Online monitoring and fault identification of submarine cable are fundamental technology for ensuring the normal operation of cross-sea transmission and communication transmission. To avoid signal distortion due to direct denoising, which affects the extraction of target features, in this paper, the variational mode decomposition (VMD) algorithm is applied to extract features directly from noisy vibration signals. Using the Brillouin optical time domain analysis experimental system for monitoring the submarine cable vibration, the vibration signals of submarine cable under the conditions of anchoring, scouring, and friction are obtained. Three types of vibration signals are divided into 200 groups, and the intrinsic mode function components are obtained using the VMD algorithm. Furthermore, the energy, energy entropy, and kurtosis combinations of each component are obtained as eigenvectors. Using 80% and 20% of the feature vectors as the training and test sets, respectively, the data are classified by inputting them into the support vector machine (SVM) based on the bird swarm algorithm (BSA). The experimental results show that compared with other SVMs, the classification accuracy of BSA-SVM is higher, reaching 99.17%, and the running time is shorter.

Silicon-based detector has the advantages of stability and reliability, low dark current, high response and low price. It is widely used in photoelectric detection and other fields. In view of the limited detection ability of silicon-based detector in the ultraviolet band, a concentrating structure which can enhance the detection ability of silicon-based detector in the ultraviolet band is designed in this paper. First, the absorbed ultraviolet light is transformed into visible light by using the fluorescence characteristics of ZnCdS∶Mn/ZnS quantum dots. Then, combined with the short wave pass cut-off color filter film, the external quantum efficiency of the detector in the 260-400 nm band is greater than 20%, the response time is limited to the order of ms, and the dark current is limited to the order of pA. The experimental results show that the focusing structure of quantum dots layer can significantly improve the detection ability of silicon-based detector in the ultraviolet band. In addition, the silicon-based detector with adjustable detection range can be realized in the ultraviolet band by changing the size of quantum dots.

Unlike the high absorptivity design at a specific wavelength, the optical absorption design of superconducting nanowire single-photon detectors in a wide wavelength range of 3?5 μm necessitates an enhanced balance between the peak absorptivity and in-band flatness. Herein, first, an initial front-illuminated device model based on the asymmetric Fabry-Pérot (F-P) cavity structure is stacked using ultranarrow NbN nanowires, SiO2 cavities, and distributed Bragg gratings (DBRs). Second, the three thicknesses of the SiO2 cavities, a high refractive index layer and a low refractive index layer in the DBR are considered as the optimization variables, and the minimum light absorptivity in the wavelength range of 3?5 μm is set as the optimization objective. Finally, the initial device structure is optimized using the particle swarm optimization algorithm. Results show that compared with the design of double-wavelength coupling, the design of a single-layer NbN nanowire detector based on the asymmetric F-P cavity structure and high-contrast DBR can afford improved minimum optical absorption and in-band flatness by 40.2% and 59.2%, respectively. Based on this, a double-layer NbN nanowire layout can enable a further enhancement in the minimum optical absorptivity and increase the maximum absorptivity to more than 0.97, a value equivalent to that obtained using the double-wavelength coupling method.

In this study, a modified Mach-Zehnder (MZ) interferometer is used to measure the orbital angular momentum (OAM) [the value and sign of topological charge (TC)] of a Laguerre-Gaussian (LG) beam. Simulated results are found to be consistent with the experimental results. Vortex-like petal patterns are observed when the LG beam interferes with the Gaussian beam. The number of petals is found to be equal to the absolute TC value of the LG beam, and the rotational direction of the interference patterns is related to the TC sign: at a positive TC value, the interference patterns show a clockwise rotation, whereas at a negative TC value, the interference patterns show a counterclockwise rotation. The OAM state can be accurately determined based on the interference patterns only when the spot size of the LG beam is smaller than that of the Gaussian beam. When the spot size of the LG beam is close to that of the Gaussian beam, the interference patterns reflect only the TC value and the TC sign cannot be identified. Compared with the conventional interferometers, the proposed interferometer can obtain a stable interference pattern and directly obtain the OAM state of the LG beam. The experimental phenomenon is obvious. The findings of this study provide a reference for the theoretical analysis of the interference between the LG and Gaussian beams and establish a research foundation for the spin-orbit interaction between light and matter.

This paper introduces a hybrid modulation end-to-end communication system based on convolutional neural network (CNN) to optimize the structure and performance of the hybrid quadrature amplitude modulation (QAM) and pulse-position modulation (PPM) modulation system applied to visible light communication. This scheme used the designed loss function to train the network in multiple stages to realize QAM and PPM. Accordingly, the two modulations were combined to realize hybrid modulation. With regard to demodulation, a method for recognizing the pulse of the received signal by changing the kernel size of CNN is proposed to improve the pulse-recognition accuracy and reduce the calculation complexity. The simulation results show that under the additive white Gaussian noise and Rayleigh fading channels, the proposed technical scheme exhibits fine generalization ability for the hybrid modulation method with different pulse time slots and modulation levels. When the symbol error rate is 10-3, the error performance improvement range is 0.4 dB?2.8 dB compared with the traditional demodulation method.

In laser processing and other fields, the focus of a fiber laser is often used to obtain a high-power-density spot. To analyze the focusing properties of mixed modes in a step-index fiber, based on the generalized Huygens-Fresnel diffraction formula, this study numerically calculates the focusing intensity distribution of the incoherent and coherent superpositions of the fundamental (LP01) and high-order linear polarization modes in a step-index fiber. The focusing properties of the mixed modes relative to the single LP01 mode are simulated and analyzed, and the change law of the average power density of the focused spot and focus shift is studied with the changing mode ratio and intermode phase difference. When the mixed modes are incoherently superimposed, with the increase in the fundamental mode ratio, the power density of the focused spot increases and the focus shift decreases. Moreover, when the mixed modes are coherently superimposed, the fundamental mode ratio and intermode phase difference affect the focusing effect. Therefore, we can achieve the purpose of focusing the spot power density higher than that of the fundamental mode and reducing the focus shift of the mixed modes by reasonably controlling the fundamental mode ratio and intermode phase difference.

The bandwidth limitation of high-power light sources and high-sensitivity detectors, as well as the signal inter-symbol interference caused by the multipath effect of seawater channels, seriously affect the performance of underwater wireless optical communication (UWOC) systems. Aiming at this problem, an inverse hyperbolic sinusoidal function variable step size dual-mode blind equalization algorithm based on fractional spaced equalizer is proposed in this paper. The algorithm combines the variable step size constant-to-mode fractional spaced equalizer algorithm and the decision directed least mean square mode-fractional spaced equalizer algorithm through the mixed parameters for convex combination, and iteratively updates the mixed parameters to achieve the adaptive switching between the two equalization algorithms does not need to manually set the switching threshold, and has a small mean square error under the condition of ensuring rapid convergence, and at the same time, it does not need to occupy additional bandwidth. The simulation results show that the dual-mode blind equalization algorithm can quickly converge under various signal-to-noise ratios, reduce the steady-state mean square error, effectively suppress inter-symbol interference, and improve UWOC systems error performance.

A quadrature demodulation algorithm for large dynamic range measurement of open-loop fiber optic gyroscope is studied in this paper. The interference signal is directly sampled every π/6 every cycle, and 12 sampling points are obtained for phase demodulation. The large dynamic range measurement of open-loop fiber optic gyroscope is realized by using fringe counting method. The relationship between the sampling phase error of phase modulator driving signal and interference signal of open-loop fiber optic gyroscope system and the demodulation error of quadrature demodulation algorithm is analyzed in detail. The evaluation parameters of modulation depth error EM and modulation initial phase error EW are constructed by using the extracted 12 sampling points, and the sinusoidal modulation signal parameters are feedback controlled to ensure the demodulation accuracy. The results show that in order to make the phase demodulation error of open-loop fiber optic gyroscope within ±10-6 rad (scale factor is 1.134 s, gyro output angular velocity error ±0.18 (°)/h), the error of modulation frequency fe of sinusoidal modulation signal should be less than ±0.072% (97.31 kHz), and the error of voltage peak to peak Vπ should be less than ±0.1% (3.654 V), the modulation initial phase error should be less than ±16.226 mV and the modulation depth error should be less than ±12.483 mV, and the digital sampling phase error should be less than 5.625×10-4 rad.

Aiming at the problem that the Euclidean distance in the weighted K nearest neighbor (WKNN) algorithm can not effectively represent the actual distance relationship between measurement points in the indoor visible light fingerprint positioning system, an improved WKNN algorithm based on weighted Euclidean distance measurement is proposed in this paper. The algorithm assigns different weighting coefficients to different signal strength differences according to the attenuation characteristics of the received signal strength varying with the actual distance. The simulation results show that under the same environmental conditions, compared with the WKNN algorithm using European distance measurement and Manhattan distance measurement, the average positioning error of the improved algorithm is reduced by 37.5% and 34.3%, respectively.

A high-precision long-term online downhole temperature and pressure monitoring system based on optical fiber Bragg grating (FBG) and extrinsic Fabry-Pérot interferometer (EFPI) is developed in this paper. The system monitored the pressure through the change in the EFPI cavity length and the temperature through the change in the FBG wavelength, and simultaneously realized the temperature compensation of the pressure. Calibration results showed that the system has the pressure measurement range of 0.1‒42 MPa, the pressure sensitivity of 203.8 nm/MPa, the precision of ±0.05%F.S (F.S means full scale), and pressure resolution of 0.0007 MPa. The system is demonstrated in a production well in Zhuangxi, Shengli Oilfield, and the downhole temperature and pressure are recorded in real time for 5 months. The results show that the system can reflect the production status of oil wells and realize the online monitoring of important parameters, which has important guiding significance for improving oil and gas recovery.

The direction of arrival estimation, which is based on microphone arrays, has crucial strategic significance in the field of field sensor network theoretical research and engineering practice. Multi-channel microphone arrays often produce orientation errors due to the inconsistencies in the amplitude and phase of each channel when sound sources are oriented. In response to this problem, this study proposes an adaptive correction method for channel inconsistencies in a microphone array. This method constructs the objective cost function of the signal spectrum space based on the principle of subspace decomposition. Furthermore, it combines the simulated annealing algorithm model to obtain the correction matrix of the array by minimizing the cost function. Finally, the 8-element microphone array is simulated by the computer using the above method, and the 4-element microphone array is used for the actual test.The simulation and actual test results confirm the feasibility of the correction method.

When an aircraft reenters the atmosphere at hypervelocity, a plasma sheath that can block communication with the ground is formed due to the air ionization on the vehicle surface. In this study, a plasma sheath model with the inhomogeneous electron density and electron collision frequency is established to investigate the plasma sheath characteristics on the surface of the reentry vehicle. The terahertz wave propagation in the plasma sheaths with different distribution characteristics is discussed based on the idea of the equivalent wave impedance in inhomogeneous media. The effects of different factors on the propagation characteristics of left-handed and right-handed circularly polarized terahertz wave in the plasma sheath are studied. The results show a periodic phase shift of the terahertz wave in the plasma sheath, which is mainly affected by the incident angle. This periodicity has nothing to do with wave polarization but is related to wave position and frequency. The propagation characteristics of the two polarization modes of terahertz waves greatly differ under the same factors at low frequencies. The propagation characteristics of the two polarization modes gradually approach with the transmission frequency increase.

Antenna array beamforming algorithm is simulated using Matlab2019b to optimize antenna array excitation for obtaining wide nulls and low sidelobe patterns. Comparative pattern analysis shows that adding quadratic constraints based on the original constraints and improving the covariance have the drawback of widening the main lobe. This study proposes a linear constrained minimum variance (LCMV) pattern correction algorithm based on parallel optimization of amplitude decile particle swarms to maintain the width of the main lobe while maintaining wide nulls and low sidelobes. The algorithm compares the characteristics of the antenna array excitation obtained using several algorithms, introduces preliminary information, optimizes only the magnitude of the weight vector to narrow the feasible solution space, improves the optimization mechanism of the particle swarm algorithm, and adopts the decile optimization method. The algorithm convergence is made more stable, and the particle swarm algorithm code is vectorized. A graphics processing unit is used to simultaneously update each particle, realize the particle swarm parallel algorithm, and speed up the computational time of the algorithm. The simulation results show that the algorithm can achieve a widening of nulls and low sidelobes while maintaining the width of the main lobe. In addition, it has the best effect among the compared algorithms. Simultaneously, the convergence of the particle swarm parallel algorithm based on the amplitude decile requires fewer iterations and it has faster computational speed, and the improvement is more obvious when the antenna scale is larger.

Aiming at three-dimensional topography measurement based on structured light projection, a dual-wavelength fringe projection correction algorithm based on color segmentation is proposed in this paper. A color fringe image is added on the basis of the wavelength-selective dual-fringe projection phase unwrapping algorithm, and the fringe image is divided into different fringe regions by color. Phase unwrapping is performed on the phase map by means of a look-up table in different fringe regions. The experimental results show that the algorithm has the advantages of wide measurement range, small amount of calculation, high precision and fast speed. The experimental results show that the algorithm has the advantages of wide measurement range, small amount of calculation, high precision and fast speed, and can effectively solve the problem of repeated lookup tables when the selected wavelength is short.

As a biconical interference model is constructed to design a double-period graded photonic crystal (GPC) structure, we design a GPC lens with graded dielectric column size based on the graded light intensity distribution of the GPC structure, and study the influence of the inner and outer cone interference angle on the GPC period and the focusing characteristics of the lens. It is found that the sine difference of the inner and outer cone angles of the interference beam determines the large period of the lens, while the outer cone angle directly affects the small period. When the large period of the lens is fixed, the smaller the small period is, the better the focusing effect will be. What’s more, when the small period is fixed, the smaller the large period is, the larger the numerical aperture of the lens will be. The designed lens can achieve sub-diffraction-limit focusing. This research is helpful for the application of lenses in optical coupling, optical integration, optical display, and imaging.

We design a novel wireless laser power transmission system in which the process of wireless power transmission to a dynamic target was completed based on the rotation of just one component. The design of this system not only reduces the load-bearing of the gimbal, but also avoids the degradation of beam quality caused by lens vibration when tracking dynamic targets. As a result, this WLPT system has been verified by tracking an unmanned aerial vehicle at 122 m away with an offset distance of ±26.7 mm. We believe this system offers great potential in high-power, long-distance dynamic laser power transmission.We design a novel wireless laser power transmission system in which the process of wireless power transmission to a dynamic target was completed based on the rotation of just one component. The design of this system not only reduces the load-bearing of the gimbal, but also avoids the degradation of beam quality caused by lens vibration when tracking dynamic targets. As a result, this WLPT system has been verified by tracking an unmanned aerial vehicle at 122 m away with an offset distance of ±26.7 mm. We believe this system offers great potential in high-power, long-distance dynamic laser power transmission.

To improve the automation of optical measurement equipment in space target measurement processes, an automated measurement method is proposed in this study. First, the composition and automatic operation process of the system are introduced. Second, the function to be optimized is designed by maximizing the number of observation targets. The observation time can be used for cataloging, and the particle swarm optimization algorithm is used to propose an observation plan. Finally, to address the problem that the target cannot be detected outside the field of view when the guidance data error is large, two active search strategies are proposed. Simulation calculation results show that the optimized observation plan enables the detection of individual targets with overlapping arc segments and automatically and reasonably controls the observation time of each target. The helical scanning search is simulated for a certain type of optical measurement equipment, achieving a maximum offset velocity of 0.126 (°)/s and a maximum acceleration of -0.053 (°)/s2, and it is continuous and stable. The combination of expansion and contraction search strategies can improve the capture probability of the target and enable the switch to the original guidance mode smooth at the end of the search. Test results show that the proposed method can effectively improve the automatic operation level of equipment and enhance the equipment efficiency.

The calibration of existing multicamera systems with no common fields of view is challenging, as it is extremely cumbersome. To solve this problem, this study proposed a calibration method for multicamera systems based on a rotating calibration plate. First, the axis of rotation was fitted and a calibration coordinate system was established by fitting the trajectory of the rotating target. Second, a single complete calibration image was captured by each camera, and then the pose relationship between the camera and the turntable system was estimated using the PnP algorithm. Third, the angle of the table was converted into a rotation matrix and translation vector of the calibration plate using the Rodrigues rotation formula. Finally, the multicamera system was estimated using these transformation relationships. The experimental results show that the proposed method is not limited by the field of view of the camera, can quickly and automatically calibrate the multicamera system, and also meets the needs of large-scale measurement in terms of measurement accuracy.

Micro-light-emitting diodes (Micro-LEDs) offer many unique advantages in materials, devices, technologies, and process applications. In the future, display devices will evolve in the direction of multi-functional integration, such as lighting, swiching, and sensing, Micro-LEDs often require low-current-density driving, and the driving mode faces considerable challenges. To modulate LED devices with a low current input, herein, we propose a new type multifunctional integrated light-emitting triode device that integrates light emission and regulation functions, based on the same GaN material used in LEDs and process platform. The device shows a vertically integrated structure comprising bipolar transistors and LEDs. The number of electrons moving to the light-emitting active layer can be controlled by changing the base voltage, and the luminous effect of the device is simultaneously adjusted. Based on the current gain effect of bipolar junction transistor (BJT), the input current under the same light effect can be reduced from the milliampere to the microampere level and a highly linear regulation is achieved within a certain voltage range. The device can be controlled and driven using low-power signals and is expected to become a revolutionary technology for high-density and high-integration smart displays.

This study proposes a broadband linearization scheme based on a single-drive dual-parallel Mach-Zehnder modulator (SD-DPMZM) to improve the spurious-free dynamic range (SFDR) of microwave photonic link in broadband transmission. The third-order intermodulation distortion (IMD3) is theoretically eliminated using an 180° hybrid, thereby optimizing the biases of the dual-parallel Mach-Zehnder modulator. The simulated results show that IMD3 is completely suppressed when the input signal had two tones. An IMD3 suppression and SFDR improvement of 68 dB and 14.5 dB, respectively, are generated when SD-DPMZM is driven by two radio frequency tones of 10 and 10.01 GHz. Furthermore, results show that SFDR can remain above 114.3 dB·Hz2/3 when the signal is changed from the X-band to K-band.

In this study, graphite/Cu composite coatings were prepared on Cu substrates using laser-assisted low pressure cold spray (CS) technology. In addition, the microstructural characteristics and thermal/electrical conductivity of composite coatings with different graphite contents were studied. The results show that both graphite and Cu particles in the composite coating undergo significant plastic deformation, and the plastically deformed graphite particles are embedded in the plastically deformed Cu particles, forming a composite coating. Using laser heating, the graphite and Cu particles in the composite coating are well bonded, resulting in the good compactness of the composite coating. The thermal and electrical conductivities of the CS-Cu coating increase from 66.2 W/(m·K) and 7.12 MS/m to 136.6 W/(m·K) and 14.65 MS/m, respectively, due to the laser heating. With the addition of 5% graphite to the coating, the thermal conductivity of the composite coating is further increased to 209.8 W/(m·K). However, with the continuous increase of the graphite content in the composite coating, the number of the inner interface of the coating increases, the interface thermal resistance and the scattering effect on electrons are enhanced, resulting in the decrease of the thermal conductivity and electrical conductivity of the composite coating.

The traditional laser drilling method is inefficient and slow. Preparation of medical titanium alloy microhole substrate by laser high-speed polygon mirror can prepare tens of thousands of microhole structures within 100 s. We primarily focused on the preparation of medical titanium alloy microhole substrates using a high-speed polygon mirror. The effects of laser parameters and the polygon mirror’s scanning speed on the drilling aperture, depth, taper, and hole morphology were investigated. The high-repetition-rate laser with a power of 500 W yields a hole diameter of 100 μm, depth of 156 μm, and zero taper. The maximum scanning speed of the high-speed polygon mirror reaches 1000 m/s. Before processing, hole spacing, row spacing, and other related parameters were determined. A processing efficiency of 10000 holes per second is achieved. In addition, to increase the machining aperture, an optimized machining technology was proposed to correct the scanning position deviation of the polygon mirror during the scanning process. A final hole diameter of 150 μm can be achieved using this method. In addition, this method is beneficial to biomaterial coatings and deposit drugs on the titanium alloy microhole substrates.

We investigated the effect of dual-beam energy ratio on the microstructure and properties of Q355ND steel laser-metal active gas (MAG) hybrid welding joint. Here, the Q355ND steel was welded using high-power dual-beam laser-MAG hybrid welding. Subsequently, we analyzed the effect of laser energy density distribution on weld cross section forming, weld penetration depth, and weld width by adjusting the energy ratio of dual-beam and obtained the well-formed butt joint of 27 mm thick plate Y-type single side welding. Furthermore, we analyzed the microstructure and distribution of the main elements of the welding seam, weld zone, and heat-affected zone, and measured the microhardness of the welded joint. Results show that the weld penetration depth first decreases and then increases with increasing laser energy ratio. Additionally, the change in the energy ratio has insignificant effect on the weld width, and the deepest weld penetration depth is obtained when the laser energy ratio is 0.75. Moreover, the microstructure of the butt joint welded with the optimum energy ratio is mainly ferrite and bainite, and the elements are evenly distributed near the fusion line of the welded joint without element migration. The hardness peak near the heat-affected zone of the fusion line and that of the weld zone was considerably higher than that of the base metal. The hardness of the heat-affected zone decreased with the increasing distance from the weld center.

Process parameters are the key factors determining the quality of laser welding aluminum alloys. Therefore, to ensure good weld morphology quality, a combined response surface methodology and particle-swarm optimization (RSM-PSO) algorithm was proposed to explore the optimal process parameters to laser weld 2 mm-thick 6061 aluminum alloy sheets. The experimental design of the fiber laser welding was performed using Desk-Expert 10.0 software. In response to weld collapse and sheet bending, multiple linear regression of the welding parameters was established. The effects of various process parameters on the welding quality were analyzed, and the particle-swarm intelligence algorithm was used for optimization. The results show that under the experimental conditions of this study, the scanning speed and defocusing have a strong influence on the weld collapse, and the laser power and scanning speed have a great influence on the sheet deformation. The optimal process parameters are laser power, scanning speed, and defocusing amount of 2629 W, 6.85 mm/s, and -0.18 mm, respectively. Under these parameters, the collapse depth and bending of the 6061 aluminum alloy sheet are only 85.66 μm and 1.2 mm, respectively, indicating that the parameters obtained via this algorithm can effectively improve the welding quality.

To examine the influence of laser power on the stability of laser-MIG hybrid aluminum alloy welding process, a high-speed camera and NI USB-6251 data acquisition card were used to study the arc parameters, droplet transfer behavior, and spatter generation behavior in the hybrid welding process. The results indicated that as the laser power increased, the peak current of the arc decreased, whereas the peak voltage increased. Under the laser power of 4 kW, the projected droplet transfer was dominant, and short-circuit transition occurred occasionally. When the laser power increased slightly, the short-circuit transition phenomenon disappeared. However, when the laser power increased to 5.5 kW, there was a transition form of one droplet every two pulses in the stable transition of one drop per pulse, reducing the stability of the droplet transition. As the laser power increased, the metal vapor shearing force on the liquid metal on the keyhole wall increased, resulting in an increased number of spatters above the keyhole wall. When the laser power was 4‒4.5 kW, the number of spatters on the rear keyhole wall was significantly higher than that on the front keyhole wall. However, when the laser power was more than 5 kW, the number of spatters on the front and back keyhole walls was almost equivalent. In addition, the force of the molten pool metal on the keyhole walls was analyzed, and the mechanism of spatters above the keyhole wall was summarized.

In this study, laser shock imprinting technology was used to prepare a hydrophobic copper foil surface with multilevel grooved microtexture. First, a micro-mold with multilevel groove characteristics was prepared by laser marking. Then, the microtexture of the multilevel groove on the micro-mold was copied to the surface of a workpiece using laser shock imprinting technology. The effects of the number of laser shocks and the thickness of the soft film on the surface morphology and static contact angle of the multilevel grooved microtextured hydrophobic surface of the workpiece were studied. The results show that when the number of laser shocks increases from 1 to 7 and the soft film thickness decreases from 300 μm to 100 μm, the degree of microtexture replication on the workpiece surface gradually increases. Simultaneously, the static contact angle and hydrophobicity of the surface increase. By measuring the microtextured surface elements and components of the workpiece, it is found that the multilevel grooved microtexture of the hydrophobic surface remains unchanged after being placed in air, water, and mass fraction 3.5% NaCl solution for 21 days. It shows that the hydrophobic surface prepared by this process has excellent aging properties.

Liquid crystal polymer (LCP) has gained attention in 5G packaging because of its excellent performance as a substrate material in microwave/millimeter-wave circuits. In this study, ultraviolet nanosecond laser was used to conduct the film removal experiment on LCP flexible copper plate. At the repetition frequency of 200 kHz, the effect of different scanning layers, scanning speed, and average power on the film removal depth of LCP material was studied using the control-variable method. To reduce the effect of heat on electronic devices and flexible circuit boards, the variation law of heat-influence zone at the frame of LCP substrate with laser parameters was analyzed based on the LCP characteristics and actual processing results. The experimental results show that when the scanning layer number is five, the scanning speed is 600 mm/s, and the average power of excitation light is 2.1 W, the machining depth can reach 49.84 µm, the uniformity is good, and the heat affected zone at the frame is small, reaching 28.43 µm. The experimental results may provide a theoretical basis for LCP substrate in flexible circuit packaging.

A fiber laser that can emit multi-wavelength simultaneously and each wavelength is single longitudinal mode is studied in this paper. The laser contains multiple laser composite resonators composed of optical fiber and fiber devices, each laser composite resonator uses a length of erbium-doped fiber as the gain medium and a fiber Bragg grating as the wavelength selector, so that each laser composite resonator can emit a specific wavelength at the same time, and the number of laser wavelengths emitted from the laser can be changed by changing the number of laser composite resonators. Each laser composite resonator is composed of two sub-resonators, by adjusting the cavity length difference between the two sub-resonators, the frequency interval of the composite resonator can be equivalent to the gain linewidth, so that the composite resonator will emit single longitudinal mode laser.

In this paper, the effects of different incident angles of laser on paint removal depth, surface morphology, and roughness are studied. By changing the angle between the laser beam and the sample, the laser paint removal test at different angles is completed, and the 2024 aluminum alloy is used as the research object to detect and analyze the surface paint removal effect. Under the same conditions, the paint removal depth increases first and then decreases with the decrease of the laser incident angle. When the laser incident angle is 70°, the maximum paint removal depth is reached. When the laser energy density is 5 J/cm2, the paint removal depth at the inflection point increases by 160.57 μm compared to 40°, and this difference increases as the paint thickness increases. In addition, the incident angle of the laser will alter the surface roughness of the sample. Similarly, the minimum surface roughness is obtained at 70°, which is increased by 0.438‒0.812 μm when compared to the initial surface roughness. The laser incident angle can also reduce the length of the smoke plume in the laser transmission direction and the concentration of plume particles. When the laser energy density is 0.5‒2 J/cm2, the paint removal mechanism is the main ablation effect, but when it exceeds 2 J/cm2, it becomes a combined effect of ablation and thermal expansion.

In the repair process of some types of equipment, the equipment must be disassembled and the faulty parts must be replaced before reassembly. Many types of adhesives are used when such equipment is manufactured, which should be removed during the repair process. Once repairing is completed, the equipment should be assembled and sealed using the necessary adhesives. In the current repair technology, adhesive removal is entirely artificial, which is inefficient and the effect is unideal. Laser cleaning technology is a new surface cleaning technology that shows high cleaning efficiency and accuracy and has been successfully used in the cleaning of oxides on metal surfaces, aircraft skins, semiconductor wafers, and other applications. This study examines the feasibility of applying the laser cleaning technology to some types of equipment repair. Moreover, the cleaning efficiencies and effects of different substrate materials, different adhesives, and different laser pulse energies are compared. Results show that the laser cleaning technology can remove adhesives from metal and glass surfaces but can cause irreversible damage to wood and circuit board surfaces.

In order to optimize the laser welding process of industrially pure titanium TA2, a nonlinear transient thermal coupling model is established by finite element analysis method on the platform of ABAQUS software in this paper. The thermal stress field during laser welding of TA2 industrial pure titanium with a thickness of 6 mm is analyzed. Considering the temperature dependence of the material thermophysical property parameters, and the combined loading of the moving Gaussian surface heat source and the cone heat source is realized by FORTRAN programming. The reliability of the composite heat source is verified by experiments, and the maximum temperature at different positions in the molten pool and the cooling rates in different temperature ranges under different process parameters are compared and analyzed. The results show that both the laser power and the welding speed have a great influence on the maximum temperature of the molten pool and the cooling rate in different temperature ranges, and the molten pool is more affected by the welding speed.

This study investigates the effect of process parameters on the relative density and microscopic pores of samples formed using selective laser melting (SLM) technology. To analyze and discuss the 18Ni-300 maraging steel, an orthogonal experimental scheme is designed. With the three-dimensional SLM forming process parameters (laser power, scanning speed, and hatch spacing), the relative density of printed parts is studied and analyzed based on the gray theory, the corresponding relationship between the relative density and volume energy density is obtained, and the microstructure and holes of the material are analyzed. The results show that when the volume energy density is 30‒50 J/mm3, the relative density is low. In addition, increasing the volume energy density within this range can significantly improve the relative density of the material and keeping the volume energy density at 50‒150 J/mm3 can achieve high relative density. With increasing relative density, the holes in the sample gradually becomes smaller and its shape becomes regular. When the relative density reaches 99%, the tiny holes with a regular shape are obtained. The samples with high or low density can be obtained by changing the range of process parameters.

The periodic Ag nanonetwork structure formed via localized surface plasmon resonance (LSPR) has potential applications in the deep-ultraviolet to near-infrared wavelengths. However, the relationship between the transmission and conductivity characteristics and the morphology of the nanonetwork structure remains to be further studied. In this paper, first, the effect of Ag nanoparticle morphology on the LSPR characteristics is theoretically analyzed using finite element analysis. Then, the effect of the deposited Ag coverage on the light transmission properties of the periodic nanonetwork structure is investigated. Finally, by establishing an equivalent resistance model, the resistivity and transmittance of the Ag nanonetwork structure are studied and analyzed. The results show that Ag nanonetwork structure with higher light transmittance and lower sheet resistance can be obtained when Ag nanoparticles with a certain thickness are deposited.

A broadband switchable bifunction terahertz polarization converter based on a Dirac semimetal is proposed in this paper. The polarization converter comprises a resonant structure and a gold film separated by a polyethylene cyclic olefin copolymer dielectric layer. By adjusting the Fermi energy level of the Dirac semimetal, the designed metasurface can be switched from a quarter-wave plate to a half-wave plate. The numerical simulation results revealed that when the Fermi energy level is 70 meV, the metasurface is a quarter-wave plate, which can convert the incident linearly polarized wave into a left-handed circularly polarized wave at frequency ranging from 1.955-2.071 THz. The plate converts the linearly polarized wave into a right-handed circularly polarized wave at frequency ranging from 2.606-3.490 THz. Furthermore, the ellipticity associated with frequency ranging from 1.955-2.071 THz and 2.606-3.490 THz is close to ±1. The metasurface behaves as a half-wave plate capable of converting y-polarized waves into x-polarized waves at frequency ranging from 2.599-3.638 THz. The corresponding polarization conversion rate exceeds 90% when the Fermi energy level is 160 meV. In addition, compared with other structures, the structure can maintain the same performance at a large incident angle, and its polarization switching performance can be dynamically tuned by changing the Fermi energy level of the Dirac semimetal. The design method can be employed in various fields including wireless communication, terahertz sensing, and imaging.

The output characteristics of GaAs solar cells irradiated by a continuous semiconductor laser with a wavelength of 532 nm are investigated in this paper. The damage to GaAs solar cells under high power density laser is investigated via X-ray diffraction, photoluminescence, electroluminescence, and optical microscopy. The results show that when the laser power density of 0.06 W/cm2, the conversion efficiency of the solar cell is the highest, which is 26%; after the cells are irradiated for 180 s by a laser with a power density of 15 W/cm2, the performance of the cells began to decay, the diffraction intensity decreased, the full width at half maximum increased, and the crystal quality deteriorated. High power density laser irradiation can cause cracks on the surface of the GaAs solar cells, and the cracks emitted no light during the electroluminescence test. In addition, the fluorescence intensity in the irradiated area decreased significantly, and the luminescence peak is shifted to the right. The comprehensive characterization results show that high power density laser irradiation will degrade the crystal quality of GaAs solar cells and generate nonradiative recombination centers. These centers will generate internal defects in the material and lead to a reduction in the solar cell photoelectric conversion efficiency.

Graphene-based composite materials have broad application prospects in infrared detection stealth, but how to improve its broadband omnidirectional infrared absorption characteristics is still lack of systematic research work. In this paper, a binary graphene-based composite micro-nano infrared absorber with alternating distribution of optical medium layer and graphene layer is designed, and its infrared absorption characteristics are systematically studied by transmission matrix method. The results show that the resonant coupling effect of gain and loss can be generated in the structure by adjusting the number of graphene layers and the structure. The absorption rate is higher than 80% in the whole band of 8-14 μm, higher than 90% in the band of 10.0-13.3 μm, and the maximum bandwidth is 3.3 μm. In addition, the micro-nano structure exhibits polarization insensitivity of infrared absorption in wide angle range (0°-60°) with oblique incidence. The results of this study provide a new idea for the design and application of a new generation of graphene-based flexible wide-band and large-angle tunable infrared absorption micro-nano structure, and also provide a feasible technical method and realization path for a new generation of flexible lightweight stealth or camouflage film materials.

By changing the forming parameters and heat treatment temperature, the forming quality of selective laser melting (SLM) TC4 titanium alloy was optimized. The results indicated that the relative density of the TC4 sample could exceed 99.90% under the given process parameters. In particular, the highest relative density, 99.993%, was obtained with a layer thickness, laser power, scan speed, and hatch spacing of 40 μm, 200 W, 1500 mm/s, and 0.065 mm, respectively. Furthermore, the corresponding tensile strength reached 1149 MPa and 1111 MPa and the relative plasticity was as low as 8.1% and 5.1% for X/Y and Z directions, respectively, owing to the existence of a large amount of martensite α' phase inside. Moreover, the martensite α' phase gradually decomposed to the (α+β) phase through heat treatment. Therefore, the tensile strength gradually decreased as the plasticity increased when the heat treatment temperature increased from 650 °C to 950 °C. After heat treatment at 950 °C, the tensile strength of the SLM TC4 samples decreased to 78.9% and 80.5% of that before heat treatment, while the elongation increased by 103.7% and 152.9% for the X/Y and Z directions, respectively.

A close-distance vehicle front-view Tessar lens with strong distinguishability and broad field of view was designed based on artificial intelligence target recognition. Using ZEMAX software, parameter optimization design is carried out by controlling geometric aberrations such as field curvature and distortion. When the designed lens has F-number of 3.4, focal length of 6 mm, maximum field of view of 50°, and depth of field of 10 m, the modulation transfer function of the entire field of view at the spatial frequency of 107 lp/mm is higher than 0.65, and the distortion is less than 0.305%, which meets the design requirements. According to the Monte Carlo study, the tolerances are within the machinable range, making them suitable for conventional production and assembly.

In comprehensive gymnasium, the lighting system suffers from disadvantages such as large number of lamps, low utilization rate, and large initial investment. Based on this, according to the class V lighting standard, taking power consumption as the optimization goal, and choosing a greedy algorithm, we propose an optimization scheme for the position and projection angle of lamps for handball courts. Furthermore, based on the existing lamps, an optimal adjustment scheme for the number of switches and projection angles of lamps in basketball and volleyball courts is proposed. Taking the venue of the 14th National Games as an example, compared with artificial lighting, the number of light-emitting diode lamps in the handball venue is reduced by 16, the total power is reduced by 19416 W, and power consumption is reduced by 26%. The power consumption of lamps and lanterns in basketball and volleyball courts is decreased by 31% and 56%, respectively. The optimized lighting system based on the greedy algorithm can effectively reduce the number of field lamps. The optimal adjustment of lamps between different competition events improves the lamp-utilization rate, thereby reducing the early purchase and installation cost as well as considerably saving energy in the later operation stage.

A metasurface with a trapezoidal unit structure is proposed to realize the free regulation of visible light beams. To achieve the adjustment from 0 to 2π transmission phase at the target wavelength, the upper and lower bases and width of the silicon nanocells are changed, and the transmission phase is modulated. The metasurface designed with this structure can control linearly and circularly polarized lights simultaneously and realize focusing under the incidence of both linearly and circularly polarized lights with a wavelength of 640 nm. Additionally, under the incidence of linear polarized light, the focusing characteristics and the influence of the lattice period on these characteristics are studied.This research proposes new ideas for the integrated optics based on the design of metasurface structures.

Herein, a vehicle-mounted head-up display system based on the reflective microprism array waveguide structure is proposed. The effects of the inclination angle, number of regions, arrangement period, and incident light width of the reflective microprism array structure on the stray light, continuity of exit pupil expansion, and uniformity of illumination are analyzed. The design method using the optimal parameters is proposed. In response to the vehicle requirements of a field of view of 10°×5° and an eyebox of 130 mm×50 mm, a specific optical waveguide design and simulation are performed. Results show that the uniformity of illumination in each field of view of the proposed system is greater than 64% and that a full-color display can be realized. Moreover, the overall volume is less than 6.5 L. The proposed structure and method are expected to be applied to the field of vehicle-mounted head-up display systems to reduce their volumes.

To effectively improve the space usage of optical systems for the light-emitting diode (LED), a freeform surface optical lens with a negative focal length transmission structure was designed. The optical lens was divided into two parts, including the transmission collimating module and reflection collimating module. The collimating lens was designed using geometrical optics, Snell’s law, and the law of energy conservation. The two-dimensional curve data of the freeform surface for the collimating module was obtained through iterative calculations with Matlab software, which was then imported into Solidwork software and rotated 360° around the central axis to obtain the three-dimensional solid model. Finally, the model was introduced into the optical simulation software, Lighttools, for light tracing and optimized according to the spot situated on the receiving surface. The optimized collimating lens was simulated with an optical energy utilization rate of 88.45% and a beam angle of ±2.23°. The results show that using a negative focal length transmission structure design can effectively reduce the volume of the collimating lens by 63.13% and improve the ability to control LED beams compared with the conventional single transmission freeform surface collimating lens.

To mitigate the demand for ultrahigh precision thermal control in the field of semiconductor lithography, a thermal control method based on model prediction is proposed in this paper. The step and pseudorandom thermal disturbance input signals of a lens system are generated. The temperature response data of the lens system are obtained using a high precision temperature-measurement system, and the thermal response model of the lens system is obtained via the model identification method. The rolling optimization strategy is used to derive the model’s predictive thermal control law, and the precision lens system’s thermal control experimental platform is established. The thermal control experiment results show that the thermal control method has a fast convergence speed, strong anti-interference ability, high precision, and the temperature control error is controlled within ±8 mK. The thermal-phase-difference test results show that the control method successfully suppresses the lens system’s focal plane drift. Further, the method is suitable for application in the field of high-end equipment with strict temperature control accuracy requirements.

The all-optical wavelength conversion technology based on four-wave mixing is important for all-optical signal processing. Wavelength conversion is the process of converting blocked data to other idle wavelengths for output through a wavelength converter, which can solve the problems of insufficient resource allocation and reduced communication quality. Both silicon-based waveguides and photonic crystal fibers can be used for wavelength conversion; however, for short distance communication, silicon-based waveguides are more advantageous. In this study, a novel MEH-PPV (1-methoxy-4-(2-ethylhexyloxy)-p-phenylenevinylene) silicon-based optical waveguide is constructed, and its dispersion is controlled using the finite element method. The phase mismatch characteristics and nonlinear coefficients of the waveguide under an optimal structure are analyzed. A four-wave mixing mathematical model based on pump degeneracy is established by combining the transmission loss, phase mismatch characteristics, and nonlinear coefficients of the waveguide. The wavelength conversion effects under different signal and pump powers and waveguide lengths are also analyzed. The maximum wavelength conversion efficiency of the slot silicon-based waveguide with the MEH-PPV material as a sandwich is approximately 16 dB, and its conversion bandwidth is approximately 400 nm, revealing its wide scope of application in the field of all-optical signal processing.

Quantum secure direct communication (QSDC) breaks the structure of traditional secret communications. It directly sends a secret message through a quantum channel without first preparing the key. But in the actual quantum communication system, the eavesdropper Eve's attack on the device will lead to the leakage of secret information, and this eavesdropping will not be detected. In addition, since the current quantum transmission mode is still based on optical fiber transmission, it is impossible to avoid the influence of noise in the process of optical fiber transmission. Among these noises, collective dephasing noise and collective rotation noise are the most serious. In order to solve these problems, two measurement-device-independent QSDC protocols that can resist collective dephasing noise and collective rotation noise respectively are proposed. The information is transmitted through the measurement of an untrusted third party, which solves the problem of eavesdroppers' attack on measurement device. At the same time, the collective noise is avoided through no decoherence subspace. Through analysis, it is found that the protocol can effectively resist attacks and achieve absolutely secure communication.

In this paper, a symmetrical all-dielectric metasurface structure is designed to achieve a high-sensitivity dual-parameter sensor. After coating a gas-sensitive thin film on the metasurface, two Fano resonance peaks labeled as dip 1 and dip 2 are generated to measure the refractive index and gas volume fraction simultaneously. The calculation results show that the refractive index and gas volume fraction sensitivity of dip 1 are 1035 nm/RIU and -0.57 nm/%, respectively, and the refractive index sensitivity and gas volume fraction sensitivity of dip 2 are 543.6 nm/RIU and -0.87 nm/%, respectively. The sensor can be used for high-sensitivity measurement of two parameters, and the transmission spectrum obtained using the symmetrical structure is not affected by the polarization angle of the light source, improving the adaptability of the sensor to the light source, and it provides a new method for detecting the environment.

A matrix layer is often used in the packaging of fiber Bragg grating strain sensors, and the matrix layer’ structure influences the accuracy of the sensor’s strain monitoring of the structure to be measured. In this study, to obtain a better base layer structure, four-dimension parameters (distance from the loop structure to the middle section, middle section’s width, and depth of the groove) are taken as the sensor variables to investigate the effect of dimension parameters on strain sensitivity using finite element simulation. The structure-optimized sensor is built, tested, and the unknown parameters are calibrated to determine the sensor’s sensitivity, precision, and effective measurement range. The sensor is compared with a standard resistance strain sensor, and the subsequent optimization scheme is given.

It is crucial to characterize optical properties of nanomaterials for application and development of nanotechnology. Specifically, instead of averaging the observation across a large number of particles, measuring the spectra of a single nanoparticle has recently gained considerable attention, which can accurately and quantitatively analyze itself and its surrounding environment. Among various near-field and far-field approaches, the spatial modulation spectroscopy (SMS) technique can be employed to determine the extinction cross-section spectra using a high signal-to-noise ratio. In this paper, we introduce the modulation scheme, approach development, applications, and the latest research progress of SMS technique, and discuss its prospect for the future application.

Opioids are among the most abused drugs globally, and their adverse effects on human health and social security cannot be disregarded. Effective drug detection technology is important in drug control and drug crime prevention. As a new molecular spectroscopic analysis technology, surface-enhanced Raman spectroscopy (SERS) is expected to become an effective method for detecting trace drugs owing to its advantages of accurate identification, high sensitivity, simple operation, and fast analysis. This study gives an overview of the recent developments in the detection of opioids (morphine, heroin, and codeine) using SERS. In addition, this study proposes the future directions of SERS technology in the application of drug detection for the relevant research and case handling.

Lasers as a form of specialized radiation appeared in the 20th century. Laser technology is still evolving after more than 60 years of development. It has achieved positive outcomes in various fields, including cultural relic protection, and has various uses. This study analyzed the application of laser cleaning technology, three-dimensional laser scanning technology, laser Raman analysis technology, laser denudation technology, laser welding technology, and other progress in cultural relic protection research. The application characteristics of these laser technologies were examined, and the future direction of laser technology in cultural relic protection was provided to establish a new standard for laser technology and cultural relic protection-related research.

The design of new material structure is an effective way to improve the performance of the infrared detector. Antimony-based type-II superlattice InAs/InAsSb, as infrared photosensitive material, has stable structure, low dark current, high temperature operating characteristics and superior photoelectric conversion efficiency, which is the ideal material for developing infrared detectors at high temperature. This paper reviews the research progress of antimony-based type-II super-lattices InAs/InAsSb, introduces the performance of two kinds of infrared detectors applied in typical unipolar barrier structures, and prospects the development of antimony-based type-II superlattice InAs/InAsSb.

All-fiber optic current sensor is applied for micro-current detection, which can expand the application of optical fiber sensing technology in weak magnetic field detection. On the basis of analyzing the basic principle and main optical path structure of the all-fiber microcurrent sensor, the latest research results of the all-fiber microcurrent sensor are reviewed from three aspects: increasing the number of optical circuit cycles, improving the performance of the sensing fiber, and reducing the system noise. And the future development trend of all-fiber microcurrent sensor is prospected.

In this study, a spectral measurement method of key characteristic parameters, such as plasma density and electron temperature, is proposed for the ion extraction simulation study, which produces plasma through argon discharging. According to the argon plasma state, a particle population equilibrium model of kinetic reaction processes among the main particles is established. By comparing and analyzing emission spectra acquired in the experiment, information on corresponding plasma characteristic parameters can be obtained. The experimental results show that under the typical working conditions, the proposed spectral measurement method is used to obtain key parameters such as the density and electron temperature of the argon plasma in the jet region, thereby providing a reliable and practical measurement method for the simulation studies on the ion extraction process.

Detection of various physical and chemical indicators in the national standard of extra virgin olive oil necessitates the use of expensive physical and chemical analysis instruments and related professionals, which limits the supervision of olive oil market. In this study, a novel olive oil quality analysis algorithm based on the regional integral ratio of the three-dimensional fluorescence characteristic peaks is proposed, in which the characteristic fluorescence peaks of extra virgin olive oil, refined olive oil, and other edible vegetable oil are extracted using their three-dimensional fluorescence spectra. Ten samples were prepared, including four brands of extra virgin olive oils, refined olive oil, and adulterated olive oils, which are extra virgin olive oil doped with 10%-50% refined oil. The quality factor’s dynamic range for olive oil is 37 dB. It can also effectively identify various proportions of doped samples, brand extra virgin olive oil, and fake extra virgin olive oil. The experimental results show that the quality factor of the proposed analysis algorithm outperforms the samples’ three traditional physical and chemical indicators. Since the approach requires less fluorescence spectroscopy data than other fluorescence approaches, it can provide a new theoretical basis for the low-cost and rapid identification instrument of olive oil quality.

Currently, optical imaging technology has played an important role in deep-sea exploration. However, there is still a lack of research on subjective deep-sea video quality assessment, especially the lack of public deep-sea video quality assessment datasets. We construct a public deep-sea video quality assessment dataset with subjective quality labels, which includes five types of representative real deep-sea scene videos. The original deep-sea video sequences are augmented by two deep-sea video quality enhancement methods that are based on deep learning and fusion respectively, and two video quality degradation methods including Gaussian blurring and Gaussian noise. Subjective video quality assessment is conducted with 20 participants and the absolute category rating method is used for rating. Finally, we obtain a deep-sea video quality assessment dataset with 142 samples. The performance of 8 objective image/video quality assessment models is verified on this dataset. The results show that the current objective video quality assessment models need to be improved for the application in deep-sea video quality assessment. The deep-sea video quality assessment dataset is publicly available at http://ieee-dataport.org/documents/deep-sea-video-quality-dataset. It could help optimize and improve the objective deep-sea video quality assessment models and underwater image/video enhancement technology.

A model of X-ray CsI(Tl) scintillation screen based on the macroporous silicon is established, and the influence of X-ray energy on the X-ray CsI (Tl) scintillation screen’s light output is simulated and analyzed. An X-ray scintillation screen with a period of 10 μm and a side length of 8 μm was prepared, and an X-ray imaging device was constructed. The X-ray images of different X-ray source-tube voltages were measured. The light output of the X-ray scintillation screen was analyzed using MATLAB software. The results show that an increase in the thickness of the scintillation screen increases the average gray value of the scintillation screen, which is consistent with the simulation results.

In order to solve the mechanical positioning error of sub-aperture in stitching interferometric measurement, we propose a mechanical error compensation method based on genetic algorithm. The algorithm uses the matching degree of sub-aperture overlapping area as the fitness function, and then uses the error search algorithm to calculate and compensate the positioning error generated in the process of sub-aperture measurement. Through simulation and experimental verification, it is proved that the algorithm can compensate the sub-aperture mechanical positioning error. The simulation results show that the angle error calculation accuracy of the algorithm is better than 0.01°, and the displacement error calculation accuracy is better than 0.16 mm. The stitching surface after compensation is basically consistent with the simulation surface. The experimental results of stitching measurement of an elliptical cylindrical mirror with the curvature radius of 100 m show that the mechanical error compensation algorithm proposed can effectively compensate the mechanical positioning error introduced in the process of stitching measurement, and reduce the dependence of sub-aperture measurement on the accuracy of mechanical displacement table.