Single-pixel imaging (SPI) uses the modulated illumination light fields and corresponding single-pixel detection values to reconstruct the image. It provides advantages in remote sensing, low light level detection and other applications. To extend the detection range, fiber laser arrays are used as light source due to their high-power output and rapid refresh rate. In this work, we designed a Fermat spiral fiber laser array with 32 sub-apertures as the illumination light source. There is no spatial periodicity in the normalized second-order intensity correlation function. Therefore, we can get better image quality of SPI compared with regular arrays, like hexagon arrays. Furthermore, we incorporated LiNbO3 modulators into the array for enhanced high-speed phase modulation. We have achieved a random illumination light field modulation frequency of at least 22 kHz. At 64x64 pixel resolution, we achieved a 100 fps frame rate and the corresponding sampling rate is 4.88%. The reconstruction algorithms are Differential Ghost Imaging (DGI) and compressed sensing (Total Variation, TV). The proposed method will greatly improve the imaging speed and illumination power of the SPI. It has great application potential in the field of remote sensing based on SPI.

In this paper, a single-pixel imaging technique based on Zernike illumination is firstly introduced to detect rotating object. By measuring the specific Zernike moments through a single-pixel detector, the rotation angle of rotating object can be obtained. This method requires only four differential Zernike patterns to illuminate a rotating object in one frame. And the Zernike moments can be calculated from the corresponding reflected intensities collected by the single-pixel detector. Then the rotation angle can be calculated from the phase change of Zernike moments due to the rotation invariant. By theoretical simulation and experimental demonstration, the Zernike moments of the targets are successfully obtained through single-pixel imaging system. The rotation angles are calculated from the measured Zernike moments and agree well with the actual rotation angles. The errors of simulated rotation angle are below 1 degrees. And the RMSEs of the experimental results are below 3 degrees for binary images and below 4 degrees for gray images. The proposed scheme provides a new method for applications on detecting rotating object.

Single-pixel imaging (SPI) is a novel computational imaging technique which combines illumination light fields and single-pixel detection values to reconstruct the image. Therefore, the generation method of the illumination light fields affects the imaging efficiency and quality. We propose a spiral line array laser source which can generate random illumination light fields without periodicity in the normalized second-order correlation function g(2). It also has a lower full width at half maxima value (FWHM). In numerical simulations and experiments, the compressed sensing based on total variation algorithm is adopted to reconstruct the image. We demonstrate that the novel array is capable of obtaining images of superior quality and resolution compared to existing array laser sources, including hexagonal and Fermat spiral arrays. Combined with the fiber lasers and electro-optical phase modulators, it is expected to achieve high-speed modulation for light fields and high emitting power. Therefore, this method has significant potential for application in remote target detection and recognition.

The single-pixel imaging (SPI) technique illuminates the object through a series of structured light fields and detects the light intensity with a single-pixel detector (SPD). However, the detection process introduces a considerable amount of unavoidable white noise, which has a detrimental effect on the image quality and limits the applicability of SPI. In this paper, we combine the untrained attention U-Net with the SPI model to reduce noise and achieve high-quality imaging at low sampling rates. The untrained U-Net has the advantage of not requiring pre-training for better generalization. The attention mechanism can highlight the main features of the image, which greatly suppresses the noise and improves the imaging quality. Numerical simulations and experimental results demonstrate that the proposed method can effectively reduce different levels of Gaussian white noise. Furthermore, it can obtain better imaging quality than existing methods at a low sampling rate of less than 10%. This study will expand the application of SPI in complex noise environments.

We propose a novel single-pixel imaging technique based on the radial Tchebichef moment. The illumination field is generated according to the radial Tchebichef polynomial. And the value of the radial Tchebichef moment is equal to the value of the single-pixel detector. We verify the imaging capability of this method by simulation and experiment. It is proved that radial Tchebichef single-pixel imaging (RT-SPI) can reconstruct the target with a sample ratio of only 3.7 %. In addition, the rotation and scale invariants are constructed by analyzing the mathematical characteristics of the radial Tchebichef moment and the invariant can be obtained by calculating the values detected by the single pixel detector. In this approach, only nine light fields can be irradiated to achieve classification, greatly reducing the number of samples and sampling time. Simulation and experimental results show that this method can classify targets efficiently and quickly.

Coherent beam combining (CBC) is a promising technique to realize high-brightness laser output. As a key point to implement CBC, an appropriate phase control feedback structure should be established. With the advantages of a compact structure and no requirement for mirrors to sample, the all-fiber phase control feedback structure has been widely studied. However, the structure faces the challenge of π phase ambiguity. We propose to introduce the target-in-the-loop (TIL) technique into the all-fiber phase-locking structure. By adding measurement laser channels outside the main laser channels, the high-intensity phase noise in amplifiers and low-intensity phase shifts induced by atmospheric turbulences could be decoupled. The π phase ambiguity could be compensated together with the low-intensity phase shifts. In this paper, the principle of the all-fiber phase-locking structure is demonstrated and corresponding numerical simulations are carried out. A TIL CBC system with six laser channels is built to verify the technique. Additionally, the all-fiber structure is easy to scale to large arrays and compatible with high-power amplifiers, which can provide a significant reference for the system design of the TIL CBC system.

This paper presents an efficient scheme for single-pixel imaging (SPI) utilizing a phase-controlled fiber laser array and an untrained deep neural network. The fiber lasers are arranged in a compact hexagonal structure and coherently combined to generate illuminating light fields. Through the utilization of high-speed electro-optic modulators in each individual fiber laser module, the randomly modulated fiber laser array enables rapid speckle projection onto the object of interest. Furthermore, the untrained deep neural network is incorporated into the image reconstructing process to enhance the quality of the reconstructed images. Through simulations and experiments, we validate the feasibility of the proposed method and successfully achieve high-quality SPI utilizing the coherent fiber laser array at a sampling ratio of 1.6%. Given its potential for high emitting power and rapid modulation, the SPI scheme based on the fiber laser array holds promise for broad applications in remote sensing and other applicable fields.

In this manuscript, an automated optimization neural network is applied in Hadamard single-pixel imaging (H-SPI) and Fourier single-pixel imaging (F-SPI) to improve the imaging quality at low sampling ratios which is called AO-Net. By projecting Hadamard or Fourier basis illumination light fields onto the object, a single-pixel detector is used to collect the reflected light intensities from object. The one-dimensional detection values are fed into the designed AO-Net, and the network can automatically optimize. Finally, high-quality images are output through multiple iterations without pre-training and datasets. Numerical simulations and experiments demonstrate that AO-Net outperforms other existing widespread methods for both binary and grayscale images at low sampling ratios. Specially, the Structure Similarity Index Measure value of the binary reconstructed image can reach more than 0.95 when the sampling ratio is less than 3%. Therefore, AO-Net holds great potential for applications in the fields of complex environment imaging and moving object imaging.

An efficient and noise-resistant single-pixel imaging (SPI) technique based on Pseudo-Zernike moments (PZ-SPI) is proposed. In this technique, the illumination light fields are modulated to satisfy the Pseudo-Zernike polynomials. Then the modulated light fields are projected onto the object. And the single-pixel detector is used to measure the reflected light intensities to calculate the Pseudo-Zernike moments. Finally, the object image is reconstructed by iterative summation of the product of the Pseudo-Zernike polynomials and the Pseudo-Zernike moments. Through the numerical simulation and experimental demonstration, PZ-SPI can effectively reconstruct image at low sampling ratios. Besides, comparing with the Fourier-SPI and Zernike-SPI, PZ-SPI has good robustness to background noise in SPI system. These advantages expand the application of PZ-SPI in complex environments.

Limited by the number of illumination fields and the speed of a spatial light modulator, single-pixel imaging (SPI) cannot realize real-time imaging and fast classification of an object. In this paper, we proposed the circular harmonic Fourier single-pixel imaging (CHF-SPI) for the first time to realize fast imaging and classification of objects. The light field distribution satisfies the circular harmonic Fourier formula, and the light intensity values of the single-pixel detector are equivalent to the circular harmonic Fourier moments. Then the target can be reconstructed under low sampling ratio by inverse transformation. Through simulation and experimental verification, clear imaging can be performed at a sampling ratio of 0.9%. In addition, circular harmonic Fourier moments are used to construct multi-distortion invariant to classify objects with rotation and scale change. The scale change multiples of objects can be calculated and the objects can be classified by using 10 light fields. It is of great significance to classify objects quickly without imaging.

We propose a Fermat spiral laser array as illumination source in ghost imaging. Due to the aperiodic structure, the Fermat spiral laser array generates illuminating light field without spatial periodicity on the normalized second-order intensity correlation function. A single-pixel detector is used to receive the signal light from object for image reconstruction. The effects of laser array parameters on the quality of ghost imaging are analyzed comprehensively. Through experimental demonstration, the Fermat spiral laser array successfully achieves ghost imaging with high quality by combining with the compressive sensing reconstruction algorithm. This method is expected to be applied in remote sensing by combining with phased and collimated fiber laser array equipped with the high emitting power and high-speed modulation frequency.

A novel single-pixel imaging (SPI) technique based on discrete orthogonal Zernike moments is proposed. In this technique, the target object is illuminated by two sets of Zernike basis patterns which satisfy the Zernike polynomials. The Zernike moments of object image are obtained by measuring the reflected light intensities with a single-pixel detector. And the object image is reconstructed by summing the product of Zernike polynomials and detected intensities iteratively. By theoretical and experimental demonstration, an image is successfully retrieved under compressive sampling. As for both gray and binary images with resolution of 128×128 pixels, the images reconstructed by Zernike patterns have better image quality compared with those reconstructed by Fourier patterns when sampling ratio is lower than 10%. This technique yields high efficiency and high imaging quality in single-pixel imaging system.

The comprehensive suppression of the stimulated Brillouin scattering (SBS) and transverse mode instability (TMI) is a critical issue for the power scaling of fiber laser with sub-GHz spectral linewidth. In this manuscript, a narrow linewidth and polarization-maintained (PM) fiber amplifier based on tapered Yb-doped fiber (T-YDF) is established, and the effects of spectral linewidth, spectral shape and pump wavelength on the SBS and/or TMI thresholds are investigated. Up to 694 W polarization-maintained fiber laser with just ∼790 MHz linewidth is obtained by combining the advantages of tapered Yb-doped fiber, near-rectangular spectral injection and 915 nm pump manner. This work could provide a well reference solution for the realization of high-power ultra-narrow linewidth fiber lasers.

High power, narrow linewidth all-fiber amplifiers are under intensive investigation in recent years. In this paper, the research status of high power, narrow linewidth all-fiber amplifiers (including those operate at single frequency regime) is briefly summarized. Then the recent progress in our research group is introduced, including more than 500 Watt level single frequency fiber amplifier, more than 4 kW linearly-polarized narrow linewidth all-fiber amplifier and more than 6 kW narrow linewidth all-fiber amplifier. Performance exploring of the operating spectrum property is also discussed.

In this report, by comparing the RIN and beam pointing error of the signal laser at different output powers, the impact of the modal degeneration on both the spacial and temporal noise properties of high-power single-frequency fiber amplifiers will be demonstrated. The new finding reveal that obvious mode-related enhancement of the RIN could occur well below the conventional transverse mode instability (TMI) threshold of the fiber amplifier while the mode-related enhancement of the beam pointing error occurs near the TMI threshold. This work could provide a new insight for obtaining high-power, high spacial stability and low-noise single-frequency fiber lasers.

A novel single-pixel imaging (SPI) technique based on discrete orthogonal Zernike moments is proposed. In this technique, the target object is illuminated by two sets of Zernike basis patterns which satisfy the Zernike polynomials. The Zernike moments of object image are obtained by measuring the reflected light intensities through a single-pixel detector. And the object image is reconstructed by summing the product of Zernike polynomials and detected intensities iteratively. By theoretical and experimental demonstrations, an image with high quality is retrieved under compressive sampling. Moreover, the Zernike illuminating patterns are used for object classification due to the rotation invariant of Zernike moments. By measuring the amplitudes of a few specific Zernike moments through the SPI system, the rotated images with different angles and the same content are classified into the same class on experiment. This classification technique has the advantages of high efficiency and high accuracy due to the high modulation speed and high sensitivity of SPI system.

An all-fiber and polarization-maintained (PM) picosecond pulses laser system is demonstrated based on tapered active fiber, which simultaneously enables high average and peak power. By carefully adjusting the input signal power and combining the advantages of tapered active fiber for high power scaling, the amplified spontaneous emission (ASE) and the stimulate Raman scattering (SRS) are effectively balanced and suppressed. An average output power of 141 W and peak power of similar to 1.3 MW pulse laser is achieved with 3.4 ps pulse width at the repetition rate of 30 MHz. The polarization extinction ratio (PER) and beam quality (M2 factor) are measured to be similar to 16 dB and 1.19, respectively. As far as we know, this is the first demonstration of all-fiberized picosecond fiber source beyond megawatt (MW) peak power and hectowatt-level average power along with linear polarization and near-diffraction-limited beam quality.