Nonlocal Imaging Research Articles

Computational ghost imaging encryption using RSA algorithm and discrete wavelet transform

Ghost imaging technology has been widely used in the field of optical image encryption owing to its unique non-local imaging characteristics. However, there are some problems such as long encryption and decrypting time, poor reliability and large number of keys. To solve these problems, this paper proposed a computational ghost imaging encryption scheme based on RSA algorithm and wavelet transform. Firstly, the representation relationship between measurement matrix and random integer sequence is established to reduce the transmission of key quantity. Secondly, RSA encryption algorithm is used to improve the security of the system. Finally, using wavelet decomposition for packet transmission. In addition, the cake cutting matrix is used as the measurement matrix to reduce the sampling times and improve the quality of reconstructed images. The simulation results show that the encryption system has strong information transmission security and good robustness. It provides some reference for image encryption and information security transmission.

High-quality reconstruction of single-pixel imaging using discrete W transform

Single-pixel imaging (SPI) achieves numerous advantages over traditional imaging methods, such as multi-wavelength detection and non-local imaging. In this paper, we report a novel single-pixel imaging technique based on discrete W transform (DWT). In this method, we adopt the star sampling strategy to generate two sets of W basis patterns, these patterns are used to differentially modulate the light source, then the spectrum of the target object is acquired from the light intensities measured by a single-pixel detector. Finally, inverse DWT is utilized the to reconstruct the image. Therefore, high-quality images can be retrieved quickly from sub-Nyquist measurements compared with other transform domain SPI methods. Simulation and experimental results validate the effectiveness of the proposed technique.

Fundamental resolution limit of quantum imaging with undetected photons

Quantum imaging with undetected photons relies on the principle of induced coherence without induced emission and uses two sources of photon-pairs with a signal- and an idler photon. Each pair shares strong quantum correlations in both position and momentum, which allows to image an object illuminated with idler photons by just measuring signal photons that never interact with the object. In this work, we theoretically investigate the transverse resolution of this non-local imaging scheme through a general formalism that treats propagating photons beyond the commonly used paraxial approximation. We hereby prove that the resolution of quantum imaging with undetected photons is fundamentally diffraction limited to the longer wavelength of the signal and idler pairs. Moreover, we conclude that this result is also valid for other non-local two-photon imaging schemes.

Ghost imaging-based optical multilevel authentication scheme using visual cryptography

As a nonlocal imaging approach, ghost imaging is of potential significance for information security. This study demonstrates a multi-level authentication approach relying on ghost imaging and visual secret sharing. Initially, multiple standard images are divided into two shared images by utilizing a visual secret sharing scheme. One of them is used as an authentication image to the authorizer, while the spatial information of the other is encoded by the ghost imaging and loaded into the illumination patterns. As the authentication image is irradiated by the illumination patterns, high-quality image fusion is realized and an entirely distinct image from the authentication image is reconstructed. Afterward, the information authentication is attained by visual evaluation and correlation analysis of the reconstructed image and the standard image. Ultimately, the authentication image is flipped and turned to reconstruct various images for achieving multi-level authentication. This scheme is the first to implement multi-level authentication using visual secret sharing method under the framework of ghost imaging. Simulation and experimental results validate that the technique features strong robustness, high security, and strong recognition ability, which provides a new way for optical authentication.

Underwater ghost imaging based on generative adversarial networks with high imaging quality.

Ghost imaging is widely used in underwater active optical imaging because of its simple structure, long distance, and non-local imaging. However, the complexity of the underwater environment will greatly reduce the imaging quality of ghost imaging. To solve this problem, an underwater ghost imaging method based on the generative adversarial networks is proposed in the study. The generator of the proposed network adopts U-Net with the double skip connections and the attention module to improve the reconstruction quality. In the network training process, the total loss function is the sum of the weighted adversarial loss, perceptual loss, and pixel loss. The experiment and simulation results show that the proposed method effectively improves the target reconstruction performance of underwater ghost imaging. The proposed method promotes the further development of active optical imaging of underwater targets based on ghost imaging technology.

Camouflaged encryption mechanism based on sparse decomposition of principal component orthogonal basis and ghost imaging

Ghost imaging (GI) is a technology of nonlocal optical imaging, which is widely used in the field of information encryption. However, there are some inherent shortcomings in the encryption process, such as imperfect security and low imaging precision. To solve these problems, we propose a camouflaged encryption mechanism based on sparse decomposition of principal component orthogonal basis and ghost imaging (CSP-GI). Unlike the traditional encryption method, there are two-level keys and ciphertexts. The information of the secret image is hidden in the camouflaged image to improve the security of the system. The use of the sparse decomposition of principal component orthogonal basis expands the information content of encrypted transmission, improves the accuracy of reconstructed image, and reduces the reconstruction time. The simulation and experimental results show that the proposed method not only has good security and robustness but also reduces reconstruction time.

Non-local spiral phase contrast imaging with thermal light (Invited)

Non-local spiral phase contrast imaging with thermal light (Invited)

Study of an encryption system based on compressive temporal ghost imaging with a chaotic laser

A chaotic laser has good time controllable randomness and second-order temporal relevance. It is widely used in chaotic encryption. Temporal ghost imaging is a non-local imaging method, and its characteristics determine that it has strong application prospects in encryption. In this paper, temporal ghost imaging with a chaotic laser is used in optical encryption. The excellent cryptographic properties of the chaotic laser and the non-linear encryption of ghost imaging are combined. The simulation results show that this encryption system has high security and anti-noise capabilities.

Sparse phase imaging based on complex domain nonlocal BM3D techniques

The paper is addressed to 2D phase and amplitude estimation of complex-valued signals – that is, in particular, to estimation of modulo-2π interferometric phase images from periodic and noisy observations. These degradation mechanisms make phase image estimation a challenging problem. A sparse nonlocal data-adaptive imaging formalized in complex domain is used for phase and amplitude image reconstruction. Following the procedure of patch-based technique, the image is partitioned into small overlapping square patches. Block Matching Three Dimensional (BM3D) technique is developed for forming complex domain sparse spectral representations of complex-valued data. High Order Singular Value Decomposition (HOSVD) applied to BM3D groups enables the design of the orthonormal complex domain 3D transforms which are data adaptive and different for each BM3Ds group. An iterative version of the complex domain BM3D is designed from variational formulation of the problem. The convergence of this algorithm is shown. The effectiveness of the new sparse coding based algorithms is illustrated in simulation experiments where they demonstrate the state-of-the-art performance.

Two- and three-mode dressed entanglement multichannel in cavity four-wave mixing of Pr3+: YSO

We report a theoretical study into the two- and three-mode entanglement inside an atom-like optical cavity. A five-level system is considered and the influence of the multi-dressed parametric amplification four-wave mixing (PA-FWM) process on the quantum correlation of fluctuation spectra is researched. Three-mode entanglement is determined by the coupling of two nonlinear gains; one of enhanced gains via the dressing state plays a dominant role in controlling and optimizing the profile of three-mode entanglement via vacuum Rabi splitting, enhancement/suppression of entanglement as well as two-mode. Specifically, increasing the quantity of dressing fields may result in the single-channel entanglement turning into nonlocal multichannel (multiple anti-crossing behaviors). Moreover, these entanglement channels can be squashed via the lateral squeezing effect of the cavity. Such multichannel entanglement has potential applications in nonlocal quantum imaging and quantum key distribution.

Foveated Nonlocal Self-Similarity

When we gaze a scene, our visual acuity is maximal at the fixation point (imaged by the fovea, the central part of the retina) and decreases rapidly towards the periphery of the visual field. This phenomenon is known as foveation. We investigate the role of foveation in nonlocal image filtering, installing a different form of self-similarity: the foveated self-similarity. We consider the image denoising problem as a simple means of assessing the effectiveness of descriptive models for natural images and we show that, in nonlocal image filtering, the foveated self-similarity is far more effective than the conventional windowed self-similarity. To facilitate the use of foveation in nonlocal imaging algorithms, we develop a general framework for designing foveation operators for patches by means of spatially variant blur. Within this framework, we construct several parametrized families of operators, including anisotropic ones. Strikingly, the foveation operators enabling the best denoising performance are the radial ones, in complete agreement with the orientation preference of the human visual system.

Nonlocal imaging of a reflective object using positive and negative correlations.

The Hanbury Brown and Twiss (HBT) effect is a classical intensity correlation effect, but it is also widely used in the quantum optics regime, and has led to many important breakthroughs in both basic and applied physics, among which ghost imaging (GI) has aroused particular interest. In this article, the positive and negative intensity correlations in HBT correlation are analyzed, based on which we describe experiments on thermal light nonlocal imaging of a reflective object using the positive and negative correlations of correspondence imaging. An improvement of 16.3% in the signal-to-noise ratio of the reconstructed image has been achieved, indicating that this method may have promising potential in future GI applications where noise is a serious problem and smaller sampling numbers are necessary.

Dressed four-wave mixing second-order Talbot effect

We theoretically demonstrate second-order Talbot effect (SOTE) based on entangled photon pairs. The photon pairs are generated from the spontaneous parametric four-wave mixing (SPFWM) process in a cold atomic medium and can be taken as the imaging light in order to realize coincidence recording. A strong standing wave is used to create the electromagnetically induced grating in the entangled photon pairs channels. By changing the frequency detuning of the standing wave or the other optical fields participating in the process, we can manipulate the contrast of the second-order Talbot image. We use the second-order correlation function and the dressed-state picture to explain the SOTE occurring in the SPFWM process. Moreover, we demonstrate the scheme for SOTE based on the spatially correlated twin beams generated from the SPFWM process with injection. This scheme provides a convenient detection proposal for the SOTE at the cost of the image contrast. Compared to the previous self-imaging schemes, the present schemes have the characteristic of controllable image contrast and of nonlocal imaging, and thus, they might broaden their applications in imaging techniques and find applications in quantum lithography.

Cloaking and illusion of quantum imaging with entangled photon pairs

Quantum ghost imaging is a nonlocal imaging technique in which the image or diffraction pattern of an object illuminated by photon pairs can be observed through the correlation measurement. This study theoretically demonstrates the cloaking effect of such a quantum imaging. Quantum ghost imaging completely offsets two objects that are placed at proper positions in the interferometer. Furthermore, illusion of quantum imaging, where an object transforms into another object, has also been observed. This phenomenon can be understood by quantum interferences in the correlation measurement.

Optical eigenmode imaging with a sparse constraint

Optical eigenmode imaging (OEI) is an interesting nonlocal imaging method but has the drawback that the completeness of eigenmodes used in OEI is hard guarantee. This may lead to significant blurring of the reconstructed images. Here we show that in OEI with a sparse constraint, the correlation between the original target and the recovered image can be extremely close to 1 by retrieving lost information, and the compressibility is enhanced. In addition, high-quality images can be received for a wide range of both object and system parameters.

Positive-negative nonlocal lensless imaging based on statistical optics

Based on correlated imaging with pseudo-thermal light, Wu and Meyers independently experimentally showed that both positive and negative images can be obtained by using a novel algorithm. With the theory of statistical optics, we construct the model of thermal light, and demonstrate the novel algorithm for image reconstruction. To deal with the data attained in the correlated imaging, we reorder the intensity recorded by the bucket detector according to the value of fluctuation. For a given fluctuation range with all the records above or below a specific value, we can obtain either positive or negative images by calculate the correlation between the selected records of the bucket detector and the reference detector. Nevertheless, without correlated calculations, positive or negative images can be also produced by directly averaging the corresponding records of the reference detector with positive or negative fluctuations. Meanwhile, the visibility of imaging is greatly enhanced. This correspondence imaging method further demonstrates the importance of intensity fluctuations in the nonlocal imaging with thermal light. We also experimentally show the images that obtained by the correlation method and the positive-negative correspondence imaging method, respectively. Our results indicate that this novel algorithm has a better visibility than that of the conventional correlated imaging.

Nonlocal Imaging by Conditional Averaging of Random Reference Measurements

We report the nonlocal imaging of an object by conditional averaging of the random exposure frames of a reference detector, which only sees the freely propagating field from a thermal light source. A bucket detector, synchronized with the reference detector, records the intensity fluctuations of an identical beam passing through the object mask. These fluctuations are sorted according to their values relative to the mean, then the reference data in the corresponding time-bins for a given fluctuation range are averaged, to produce either positive or negative images. Since no correlation calculations are involved, this correspondence imaging technique challenges our former interpretations of “ghost" imaging. Compared with conventional correlation imaging or compressed sensing schemes, both the number of exposures and computation time are greatly reduced, while the visibility is much improved. A simple statistical model is presented to explain the phenomenon.

The physics of ghost imaging: nonlocal interference or local intensity fluctuation correlation?

In this special Volume on Quantum Imaging, Shapiro and Boyd present a review on The Physics of Ghost Imaging. Here I argue that their Review is incomplete, as it overlooks a form of ghost imaging that requires quantum mechanical nonlocal effects for their understanding. From the very beginning, Klyshko brought attention to the nonlocal nature of biphoton interference and biphoton imaging by introducing his “advanced wave” theory [1]. His “advanced wave” propagates backward in time from a photodetector to the source and then propagates forward in time from the source to another distant photodetector. The “advanced wave” connects the object-arm and the image-arm, as well as two independent photodetection events, in his biphoton interference and imaging model. Strekalov et al. and Pittman et al. realized nonlocal biphoton interference [2] and biphoton imaging [3] experimentally. The physics community immediately named these two experiments “ghost interference” and “ghost imaging”. Simultaneously with the experimental realization, we found that Klyshko’s advanced wave theory can be replaced by a standard quantum theory of second-order coherence in which a nonlocal biphoton wavepacket is introduced to connect the two arms and two photodetection events [4]. Soon after that, we realized that nonlocal interference and imaging are not restricted to entangled biphoton systems: it also happens in thermal radiation. Ghost imaging can be observed from thermal light in the Fresnel near-field zone in a lensless configuration [5–7]. Although nonlocality is a feature of quantum mechanics [8], this concept is not part of classical physics. In the classical theory of light, ghost imaging, especially thermal light ghost imaging, is a result of locally measured intensity fluctuation correlations. So this brings us to ask, is ghost imaging a nonlocal interference phenomenon (and hence quantum) or is it a result of local intensity fluctuation

Cloaking of a phase object in ghost imaging

Ghost imaging is a nonlocal imaging technique in which the image or diffraction pattern of an object can be observed through the intensity correlation measurement other than the intensity itself. Here, we report the experimental observation of invisibility cloaking in ghost imaging with thermal light. We show that when two identical phase-modulated objects are placed at equal distances from the thermal light source, they are offset completely in ghost imaging. The experimental results can be understood through the phase conjugation established by the intensity correlation of thermal light.

High-quality quantum-imaging algorithm and experiment based on compressive sensing

Quantum imaging (QI) has some unique advantages, such as nonlocal imaging and enhanced space resolution. However, the quality of the reconstructed images and the time of data acquisition leave much to be desired. Based on the framework of compressive sensing, we propose an optimization criterion for high-quality QI whereby total variation restriction is specifically utilized for noise suppression. The corresponding reported algorithm uses a combination of a greedy strategy and the interactive reweight least-squares method. The simulation and the actual imaging experiment both show a significant improvement of the proposed algorithm the over previous imaging method.