Among the various methods for imaging through scattering media, the speckle autocorrelation imaging method based on optical memory effect (OME) has gained significant attention for its non-invasive single-shot imaging capability through scatter media. However, the imaging range of this method is limited by OME. This paper presents a physics-informed deep learning strategy that establishes relationships among different linearly-shift-invariant subsystems based on OME to explore the range of OME range. By leveraging the feature extraction capabilities of deep learning, the proposed approach recovers sidelobes from the speckle autocorrelation patterns of objects in several OME regions. Then, a phase retrieval algorithm is employed to achieve object reconstruction. In the future, the approach can be extended to integrate different small regions of the object plane into a big one which can be linear shift invariant.
A single-shot dual-wavelength lensless digital holography based on a dichroic mirror is presented to achieve quantitative phase imaging. The lensless digital holography is designed by a wavefront division transmission configuration with only a plane mirror and a beam splitter. By merely adding a dichroic mirror between plane mirror and beam splitter in lensless transmission digital holography, the propagation direction of two reference waves for different wavelengths can be adjusted separately by dichroic mirror and plane mirror. Therefore, a multiplexed hologram with different fringe directions for two wavelengths can be simultaneously obtained. Our technique is capable of real-time wavelength-multiplexing with minimum optical element and system modification.
Optical imaging through complex, inhomogeneous media is a long-standing challenge due to the presence of scattered light, which causes a degradation of resolution. Thanks to the discovery of the optical memory effect (OME), a variety of novel and breakthrough approaches have been proposed to find the hidden information behind the scattering media. However, those ME-based methods usually suffer from a limited field-of-view (FOV). An object of size beyond the ME region cannot be reconstructed completely and will produce artifacts. Here, we propose a non-invasive method that exploits a moving object behind the scattering media to extend the FOV
Optical cryptosystem based on phase-truncated-Fourier-transforms (PTFT) is one of the most interesting optical cryptographic schemes due to its unique mechanism of encryption/decryption. Conventional learning-based attack method need a large number of plaintext-ciphertext pairs to train a neural network and then predict the plaintexts from subsequent ciphertexts. In this work, we propose an alternative method of attack on PTFT-based optical asymmetric cryptosystem by using an untrained neural network. We optimize the parameters of a neural network with the help of the encryption model of PTFT-based cryptosystem, hoping to get the ability of retrieving any plaintext from the corresponding unknown ciphertext but without help of the decryption keys. The proposed untrained-neural-network-based attack approach eliminates the requirement of tens of thousands of training images and might open up a new avenue for optical cryptanalysis.
Scattering light imaging technique has attracted extensive research because of its huge potential in the fields of biomedical microscopy, remote-sensing mapping etc. For most methods now available to reconstruct an object hidden behind scattering media, the main focus is on reconstructing the shape of the object without considering its spectral information. While imaging a color object, it is often necessary to measure a series of Point Spread Functions (PSFs) or Wavelength-Dependent Speckle Patterns (WDSPs) under various wavelengths of illumination. It’s obvious that these methods are either invasive to the object or require multiple exposures. Here, by taking advantage of the Wavelength- Dependent Response Characteristics (WDRC) of the Liquid Crystal Spatial Light Modulator (LC-SLM), we propose an alternative way to reconstruct a hidden color object with noninvasive and single-exposure strategy. A monochromatic camera is adopted to capture the wavelength-multiplexing gray-scale speckle pattern, which can be then demultiplexed into a number of WDSPs by utilizing of a designed Multi-modal Phase Retrieval Algorithm (MM-PRA). Then, a typical speckle correlation technique (SCT) is applied to reconstruct each component of the hidden color object. The feasibility and effectiveness of the proposed method are demonstrated by numerical results in this work while the optical experiments are on the way.
Deconvolution-based techniques have been widely used for imaging through scattering medium due to the optical memory effect (OME) in speckles. Once the point spread function (PSF) of a scattering system is measured, a smallscale object within the OME region can be easily recovered. However, an extended object larger than the OME region can only be partially reconstructed due to the limited field of view (FOV). Here, we find a way to get an integrated PSF by exploiting a point source with different locations in object plane. Thereafter, an extended object, within the FOV but exceeding the OME region, could be recovered by the integrated PSF without knowing any other system parameters even the locations of the point source.
An approach for constructing optical hash function has been proposed based on the interaction between multiple scattering media and coherent radiation. Unlike the traditional Hash function via mathematical transformations or complex logic operations, the proposed method employs a multiple scattering media and Sobel filters for data scrambling and features extraction. An arbitrary length input data can be compressed into a fixed length (256-bit) Hash value after a cascade iterative processing. Its safety relies on the unpredicted and non-duplicated disorder multiple scattering media, in other word, there is tremendous difficulty of knowing the multiple scatting media with a specific internal state or efficiently simulating the light interaction effect between the multiple scattering media. Simulation results are presented to demonstrate the avalanche effect and collision resistance performance of the proposed designing strategy of the optical Hash function.
Digital holographic microscopy is a well-known powerful technique for quantitative phase measurement. However, the object phase is always embedded in aberrations. Here, a simple numerical compensation method based on rotation and transpose is reported. At first, we can obtain transpose phase by doing transpose transformation for original unwrapped phase. After subtracting transpose phase from original unwrapped phase, the subtraction phase is obtained and parts of aberrations also can be compensated. Subsequently, the rotation phase is obtained by doing rotation transformation with 180° for subtraction phase. Then, the residual phase aberrations are eliminated by subtracting rotation phase from subtraction phase. Not only off-axis tilt and parabolic phase aberration but also high order aberrations are removed without fitting operation or prior parameter of the specimen. The great performance makes our scheme available for single-shot quantitative phase imaging. The simulation results demonstrate the feasibility of our proposal.
This letter reports a novel method for light field three-dimensional measurement by using unfocused plenoptic cameras. A light field metric model, based on which nonmetric depths in the image space can be mapped to metric dimensions in the object space, was established. Furthermore, with the aid of a three-dimensional measurement system, light field metric calibration was carried out by determining light rays with spatio-angular parameters and set up the depth relationship between the object and image spaces in accordance with the light field image properties.
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 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.
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 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.
A generalized amplitude-phase retrieval algorithm (GAPRA) attack on ‘double images encryption method with resistance against the special attack based on an asymmetric algorithm’ (DIEM) is presented in this paper. The analysis shows that the DIEM is a cascaded cryptosystem, which consist of a joint transform correlator architecture and a phasetruncated Fourier transform scheme. A GAPRA attack is proposed and the potential risk of the cascaded cryptosystems is discussed. By using our method, an attacker could crack high-quality results of the plaintexts. A set of simulation results demonstrate the validity and feasibility of the proposed 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.
We present a fingerprint authentication scheme based on the optical joint transform correlator (JTC) and further describe its application to the remote access control of a Network-based Remote Laboratory (NRL). It is built to share a 3D microscopy system of our realistic laboratory in Shenzhen University with the remote co-researchers in Stuttgart University. In this article, we would like to focus on the involved security issues, mainly on the verification of various remote visitors to our NRL. By making use of the JTC-based optical pattern recognition technique as well as the Personal Identification Number (PIN), we are able to achieve the aim of authentication and access control for any remote visitors. Note that only the authorized remote visitors could be guided to the Virtual Network Computer (VNC), a cross-platform software, which allows the remote visitor to access the desktop applications and visually manipulate the instruments of our NRL through the internet. Specifically to say, when a remote visitor attempts to access to our NRL, a PIN is mandatory required in advance, which is followed by fingerprint capturing and verification. Only if both the PIN and the fingerprint are correct, can one be regarded as an authorized visitor, and then he/she would get the authority to visit our NRL by the VNC. It is also worth noting that the aforementioned “two-step verification” strategy could be further applied to verify the identity levels of various remote visitors, and therefore realize the purpose of diversified visitor management.
KEYWORDS: 3D image processing, 3D metrology, Metrology, Imaging systems, Stereoscopy, Data storage, Cameras, Computer security, Computer networks, 3D image reconstruction
In this paper, the establishment of a remote laboratory for phase-aided 3D microscopic imaging and metrology is presented. Proposed remote laboratory consists of three major components, including the network-based infrastructure for remote control and data management, the identity verification scheme for user authentication and management, and the local experimental system for phase-aided 3D microscopic imaging and metrology. The virtual network computer (VNC) is introduced to remotely control the 3D microscopic imaging system. Data storage and management are handled through the open source project eSciDoc. Considering the security of remote laboratory, the fingerprint is used for authentication with an optical joint transform correlation (JTC) system. The phase-aided fringe projection 3D microscope (FP-3DM), which can be remotely controlled, is employed to achieve the 3D imaging and metrology of micro objects.
We present a two-factor authentication method to verify the personal identification who tries to access an optoelectronic system. This method is based on the optical interference principle and the traditional one-way Hash function (e.g. MD5). The authentication process is straightforward, the phase key and the password-controlled phase lock of one user are loading on two Spatial Light Modulators (SLMs) in advance, by which two coherent beams are modulated and then interference with each other at the output plane leading to an output image. By comparing the output image with all the standard certification images in the database, the system can thus verify the user’s identity. However, the system designing process involves an iterative Modified Phase Retrieval Algorithm (MPRA). For an uthorized user, a phase lock is first created based on a “Digital Fingerprint (DF)”, which is the result of a Hash function on a preselected user password. The corresponding phase key can then be determined by use of the phase lock and a designated standard certification image. Note that the encode/design process can only be realized by digital means while the authentication process could be achieved digitally or optically. Computer simulations were also given to validate the proposed approach.
In this paper, we propose an approach for the automatic fast registration of range images which are captured by the 3D optical measurement system. The measurement system consists of multiple 3D sensors distributed from the top to the bottom separately, which are used to measure object from different views. And a one-axis turntable is constructed to drive object revolve around the axis with eight angles. In each orientation, we can obtain multiple range images of object with the measurement system. And then all range images of object are needed to register to uniform coordinate frame. Firstly, we establish an in-situ 3-D calibration target in a measurement volume, which consists of a number of marker points. The coordinates of those marker points are obtained from the photogrammetry technique and they are thereafter employed for the determination of the locations and orientations of 3D sensors, which will be used to implement the registration among the range images taken from multi-sensors in one angle view. In addition, the registration of range images of eight angles can be achieved by the calibration of the rotation axis. In the end, the global iterative closest points method is proposed to attain the fine registration of all range images. The experimental results demonstrate the validity of the registration approach.
In this paper, we introduced a concept of cascaded phase-truncated Fourier transforms (CPTFTs), which is a nonlinear
iterative operator. Meanwhile, an optical/digital hybrid system was presented to implement the operator of CPTFTs.
Thereafter, by adopting CPTFTs as main processing unit, we have done some research on optical one-way cryptosystem:
an optical Hash function (O-Hash) and a keyed optical Hash function (K-O-Hash) were put forward respectively, which
can be applied to message integrity check and authentication. Both of the O-Hash and K-O-Hash can transform an
arbitrary-length pre-encoded message (without or with a secret key) into a fixed-length output by means of taking a
two-step one-way encryption process. Finally, a set of numerical experiments were carried out to evaluate the performance
of avalanche effect and collision resistance of the O-Hash and K-O-Hash constructed with our approach.
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