We address a non-invasive imaging method to observe dynamic objects hidden behind a turbid medium. An initial image of the objects is first recovered by speckle correlation technique (SCT) with a single shot speckle pattern. The scattered point spread function (PSF) is then extracted by taking a deconvolution process between the initial image and its corresponding speckle pattern. Consequently, the images of the dynamic objects, within the optical memory effect (OME) range, can then be reconstructed directly with the same deconvolution process between the sequential speckle patterns and the estimated PSF. In addition, a further calibration operation is employed to enhance the robustness of the PSF, ensuring sharp images can still be observed when objects are close to or even cross the edge of OME. Experimental demonstration is presented to verify the feasibility of our proposed method.
The depth-of-field (DOF) characteristic of the imaging system with scattering medium is analyzed based on the analytical model of ambiguity function as a polar display of the optical transfer function (OTF) in this paper. It is indicated that the scattering medium can help re-collect more high spatial frequencies, which are normally lost with defocusing in traditional imaging systems. Therefore, the scattering medium can be considered not as an obstacle for imaging but as a useful tool to extend the DOF of the imaging system. To test the imaging properties and limitations, we performed optical experiments in a single-lens imaging system.
Random-phase-based optical image encryption techniques have drawn a lot of attention in recent years. However, in this contribution those schemes have been demonstrated to be vulnerable to chosen-plaintext attack (CPA) by employing the deep learning strategy. Specifically, by optimizing the parameters, the chosen deep neural network (DNN) can be trained to learn the sensing of an optical cryptosystem and thus get the ability to reconstruct any plaintext image from its corresponding ciphertext. A set of numerical simulation results have been further provided to shown its ability on cracking not only the classical double random phase encryption (DRPE), but also the tripe random-phase encryption (TRPE).
The speckle correlation technique is applied to ciphertext-only attack (COA) on optical cryptosystem based on double random phase encoding. According to the inherent merits of speckle correlation, we have revealed a fact that the ciphertext’s autocorrelation is essentially identical to the plaintext’s own autocorrelation. Then, a plaintext image can be directly reconstructed from the autocorrelation of its corresponding ciphertext by employing a iterate phase-retrieval algorithm. This could then lead to a potential security flaw because an unauthorized user could directly retrieve the plaintext from an intercepted ciphertext by performing proposed COA approach. Meanwhile, a series of numerical simulations will also be provided to verify the validity and feasibility of our proposed COA method.
We propose a novel method to achieve the purpose of hierarchical authentication based on two beams interference. In this method, different target images indicating different authentication levels are analytically encoded into corresponding phase-only masks (phase keys) and amplitude-only masks (amplitude keys) with the help of a random phase mask, which is created in advance and acts as the fixed lock of this authentication system. For the authentication process, a legal user can obtain a specified target image at the output plane if his/her phase key, and amplitude key, which should be settled close against the fixed internal phase lock, are respectively illuminated by two coherent beams. By comparing the target image with all the standard certification images in the database, the system can thus verify the user’s identity. In simple terms, this system can not only confirm the legality of a user but also distinguish his/her identity level. Moreover, in despite of the internal phase lock of this system being fixed, the crosstalk between different pairs of keys hold by different users is low. Theoretical analysis and numerical simulation are both provided to demonstrate the validity of this method.
We present an optical image encryption method based on a modified radial shearing interferometer. In our encryption
process, a plaintext image is first encoded into a phase-only mask (POM), and then modulated by a random phase mask
(RPM), the result is regarded as the input of the radial shearing interferometer and divided into two coherent lights, one
of which will be further modulated by a random amplitude mask (RAM). After all, these two coherent lights will
interfere with each other leading to an interferogram, i.e., ciphertext. And the ciphertext can be used to retrieve the
plaintext image with the help of a recursive algorithm and all correct keys. The aforementioned encryption procedure can
be achieved digitally or optically while the decryption process can be analytically accomplished. Numerical simulation is
provided to demonstrate the validity of this method.