Multi-dimensional Optical Encryption Based On Compressive Holography

With the rapid development of the information area,lots of data are transmitted and exchanged in the Internet,such as text,audio,images,and videos.So the information security attracts more and more attention during the process of transmission.As early as the 1980 s,researchers combined optical information technology to conduct research in the field of information security due to good parallelism and multi-degrees of freedom,such as amplitude,phase,polarization,wavelength and so on.Optical information security is the use of modern optical theory to transform information.With the rapid increase in the amount of information,the traditional single two-dimensional image encryption cannot meet the increasing needs of the current society.Many researchers have started the research on optical encryption of multi-dimensional information.Traditional photography cannot record the phase information of the object,but can only record its intensity information,and many information contained in the phase,such as depth information,which play a vital role in the decryption of the object.The application of holography enables the preservation of the phase information of the measured light field.However,the quality of decryption reconstruction is more severely affected by twin image interference in the process of encryption and decryption based on digital holography.And with the development of the Internet era,the complexity of the light field and the total amount of information contained in it have also increased significantly.It has become the main factor limiting the development of optical encryption technology.The compressive sensing theory was proposed,which breaks the limitations of the traditional Shannon sampling theorem.The original signal can be accurately recovered by collecting a small set of linear measurement.Optical encryption based on compressive sensing can greatly reduce the amount of data acquired for storing or transmitting holograms,save a lot of resources,reducing the transmission load,which opens a new way for the multi-dimensional optical information encryption.The main research work and innovation points of this thesis are as follows:(1)In order to solve the problems of huge amount of data required for encryption,heavy load of hardware equipment,and internal crosstalk in the process of three-dimensional(3D)space field encryption and decryption,a method of 3D space field optical encryption based on phase-shifting compressive holography is presented.In the optical encryption step,the 3D field is encrypted with a random phase masks using phase-shifting interferometry to record three intensity images with different phase-shifting.In the decryption step,three-step phase-shifting technique is firstly used to extract the complex optical field at the recording plane,and finally the 3D object is reconstructed from the recovered complex optical field using compressive Fresnel holography with the correct key.Multiple sets of numerical experiments demonstrate the feasibility,security and robustness of our proposed the 3D space light field encryption method for light fields of different complexity.(2)In order to solve the problems of low encryption capacity,large amount of information and many exposures in phase-shifting recording,a method of multiple color images encryption via compressive holography and spatial multiplexing is proposed.In the optical encryption step,multiple color images encrypted by different random phase masks.Combine space division multiplexing with modifying the Mach-Zehnder interferometer,which implemented for encrypting multiple color images simultaneously into one hologram by single shot.This method reduces the record and transmission load,expands the encryption capacity,multiple random phase masks and propagation distance play the key and enhance the security of encryption system,and improves the quality of decryption.Finally,numerical experiments verify the effectiveness,security and robustness of our proposed the multi-color image encryption method in this thesis.(3)In order to solve the problems of the large amount of data,complex encryption system,and serious crosstalk during space-time field encryption and decryption in the complex scene,a method of multi-dimensional space-time field via compressive holography is proposed,which covers 3D space-time field,color space-time field and 4D space-time field.A composite phase mask composed of a random phase mask and a lens phase factor generated by a spatial light modulator is used to encrypt the field.The encrypted hologram can be recorded by single exposure on the detector plane.The method effectively uses the redundancy of the space-time field to expand the time dimension,expands the encryption capacity,and improves the encryption speed.It also uses different lens phase factors in the encryption system to achieve frame separation,which effectively eliminating crosstalk effects between different times,and improves the quality of decryption.Numerical experiments demonstrate the feasibility,security and robustness of our proposed the multi-dimensional space-time field encrypted method.