Abstract:A simple strategy for synthesizing Ag decorated TiO2/WO3 composite nanoparticles by sol-gel method used as recyclable photocatalyst is introduced. The photocatalytic efficiency to the degradation of methyl blue (MB) by Ag/TiO2/WO3 nanoparticles is studied under ultraviolet-visible (UV-Vis) light irradiation. It shows that the photocatalytic efficiency of Ag/TiO2/WO3 photocatalyst achieves 96% in 20 min, which is 16 times higher than that of pristine TiO2 at the same conditions. The Ag/TiO2/WO3 photocatalyst can still reach the degradation rate of 90% in the fifth degradation experiment, indicating a good stability and photocatalytic activity.

Abstract:A photonic approach that can generate triangular and rectangular waveforms is proposed. A dual-electrode Mach-Zehnder modulator (De-MZM) is used to fulfill the external optical carrier suppression (OCS) modulation of a continuous wave (CW). The follow-up four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) makes four primary sidebands exist in the spectrum. Then filtering and optical carrier recovery techniques are used to construct the spectrum aligning with that of a triangular/rectangular waveform. In this work, we also elaborate the influence of errors of key device parameters, by which the feasibility and stability of the system have been verified. Based on this photonic approach, a 10 GHz full-duty-cycle triangular waveform and a 50%-duty-cycle rectangular waveform are successfully obtained. This approach provides a feasible method to generate multiple waveforms.

Abstract:Aiming at low stability and high harmonic distortion of the traditional phase-generated carrier (PGC) demodulation algorithm, we propose a modified demodulation algorithm for distributed strain sensing in phase-sensitive optical frequency domain reflectometry (OFDR). The proposed algorithm combines the arctangent function and differential-self-multiplying (ARC-DSM), which eliminates the effect of modulation depth and realizes the high precision strain variation measurements. Simulation results show that distortion and harmonic distortion are effectively suppressed by the ARC-DSM algorithm. The minimum variation of the measurable static strain is about 0.3με and the spatial resolution can reach 0.2 m within 270 m range.

Abstract:The application of high-frame-rate cameras as well as the complex image processing techniques will lead to a series of problems, such as high system cost and long transmission delay. In this paper, we introduce narrow-band filtering technology to reduce the impact of optical noise and reduce the complexity of image processing from the physical level. We also introduce multiple-input multiple-output (MIMO) technology into the optical camera communication (OCC) system to increase system transmission rate, and propose a light emitting diode (LED) array decoding algorithm based on the directional projection method to reduce the system delay. By accumulating the target pixel values in each row and column of the image, the proposed method then determines the position and boundary of the detected target to distinguish the target area from the background. Experimental results indicate that the communication distance can reach up to 5.5 m without error bits detected. When the LED array at the transmitter of this system flashes at a frequency of 12 Hz, the transmission rate can reach 126.32 bit/s.

Abstract:In this work, a visible light photocatalyst based on Au modified BiVO4 microspheres was synthesized successfully through using a facile photodeposition method for visible light N2 fixation. Compared with pure BiVO4 microparticles (MPs), the obtained Au/BiVO4 MPs show superior N2 photofixation performance to BiVO4, owing to the enhancements of both the visible light absorption and charge carrier separation. After optimization, the actual NH4+ generation rate of Au/BiVO4 reaches 0.419 mg.L-1, which is approximately 2 times higher than that of the pure BiVO4 one. The results presented herein provide new insights into rational design of highly active catalysts with Au NPs toward efficient, stable, and sustainable visible light N2 fixation in mild conditions.

Abstract:Q-switched erbium doped fiber laser (EDFL) was passively realized using vanadium pentoxide (V2O5) embedded into polyethylene glycol (PEG) film as saturable absorber (SA). The laser could successfully generate stable self-starting pulses when the V2O5 film was placed in an EDFL cavity. It operated at 1 562.4 nm wavelength. The repetition rate can be varied from 91.7 kHz to 128.2 kHz while the pulse width shrank from 10.90 μs to 7.81 μs with rising pump power from 110.9 mW to 166.5 mW. The pulse energy recorded was 3.2 nJ at pump power of 166.5 mW. The results indicate that the saturable absorption of V2O5 has promising nonlinear photonic applications especially in fiber laser development for 1.5-μm region.

Abstract:The heavily germanium (Ge)-doped silica fiber assisted by two air holes in the cladding exhibits high nonlinearity and birefringence, low loss and normal group velocity dispersion (GVD) for two fundamental modes (FMs). When the 1 920 nm and 0.1 ps pump pulse with 100 kW peak power is coupled into the 0.5-m-long fiber and polarized along one of two principle axes, the generated spectra can cover the wavelength range around 1 000—2 500 nm at −20 dB. Furthermore, the output pulse has an excellent coherence in the whole wavelength range.

Abstract:A detecting method of investigating the function of crack width versus fiber Bragg grating (FBG) spectrum deformation was proposed. In this paper, the bond-slip model of deformed steel bar in concrete slab was used to calculate the crack width. The stress distributions along optic-fiber grating were extracted by the three-dimensional (3D) finite element method (FEM) and the spectrum deformation of FBG induced by the uneven distribution of the stress was calculated. Experiments were carried out with an FBG fixed on the bottom of concrete slab. The crack width and FBG spectrum deformation of experimental results were given, and the function of crack width versus wavelength shift of FBG sensor was given also. The proposed technology in this paper could improve the safety of large-scale concrete building by early identification of structural crack.

Abstract:It is novel to apply three-dimensional (3D) light field imaging technology to recognize two-dimensional (2D) fake pedestrians. In this paper, we propose a parallel support vector machine (SVM) method based on 3D light field imaging (light field camera) and machine learning techniques. A light field (LF) camera with robust sensors, which is able to record rich 3D information, is used as hardware equipment. Histogram of oriented gradient (HOG) feature extraction algorithm and SVM classification method are used to recognize the real and 2D fake pedestrians efficiently. Besides, we carry out an experiment on our improved LF pedestrian dataset. The experimental results of parameter optimization study show that in the case of 400 training samples (200 positive samples and 200 negative samples), 120 to 420 testing samples, and an HOG cellsize as 8×8, the best recognition accuracy with polynomial kernel function is improved by more than 2% compared with the previous method. The best accuracy is 99.17%. Otherwise, the recognition accuracy of more than 98.00% will be obtained even under other experimental conditions.

Abstract:Magnetic resonance imaging (MRI) is a common way to diagnose related diseases. However, the magnetic resonance (MR) images are easily defected by motion artifacts in their acquisition process, which affects the clinicians' diagnosis. In order to correct the motion artifacts of MR images, we propose a convolutional neural network (CNN)-based method to solve the problem. Our method achieves a mean peak signal-to-noise ratio (PSNR) of (35.212±3.321) dB and a mean structural similarity (SSIM) of 0.974 ± 0.015 on the test set, which are better than those of the comparison methods.

Abstract:Aiming at the security problem of range gated laser imaging in high noise background, a range gated laser image encryption scheme based on the quantum genetic algorithm (QGA) is proposed. Due to the fuzziness of the laser image itself, the randomness and security of the key become more and more important in encryption. In this paper, the chaotic sequence is used as the parent chromosome of the QGA, and the random number satisfying the encryption algorithm is obtained by an iterative genetic algorithm. To further improve the security of laser images, some random pixels are stochastically inserted around the laser image before scrambling. These random pixels are scrambled together with the image. Finally, an adaptive diffusion method is designed to completely change the original statistical information of the image. Experimental simulation and performance analysis show that the scheme has high security.