Ghost Imaging System Research Articles

Remote sensing ghost imaging based on Hadamard modulated Gaussian array beam

A ghost imaging (GI) scheme by using Hadamard modulated Gaussian array beam (HMGAB) is proposed. Compared to traditional light sources modulated using ground glass, DMD, or SLM, HMGAB has higher emitting energy, making it advantageous for remote sensing GI. Moreover, the incoherent superposition of array sub-beams makes our scheme avoid the periodic aliasing which usually occurs in GI systems using optical phased array beam. The relationship between imaging maximum distance and target size is established and verified. In addition, GANs are used to address the issue of point-like reconstructed images caused by the spacing between array sub-beams.

Coherent ghost imaging via phase compensation

The 4-f optical illumination structure is widely used in coherent ghost imaging (CGI) system but its imaging field of view (FOV) is usually restricted by the transmission aperture of the lens. Therefore, this optical illumination structure cannot be applied to remote imaging. Based on conventional imaging illumination structure, a large-FOV CGI via phase compensation (CGI-PC) is proposed and its imaging property is investigated. The experimental results demonstrate that both the FOV and the quality of CGI can be dramatically improved when a lens is introduced into the receiving system to compensate the system’s spatial phase difference. Factors influencing the quality of CGI-PC are also discussed.

Detection Model and Correction Method for Quadrant Detector-Based Computational Ghost Imaging System

Detection Model and Correction Method for Quadrant Detector-Based Computational Ghost Imaging System

Digit classification of ghost imaging based on similarity measures

In this paper, a pattern recognition scheme based on ghost imaging (GI) system is proposed, which is inspired by the fact that the one-dimensional vectors obtained by the GI system can be considered as an alternative representation of the original object, and these vectors will be able to greatly preserve the original object features when appropriate illumination patterns are adopted. The characteristics of GI is combined with discrete Fourier transform (DFT) to generate illumination patterns based on the DFT matrix, which are used to illuminate objects. The obtained bucket detector measurements are utilized to perform similarity metrics and output classification results. The scheme can classify objects with no need of reconstruction and neural network, thus reducing the running time. The experimental and numerical simulation results demonstrate that the proposed scheme requires less computation but has high recognition accuracy, and is also robust to environment noise. In addition, the recognition accuracy of the proposed scheme can also be well maintained when the sampling rate is 50%.

Ghost imaging under direct sunlight conditions using FADOF

Sunlight background noise significantly hinders the operation of ghost imaging systems, posing a considerable challenge for target imaging under daytime sunlight conditions. This paper introduces a method to eliminate sunlight background noise using a Faraday anomalous dispersion optical filter (FADOF). A ghost imaging system based on FADOF is constructed, and experiments are conducted under strong background noise conditions. The system operates outdoors in direct sunlight, utilizing sunlight introduction system to introduce light into the detection path, directly reaching the detection end of the system. In this real sunlight noise condition, the ghost imaging system using FADOF filtering achieved nearly continuous and stable imaging throughout three summer days, contrasting with a system using a 10 nm filter that only functions properly after sunset. The research findings indicate that FADOF effectively enhances the ghost imaging system's resistance to background light noise, enabling continuous operation under conditions of strong background noise throughout the day.

Quality Assessment Method of Ghost Imaging System Based on Communication Channel Model

Quality Assessment Method of Ghost Imaging System Based on Communication Channel Model

Reconstruction method of computational ghost imaging under atmospheric turbulence based on deep learning

Ghost imaging, as an emerging imaging method, has great advantages in harsh environment with its off-object imaging characteristics. In this paper, we use a turbulence model based compressive sensing computational ghost imaging system to simulate atmospheric turbulence, analyze the effects of various factors on the imaging results, and recover the images under extreme turbulence conditions using conditional generation adversarial network, which can finally recover the images well. The simulation results show that the image reconstruction method proposed in this paper can recover the image well under the condition of very low sampling rate (1.56%).

Anti-scattering medium computational ghost imaging with modified Hadamard patterns

Illumination patterns of computational ghost imaging (CGI) systems suffer from reduced contrast when passing through a scattering medium, which causes the effective information in the reconstruction result to be drowned out by noise. A two-dimensional (2D) Gaussian filter performs linear smoothing operation on the whole image for image denoising. It can be combined with linear reconstruction algorithms of CGI to obtain the noise-reduced results directly, without post-processing. However, it results in blurred image edges while performing denoising and, in addition, a suitable standard deviation is difficult to choose in advance, especially in an unknown scattering environment. In this work, we subtly exploit the characteristics of CGI to solve these two problems very well. A kind of modified Hadamard pattern based on the 2D Gaussian filter and the differential operation features of Hadamard-based CGI is developed. We analyze and demonstrate experimentally that using Hadamard patterns for illumination but using our developed modified Hadamard patterns for reconstruction (MHCGI) can enhance the robustness of CGI against turbid scattering medium. Our method not only helps directly obtain noise-reduced results without blurred edges but also requires only an approximate standard deviation, i.e., it can be set in advance. The experimental results on transmitted and reflected targets demonstrate the feasibility of our method. Our method helps to promote the practical application of CGI in the scattering environment.

Feeble-light ghost imaging via correlation calculation

Noise is a significant factor affecting imaging quality because it seriously reduces the detection signal-to-noise ratio (SNR), especially in feeble-light detection. In this paper, we propose a practical method to separate signal from noise background in ghost imaging (GI) systems based on correlation calculation. Experiments have shown that this method can significantly increase the SNR of the reconstructed images. Our research provides a novel method for suppressing noise influence on feeble-light GI, which has valuable reference value in biomedicine and remote sensing.

Visualizing the Hardy's Paradox using Hyper‐Entanglement‐Assisted Ghost Imaging

AbstractThe concept of quantum nonlocality, lying at the heart of quantum information science and technologies, is physically counter‐intuitive and mathematically elusive. Here, a hyper‐entanglement‐assisted ghost imaging system is designed to visualize the evidence of Hardy's paradox by capturing the purely nonlocal photonic events with a spatially resolved intensified charge‐coupled device (ICCD) camera. In the two‐photon polarization‐spatial‐mode hyper‐entangled state, spatial entanglement conveys the ghost images while polarization entanglement encodes the imaging channels in the logical structure of Hardy's nonlocality proof. Then whether the single ghost image of a skull‐shape object is observed or not can be a direct yet intuitive signature to support or defy quantum mechanics. Moreover, the degree of the violation of locality can be characterized by the contrast‐to‐noise ratio of ghost images macroscopically, and the nonlocal behavior of violating the locality microscopically at the single‐pixel level with a reasonable confidence level of 75% is also achieved. The proposed strategy not only sheds new light on the fundamental issue of quantum mechanics, but also holds promise for developing hyper‐entanglement‐based quantum imaging technology.

Long-distance ghost imaging with incoherent four-petal Gaussian sources in atmospheric turbulence

In this study, we investigate the use of incoherent four-petal Gaussian sources for ghost imaging (GI) through atmospheric turbulence. A GI imaging formula for incoherent four-petal Gaussian sources in turbulent conditions is derived. The impact of propagation distance, turbulence strength and beam orders on the imaging quality is analyzed numerically in detail. Our findings indicate that the use of a four-petal Gaussian source can significantly improve the quality of the GI system under long-distance imaging conditions, as compared to the commonly used Gaussian sources.

Polarization-sensitive-metasurface-based microwave computational ghost imaging

Conventional multi-transmitter-based microwave computational ghost imaging (MCGI) systems have suffered from radiation source errors due to the limitation of unit performance in arrays. Radiation source errors can cause inaccuracy of the reference radiation field in MCGI, which will reduce the reconstruction quality of the target image. In this paper, a detailed error analysis of radiation sources in MCGI systems is conducted. The relationships between radiation source errors, reference radiation field and imaging results are determined. Furthermore, to mitigate the influence of radiation source error and other problems in conventional MCGI systems, such as high cost, complex design and implementation, and the interference between array elements, an improved MCGI method based on a broadband polarization-sensitive-metasurface is proposed. The metasurface in this work can modulate the incident signal and distribute the reflected signal randomly in space. Therefore, by changing the polarization angle of the radiation signal, a time-space independent signal is produced, which can achieve better detection effects in the application system. A series of simulations and experiments are performed to validate the analysis results and evaluate the proposed method’s performance. The results show that the target information can be effectively obtained by the proposed method.

Edge detection based on ghost imaging through biological tissue

Edge detection is an essential procedure in biomedical image processing. Note that several edge detection schemes based on ghost imaging (GI) have been proposed, while a practical application environment is not considered. In this paper, we first investigate the edge detection of target objects inside biological tissue in a GI system. The performances of four edge detection operators are compared in GI through biological tissue when refractive index turbulence is considered. The numerical results demonstrate that the Standard operator performs better in edge extraction regardless of the strength of refractive index fluctuations. Our results may provide potential applications of GI in the field of biomedical imaging.

Patterns for all-digital quantum ghost imaging generated by the Ising model

We present new illumination patterns for imaging in all-digital quantum ghost imaging (GI) systems. The digital patterns, written as computer generated holograms on spatial light modulators (SLM), are generated by the Ising model, a well-known ferromagnetic model. In general, Ising patterns are affected by two parameters: temperature (T) and magnetic field (H). Here, we set H to 0 and offer a method for applying Ising patterns made with various T values to reconstruct high quality ghost images with very little background noise.

Optical encryption scheme based on spread spectrum ghost imaging

An optical encryption (OE) scheme based on the spread spectrum ghost imaging (SSGI), named as SSGI-OE, is proposed to obtain a high security with a smaller key. In the scheme, the randomly selected row number of a Hadamard matrix of order N is used as the secure key, and shared with the authorized user, Bob, through a private channel. Each corresponding row vector of the order-N Hadamard matrix is then used as the direct sequence code to modulate a speckle pattern for the ghost imaging system, and an image is encrypted with the help of the SSGI. The measurement results from the bucket detector, named as ciphertext, are then transmitted to Bob through a public channel. The illuminating speckle patterns are also shared with Bob by the public channel. With the correct secure key, Bob could reconstruct the image with the aid of the SSGI system, whereas the unauthorized user, Eve, could not obtain any useful information of the encrypted image. The numerical simulations and experimental results show that the proposed scheme is feasible with a higher security and a smaller key. For the 32 × 32 pixels image, the number of bits sent from Alice to Bob by using SSGI-OE (M = 1024, N = 2048) scheme is only 0.0107 times over a computational ghost imaging optical encryption scheme. When the eavesdropping ratio (ER) is less than 40%, the eavesdropper cannot acquire any information of the encrypted image. The extreme circumstance for the proposed SSGI-OE scheme is also discussed, where the eavesdropper begins to extract the information when ER is up to 15%.

High-speed ghost imaging by an unpredictable optical phased array

Ghost imaging (GI) retrieves an image from the correlation between a sequence of illumination patterns on the object and their corresponding bucket detections. Traditionally, GI requires the precise information of the illumination patterns, which raises technology barriers on building a high-speed illumination source, limiting the scope of its application. In this study, we propose a high-speed GI system, which implements a self-correlation with a purely optical operation without determining illumination patterns. The light source is an optical phased array (OPA), built of a set of waveguide-type electro-optic phase modulators. The OPA is driven to randomly change the phases in every 200 ns, generating speckle patterns at a rate of 5 MHz. Although the speckle patterns are not predictable or post-determinable, with the help of the naked-eye GI scheme, the system in real time optically generates the images of the object at a frame rate of more than 1 kHz, which can be directly observed by eyes or using a camera. This method avoids acquiring the information of the illumination, thus providing a simple and easy way to realize high-speed GI. It also inspires a different way of applying OPAs to high-speed imaging.

Lensless ghost imaging of a partially coherent vortex source in atmospheric turbulence

The image quality of ghost imaging was mainly degraded because of the beam wander and scintillation caused by atmospheric turbulence. References show that the vortex phase can effectively deduce the negative effects and improve the critical resolution and image quality of ghost imaging in free space which can be used to improve its quality through turbulence. In this study, we investigate the quality of the ghost imaging of a Gaussian Schell-model vortex source with different topological charges and coherent widths during propagation through atmospheric turbulence with different strengths using numerical simulations. The results show that the image quality is improved with increasing topological charge in turbulence, which was further proved via experimental measurements. Our study can be applied to free space optical communication and information encryption based on ghost imaging systems to reduce the influence of turbulence.

On Ghost Imaging Studies for Information Optical Imaging

Since the birth of information theory, to understand, study, and optimize optical imaging systems from the information–theoretic viewpoint has been an important research subfield of optical imaging, accompanied by a series of corresponding advances. However, since the “direct point-to-point” image information acquisition mode of traditional optical imaging systems, which directly performs one-to-one signal mapping from the object to the detection plane, lacks a “coding–decoding” operation on the image information, related studies based on information theory are more meaningful in the theoretical sense, while almost acting as icing on the cake for the optimization and design of practical systems and contributing little to substantive breakthroughs in further imaging capabilities. With breakthroughs in modern light-field modulation techniques as well as ghost imaging techniques, which establish point-to-point image signal reproduction based on high-order correlation of light fields, currently, it is able to encode the image information with controllable spatiotemporal light-field fluctuations during the ghost imaging process. Combined with modern digital photoelectric detection technologies, ghost imaging systems behave more in line with the modulation–demodulation information transmission mode compared to traditional optical imaging. This puts forward imperative demands and challenges for understanding and optimizing ghost imaging systems from the viewpoint of information theory, as well as bringing more development opportunities for the research field of information optical imaging. This article will briefly review the development of information optical imaging since the birth of information theory, overview its current research status by combining with latest related progresses in ghost imaging, and discuss the potential developing tendency of this research topic.

Scattering medium-robust computational ghost imaging with random superimposed-speckle patterns

Illumination patterns of a ghost imaging (GI) system disturb when passing through a scattering medium. Within limits, the larger the speckle size, the stronger the anti-interference ability of illumination pattern to scattering medium, but the lower the imaging resolution. Computational ghost imaging (CGI) system has the advantage of flexible design of illumination patterns. We analyze and demonstrate that using random superimposed-speckle patterns as the illumination pattern of CGI system (RSCGI) can enhance the anti-interference ability of illumination pattern to scattering medium without reducing the imaging resolution when intensity fluctuation correlation reconstruction algorithm is used. Experimental results show that the contrast-to-noise ratio (CNR) and imaging resolution are obviously improved.

Ghost diffraction: A spatial statistical approach

We report a new method to reconstruct a two-dimensional object in Ghost diffraction scheme using a spatial statistical optics approach. This is implemented by using a static diffuser rather than a pseudo thermal light source generated with a rotating diffuser as used in conventional ghost imaging systems. The experimental implementation makes use of spatial ergodicity and spatial stationarity for spatially distributed random fields by following an analogy between time average and space average. The ensemble average is replaced by space average under the condition of spatial stationarity and ergodicity. A strategy to realize the Ghost diffraction scheme through spatial intensity correlation with a phase retrieval algorithm permits reconstruction of the transparency.