensional object, the experimental system is completed. The two-dimensional image and three-dimensional object are reconstructed from each recorded hologram by Fresnel approximation method and the convolution method.Information encryption method based on digital holographic technique and phase retrieve algorithm is proposed. The phase-only information of the hologram is gotten by using phase retrieve algorithm, and the hologram is encrypted. The reconstructed hologram is obtained by applying inverse Fourier transform to encrypted hologram. The image can be reconstructed through Fresnel approximation method or convolution method. The presented method is quite different to ordinary random phase encryption method, and the random phase mask is not needed. Experimental results show that this method is suitable for not only two-dimensional image but also three-dimensional object encryption.Using the above experimental system of digital holographic recording and reconstruction, we also realize the three-dimensional phase object detection by use of four-step phase shift method and phase-unwrapping algorithm.