Ghost imaging is a novel active imaging technique in which the information of the object is obtained based on high-order correlation of light fields. It has the characteristics of high sensitivity and anti-interference, and has broad application prospects in biomedicine, remote sensing imaging, and other fields. Ghost imaging requires multiple samplings to reconstruct the object image, and the imaging process takes a certain time, during which the relative motion between the object and the imaging system will lead to the degradation of image quality. How to improve the performance of imaging for moving objects is one of the key problems to be solved in the application of correlation imaging. In this paper, the basic concepts of ghost imaging are briefly reviewed; the principle of method, development, and current status of ghost imaging for moving objects are introduced. The applicable scenarios of the proposed technique are compared and the development trend is forecasted

Single-photon imaging is a technology that detects the spatial and temporal information carried by each photon to reconstruct an object image. Single-photon detectors based on superconducting nanowires have the advantages of high efficiency, low time jitter, and wide response spectrum, which is suitable for single-photon imaging applications. The superconducting nanowire delay-line single-photon imager is a novel single-photon imager. It utilizes the high kinetic inductance of the superconducting nanowires to build an ultraslow microwave transmission line. The arrival time and spatial position of photons can be simultaneously measured by reading the arrival times of the output pulses. This study introduces the design principle, geometry structure, and readout method of this imager. Besides, we introduce a single-photon imaging experiment in presence of strong background noise to demonstrate the performance enhancement using the joint optimization of high-performance imaging devices and reconstruction algorithms.

Single-pixel imaging lidar via coherent detection is a computational imaging method that obtains the target's information through a detector without the ability of spatial resolution, by combining active modulation of light field with optical coherent detection. This method has significant advantages in high-dimensional information acquisition and anti-background light disturbance. The basic principles and characteristics of two new single-pixel imaging lidar via coherent detection such as synthetic aperture imaging lidar and ghost imaging lidar, are briefly reviewed and their main research progress are introduced in recent years. The future development trend is also prospected.

To describe the results of a weak measurement of post- and preselected quantum systems, Aharonov, Albert, and Vaidman proposed the concept of weak-value in 1988. Weak-values can lie far outside the eigenvalue spectrum of the observable and even be complex, which provides rich physical insight in the investigation of quantum foundations and development of quantum technologies. This paper mainly reviews the progress of weak-value applied to quantum metrology and tomography. The former, known as weak-value amplification (WVA), can amplify ultrasmall physical effects, thus attracting extensive interest in precision metrology. Because the amplified signals are received from the successful post-selection with low probabilities, whether the WVA outperforms the conventional measurement schemes in terms of precision remains unclear. Here, we review the comparison in precision between the WVA and the conventional measurement and clarify the potential advantages of WVA under certain circumstances. Subsequently, we review the recent progress in the modified WVA. The application of weak-value in quantum tomography is known as direct quantum tomography, in which “direct” refers to the ability to directly measure the probability amplitude of the wave function based on the measurable complex weak-value. We review the generalization of the direct tomography method to characterize various quantum states, processes, and measurements. The accuracy, precision, and feasibility of the direct tomography protocol are analyzed. We also review the advances in promoting the operational efficiency of direct tomography. Finally, we draw conclusions regarding these two techniques based on weak-value and propose possible future research directions.

Superconducting nanowire single-photon detector (SNSPD) is a new type of single-photon detector with high detection efficiency, low dark count rate, low timing jitter, high count rate, and wide spectral response compared to traditional semiconductor single-photon detectors. This allows it to be applied in many applications, such as quantum communication, quantum light source characterization, laser ranging, quantum radar, etc. This paper will give a brief introduction to SNSPD and focus on the progress of SNSPD applications in imaging, mainly including the introduction of different imaging principles and the latest research progress of SNSPD imaging technology based on these principles, and the future development trend of this technology is prospected as well.

Superconducting nanowires single photon detection (SNSPD) is considered as a technology with excellent comprehensive performances. In particular, its excellent temporal resolution makes itself possess a wide application in the fields including quantum precision measurement and time-varying astronomical observation. In this paper, from three aspects of heat cycle, electrical cycle and time jitter, we reviewed the influence factors of temporal resolution and underlying physical mechanism, intrinsic limits, and possible optimization directions in SNSPD. In addition, we introduced the recent temporal resolution works related to X-ray SNSPDs in our group. The study in SNSPD is helpful to disclose the internal physical mechanism of the SNSPD technology and shows some value in the practical engineering application related to time measurement.

Conventional ghost imaging is achieved by the position--position or momentum--momentum correlation between two beams. These correlations cannot be preserved when the beams propagate along single-mode optical fibers. Thus, conventional ghost imaging cannot be achieved distantly over single-mode fibers. Frequency correlations between signal photons and idler photons generated from the spontaneous nonlinear parametric process or between two light beams from the same thermal light source are noted. The frequency correlation can be stably preserved over optical fibers. Thus, we propose and demonstrate long-distance temporal ghost imaging schemes over optical fibers based on frequency correlations in correlated photon pairs and thermal light beams. This work extends the method for achieving ghost imaging, providing new ideas for applying ghost imaging over a large geographical scale. In this study, we review the principles and methods for quantum and thermal temporal ghost imaging over optical fibers. We introduce an application of temporal ghost imaging—quantum secure ghost imaging. Furthermore, a perspective on the development of temporal ghost imaging is provided.

Imaging with X-ray and particles provides a powerful tool to explore the internal structure of matter, which plays an important role in the development of physics, materials science, life science and other fields. Different from traditional imaging methods, ghost imaging exploits the characteristics of high-order correlation of optical fields to obtain sample information, which has its unique advantages. Lots of achievements have been made in the field of visible light ghost imaging. In recent years, with the development of ghost imaging technology, X-ray and particle ghost imaging has become a frontier research field. This paper summarizes X-ray correlation imaging methods based on thermal source, pseudothermal source and entangled light source, and the research progress of correlation imaging technology in the regime of atomic, neutron, and electron imaging. The future development of X-ray and particle ghost imaging technology and some problems that need to be solved in application are discussed.

After nearly 40 years of development, the performance of InP/InGaAs single photon detectors have been improved significantly. The photon detection efficiency has reached 60%, the dark count rate is already within 20 kHz (-20 ℃), and the time jitter, afterpulse and photon counting rate are also further improved. At present, the time jitter is within 100ps, and the afterpulse probability is within 1%--5%, and the photon counting rate reaches GHz. Further performance improvement needs to consider the material system with smaller ionization coefficient ratio and excess noise, the device with multiple amplification gain and gain control, which can reduce the afterpulse while maintaining a certain device gain. The wavelength needs further expanded to provide more wavelength options. The chip needs internally integrated with self-quenching to simplify the circuit and realize free running single photon detection. And the chip could easy to integrate into single photon focal plane array at Geiger mode. In this paper, the latest development of InP / InGaAs single photon detectors based on conventional SAGCM (separated absorption, grading, charge, multiplication) and the new devices based on this technology are introduced.

Different from traditional pixel array cameras, single-pixel imaging, as a new type of computational imaging technology, uses bucket detector without spatial resolution to detect light intensity reflected or transmitted by the target object, this intensity is calculated correlatively to the structured light intensity with specific spatial distribution modulated by mask patterns, and finally a clear object image is reconstructed. Single-pixel imaging has attracted widespread attention in scientific research circles because of its low cost and the ability to image in special wavebands. This article mainly discusses the signal-to-noise ratio of single-pixel imaging in different sampling methods, and describes imaging in special wavebands and experimental research of atomic and neutron imaging. Finally, in view of the disadvantages of single-pixel imaging in imaging time, ultra-fast imaging is discussed and expected to overcome the problem of long imaging time.

Correlation holography uses incoherent light to reconstruct holograms. This technique reconstructs objects as distributions of two-point coherence function rather than using optical fields, as in conventional holography. The basic principle of correlation holography is derived from the van Cittert--Zernike theorem and relies on the similarity between the optical field and the coherence functions. Experimental implementation of the correlation holography techniques requires a field or intensity interferometer, and fringe analysis and cross-covariance measurement in these interferometers require a conventional camera with array detectors. With the availability of digitally controlled diffractive elements, it is possible to replace the incoherent light source, such as a rotating ground glass, with a digital source loaded with the random patterns in sequence. Such strategies ease the burden on the detector and allow for correlation holography with a single-pixel detector (SPD) to be used. This review paper discusses a close connection between digital holography and correlation holography. The principles of correlation holography with the SPD are reviewed in detail, and the advantages of using digital sources to mimic incoherent illumination in the correlation holography are examined in the context of three-dimensional and complex field imaging.

Super-resolution fluorescence microscopy has always been a hot research field. The emergence of various super-resolution fluorescence imaging techniques has broken the optical diffraction limit and improved the spatial resolution to nanoscale. However, for higher requirements on temporal and spatial resolution, the current super-resolution fluorescence microscopes still face two problems of the triangular constraint relation of spatial resolution, temporal resolution and field of view, and low detection sensitivity. However, with the recent development of the new imaging mechanism based on quantum correlation, the super-resolution fluorescence microscopes based on fluorescence quantum property and quantum correlation imaging have been developed. The introduction of new imaging modes and new physical quantities not only increases the amount of information but also improves the efficiency of image information acquisition. A new research route for the development of super-resolution fluorescence microscopy is provide. This review introduces the technological principle, advantages and disadvantages of the current super-resolution fluorescence microscopes as well as the main technical problems faced by them. Some new super-resolution fluorescence microscopes based on quantum correlation are introduced and the future development direction of super-resolution fluorescence microscopy is discussed. It is expected that this review can provide some references for the researches in this field.

Single-pixel imaging uses multiple pattern modulation and calculation of single-pixel measurement values to obtain the multi-dimensional light field information of the target object. Its characteristics such as dimension reduction sub-sampling, high-sensitivity detection, and spectral adaptability brought good news for non-visible band imaging, extremely weak light detection, lidar, and other fields. For a dynamic scene, multiple single-pixel measurements in a single motion frame contradict the motion of the object, causing image blur and noise problems. Aiming at the above problems, the mathematical model of single-pixel imaging and its imaging mechanism are introduced, and the development history and application status of dynamic single-pixel imaging are reviewed, especially the achievements that researchers have made in increasing the imaging frame rate and improving imaging schemes or imaging mechanisms. The current problems of dynamic single-pixel imaging are discussed, and the future development trend is considered and prospected, so as to provide a useful reference for further scientific research in this field.

With the development of optical information processing technology, image edge detection has been widely used in optical high-contrast imaging, automatic driving, face recognition, astronomical observation and other fields. Optical edge detection mainly employs 4-f spatial filtering imaging system with a filtering element in a Fourier plane to modify the spectral information of the image,which results in a strong edge enhancement of object structures. In this paper, several different methods of optical image edge detection and their theoretical analyses are demonstrated. Besides, relevant research progresses at home and abroad are reviewed.

For incoherent imaging systems, we can regard the spatial resolution of two incoherent point sources as the standard of resolution. In addition to direct imaging, we can perform measurements on the optical field on the image plane and statistically infer the source information from measurement results. The error limit of statistical inference is determined by the randomness of measurement results. Moreover, the randomness of different measurement schemes is different. By considering the quantum state of the light field in the image plane and using the quantum detection and estimation theory, the quantum limit of the resolution of the two incoherent point light sources and optimal measurement scheme can be obtained. According to recent studies, the resolution of two incoherent point sources in the sub-Rayleigh region can be significantly improved using the method of transverse spatial mode decomposition and multiplexing, which is beyond the classical resolution limit of direct imaging method. In this review, we will introduce the research and development of incoherent super-resolution imaging based on quantum detection and estimation theory.

Compressed sensing imaging can break through the limitation of Nyquist sampling theorem and realize sub sampling imaging, and has the advantages of dimension-reducing detection and high-throughput acquisition. In this paper, we reviewed the research progresses of compressed sensing theory in single-photon imaging and imaging spectra and analyzed compressed sensing single-photon imaging spectroscopy in detail. The influence and removal methods of pile-up effects in compressed sensing time-resolved imaging was discussed. The application of compressed sensing in the field of single-photon time-resolved imaging spectroscopy was summarized.

The channel airflow caused by wind is an important influencing factor for correlation imaging. Therefore, this paper summarizes the correlation imaging research under the disturbance of channel airflow. First, the phase model affected by the near-field airflow is given, and the effectiveness of the model is verified from the perspectives of optical transmission and correlation imaging. Then, the model is extended to high wind speed regions, the influence law of wind speed and boundary layer thickness under supersonic airflow on correlation imaging is obtained, and the change of imaging quality is quantitatively analyzed. Finally, aiming at the problem of detection jitter in the actual imaging process, the suppression method based on the correlation imaging time characteristic and the small sample imaging algorithm are introduced. The results can not only evaluate the influence of channel airflow on correlation imaging, but also provide important reference value for the application of correlation imaging in airborne remote sensing and other fields.

The image restoration of single-pixel imaging relies on the connection between the received signal and the modulated light source, including computational ghost imaging and compressed sensing imaging. Computational ghost imaging uses a high-order intensity correlation function between the light source and the single-pixel signal to restore the image, while compressed sensing imaging uses an optimized compressed sensing algorithm to restore the image. Typically, single-pixel imaging experiments use a wide variety of light sources, including physical light sources, such as thermal light, X-rays, electrons, neutrons, and single photon sources, and artificial light sources modulated by spatial light modulators and digital micromirror systems. These light sources follow different statistical probability distributions, and the light field intensity of the illuminated object can be considered as a statistically independent continuous or discrete random variable, also known as a reference signal. The single-pixel signal is a linear combination of all reference signals. The joint statistical probability distribution between the reference signal and the single pixel signal is determined according to the statistical properties of the light source. In addition, we investigate the effects of the probability distribution functions on the image quality, providing theoretical bases of physics and statistics for single-pixel imaging.

Obtaining clear object images in the scattering media has an important application value in military counterterrorism, medical imaging, and ocean exploration. The essence of classic optical imaging is to directly record the first-order correlation imaging of the reflected light intensity of the object. However, as the mass concentration of the scattering media and the light transmission distance increase, the image quality declines rapidly and even imaging cannot be performed. Correlation imaging technology uses statistical properties of light field fluctuations to reconstruct images through coincidence measurement and second-order intensity correlation characteristics. The use of correlation imaging can reduce the environmental impact on imaging quality and provide a new imaging method for obtaining object images in scattering media. Therefore, the research results of intensity correlation imaging in scattering media at home and abroad in recent years are expounded from three aspects of various scattering media types, paths, and compensation reconstruction algorithms in this paper, and the application of intensity correlation imaging is summarized and prospected.

With the development of industry, the single photon laser ranging plays an indispensable role in the field of surveying and mapping with its long detection distance and high detection sensitivity. This paper introduces the key technology of single photon laser ranging, single photon detector, and focuses on the research progress of single photon laser ranging technology, and summarizes and prospects the development of single photon laser ranging in the future.

Single-pixel imaging(SPI) as a new imaging technology with low cost of detectors and wide imaging range has wide applications in remote sensing imaging, hyperspectral imaging, and lidar detection, etc. Since SPI has a unique imaging mechanism and framework, specialized image processing algorithms need to be designed. This review, based on the development of SPI, describes the research progresses of SPI in image classification, moving object imaging, blind reconstruction, image encryption and hiding, edge detection, illumination pattern optimization, low-sampling rate image quality improvement. In addition, we briefly discuss the future directions of image processing algorithms related to SPI.

For fast and stable packaging of superconducting nanowire single photon detector (SNSPD), a self-aligned packaging method is developed that directly couples the optical fiber and the photosensitive area of the device. First, the SNSPD devices based on the dielectric mirror structure are fabricated by semiconductor micro-nano processing technology. The double-sided exposure and deep silicon etching technology are used to prepare the SNSPD chips, whose size matches well with the fiber sleeves. Then the main packaging structure including optical fiber sleeve, PCB, zirconia ferrule, etc. are glued together and packaged with the SNSPD chips. Finally, the self-aligned SNSPDs are characterized at the temperature of 2.2 K. The optimal result is 93.7% of detection efficiency at 1550 nm. The stability of the self-aligned SNSPD is verified by repeated experiments. The results show that the standard deviation of the device efficiency fluctuation is within ±0.60% in the case of repeated temperature rise and fall. The standard deviation of the device efficiency fluctuation is ±1.80%, and the maximum is 3.24% in the case of repeated insertion and extraction of optical fibers. Experimental results show that the self-aligned SNSPD has good stability, and this packaging method is expected to provide a reference for the future SNSPD packaging mode and provide early exploration possibilities for its integration and commercialization.

In this study, a solar-blind ultraviolet single-photon imaging system was developed. The laser three-dimensional imaging was realized within a distance of 0--400 m with 22-mm imaging precision by combining the single-photon detector with Geiger-mode Si avalanche photodiode (Si APD) and the time-correlated single-photon counting technique. In the experiment, a 266-nm pulsed laser source was used, which is in the solar-blind band. Due to the atmospheric absorption, there is no background light noise at 266-nm wavelength on the surface of the Earth. This significantly improves the antibackground noise ability of the single-photon imaging system. Thus, this system can be operated on a sunny day to realize all-day single-photon imaging within a middle-long distance.

Three-dimensional (3D) imaging technology based on single-photon avalanche diode (SPAD) array detectors has important industrial and scientific applications. However, existing SPAD array devices are limited by low spatial resolution due to small array size and low pixel-filling factor. Therefore, a coaxial scanning 3D imaging experiment system is built using a SPAD array (32 pixel×32 pixel) and a diffractive optical element (DOE). Using the DOE to shape an outgoing laser into a laser lattice and match it with the receiving field of view can improve laser energy utilization efficiency and achieve high-resolution 3D imaging through coaxial scanning. A noise photon-filtering algorithm based on a sliding time window and an image reconstruction algorithm based on total variational regularization are used to process the echo photon data. Experimental results show that, a 64 pixel×64 pixel 3D image of a target at a distance of 10 m can be obtained with an average of 0.86 signal photons per pixel to achieve clear imaging, the average absolute error of imaging results is 0.016 m.

Low quality of images is a critical problem that inhibits the application of computational ghost imaging (CGI) technology. Therefore, a special RGB (Red, Green, Blue) arrangement is designed for the chromatic light-emitting diode (LED) array of the CGI system in this study. First, a 64×64 chromatic LED array is independently developed to provide structural lighting for the CGI system. Then, the chips on the LED array are arranged according to a designed basket-weave arrangement. Finally, considering the physical structure of the chromatic LED array, an interpolation algorithm is proposed for sampled images. Experiment results show that the root mean square error (RMSE) of the basket-weave sampling is reduced by 4.6%, compared with Cartesian sampling and it has better performance in storing high-frequency information of chromatic images. In addition, compared with the bilinear and bicubic interpolation algorithms, the average RMSE of the algorithm is reduced by 2.0% and 6.4%, respectively.

To realize long-distance, highly sensitivity three-dimensional imaging, photon counting computational ghost imaging has been researched in experiments. Structured light illumination is realized using an amplitude-type spatial light modulator based on a discrete cosine transform matrix or Walsh transform matrix as the measurement basis, and single-photon detection technology is used to achieve a 700 m distance, highly sensitivity three-dimensional imaging. Two algorithms, fast Fourier transform and iterative optimization, are researched and compared. The error in images reconstructed by the discrete cosine measurement basis is smaller than that in images reconstructed by the Walsh observation matrix under the same sampling rate, while the resolution of images reconstructed by the Walsh observation matrix is higher. Theoretically, the resolution of the computational ghost imaging system is not restricted by the diffraction limit of the receiving lens; however, resolution is still affected by the collection efficiency of the receiving lens, the counting rate of the single-photon detector, and exposure time, among others. We demonstrated that the imaging resolution of our experimental system improved on the Rayleigh diffraction limit resolution of the receiving lens by a factor of two. The photon counting computational ghost imaging scheme has the potential to visualize the imaging target in three dimensions under weak illumination, without the need of a rotating platform and scanning mirror. Our research method has reference value for research on single-pixel imaging technology based on photon counting and computational ghost imaging technology.

To eliminate the influence of profile on the extraction accuracy of optical characteristics of the tissue in spatial frequency domain (SFD) imaging, an SFD imaging correction method based on the target profile is proposed in this study. The method uses phase contour technology to obtain the three-dimensional (3D) profile of the target, and corrects the frequency and light intensity of the obtained SFD diffuse reflection image. The frequency correction adopts the optical characteristic interpolation method based on the multifrequency lookup table, and the correction of the incident and reflected light intensity is based on the law of illuminance and the Minnaert model. Experiments are performed using a single-pixel SFD imaging system based on a high-sensitivity phase-locked photon-counting detection technology, and a single-pixel imaging method based on two-dimensional(2D) discrete cosine transform is used to obtain topological images of the target profile and multiwavelength optical characteristics at low sampling rates. The experimental results show that the error of the target surface profile height at each pixel is not more than 1 mm, and the reconstructed absorption coefficient and reduced scattering coefficient after correction are reduced by 51.1 percentage points and 6.7 percentage points, respectively.

Through the study of single microwave quantum detection of single carrier signal and thermal noise signal, the response ability of single microwave quantum detector based on microwave optical upconversion to weak microwave signals is verified. Based on the quantum optical theory, the second-order coherence properties of microwave signals are studied experimentally. It is proved that the second-order quantum coherence of single carrier signal and thermal noise in microwave band has the same quantum properties as the coherent light source and thermal light source in optical band.

Theoretically, the effect of scattering and absorption in the detected light path on the computational ghost imaging can approximately equal the multiplicative noise, and it can be eliminated. The impulse response function model of the point light source in a smoke screen was established using the Monte Carlo method. The influence of the smoke screen in different states on imaging was analyzed, and the feasibility of penetrating smoke imaging was discussed. Results show that when the intrinsic noise Ni=0, the effect of the scattering medium on the resulting imaging can be deemed negligible. Moreover, the applicable scene of the computational ghost imaging technology in a smoke medium was summarized. The research has important reference significance for computational correlation imaging applications.

We always want to get some spacial information about occluded objects. However, traditional imaging techniques can not recover the spacial information of occluded objects to be tested. Ghost imaging, as a novel computational imaging scheme, recently has been used to recover the information of occluded objects. In this paper, we carry out experimental research based on previous theoretical research and analyze the experimental results, and the feasibility of using the ghost imaging technique to retrieve the information of occluded objects is verified. Furthermore, we confirm that the distance between the object to be tested and the occluded objects is an important factor affecting the recovery of the occluded object information.

During underwater detection operations, the water body is disturbed by the external environment, which changes the underwater refractive index, enhances the scattering effect of the water body on light, and causes the underwater optical target to be blurred and the image quality is reduced. In view of this, the ghost imaging method is used to overcome underwater disturbances, and the second-order coherence of the reference light field and the measurement light field are used to measure separately. At a certain moment, the light field distribution of the reference beam on the collection plane and the measurement beam on the collection plane. According to the total light intensity, the ghost image is reconstructed. During the experiment, ultrasonic waves are used to disturb the water body, the imaging results of ghost imaging methods and classic imaging methods are compared, and the peak signal-to-noise ratio of the two imaging results are compared to study the anti-disturbance ability of the ghost imaging system under water. The experimental results show that the image quality of ghost imaging method is higher than that of classic imaging method in the environment of underwater disturbance.

In this article, the compressed sensing reconstruction algorithm is incorporated into the Hadamard ghost imaging scheme to recover the information of objects to be measured at a lower sampling rate. The proposed scheme has fewer reconstruction times than the Hadamard ghost imaging scheme, and the required sampling time is also reduced. Observation time and structural similarity index are considered the objective evaluation norm for image reconstruction results of Hadamard ghost imaging scheme, which uses subspace pursuit (SP) algorithm and orthogonal matching pursuit (OMP) algorithm. After simulation and experimental verification, we conclude that the combination of the OMP algorithm and Hadamard ghost imaging scheme can result in faster imaging speed and better image quality.