Haze significantly impacts various fields, such as autonomous driving, smart cities, and security monitoring. Deep learning has been proven effective in removing haze from images. However, obtaining pixel-aligned hazy and clear paired images in the real world can be challenging. Therefore, synthesized hazed images are often used for training deep networks. These images are typically generated based on parameters such as depth information and atmospheric scattering coefficient. However, this approach may cause the loss of important haze details, leading to color distortion or incomplete dehazed images. To address this problem, this paper proposes a method for synthesizing hazed images using a cycle generative adversarial network (CycleGAN). The CycleGAN is trained with unpaired hazy and clear images to learn the features of the hazy images. Then, the real haze features are added to clear images using the trained CycleGAN, resulting in well-pixel-aligned synthesized hazy and clear paired images that can be used for dehaze training. The results demonstrate that the dataset synthesized using this method efficiently solves the problem associated with traditional synthesized datasets. Furthermore, the dehazed images are restored using a super-resolution algorithm, enabling the obtainment of high-resolution clear images. This method has broadened the applications of deep learning in haze removal, particularly highlighting its potential in the fields of autonomous driving and smart cities.

Aerosol lidar has been widely used in environmental monitoring. It is necessary to correct the distance before calculating the backscatter coefficient. However, the problem in this process is that the noise is greatly amplified, especially for long-distance signals. Based on previous theoretical research and signal characteristics, a segment empirical mode decomposition (EMD) filtering method that can denoise the distance correction signal is developed. Taking measured data of aerosol lidar as an example, the distance correction signal is divided into four segments, and each segment is decomposed by EMD. For low-height signals with low noise, the signal is reconstructed as comprehensively as possible. For high-height signals with high noise, most high-frequency signals are removed. This method is feasible because the aerosol concentration decreases with the increase in height. After segment EMD filtering, four segments of signals are recombined. Compared with the classical EMD, the segmented EMD filtering method not only retains the details of the low-height signal but also removes the high-height noise as much as possible. The segmented EMD filtering method is proven to be effective for aerosol lidar that conducts profile monitoring on the ground.

Low optical efficiency is a drawback of a dual-view integral imaging display based on a pinhole array. Therefore, we propose a high optical-efficiency dual-view integral imaging display. It is composed of a display panel and a non-uniform pinhole array. The left-view and right-view sub-elemental images are alternatively aligned in horizontal direction. The horizontal aperture widths of the pinholes are identical. The horizontal light rays from the left-view and right-view sub-elemental images are modulated into different directions. The vertical aperture widths of the pinholes are enlarged from upper and lower edges to center. Therefore, the vertical light rays from the sub-elemental images are not parallel. The vertical viewing angle is related to the vertical aperture width of the first row pinhole, whereas the optical efficiency is related to the vertical aperture widths of all pinholes. The optical efficiency is improved by optimizing the vertical aperture widths of the pinholes. A prototype is developed, and the experimental results prove the hypothesis.

An approach for wavelength characterization whereby dynamic Fresnel zone plate (FZP) patterns are written to a digital micromirror device (DMD) and used to focus incoming light onto a camera is proposed. The incoming wavelength is then assessed by scanning the focal length. Rectangular basis Zernike modes are implemented to match the rectangular geometry of the DMD, we believe for the first time. A procedure is developed to correct for inherent aberrations of the optical system by adjusting the Zernike mode amplitudes, thus improving focal spot quality. The aberration corrected FZPs are used to assess the focusing conditions needed for four lasers of different visible wavelengths ranging from blue (405 nm) to near infrared (760 nm). The system is able to produce focused beams with a width of twice the diffraction limit and achieve a wavelength resolution of 3 nm. The operational wavelength of the system is ultimately limited by the spectral bandwidth of the detector.

We propose an ex-situ reposition error compensation method to solve the reposition error in the ex-situ state of 2D digital image correlation (2D-DIC) in the long-term deformation of the measurement specimen or under special load deformation. Using the dual-reflector auxiliary measurement system with an included angle of 90 deg, the two sides of the repositioned specimen are mapped into left and right mirrors. The in- and out-of-plane rigid body displacements are compensated via the error compensation method, and the real in-plane displacement of the tested specimen is obtained. The accuracy and practicability of this method are verified by conducting an in-plane rigid body displacement experiment, unloaded specimen reposition experiment, thermal deformation experiment, and finite element analysis. We provide a simple, effective, and high-precision deformation measurement method for 2D-DIC to realize ex-situ measurement.

An all-optical digital-to-analog conversion (DAC) scheme based on time-domain pulse spectrum encoding is proposed and experimentally demonstrated. In this approach, the ultrafast optical pulses are first time-broadened and frequency-chirped based on wavelength-to-time mapping and then segmented and power weighted in both time and spectrum domains to produce the multi-band optical carrier. The optical carrier is intensity-modulated by the serial digital inputs to realize the time-domain pulse spectrum encoding. Each spectrum-encoded pulse is then time-compressed to achieve the incoherent weighted intensity summation of digital bits within each word. This approach generates the multi-band optical carrier and achieves the corresponding incoherent intensity summation using all-fiber structure; the system configuration is greatly simplified. Moreover, the time-domain pulse spectrum encoding could efficiently exploit the superwide spectrum resource offered by ultrafast optical pulses and potentially improve the system conversion resolution. A proof-of-concept experiment of a 4-bit DAC system based on time-domain pulse spectrum encoding is carried out, and the obtained results validate the feasibility of the proposed approach. In addition, the system performance in terms of the effective number of bits is investigated.

In this analytical approach, electro-optically tunable second-order cascaded nonlinearity was targeted to investigate the potential of ultrashort pulse compression in a tapering nonlinear medium. The proposed framework is ideally suited to generating high-intensity pulses with small pulse widths by exploiting second-harmonic generation and the electro-optic effect in a bulk beta-barium borate with exceptional optical advantages. Considering both linear and nonlinear absorption losses, the necessary and sufficient conditions for the compression of ultrashort pulses were developed using the generalized nonlinear Schrödinger equation. In agreement with simulations, an attempt is made to compress an optical pulse from 120 to 39 fs using an external voltage of ∓5.69 KV, which leads to a phase mismatch ( Δk ) = ± 124.8 m ^{− 1}, a phase shift ( Δϕ^NL ) = ± 1.26π, and an effective cascaded refractive index (n2cascade)=±3.371×10−20 m2/W. The results suggest that the technology developed in this study will open the door to a plethora of applications, including fields as diverse as laser surgery, range finding through LIDAR, and many more.

Data-driven approaches have proven to be very efficient in many vision tasks, and they are now used for optical parameters’ optimization for application-specific camera designs. Methods such as neural networks are used to estimate camera performance indicators related to the point spread function—such as the root mean square (RMS) spot size—from optical parameters. Such procedures help to understand the connection between optical characteristics and push optical design expertize beyond its limits. We investigate these approaches to model the interaction between the distortion of wide-angle designs and their RMS spot size, which is not explained by aberration theory. Specifically, we test off-the-shelf data-driven methods to determine in which conditions we can establish a model that is able to predict the variations of the RMS spot size along the field of view from the distortion function even in the absence of a mathematical model. Although current methods focus on building accurate models often usable for very specific designs—composed of a few elements only, we present a methodology focusing on more complex and realistic wide-angle designs.

The disturbance in the adaptive optical system includes not only the low-frequency broadband disturbance but also the high-frequency narrow-band disturbance caused by the vibration of system components and atmospheric turbulence. A nonlinear active disturbance rejection control (NLADRC) method is proposed to solve the control problem of a deformable mirror under high-frequency narrow-band disturbance. This method does not completely depend on the mathematical model, and the algorithm structure is simple. The differential tracker flattens the abrupt part of the signal, and the extended state observer is used to estimate the disturbance in real time. Finally, the nonlinear control rate is used to compensate the disturbance. The simulation results show that compared with the classical PID control and the classical linear active disturbance rejection control, the NLADRC method can effectively improve the bandwidth of the control system and show good suppression performance against high-frequency narrow-band disturbance, and the system is more robust. Both in time domain and frequency domain, it can accurately track the system state, reduce the system delay and system error, and has better dynamic performance.

Liquid crystal on silicon (LCoS) phase modulators spatially modulate the phase of light across the panel. The orientation order and elongated molecules of nematic liquid crystals (LCs) means that traditional LCoS phase modulators are inherently polarization-dependent, resulting in either complicated polarization manipulation systems or high optical power loss for unpolarized incident light. We propose a polarization-independent LCoS (PI-LCoS) device that combines existing technologies, which allows for cost-effective fabrication. Our PI-LCoS phase modulator is suitable for a wide variety of applications in telecommunication, adaptive optics, and display technologies. We have demonstrated the feasibility of the proposed PI-LCoS device by fabricating polarization-independent LC cells using a thin-film quarter-wave plate composed of a photoalignment layer and a layer of LC polymer. We show experimentally that the proposed design can efficiently modulate the phase of light with arbitrary input polarization.

A novel two-dimensional photonic crystal broadband Y-shaped 1 × 2 beam splitter is proposed. Broadband performance of the 1 × 2 beam splitter can be greatly improved by optimizing the z-axis offset of the dielectric rods adjacent to the input and output waveguides, and the offset along the V-shaped oblique waveguide of the dielectric rods at the junction area. To enhance the optimization efficiency and achieve excellent splitting performance of the 1 × 2 beam splitter, the genetic algorithm is applied to inversely design the above offsets of the 1 × 2 beam splitter. The results show that, in the bandwidth range of 1515 to 1587 nm, the highest and lowest transmittance of the 1 × 2 beam splitter are 99.6% and 97.9%, respectively, the additional loss is <0.1 dB, and the uniformity tends to 0 dB. Finally, the tolerance analysis of the 1 × 2 beam splitter is carried out. When the deviation of each variable reaches ±10 nm, the total transmittance of the 1 × 2 beam splitter in the bandwidth range of 1515 to 1587 nm is still higher than 95.2%, with the additional loss <0.22 dB. Due to the virtues of broad operating bandwidth, high transmittance, good uniformity, and strong robustness, the proposed 1 × 2 beam splitter will have great application prospects in the field of photonic integrated circuits, all-optical communication network, and so on.

In the Taiji Program, the space gravitational wave (GW) telescope is an important component of the space laser interferometer, which is used to receive and transmit laser signals, and has strict requirements in terms of light intensity signals and tilt-to-length (TTL) noise. Therefore, the telescope has a particular design; it should have a large aperture to meet the demand for light intensity signals, and the TTL coupling noise should be suppressed in the design process. Based on the primary aberration theory, the solution of the four-mirror off-axis initial structure is described. According to the interference model of flat-topped and Gaussian beams, the coupling coefficient of wavefront error and TTL noise at the exit pupil of the telescope are analytically calculated using the average phase signal. The optimization method and design flow are established, considering the special requirements of the space GW telescope. The results indicate that the diameter of the telescope entrance pupil is 400 mm, and the system magnification is 80 × . The root mean square (RMS) value of wavefront errors is better than 0.00504 λ (λ = 1064 nm) within ±8 μrad of the scientific field of view, and the coupling coefficient is not more than 1.7 pm / μrad within ±600 μrad of jitter angle. The tolerance analysis of the design results shows that the RMS value and coupling coefficient meet the requirements of space GW detection. Therefore, the proposed design is a good candidate for the Taiji Program.

We describe the temperature-dependence polarization properties of grating-gated AlGaN/GaN heterostructures at terahertz frequencies. Using the finite-difference time-domain method, it was demonstrated that as the temperature increases, the resonant frequency of the incident light was red-shifted. Simultaneously, a shorter gate length leads to a higher resonant frequency. In addition, at a lower temperature, the coupling efficiency of terahertz radiation and plasmon is higher. In our simulation results, the maximum modulation depth is 88%; at a gate length of 800 nm and lattice temperature of 77 K. For the same gate length, with higher electron gas concentrations and filling factor, greater modulation depths were produced. Studies on these properties may help in the design and optimization of terahertz detectors and modulators.

The universal dispersion graph and mode field profile of different transverse electric (TE)/transverse magnetic (TM) modes are evaluated of the α-power refractive index (RI) profile curved optical waveguide. To maintain the high-power confinement in the core high refractive index contrast guiding approximation condition is applied. The finite difference method in conjunction with the conformal transformation technique has been devised to extract the TE/TM modes of a bent optical waveguide. A very efficient Eigenvalue/Eigenvector solver algorithm based on MATLAB software has been devised to extract allowed TE/TM modes of a bent optical waveguide. It has been found that upon bending of optical waveguide multimode nature emerges with good mode conversion capability. To avoid the radiation mode generation perfectly absorbing boundary has been applied in our numerical technique so the modes remain guided throughout of computational window. The objective is then to study the TE/TM mode cut-off conditions of curved waveguides irrespective of their RI profile parameters and curvature. The effect of waveguide bending on mode field profile and power confinement factor is also discussed.

High power fiber-coupled diode lasers are widely applied in laser material processing. Based on the commercial diode laser stacks, a comprehensive study of fiber-coupled diode lasers was presented using visualized beam shaping simulations. And then in experiment, refraction optical beam shaping, polarization multiplexing, wavelength multiplexing, and fiber coupling were used to produce a 4.08 kW output from an optical fiber with core diameter of 800 μm and NA of 0.2. An average fiber coupling efficiency about 95% was obtained, which was in good agreement with the simulation.

We propose and demonstrate the implementation and application of a new configuration of an all-fiber comb filter based on the Vernier effect produced by parallel-connected two in-line Mach–Zehnder interferometers (MZIs). Each in-line MZI was fabricated by fusion splicing a section of panda-type polarization maintaining fiber (PMF) with peanut-shaped tapers between two single-mode fibers. These two in-line MZIs, respectively, form reference and sensing interferometers, which are parallel-connected by two 3-dB optical fiber couplers to realize the Vernier effect. By incorporating the proposed comb-filter into the erbium-doped fiber laser cavity, two output channels at 1533.2 and 1558.2 nm have been achieved. Further, the combination of the parallel-connected two in-line MZIs and polarization controllers (PC1 and PC2) promotes the lasing in a switchable and selective way. To the best of the authors’ knowledge, this is the first demonstration of a comb filter that employs paralleled two peanut-shaped MZIs in PMF. The experimental results indicate that the proposed filter has the potential to be used in communication systems.

An indoor multi-dimensional visible light positioning method on the basis of visible light communication (VLC) has been proposed considering the impact of vertical and horizontal inclination angles of the target besides the traditional three-dimensional position parameters that can be expressed as ( x , y , z ) in the coordinate system. Specifically, the adaptive particle swarm optimization algorithm is adopted to search the global optimum in the whole space as the estimation position, which can efficiently improve searching ability and avoid premature convergence, thus efficiently improving the accuracy and stability of positioning results. Simulation results show that when the signal-to-noise ratio is equal to 25, 30, and 35 dB, over 91%, 93%, and 98% test points could achieve sub-centimeter level positioning, and ∼94 % , 90%, and 99% test points could satisfy the requirements of small angle in physics of horizontal inclination, respectively. And under such conditions, nearly all the test errors of vertical inclination are lower than 5 deg except one in 30 dB. Our work provides a good reference for the study of indoor VLC positioning method.

In fiber Bragg grating (FBG) sensor networks, the highly overlapped spectral signals can lead to considerable errors in center wavelength demodulation. To tackle this problem, we utilize the fully convolutional time-domain audio separation network (Conv-TasNet) model to produce a distinct spectral signal, which is then demodulated using the dual-weight centroid approach to determine the spectral signal’s center wavelength. Specifically, we first demonstrate the theoretical feasibility of the Conv-TasNet model on simulated data. Experimental results show that the Conv-TasNet model can separate the signals of three FBG sensors. After that, we collect the spectral data and further train and validate the model based on the pretrained model of the simulated data to see how it performs on the real data. The experiments consistently illustrate superior performance of our Conv-TasNet model that can also separate actual spectrum signals. The same performance can be achieved by applying the pretrained model but with less training data. The model obtains a competitive performance compared to currently available methods. Moreover, the method provides a solution for improving the multiplexing performance of the FBG sensor network.

One of the modern ways to diagnose diseases is through exhale gas of patients, which is non-invasive and therefore desirable to doctors. The composition of exhaled breath contains valuable information for identifying hyperbilirubinemia disease. The accumulation of bilirubin and its lack of excretion causes jaundice, and the production of bilirubin has a direct relationship with exhaled carbon monoxide (CO). A CO diagnostic sensor based on a photonic crystal fiber (PCF) that can detect hyperbilirubinemia has been designed. This method can be used repeatedly to detect and treated jaundice in time. The PCF is designed as a hexagon. The holes in the cladding are circular and the holes in the core are circular and oval. Finite element method is used to do all the numerical simulations. COMSOL Multiphysics software was used to obtain the results. In this setup, CO absorption wavelength is 1.567 μm, and the relative sensitivity of 64.28% is reported with confinement loss of 3.81 × 10 ^{− 3} dB / m.

A power-tunable local oscillator (LO) is utilized for long-distance phase-sensitive optical time-domain reflectometry (ϕ-OTDR) systems. The scheme uses a LO whose power is intentionally varied inversely with the backscattered signal power to suppress the dynamic signal range before receiving, which realizes a higher far-end signal-to-noise ratio (SNR) while avoiding receiver power saturation. Meanwhile, the suppressed signal range allows for the use of low-resolution analog-to-digital converters (ADC). We implemented the scheme over a 98-km standard single-mode fiber, and the results show that the scheme achieves a 3.4 dB far-end SNR improvement. When the ADC resolution decreases from 13 to 8 bits, the proposed scheme shows a negligible SNR penalty. Compared to systems using power-fixed LO and 8-bit ADCs, our proposed scheme achieves a 4.8-dB reduction in self-phase noise power under the same conditions.

Dipole-allowed optical transitions between quasi-stationary and stationary states, which occur over the spherical surface of a single germanium quantum dot (QD) embedded in a silicon matrix, are theoretically investigated. These optical electron transitions, which occur in the real space of the silicon matrix, allow for solving the problem of a significant increase in the radiation intensity in germanium/silicon heterostructures with germanium QDs. Long-lived quasistationary and stationary states will make it possible to realize high-temperature quantum Bose-gases states in the nanosystem under study.

To realize the electromagnetically induced transparency (EIT) or reflection (EIR) effect in the terahertz band, many metamaterial structures have been proposed. However, these structures usually have a single function of EIT effect or EIR effect, and it is a major challenge for a metamaterial structure to perform multiple functions. In this study, a switchable multifunctional hybrid metamaterial is proposed, which realizes the combined function of tunable EIT effect and EIR effect at THz regions through the integration of vanadium dioxide (VO₂) and metal metamaterial. Moreover, by changing the conductivity of VO₂, the intensity modulations of EIT window and EIR window reach 36.11% and 50.59%, respectively. The surface current distribution and electric field responses are used to analyze the physical mechanisms of the EIT effect and the EIR effect. In addition, the active tuning mechanism of the metamaterial is theoretically explored based on the “two-particle” model. The designed hybrid metamaterial provides a simple approach to realize tunable EIT effect and EIR effect in THz metamaterials. This work opens up a possible way to achieve switchable functions (EIT or EIR) in a single device, which may find potential applications in optical switches, sensing, filtering, and slow light devices.

Physical layer security of a free-space optical (FSO) communication link is investigated for certain eavesdropping scenarios in which the eavesdropper exploits the divergence of the transmitted laser beam, which is subject to atmospheric turbulence, to compromise the security of the transmission link. A solution for physical layer security in which the legitimate receiver is positioned to receive only the coherent component of the transmitted laser beam is proposed. The irradiance fluctuations are modeled with separate distributions for the coherent and non-coherent components of the transmitted beam, corresponding to the main channel and the eavesdropper’s channel, respectively. Complete secrecy analysis of this setup is presented, and closed form expressions of the probability of strictly positive secrecy capacity, average secrecy capacity, and secrecy outage probability are derived. The analytical results are verified by Monte-Carlo simulations. Secrecy performance for worst-case scenarios corresponding to an adversary with powerful resources to capture all of the leaked information is explored. Results are analyzed for different turbulence regimes, and it was found that secure communication is possible even in the region of strong turbulence.

A subcarrier-partition (SP) particle swarm optimization (SP-PSO) algorithm was proposed to search the optimal power allocation in discrete multi-tone signal for visible light communication (VLC) systems. Combining non-linear modeling of Volterra series, the relationship between the transmitted power and the effective signal-to-noise ratio of every subcarrier could be easily evaluated, which avoids the complicated deep neural network used in the iteration of the PSO. By SP and linearly interpolation, we further improved the performance of the PSO-based power allocation scheme. Simulation results show that only eight sub-channels are sufficient for the SP-PSO algorithm to search for the optimal power allocation. It has a gain of 0.03 to 0.2 bit / s / Hz when compared to uniform power allocation, water filling, and the pre-frequency domain equalization, which shows the great potential of increasing the channel capacity of the VLC systems.

The quality of underwater polarization imaging is mainly affected by the polarization properties of the target and impurity particles. Traditional methods often assume uniform polarization characteristics of the target, which make it difficult to address the restoration issues of complex targets. In response, a partition-based method for recovering underwater polarization images is proposed. The method involves pre-processing the image using the Gaussian curvature filtering algorithm, partitioning the image based on polarization information. In addition, a joint image evaluation method is used to achieve restoration of complex polarized characteristic targets. The method estimates the value of the reflected light polarization of one partition to estimate the value of the next partition and links the polarization values of each partition. Our approach achieves clear restoration results for multiple targets or complex structural objects underwater. Achieving significant improvement in image quality in multi-target underwater scenes, our method is highly effective for complex underwater environments. Experimental results show that our method, when compared with three other newer methods on multiple images of different targets and under varying scattering conditions, achieves an average increase of 617% in the standard deviation image evaluation index and a 61% optimization in the natural image quality evaluator index. Furthermore, our method is robust for different degrees of water turbidity.

A hybrid shaping (HS) scheme based on geometric shaping (GS) and probabilistic shaping (PS) in a coherent optical communication system is proposed. A particle swarm optimization algorithm and Maxwell-Boltzmann distribution are employed to sequentially implement GS and PS. The results demonstrate that hybrid shaped 8/12-ary quadrature amplitude modulation (HS-8/12QAM) is superior to regular-8/12QAM (R-8/12QAM) in terms of reducing the bit error rate (BER) and increasing the generalized mutual information (GMI). HS-8QAM achieves a 2 dB optical signal-to-noise ratio (OSNR) gain and 0.45 bits / symbol GMI gain compared with R-8QAM. Meanwhile, HS-12QAM achieves 1.9 dB OSNR gain and 0.68 bits/symbol GMI gain compared with R-12QAM. In addition, HS-8/12QAM is better than R-8/12QAM in terms of transmission distance and data rate.

We propose and demonstrate an electro-optical chaotic communication system with additional chaotic phase-shift based on the mutual coupling structure. Under the condition of complete concealment of time-delayed signatures (TDSs), the key space of the system is greatly enhanced and highly reliable chaotic communication is finally realized. The additional-phase introduced by the new branch is nonlinearly superimposed on the phase generated by the chaotic signal of the original branch, which improves the complexity and aperiodicity of chaos. For security performance, the system only needs a very small feedback gain (i.e., β_i = 2.5) to conceal TDSs. Moreover, since the system has only one chaotic signal transmitted in the transmission link, it overcomes the exposure of TDSs caused by the cross-correlation characteristics between different links. At the same time, the system has strong synchronization robustness and can achieve high-quality communication when the parameters are well-matched. To sum up, the proposed system can effectively resist eavesdropping, which provides security for the physical layer of optical networks.

With the development and popularity of the Internet, network security has become a popular topic. The traditional solution for screening the security of network information is to convert the signal transmitted in the optical fiber into an electrical signal through an optical conversion. Then we perform symbol matching within the electronic firewall to determine whether the signal is a risk. However, due to the limitation of carrier recovery time in the semiconductor, the photoelectric converter cannot handle signals with too high rate, and it also causes a large power consumption. To improve the efficiency and scalability of signal matching, we propose an all-optical matching structure. This structure can identify the position of the target sequence in the input data sequence in the all-optical environment, and the structure is suitable for any amplitude and phase modulation format. The matching result of each bit of the target sequence and input data sequence is obtained by phase delay and interference. Then the matching result of each bit of the target sequence and input data sequence is integrated by logic AND gate, regenerator, and delay line. Finally, the matching result between the whole target sequence and the input data sequence is obtained. This structure can avoid photoelectric transformation and processes the signal directly at the optical domain, which greatly reduces the consumption of time and energy. We use VPItransmissionMaker software to simulate and verify the structure. The length of the input signal during the simulation is 8 bits, the length of the target signal is 4 bits, and the transmission rate of the signal is 100 GBaud. We simulated the binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-phase shift keying (8PSK), and 16 quadrature amplitude modulation (16QAM) modulation formats and analyzed the noise performance of the system. The results show that the structure can achieve all-optical matching of high-speed optical signals in BPSK, QPSK, 8PSK, and 16QAM modulation formats and has good anti-noise performance.

Computed tomography (CT) sequentially interrogates the object of interest from a complete set of view angles. Sequential scanning in CT introduces an acquisition delay and high radiation dose. This paper proposes a compressive sensing based “snapshot” coded X-ray CT (CXCT) method, where the object is simultaneously illuminated by multiple fan-beam X-ray sources equipped with coding masks in a fixed circular gantry. Low radiation dose is achieved by the use of incomplete projection measurements and encoded structured illuminations. Since all the measurement data are produced in one snapshot, the inspection time and motion artifacts are effectively reduced. Due to the overlap of X-rays in the measurements from several sources, a nonlinear reconstruction framework is established based on rank, intensity and sparsity priors. Then, a Newton split Bregman algorithm is exploited to reconstruct the object from a small set of nonlinear encoded measurements. Compared to the state-of-the-art CXCT approaches based on a linear model, the proposed method reduces the inspection time and motion artifacts significantly, achieving higher or comparable reconstruction accuracy.