The Research On The System Of Photoelectric Image Encryption

Optical technology is enjoying more and more attention due to its application into the data protection and encryption concerning our national as well as financial safety. The formulation of double random phase encoding technology, a part of the optical technology for encrypting images, helps a lot in perfecting optical technology in question. In order to explore for the technology deeply, this thesis, based on the job done before, is doing something significant in the research on the system of photoelectric images encryption.First of all, this thesis gives a general introduction to the application of data security system into the optical intention, which is followed by a discussion about the two optical methods employed in safety authentication as well as a look-back into how double random phase encoding is being developed in recent years both at home and abroad.Secondly, this thesis does a research on double random encoding theory in Fourier transform domain with the help of computer simulation, and discusses two typical optical image encryption technologies. A special attention is paid to the detailed discussion about the polarization encoding principle and conditions for modulating phase, which both depend on the spatial light modulator used in the job of this thesis.Thirdly, this thesis makes a detailed introduction about fractional Fourier transform recently applied into the optical image encryption as well as a discussion about the relation between the two dimensional fractional Fourier transform and the Fresnel diffraction. It also introduces the optical implementation of fractional Fourier transform. A research is carried out on the fast algorithm of fractional Fourier transform based on FFT. Computer programs are devised to caculate thefractional Fourier transform and the results of computation are gives out. Based on this achievement, some numerical simulations are performed to the method of double phase encoding in fractional Fourier domain.The security performance of this method is analyzed with the result of simulations.Fourthly, this thesis proposes a new optical image encryption method based on the implementation theory of anamorphic fractional Fourier transform. This method has a unique property to use nonnegative fractional orders in decryption for purpose of its optical implementing easily. The new method can provide more degrees of freedom in encryption .The amount of encryption keys is more than that of using normal fractional Fourier transform with the same stages. The numerical simulations show that the fractional orders used as encryption keys are quite robust in blind decryption. Therefore, it can effectively improve the security of the encrypted image.Finally, in order to verify the new method proposed in the thesis, an experimental photoelectric image encryption system is set up. The thesis also discusses its light route and the parameters of main optical units in the system. Three successful basic experiments show that the laboratorial system can accomplish the optical information processing experiments and the optical image encryption experiments.