In this paper, a weak fiber Bragg grating (WFBG) based sensing system applied to the cryogenic static test of launch vehicle oxygen tanks has been developed and the results of an evaluation are reported. A customized sensor encapsulation and installation method allow for precise strain measurement at cryogenic temperatures. The reflection peaks of series-connected WFBGs with low optical loss are obtained, ensuring high system reliability in harsh environments. The experimental results show that the maximum full-scale error is less than 0.81% full-scale error. The temperature is as low as -193 °C during the test. This study also demonstrates a practical method in which WFBG can be used to obtain critical parameters for structural monitoring in a cryogenic environment.

Atmospheric optical turbulence is the fundamental parameter closely related to the design and application of optoelectronic systems. The field measurements of atmospheric optical turbulence profiles by instruments are limited by labor, materials, financial resources, and other conditions. Therefore, it is of great significance to estimate the intensity of atmospheric optical turbulence according to the conventional meteorological parameters. A back propagation combined with genetic algorithm (GA-BP) neural network is proposed.First, based on Tatarski atmospheric optical turbulence parameterization scheme, the HMNSP99 outer-scale model is used to estimate the optical turbulence profiles; second, attempting to construct BP artificial neural network combined with genetic algorithm, which are trained by measured data to predict atmospheric optical turbulence profiles. The atmospheric optical turbulence profiles estimated by the two methods are compared with the measured profiles. The results show that the root mean square error (RMSE) between the estimated values of GA-BP neural network and measured values is smaller than that of HMNSP99 model, which proves that it is a feasible method to use GA-BP artificial neural network model to estimate the optical turbulence profiles.

This study derives the analytical expressions for the propagation factor and spatial expansion of radially polarized partially coherent twisted beams (RPPCTBs) in anisotropic atmospheric turbulence, with a focus on the effects of beam parameters, such as twisting factors and atmospheric turbulence parameters including anisotropic factors, on beam propagation characteristics. Using numerical simulation calculations, the effects of the initial coherence length, beam waist width, wavelength, twist factor, anisotropy factor, turbulence inner scale, turbulence outer scale, and generalized exponential parameters on the beam transmission quality are analyzed. Simulation results show that by decreasing the initial coherence length of the beam and increasing the beam waist width and wavelength, the transmission quality of the beam can be improved. Moreover, the twisting factor of the beam is increased and the beam shows a small transmission factor, demonstrating that the beam can be adjusted reasonably and the twisting phase can effectively improve the antiturbulence ability of the beam.

A polarization-maintaining chalcogenide glass fiber with a ridged core was designed and fabricated using Ge12As24Se64 (Ge-As-Se) glass as the core material and Ge10As24S66 (Ge-As-S) glass as the cladding material for generating linearly polarized mid-infrared supercontinuum (MIR SC). The ridged core fiber's group velocity dispersion was simulated using the finite element method, and the ridged core's geometrical size was determined. A multiple-stage rod-in-tube process paired with an extrusion technique was used to fabricate the fiber. The fabricated fiber exhibits a typical transmission loss of approximately 4 dB/m and a polarization extinction ratio of 19.4 dB-19.6 dB in the 2.9-5.5-μm spectral range. SC ranging from 2 to 9.5 μm with an average power of approximately 4 mW was generated when the fiber with a length of 12 cm was pumped by laser with a central wavelength of 3.7 μm, a pulse width of 170 fs, the repetition rate of 100 kHz, and average power of 40 mW. The SC has a measured polarization extinction ratio of 19.2 dB. These results indicate that the Ge-As-Se/Ge-As-S fiber with a ridged core is a promising nonlinear medium for generating linearly polarized broadband MIR SC.

The photon-assisted method easily generates and modulates broadband vector millimetre-wave or terahertz signals. The generation and transmission performance of its multi-band vector millimetre-wave signal is analysed in VPI and MATLAB environments using the coherent optical path structure of the cascade of the intensity modulator and the in-phase/quadrature (I/Q) modulator, combined with the probabilistic shaping technology. The transmission performance of two single-sideband vector signals with a net bit rate of 32 Gbit/s in uniform 16-ary quadrature amplitude modulation (16QAM) format and in a probability-shaping 16QAM format is compared and studied on the carrier frequencies about 70 GHz and 130 GHz, respectively. The simulation results show that the probabilistically shaped 16QAM millimetre-wave signal outperforms the uniform 16QAM millimetre-wave signal in optical fibre transmission. When the nonlinear effect of the fiber is considered, the probabilistically shaped signal has greater transmission advantages.

To solve the electromagnetic interference of electrochemical biosensing and improve the sensitivity of optical biosensing, this paper proposes photonic crystal fiber (PCF) sensing structure based on surface plasmon resonance (SRR) and applies to the detection of deoxyribonucleic acid. A thin Au film is coated on the outer layer of the PCF to make direct contact with the solution to be tested. The full vector finite element method combined with an anisotropic perfect matching layer is used to numerically study the structure. The results show that obvious SPR effect is gotten in the refractive index range of 1.333-1.347, and the resonance loss peaks are shifted in the wavelength range of 1300-1400 nm. When the Au film thickness is 60 nm, the duty ratio is 0.6 and the diameter of the air hole is 1.2 μm, the sensitivity of the structure can reach 7250 nm/RIU (RIU is a refractive index unit), the detection limit can reach the order of 10-6,and the quality factor can be 145 RIU-1 .

Linear and nonlinear channel distortion could degrade the performance of short reach optical interconnection system based on four-level pulse amplitude modulation (PAM4). Using PAM4 transmitter integrated circuits to pre-compensate the signal can alleviate the impact of channel distortion. This paper studies the architecture of PAM4 transmitter chip suitable for short reach optical interconnection. The architecture is based on look-up table (LUT) equalizer and source series terminated digital-to-analog converter, which can flexibly compensate the optical channel distortion. The pipelined multiplexer is used for high speed LUT reading. Digital-to-analog converter pre-driver circuit with feedback resistance is used to decrease the inter-symbol-interference. The post simulation results show that the PAM4 transmitter integrated circuits based on 55 nm process is able to reach 40 Gbit/s. It also enables reconfigurability of various types of equalizers and meets the requirements of next generation data center, access and other optical interconnection networks.

In order to improve the spectral efficiency and power efficiency for underwater optical-wireless communication (UOWC), a UOWC system based on layered asymmetrically clipped optical orthogonal frequency division multiplexing (Layered-ACO-OFDM) is proposed. The system makes full use of the spectrum resources lost in traditional asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) by the means of layered modulation of subcarriers, which greatly improves the spectrum efficiency for optical wireless communication system. Moreover, since the Layered-ACO-OFDM system does not need to add direct current bias, the power efficiency is also greatly improved. A UOWC channel model based on Monte Carlo method is established considering the absorption and scattering effects of visible light transmission in seawater, and the channel response under different chlorophyll concentrations and different receiver parameters is studied comprehensively. The results show that the UOWC system based on Layered-ACO-OFDM has the advantage of high spectrum efficiency compared with the traditional ACO-OFDM. When the signal-to-noise ratio is 27 dB, it can achieve high-speed communication of 1 Gb/s at a distance of 10 m in clean seawater.

Aiming at the problem of limited power consumption and battery capacity in unmanned aerial vehicle(UAV)-assisted multi-user multiple input multiple output (MU-MIMO) emergency communication networks, a method is proposed for power-constrained conditions. The design of beamforming to maximize the total transmission rate of the system is optimized. First, a method for easy determination of UAV position without iteration is proposed. Second, considering that the problem is non-convex, the first-order Taylor approximation is used to approximate it convexly. The second-order cone programming (SOCP) reduces the computational complexity and solves the best beamforming vector. The simulation results show that the proposed method is suitable for multi-user communication systems. Although the interference cannot be reset to zero during the simulation process, the system's total transmission rate can be maximized by suppressing the interference.

An integrated three-dimensional acceleration sensor based on fiber Bragg grating (FBG) was presented in this paper. The sensor took the cross-beams as the elastomer, and the strain distribution characteristics of the elastomer were studied by using the finite element analysis method. Five FBGs were encapsulated on the surfaces of the beams according to specific rules. The difference of wavelength shifts of pairwise FBGs was used as the output signal of the sensor in different vibration directions to realize low coupling measurement of three-dimensional acceleration and temperature compensation. The vibration test results show that: the resonant frequencies of the sensor in the x, y, and z directions are 2000, 1920, and 1160 Hz, respectively; the operating frequency bands are 20?1400 Hz, 20?1300 Hz, and 10?800 Hz, respectively; the sensitivities in the x, y, and z directions are 1.36, 1.70, and 1.31 pm/g, respectively. Moreover, the sensor has good linearity, weak coupling, and temperature compensation capability.

Aiming at the precise coupling problem of the optical fiber collimating lens signal, one of the core components of the optical fiber joint, a single-mode large beam optical fiber connector is designed using a doublet lens. By analyzing the characteristics of dual lens, the coupling mechanism of the multi-optical devices in the fiber collimator array, and the transmission loss caused by the three coupling deviations between the collimating lenses, the transmission loss formula of the coupling system is derive. Based on MATLAB analysis, the angular mismatch has the greatest effect on the coupling loss of the collimator, and the axial mismatch has the least effect. The optical simulation software ZEMAX is used to simulate the joint in sequence and hybrid modes, and Origin is used to plot the signal coupling efficiency curves under different mismatch conditions. The results show that when the core diameter of single-mode fiber is 12 μm, the coupling efficiency reaches 92.42%. Finally, an experimental system is built through the optical platform to verify the accuracy of the simulation results.

In theory, the total-internal-reflection lens can collect all the rays from the source, thus it is the preferred structure for secondary optical design in long-distance collimating illumination systems. The illumination characteristics of a collimating illumination system with extended source based on this type of light distribution element, including the intensity distribution characteristic, spot illuminance uniformity, and flux utilization, are analyzed by using optical software and experiment measurement, and the determining mechanism of divergence characteristic of the outgoing beam is explored. It is found that compared with the light distribution effect of the same-aperture plano-convex collimating lens, the flux utilization of the total-internal-reflection lens is improved significantly. However, the divergence angle of the outgoing beam is also remarkbly increased, which leads to no essential difference in the outgoing beam intensities of these two light distribution elements. Because the divergence angle of the outgoing beam from the core refraction part is different from that from the edge total-internal-reflection part, the illuminance uniformity of illumination spot for the total-internal-reflection lens is obviously deteriorated.

In order to study the frequency range of the negative refractive index of the photonic crystal, the band gap structure of the two-dimensional photonic crystal is solved by analyzing the numerical value based on the finite element algorithm. This process involves how to design the mathematical and physical models, design the solving equation of the finite element algorithm, and the numerical results were physically analyzed. First, the finite element algorithm is used to calculate the points in the wave vector space of all relevant frequencies in the Brillouin region to plot the isofrequency surface. Then, the isofrequency surface under different air hole radii is drawn. Finally, the frequency interval between the negative refractive index can be obtained by finding the direction with negative group velocity on the structure of the isofrequency surface. At the same time, comparing the influence of different air hole radii on the frequency range of the negative refraction of photonic crystals can provide support for the preparation of photonic crystal devices.

The intersatellite laser interferometric range measurement system is the core load of the next generation low-low tracking gravity measurement satellites. This system requires measurement accuracy of interstar distance change to the extent of a nanoscale. Considering this request, a laser interferometric ranging system with a corresponding answer-and-forward system is designed. The system measurement principle and frequency transmission relationship are deduced according to the system composition and the working principle. The measurement error items in the laser interferometric range measurement system are decomposed at the top-level analysis. The mathematical evaluation model is established for each error item, and numerical analysis is conducted. According to the laser interferometric range measurement system, the interstar distance change measurement accuracy greater than 7.5 nm/Hz1/2@0.1 Hz (0.1 Hz is Fourier frequency point) is finally realized, to meet the requirements of the next generation low-low tracking gravity field high-precision inversion for intersatellite laser interferometric ranging system.

When a laser radar is used to measure large structural parts, it is often necessary to establish multiple measurement stations to construct a large measurement network, for which the station positions and the number of laser radars are key factors affecting the measurement results. A method for laser radar measurement planning of large structural parts is designed for large component contour measurements of large aircraft component. The measurement accuracy is considered as a constraint, and the method considers the number of measurement stations and the division results of measurement area as the evaluation target. Further, a measurement mathematical model reflects the characteristics of discrete information and establishes a discrete point method. Using the method of measurement station planning based on the region growing algorithm, the initial number and location of stations are determined. Moreover, measurement uncertainty optimization considering the division of the measurement area and results is adopted. Experimental results show that compared with experience-based manual measurement planning, the proposed method is more feasible and effective in performing large-area measurements with a small number of measurement area divisions and a reasonable number of measurement stations.

In view of the problems that the slow processing speed of the traditional phase detection algorithm on the beat signal, a fast signal processing method of frequency-modulated continuous-wave interferometric fiber-optic displacement sensor based on digital signal processing (DSP) technology is proposed. With the DSP technology as the core, fast data transmission is realized through direct memory access (DMA), and the multi-fixed-point peak prediction phase detection algorithm is used to quickly solve the beat signal and optimize the direction. The experimental results show that in the dynamic measurement range of 600 mm, the standard deviation of displacement measurement is less than 5 nm, the linear fitting coefficient is above 0.99997, and the adaptive speed to the measured target reaches 15 mm/s. The proposed method can achieve higher measurement accuracy and faster dynamic measurement speed.

Aiming at the problem that the pulse width range of the driving circuit with nanosecond pulse width in semiconductor lasers is small and cannot be adjusted, a design scheme of a narrow pulse laser driving circuit with adjustable pulse width is proposed. According to the field programmable logic gate array (FPGA) technology and the working principle of the semiconductor laser, a general model of the semiconductor laser drive circuit is built, and simulation and experimental analysis are performed. Taking FPGA development board as the control core, using high-speed metal oxide semiconductor field effect transistor (MOSFET) drive chip DE375 as a switch to achieve precise control of the drive power and semiconductor laser. The output pulse current amplitude of the circuit can reach 40 A, pulse width is 5-200 ns, repetition frequency is 0-50 kHz, and rising edge width is less than 5 ns, which effectively improves the function of the semiconductor laser drive circuit.

In this paper, a TC4 component produced by laser selective melting was used as the research objects and the influence of inclination angle on the forming accuracy of their internal structure was explored. A TC4 component with different inclined channel structures was designed and printed under optimized parameters. The internal structure of the sample was observed using industrial computed tomography equipment. Then, it was imported to PolyWorks software for fitting and comparison to detect the deviation degree and surface quality of the internal structure of the sample. The results demonstrate that the inclination angle greatly influences the overhang degree and surface quality of the internal structure of the TC4 component. When the inclination angle increases gradually to 50°, the deviation degree of the suspended surface of the internal structure is reduced and the printing quality is considerably improved. Additionally, as the inclination angle continues to increase, the deviation degree increases and the printing quality is notably reduced.

To obtain a high-gray two-dimensional code on the surface of packaging aluminum, a nanosecond pulse laser is used to mark the aluminum alloy surface. Further, the effect of the marking process on grayscale and the change of grayscale are investigated. CCD industrial camera, UV-visible spectrophotometer, scanning electron microscope, and energy spectrum analyzer are used to measure grayscale and spectral reflectance and observe the morphology of sample surface before and after direct low-speed labeling and high-speed labeling and then low-speed labeling. Consequently, a consistent correspondence is found between the gray level of each sample and the change in spectral reflectivity. The grayscale of the sample surface obtained using the second process reaches 92%, and the reflectivity is reduced to 10%-17%. The cause of the change in grayscale is the antireflective structure formation on aluminum alloy, and the structure has micron furrows and absorbs many nanospherical particles and flocculants.

The pulsed 1064 nm fiber laser is used to clean the thermal oxide layer of FV520B steel. The effects of processing parameters including laser power, pulse frequency, cleaning times, and substrate roughness, on the cleaning effectiveness of thermal oxide layer and the surface roughness after cleaning are investigated. The results show that for the pretreated samples (the roughness is approximately 0.503 μm) by polishing with 200# abrasive paper, the surface roughness remains almost unchanged after cleaning in the laser power range of 40-120 W, while the roughness decreases with increasing power in the range of 120-200 W. When the above pretreated samples are cleaned under laser power of 120 W and pulse frequency of 20 kHz, the surface roughness presents an obvious decrease (dropped by nearly 40.8 %) after laser cleaning for two times, and the roughness does not basically decrease with the increase of cleaning times. In addition, under the same laser cleaning parameters, the cleaning effectiveness of oxide layer becomes lower and the roughness does not exhibit any obvious change with the decrease in roughness of pretreated samples.

Metal additive manufacturing has been successfully applied in aviation, aerospace, mold, medical and other fields due to its characteristics such as rapid, mold-free, and free-form complex structure. As the complexity and volume of manufactured parts continue to increase, the amount of data in 3D models is increasing, and the time required for data processing has increased significantly, especially the steep increase in path planning, which has become the main bottleneck restricting the application of this technology. This problem needs to be solved urgently. In order to reduce the time required for path planning, based on the basic fact that the contours between two consecutive layers of additive manufacturing are similar, here the two-dimensional contours obtained by the slices of the three-dimensional model are divided into groups according to characteristics, and an innovative inter-layer information inheritance algorithm is proposed. Using the calculated filling path information of the previous layer, the filling path of the current layer can be quickly calculated. This algorithm does not need to calculate the intersections of each scan line and many contour loops of the current layer, which greatly reduces the calculation amount of path filling and speeds up the filling. The experimental results have proved that the overall calculation efficiency of the proposed algorithm is significantly higher than that of the traditional path filling algorithm, especially for the models with a constant cross-section or continuous cross-section, and the acceleration effect of the proposed algorithm is more excellent.

In this paper, laser cladding coaxial powder feeding technology was used to successfully prepare Ni60A composite coatings with varying CeO2 content on the surface of TC4 alloy to improve the corrosion resistance of the alloy. The CeO2/Ni60A composite coating was characterized and tested by XRD, SEM, and EDS. The results show that an appropriate amount of rare earth oxide CeO2 could refine the grain and improve the microstructure distribution in the coating, resulting in the formation of NiTi, Ti2Ni, and TiC. In electrochemical detection, CeO2/Ni60A composite coating with CeO2 mass fraction of 3% shows excellent corrosion resistance, where its self-corrosion current density Icorr is merely 2.110 × 10-7 A·cm-2 and polarization impedance RP is 190674.0 Ω·cm-2. Rare earth oxide CeO2 mainly accumulates at the boundary in Ni60A coating. It reduces the contact area with corrosive medium, which reduces the residual tensile stress in the coating to protect the passive film. Finally, it improves the corrosion resistance of the coating.

A 3 μm passively Q-switched Ho3+/Pr3+ co-doped fiber laser by using Au nanocages as saturable absorber is demonstrated. Stable Q-switched pulse trains with a repetition rate of 82.0 kHz are initially obtained as the pump power increases to 99.7 mW. When the pump power increases to 347.1 mW, the largest output power of 50.7 mW with a pulse duration of 2.21 μs and a corresponding repetition rate of 169.5 kHz is obtained. This study indicates that Au nanocages have a great potential as an outstanding optical modulator for mid-infrared pulses generation.

Although high-speed laser cladding significantly enhances cladding efficiency, surface coarse defects easily occur on the high-speed cladding layer surfaces. The hybrid process of high-speed laser cladding and laser remelting can obviously improve the cladding layer surface quality. The Fe90 stainless steel coating was prepared on the surface of 27SiMn hydraulic column material by laser cladding. The surface morphology, microstructure, element distribution and phase composition of the cladding layer were analyzed by using the ultra depth of field microscope and X-ray polycrystalline diffractometer. The properties of the coating were verified by the hardness test, wear resistance test and electrochemical corrosion test. The experimental results show that the surface roughness of laser remelting coating is reduced by 8.5% compared with that before remelting, and the microstructure inside the coating is finer and uniform. There is not phase disappearance and new phase appearance, but the phase content increases. In terms of performance, the hardness after remelting is 2.6 times that of the substrate, the wear weight loss is reduced by 95%. The laser remelting technology improves the surface quality of the cladding layer and effectively improves the coating performance.

Using the hydraulic column material 45 steel as the substrate and 316 stainless steel cladding powder as the cladding material, we performed laser cladding experiments on the substrate surface to fabricate the 316 stainless steel coating under various process parameters. Then, we used a FANUC CNC machine to complete the turning of the cladding layer and study its macro morphology, chip morphology, surface roughness, cylindricity, Rockwell hardness, and microstructure after turning using digital testing technology. The turning performance of the laser cladding layer on a 45 steel surface was thoroughly analyzed to select the best laser cladding parameters. When the laser power is 800 W, the powder feeding rate is 0.28 g/s, and the axial feed rate is 0.110 mm/s. The cladding layer's macro morphology and turning chip morphology are the best, and the turned surface has the lowest surface roughness and the best cylindricity. The cladding layer's hardness can reach 40.3 HRC, and the internal metallographic structure shows a trend of refinement.The new technology of laser cladding the 316 stainless steel cladding layer on the surface of 45 steel coupled with turning processing can provide an important reference for the high-quality repair and reuse of hydraulic column material 45 steel.

This paper proposes a microsystem composed of vertical cavity surface-emitting laser arrays, laser driver chips, and power chips based on system in package technology to meet the needs of the hardware-in-the-loop simulation system. In addition, a manufacturing process flow based on microelectromechanical systems technology was developed. The packaging method has a high level of integration and high reliability. Driving efficiency and space utilization are significantly improved compared with other driving and packaging methods. Consequently, it has broad application prospects in optical imaging, communication, and interconnection, laying the groundwork for realizing the laser-imaging generator in semi-physical simulation systems.

The surface oxidation of titanium alloy will occur severely in a high-temperature environment, affecting subsequent processing and use. Laser cleaning technology was used to remove this oxide layer. A high-speed camera was used to analyze the removal mechanism of the oxide layer. The influences of laser cleaning, abrading, and pickling processes on the macroscopic morphology, microscopic morphology, chemical composition, flatness, and microhardness of the sample surface were studied. The results show that the mechanism of laser removal of the oxide layer was mainly performed through ablation. The oxides on the surface of the samples were removed after cleaning them with appropriate laser parameters, resulting in a silver-white metallic luster. The oxygen content of the samples was significantly lower than that of the original samples, and the surface smoothness was superior to that of the pickling and abrading samples. In addition, due to the thermal effect of the laser cleaning process, the microhardness of the laser cleaning sample surface was significantly higher than that of the abrading and pickling samples.

A Mach-Zehnder interferometer is connected outside the dissipative soliton mode-locked fiber laser to realize the ultrashort pulse output of the dissipative soliton molecule with controllable separation. The Mach-Zehnder interferometer is constructed by two 50∶50 optical coupler and a tunable optical time delay line. The separation of the dissipative soliton molecule can be adjusted with the optical path difference of the Mach-Zehnder interferometer, by adjusting the time delay line. The dissipative soliton molecules with the pulse separation of 0.8 ps, 1.3 ps, 2.37 ps, 4.25 ps, 6.24 ps, 9.4 ps, and 15.3 ps are observed, respectively, the corresponding spectrum separation are 8.3 nm, 6.1 nm, 3.83 nm, 1.88 nm, 1.27 nm, 0.85 nm, and 0.52 nm. The generation mechanism of the soliton molecule are analyzed theoretically, which agree well with the experimental results. The work provides an effective way to realize dissipative soliton molecule with controllable separation.

Hydrogen embrittlement has strong microstructural sensitivity, which threatens the safe service of all kinds of high strength structural materials. BS960E high strength steel is welded by laser-arc composite welding process, and the joints are subjected to slow strain rate (10-5 s-1) tensile test under the condition of in-situ electrochemical hydrogen charging. The microstructure and fracture characteristics of the joints are analyzed, and the hydrogen embrittlement behavior of the joints is studied. Results show that the welding thermal cycle of rich martensite formed by fine grain area can make joint show some hydrogen embrittlement sensitivity, martensite higher hydrogen diffusion coefficient and lower hydrogen solubility and rapid diffusion of hydrogen on the grain boundary is the main cause of joint is sensitive to hydrogen embrittlement, by controlling the welding process parameters can inhibit the welding thermal cycle caused by the martensitic transformation, it can reduce the hydrogen embrittance sensitivity of BS960E high strength steel laser-arc composite welding joint.

The Zn1+xGa2-0.01-yGexO3x+4∶0.01Cr,yBi (x=1－4; y=0.00－0.04) persistent luminescence nanoparticles (PLNPs) are synthesised via hydrothermal synthesis followed by calcinations. The persistent luminescence properties are improved by optimising the reaction conditions, composition of Zn and Ge, and Cr/Bi co-doping ratio. In this study, the effects of calcination temperature and Cr/Bi co-doping ratio on the persistent luminescence properties and phase of PLNPs are investigated. The PLNPs prepared at hydrothermal temperature of 180 ℃ and hydrothermal reaction time of 24 h have the best afterflow luminescence properties when x and y are 2 and 1.02, respectively. The optimal composition of the prepared PLNPs is Zn3Ga1.97Ge2O10∶0.01Cr, 0.02Bi, which has a spinel structure and persistent luminescence time over 15 d, demonstrating good persistent luminescence performance.

A broadband terahertz (THz) perfect absorber that can be dynamically adjustable is designed. The absorber consists of a cross-shaped vanadium dioxide layer, metal ground plane, and sandwiched silicon dioxide layer. Simulation results indicate that a bandwidth of 1.06 THz (ranging from 0.71 to 1.77 THz) provides greater than 90% absorption. The absorptivity varies with VO2 conductivity and can be dynamically adjusted from 4% to 99.5%. To obtain the physical mechanism of the absorber operation, impedance matching theory and wave-interference theory are introduced, and the physical source of the two perfect absorption peaks is analysed by electric field distribution. The absorber has the characteristics of wide-angle absorption and polarisation insensitivity and can be used in THz sensors, detectors, and stealth equipment.

Metamaterial absorbers in terahertz band can be widely used in military radar and biological detection. In this paper, a terahertz metamaterial absorber with a T-shape structure is proposed. Its absorptivity can reach 99.99%, close to perfect absorption. The factors influencing absorptivity and the absorptivity mechanism of the structure are disclosed from the aspects of structural size and current distribution. In order to make the above T-shaped structure apply to a wider range, the designs of a polarization- insensitive T-shaped absorber and a frequency- adjustable T-shaped structure absorber are further proposed. The simulation shows that the designed metamaterial absorber has high absorptivity, flexible frequency adjustment range, and insensitive polarization angle, so it has good research value.

In nonlinear media, the evolution of off-axis offset vortex beams obeys the non-local and nonlinear Schrodinger equation. The expressions of initial light intensity and orbital angular momentum can be obtained by analytical methods. The split-step Fourier method is used to numerically simulate the influence of factors, such as off-axis vortex position, topological charge, and vortex circulation direction on the critical power, beam width, orbital angular momentum, phase structure distribution, and transmission direction of the beam. The results show that by selecting the appropriate off-axis vortex position and topological charge, the single beam of the double vortex can achieve the light intensity distribution of the double vortex structure, and it can also transmit obliquely. The magnitude of the orbital angular momentum depends not only on the traditional topological charge, but also on the position of the off-axis vortex. Therefore, the controllable propagation of this type of double vortex single beam has important theoretical guiding significance and application prospects in the information carrying and transmission of the beam.

The traditional ABC model is used to study the dynamic recombination process of carriers in InGaN quantum wells. Based on the traditional ABC model, the carrier recombination rate and lifetime are calculated and the relationship between the 3 dB modulation bandwidth of InGaN-based LEDs with different emission wavelengths and the carrier recombination mechanism is studied. The calculation and analysis results show that under the same injection current, with the reduction in the effective active region thickness and quantum well layer thickness, the 3 dB modulation bandwidth of the 400 nm near-ultraviolet, 455 nm blue, and 525 nm green light-emitting wavelength of LEDs increases significantly. At the injection current density of 100 A/cm2, the 3 dB modulation bandwidth of the 400, 455, and 525 nm wavelength LEDs are 62, 88, and 376 MHz, respectively. At the same current density, the 3 dB modulation bandwidth of LED increases with the increase of the In composition (the ratio of the atomic number fraction of In element to the sum of the atomic number fraction of In and Ga elements). Moreover, because of the high In composition of the 525 nm wavelength LED, the thickness of effective active region is small and the carrier concentration in the active region is high. Moreover, the 3 dB modulation bandwidth of the 525 nm green LED reaches 376 MHz at high current density.

In this paper, we propose a fiber-optic multifrequency Fabry-Perot (FP) acoustic vibration sensor based on a graphene oxide (GO) microcavity. The sensor uses a single-mode fiber end face and GO film to form a micron-scale FP interference microcavity structure. The GO film is prepared by liquid-phase method and used as a sensitive material to detect the external acoustic vibration signals. Through controlling and optimizing the length of the FP microcavity, the interference spectrum with the largest extinction ratio can be obtained, and single-, dual-, and triple-frequency acoustic vibration signals of different frequencies are applied to the sensor to test its response capability to multifrequency signals. The experimental results show that the sensor has a high signal-to-noise ratio (SNR); the SNR for single-frequency vibration signal sensing can reach up to 61.8 dB, and the frequency response range is wide, approximately 500 Hz?20 kHz; the highest SNR for dual- and triple-frequency acoustic vibration signal sensing can reach 56.8 dB and 54.4 dB, respectively.

In order to calculate the surface of the nanoparticles large size aggregate local electromagnetic fields distribution and to evaluate its effect, the scripting language is used to write the local and the grid in the software program to implement the nanoparticles large size aggregate model of discrete non-uniform grid, combined with the finite difference time domain (FDTD) method to implement three sizes aggregate model of electromagnetic field simulation. The K-means clustering algorithm is used to cluster the calculated electric field data, and finally the average enhancement factor is obtained which could reflect the electromagnetic enhancement effect at all “hot spots” locations of the large-size aggregation of gold nanoparticles. The results show that the memory usage of the sub-grid discrete gold nanosphere dimer simulation model is reduced by 81%, and the simulation speed is doubled, which effectively improves the simulation efficiency of FDTD. In addition, the enhancement factor AEF 2, which is the same as the average enhancement factor (AEF 1) calculated by traditional integration method, can be obtained by K-means clustering algorithm and electromagnetic data of the aggregate of gold nanoparticles of three sizes.

Aiming at the problem that the multi-pixel photon counter (MPPC) is susceptible to background light interference and the synchronization clock signal is difficult to extract in the process of signal recovery, an improved synchronous communication method of photon counting based on MPPC is proposed. First, the MPPC is use to complete the photoelectric conversion, the mean value (MV), Anscombe root (AR) transformation and maximum likelihood (ML) optimal threshold detection algorithm of the Poisson distribution model are used to pre-judge the electrical pulse. Second, the gated periodic clock with different phases is generated, which is used as the enabling signal to count the sum of pulse counts, and the best slot-dependent synchronous clock is determined by searching its maximum value. Finally, the relative size of pulse count per bit and count threshold is compared to determine bit information. In order to verify the effectiveness of the method, a wireless optical communication system based on MPPC is built. The experimental results show that under the conditions of a wavelength of 520 nm, a communication rate of 2 Mbit/s, a sampling frequency of 200 MHz and a bit error rate of 3.8×10-3, the sensitivity of the improved PCPB-MV, PCPB-AR, and PCPB-ML detection algorithms is 3.0 dB, 3.2 dB, and 3.8 dB higher than that of the traditional detection algorithms, respectively.

The coherent state orthogonalization expansion method is used to analyze and investigate the factors influencing the three-qubit entanglement degree. In addition, the three-qubit entanglement in the interaction process with the vacuum state as the initial state of the light field is investigated by numerical calculation combined with analytical solution. The relationship between the entanglement degree of three identical qubits and the light field frequency as well as the influence of light-field-qubit coupling strength on the three-qubit entanglement degree is analyzed. The research results show that the evolutions of the three-qubit intrinsic energy and the three-qubit co-occurrence entanglement degree with light field frequency and time g0t are related to the coupling strength, while the evolutions with time gt have nothing to do with the coupling strength.

The dynamic evolution of the fidelity of quantum teleportation in a single three-level atom coupled to a multi-mode non-Markovian bosonic environment is studied by using the quantum state diffusion method, and the effects of different parameters on the fidelity are analyzed. The results show that when the three-level atom is coupled with the strong non-Markovian environment, and the initial state of the three-level atom is in excited state or metastable state, the fidelity of quantum teleportation of three-level atoms has long relaxation time and good robustness. In addition, the external magnetic field is used to control the quantum teleportation of the three-level atom, which can make the three-level atom have a fidelity with good robustness.

Visible light and near infrared (Vis-NIR) spectrometer is a practical tool that can be used for alternative soil physical and chemical analysis to assess soil properties. The optimal band combination algorithm is an effective method to extract spectral variables by considering the interaction information between bands. However, for laboratory Vis-NIR spectral data, this method is vulnerable to the “dimension disaster”.A method that appropriately reduces the spectral configuration (reducing the number of spectral bands and coarsening the spectral resolution) to improve the calculation efficiency without significantly affecting the prediction accuracy is proposed. First, six spectral configurations are constructed, which means that the number of spectral bands is reduced from 2001 to 19, the spectral resolution is increased from 3 nm to 100 nm, and the spectral sampling interval is equal to the spectral resolution (uniformly spaced sampling). Then, partial least squares regression combined with the optimal band combination algorithm is used to predict the optimal spectral parameters of soil organic matter (SOM) and electrical conductivity (EC) under different spectral configurations. The results show that until the spectral resolution is 60 nm (32 wavelengths per spectrum), the optimal band combination algorithm can improve the prediction accuracy compared with the full band spectrum data. The best band combination algorithm has no significant difference in prediction accuracy under 1?20 nm spectral resolution (about 2%); SOM [determination coefficient(Rv2) is 0.77, root mean square error(REMSP) is 0.325%, ratio of performance to inter-quartiledistance(RPIQv) is 3] and EC (Rv2 is 0.69, RMSEP is 6.88 dS·m-1, RPIQv is 2.21) obtain the best prediction performance at the spectral resolution of 20 nm and 10 nm.

The policy for controlling air particulate matter pollution is becoming increasingly stringent. To address the issue of measurement stability, researchers proposed the sheath flow structure used to limit particle overlap and the pollution of light cavity. To achieve high stability concentration measurement, this paper optimizes the measurement accuracy and antipollution performance of the sensor from three perspectives: optical cavity structure, mass concentration calculation method, and gas path structure. The optical cavity structure is simulated using optical tracing to achieve the best-scattered light collection effect. Modifying the sensor's characteristic parameters reduces its measurement error. The simple sheath gas protection structure with internal circulation mode is designed to reduce measurement error caused by particle overlap and protect the optical cavity. The effect of gas flow rate on the detection results of total dust concentration (TSP), PM10, and PM2.5 is studied, and the optimal air pump flow rate is set. The experimental results show that the aerosol concentration sensor simultaneously achieves a high stable mass concentration measurement of TSP, PM10, and PM2.5, and the measurement error is <±5%.

Star sensor is an important device of satellite attitude control. The star simulator is used as a ground performance test and precision calibration equipment of the star sensor, of which accuracy plays an important role in the precision of attitude control. The composition and working principle of the star simulator are briefly described in this paper. In the last 20 years, the selection of light source for the representative star simulator with adjustable colour temperature has been emphatically described. LED, tungsten bromide lamp, xenon lamp and supercontinuum laser are the most common light sources. The development trend of colour temperature tunable star simulator light source is provided through a comparative analysis of these light source simulation schemes.

In order to verify the accuracy of scattering phase function used in ocean optics in the simulation of key performance indexes of underwater wireless optical communication (UWOC) system, based on Monte Carlo method, the influence of five approximate phase functions on receiver bit error rate (BER) of UWOC system is studied by simulations in order to obtain the phase function model suitable for channel simulation and system performance detection under different water quality conditions. The results show that the Sahu-Shanmugam (SS) and Fournier-Forand (FF) functions have the least influence on BER simulation; the influence of Henyey-Greenstein (HG) and Two-Term Henyey-Greenstein (TTHG) on BER simulation is closely related to water types; and the BER simulation deviation caused by Haltrin function is the largest.