Vortex optical multiplexing communication technology can effectively improve the channel capacity of a communication system in an underwater channel. However, ocean turbulence causes the inter modal crosstalk of the vortex beam, degrading the performance of the communication system. To alleviate the modal crosstalk problem, this study presents a blind equalization algorithm based on a back propagation (BP) neural network. Four channels of vortex light are used for multiplexing transmission, and the random phase screen method is used to simulate ocean turbulence. After the BP blind equalization algorithm is implemented, the improvement in the system bit error rate is simulated and analyzed under conditions of varying ocean turbulence intensities, transmission distances, and vortex light multiplexing modes. The simulation results show that the blind equalization algorithm using the BP neural network can effectively reduce the impact of ocean turbulence on the bit error rate of the system, and the system performance significantly improves when the multiplexing mode interval is 2.

Generative adversarial network (GAN), a deep learning technique, is widely applied in the field of remote sensing because of its ability to extract features from large input data and generate more realistic forecasts of meteorological images. At present, however, the application of GANs in atmospheric motion vector (AMV) retrieval is rare, although AMVs are important data source for numerical weather prediction (NWP), especially in data assimilation. Based on this, a method for retrieving AMVs from geostationary satellite images using pix2pix, a type of GAN, is proposed. The pix2pix model is used to convert remote sensing images into wind vector fields at 850 hPa and 200 hPa. With the best data and model architecture, the AMVs obtained by this method are comparable to the AMVs retrieved using traditional algorithms. This method avoids the drawbacks of traditional algorithms, such as the inability to obtain complete wind fields at a certain level, difficulty of height assignment, and sparse AMVs at lower atmospheric levels. Case analysis shows that this method also performs well for specific weather systems.

In this study, the analytical expression of field distribution of twisted elliptical Gaussian Schell-Model beams after they pass through a Gaussian absorption-type obstacle is derived based on the Collins formula, and a basic twisted-beam model is obtained that effectively enhances the beam's self-healing capability. The effects of the light source parameters on the beam's self-healing properties are analyzed. The laws of intensity, coherence, and orbital angular momentum flux density transmitted when partially blocked by obstacles and the intrinsic connection among the three quantities are revealed. The intrinsic self-healing properties of twisted beams are explained. It is shown that appropriately reducing the coherence length and twist factor can enhance the beam's self-healing capability while preserving the characteristics of the twisted beam. The findings can help optimize the overall performance of partially coherent light transmission in free space, thus enhancing potential applications in free space optical communication, LIDAR, remote sensing imaging, and other fields.

A hierarchical modulation joint-physical layer network coding scheme is proposed to address the problems of incomplete channel condition utilization in asymmetric cooperative free space optical communication system and deterioration of data reliability due to high-order modulation. In this scheme, the information to be transmitted is classified first in data priorities at the source node followed by the allocation of transmission powers of different proportions to the prioritized data. Subsequently, the modulated data are sent to each node, and physical layer network coding is performed on the received data at the relay node. Finally, the relay node sends the encoded information to the destination node, and the destination node recovers the original information using the physical layer network coding scheme. The simulation results show that the bit error rate (BER) of the system can be reduced to values < 10-8 in high-signal-to-noise ratio (SNR) channels. The system can achieve SNR gains ≥1.5 dB by using this scheme in the intense atmospheric turbulence channel. This scheme yields better antijamming performance in intense atmospheric turbulence channel cases.

In this study, a high-sensitivity temperature sensor based on the sandwich multimode fiber Mach-Zehnder interferometer (MZI) with the virtual vernier effect is developed, and theoretical analysis and experimental verification are performed. The MZI was made by splicing a graded-index multimode fiber with a length of 20 mm between two pieces of stepped-index multimode fibers with lengths of 1 mm. The sandwich multimode fiber MZI was used as the sensor interferometer to evaluate the vernier effect, and the reference interferometer spectrum was obtained via frequency conversion of the interference spectrum of the fiber MZI through signal processing. The virtual vernier spectrum was obtained by superimposing waveforms of the sensing and reference interferometers. The experimental results show that the temperature sensitivity of the sensor system is 3.884 nm/℃ within the temperature range of 40-100 ℃, which is 37.346 times higher than that of a single-sandwich multimode fiber MZI. Compared with the traditional fiber sensors based on the vernier effect, the proposed sandwich multimode fiber MZI temperature sensor based on the virtual vernier effect has exceptionally high sensitivity, compact size, simple fabrication, low cost, and more reliable results.

To absorb the traffic uncertainty and map the service network to the physical network of the data center flexibly and efficiently, this paper studies the dynamic virtual data center mapping problem in an elastic optical data center network, where the service model is a hose model. First, the mapping model of a flexible virtual machine is established in an elastic optical data center network, and then the virtual machine placement algorithm based on virtual topology (VT-VMPA) is proposed. The VT-VMPA first converts the hose model into the pipe model before looking for the core virtual machine using the maximization of traffic volume as a guideline. Then, in descending order of service volume, the virtual machines that adhere to the resource constraints and are linked to the core virtual machines are combined into clusters. The communication bandwidth requirement is reduced after the cluster is mapped to the server. Finally, the cluster sets are mapped to the servers and virtual links between clusters are mapped to optical paths of the elastic optical data center network according to hop distance adaptive and shortest path principles. In comparison to previous methods, the proposed algorithm has decreased blocking rate by 27%, increased average time revenue by 117%, and decreased average bandwidth usage by 21%. It demonstrates that this method may increase network mapping speed while consuming fewer network traffic.

Because of dispersion and nonlinear effects in optical fibers, chaotic signals are difficult to obtain long-range synchronization. Meanwhile, due to the characteristics of pure optical domain signal processing used for optical injection chaos synchronization, it cannot be fused with existing communication systems' electric domain nonlinear compensation. As a result, this paper proposes a technical solution for realizing laser chaotic long-distance synchronization by combining dispersion management with optical domain-based nonlinear management based on the NLS equation. The synchronization and transmission characteristics at various transmission distances and different injection intensities are studied in detail. The findings demonstrate that the system is capable of achieving secure communication at a 1 Gb/s information rate, 1000 km of transmission distance, and 0.5 mW of injection intensity. The synchronous carrier correlation coefficient can exceed 0.97.

In the operation of lithium-ion batteries, particularly at the high discharge rate, the temperature of the battery significantly increases owing to heat generation. The most accurate and reliable sensor data for the battery management system (BMS) cannot be obtained by relying solely on temperature monitoring of the surface of individual cells. In-situ monitoring of lithium-ion batteries is one of the most effective methods to prevent the thermal runaway of lithium-ion batteries. A sensor is implanted in the heat source core of the lithium-ion battery, and the temperature change can be sensed immediately. A fiber optic composite temperature sensor is embedded in the inner center of the 18650 cylindrical lithium-ion battery, and the cross sensitivity of temperature and stress inherent in the Bragg grating sensing mechanism is eliminated using the Fabry-Perot (F-P) air cavity on the same fiber. The experimental results show that the internal temperature change of the battery can be monitored in real time in the charge and discharge stages, and the optical fiber sensor is compatible with the internal cell of the battery. This can facilitate the long-term health monitoring of large-scale lithium-ion battery-integrated components.

Conversion efficiency is the primary performance metric of a periodically poled lithium niobate (PPLN) waveguide and strongly correlates with temperature. Multichannel waveguides are limited by process issues; accordingly, ensuring consistency between each waveguide channel is difficult. This paper proposes an automatic temperature control method for multichannel waveguides. In this method, number of photons detected using multiple single photon detectors corresponding to the multichannel waveguide is obtained by field-programmable gate array (FPGA) chips. Thereafter, the photon number data of each channel is processed using equalization algorithms to determine the optimal temperature working point of the multichannel waveguide and achieve automatic adjustment of the waveguide temperature. FPGA chips are used in this study to achieve TEC driving control, construct a single photon detector with active quenching and fast recovery functions, and achieve automatic control of multichannel waveguide temperature using an equalization algorithm. Additionally, we develop a multichannel up-conversion single photon array detector with more uniform detection efficiency, greatly reducing initial manpower investment and avoiding errors caused by human factors.

We report the effective slowing and trapping of Cs atoms in an ultrahigh-vacuum apparatus. The heated Cs atoms in an oven are slowed using a Zeeman slower after the oven chamber and then trapped using a magneto-optical trap in a science chamber. Compared to the traditional vacuum pressure of ~10-7 Pa determined by the vapor pressure of Cs atoms in the oven chamber, the designed cold nipple and differential pumping tube are used between the oven and the oven chamber to achieve a lower vacuum pressure of ~3.6×10-9 Pa. This is beneficial for achieving and maintaining an ultrahigh vacuum in the science chamber. We demonstrate the performance of our apparatus through the effective slowing of Cs atoms and an optimal magneto-optical trap.

Instantaneous frequency measurements (IFM) are of great importance in modern electronic warfare. However, traditional methods based on electronics are facing considerable challenges because of their shortcomings. Particular attention has been paid to photon-assisted technologies owing to their large bandwidth, low loss, small size, lightweight, and electromagnetic interference immunity characteristics. In this study, the operational fundamentals of IFM are presented and analyzed based on a dual-path-imbalanced optical link. A demo system is also constructed with ordinary devices to measure the signal (0.5-18.5 GHz). It is demonstrated that the experimental and theoretical results are consistent, and we achieve excellent measurement accuracy (within ±60 MHz). This method has great potential for military applications owing to the simplicity of its front-end structure, which benefits from the use of the ordinary, phase-modulated optical link.

Non-linear errors introduced by a non-polarized beam splitter considerably impact the measurement accuracy of an interferometer. Therefore, it is necessary to measure phase shift characteristics introduced by the non-polarized beam splitter and explore the compensation method of the non-polarized beam splitter. Based on the Jones matrix method describing polarization states, we set up a measurement system for the transmission and reflection phase shifts of the non-polarized beam splitter and the effective compensation of the reflection phase shifts. In addition, the temperature characteristics of the phase shifts are experimentally investigated. The aforementioned system uses the balanced detection method of dual photo-detectors; this method exhibits high detection accuracy, good stability, and anti-interference and can also eliminate the fluctuation in light power. The results show that the reflection phase shift of the non-polarized beam splitter is larger than the transmission phase shift, and the overall phase shift is effectively reduced by combining two non-polarized beam splitters with almost the same reflection phase shifts. Moreover, the phase shift changes with a change in temperature. An inflection point of the minimum phase shift in the temperature characteristic curve is observed, which helps determine the optimal operating temperature of the non-polarized beam splitter.

Strong background noise can considerably reduce the probability of ranging success in lunar laser ranging and space target daytime laser ranging. The 1.2 m telescope laser ranging system of Yunnan Observatories uses an adjustable field diaphragm in the receiving light path to reduce the background noise by changing its aperture size. However, because of velocity aberrations, when the receiving field of view is reduced to a few arcseconds, the echo is blocked by the aperture and the detector does not receive the echo photon. To address this problem, a method of adding a two-dimensional tip/tilt mirror in front of the field diaphragm is proposed. The tip/tilt mirror can allow the deviated echo to be received by the detector through the aperture center. The deviating angles of the echo are measured by observing some high-orbit satellites and geostationary satellites. Additionally, the effect of using the tip/tilt mirror to correct the deviation angles is simulated and analyzed. The results show that this method can quickly and accurately correct the deviating angles of the echo in laser ranging with a small field of view and can provide support for lunar laser ranging at full moon and space target daytime laser ranging.

In this paper, a set of birefringent element measurement systems is constructed based on the principle of laser feedback and measures the phase delay of the birefringent element, which is a 1/4 wave plate widely used in the optical system. The temperature frequency stabilization method was introduced into the system's He-Ne laser light source to improve further the stability of the system. The temperature of the laser cavity was controlled by changing the cavity length, thereby making the laser work steadily in the single longitudinal mode for a long time. Moreover, this frequency stabilization method attained a frequency stability of 10-7 for the He-Ne laser, thus meeting the laser feedback measurement requirements. The phase delay of the 1/4 wave plate was measured herein for 10 times in two different ways, unsteadiness and temperature stabilization, using the same system. The experimental results show that the maximum deviation of the 10 repeated system measurements without frequency stabilization is 1.29° and the standard deviation is 0.47°. In contrast, the maximum deviation of 10 repeated measurements reduces to 0.83° and the standard deviation to 0.29° after the temperature stabilization. Hence, it is concluded that the stability of the system greatly improves with frequency stabilization.

Multiple light-emitting diode (LED) arrays are often used as light sources because of the high lamp-emitting port intensity and large light outlet size of navigation lights in airports. Online fault detection of such navigational lights is challenging, and no convenient and effective detection method has been developed. In this study, an illumination approximation algorithm based on Fourier series fitting is proposed. The illumination distribution of a single LED light source is obtained within a suitable detection distance, and the intensity distribution approximating to real value of the single LED light source is obtained via iterative calculations. Aiming at the problem of high peak-region error of traditional Fourier series fitting, a single-point variance threshold index is introduced to suppress the peak-region error of fitting and improve the matched degree of the single LED light source by 1%. The simulation results of the five typical array faults show that the proposed method exhibits high versatility, and the matched degree of common faults exceeds 94%.

In this paper, a double-temperature refractive index model, which can be used to simultaneously obtain the temperatures of the electron and gas for plasma, is introduced. In addition, the rationality and superiority of the proposed model are theoretically discussed. Furthermore, argon arc plasmas with different injected pressures are selected as practical examples for experiments. During the experiments, refractive index measurements are performed using two-wavelength moiré tomography with probe wavelengths of 532 nm and 808 nm. The region division of the measured argon plasmas is achieved using emission tomography. Finally, the temperatures of the electron and gas are reconstructed to verify the feasibility of the double-temperature refractive index model, and the factors that might cause imprecision are analyzed. The findings of this study will be valuable for expanding the applicable region of optical computerized tomography methods and facilitating optical diagnosis in plasma flow fields .

Based on microwave resonance technology, a microwave amplitude change signal acquisition device of an activated carbon filter rod is created, and noise reduction and baseline deduction of the microwave amplitude change signal is combined with Gaussian filtering and the penalty least squares algorithm to improve the efficiency and accuracy of the detected activated carbon content. At first, the filtering effects of different Gaussian window lengths are compared. Following that, four processing methods were used to correct the baseline of the signal spectrum, including asymmetric least squares, adaptive iteratively reweighted penalized least squares, asymmetric reweighted penalized least squares, and multi-constrained reweighted penalized least squares, the peak height, peak area, and half-peak width of the microwave amplitude change signals after baseline correction were obtained. The models developed using the partial least squares algorithm, neural networks, and support vector regression were then compared. Finally, the repeatability, accuracy, and sensitivity of the detection device were assessed. The results revealed that the best model for activated carbon weight was “peak area-activated carbon weight” with a model determination coefficient of 0.9924, an average absolute error of 0.7979 mg, and a relative standard deviation of 1.4962%. The maximum standard deviation of activated carbon weight repeatability was 1.85 mg, the minimum absolute deviation for activated carbon weight testing was 0.03 mg, and the minimum relative deviation of activated carbon weight detection was 0.05%, resulting in a quick and effective method for quantifying analysis of activated carbon in an activated carbonfilter rod for tobacco.

In order to obtain the optimal process parameters for laser melting of TiC iron-based alloy powder on 316L stainless steel, a back propagation (BP) neural network based on genetic algorithm optimization for laser melting parameters optimization is proposed. A three-factor, five-level full factorial experiment was designed to measure the macroscopic morphology and average hardness of the melted layer, and a neural network model was established for the input parameters (laser power, scanning speed, and protective gas flow rate) and response quantities (melted layer width, melted layer height, dilution rate, and microhardness). The effect of the process parameters on the response quantity was analyzed by multiple non-linear regression, and the overall performance of the clad layer was characterized by the integrated gray correlation, and the optimal parameters were obtained. The experimental results show that the laser power and scanning speed have obvious effects on the width of the molten layer, dilution rate and microhardness, while the protective gas flow rate has the most significant effect on the height of the molten layer. The goodness of fit of each response quantity model of the BP neural network model optimized by the genetic algorithm reaches between 0.85 and 0.91, and the GA-BP model has good accuracy. The best overall performance was achieved when the parameter was 1090 W, the scanning speed was 4.4 mm/s, and the protective gas flow rate was 10 L/min, indicating that the BP neural network algorithm was suitable for the quality control and parameter optimization of the laser cladding layer.

The application of laser multibeam combining technology in the field of electro-optical countermeasures is receiving increased attention. This study proposes a laser multibeam method using a refractive prism group and three flint glasses (grades H-ZLaF92, D-ZLaF85LS, and H-ZBaF21) as the prism materials. By calculating and simulating the vertex angle, incident angle, and position relationship of the prism group, a beam combination scheme is designed based on the use of an adjusting mirror group, refracting prism group, reflecting mirror group, and polarizing filter. The reflection loss is reduced by adjusting the electric vector direction of a single, linearly polarized laser beam parallel to the incident plane. The analysis and calculations show that the wavelengths, incident angles, and apical prism angles of the three materials are 550, 1060, and 2000 nm; 63.05, 61.35, and 59.58; and 51, 55, and 60, respectively. When the spot distances ΔX1 and ΔX2 are 10 and 20 mm, respectively, the far surface distance D and near surface distance d values of the three materials corresponding to the prisms are 289 and 83.5 mm; 366.4 and 107.7 mm; and 381.6 and 103.6 mm, respectively. Without optical coating, a beam combining efficiency in the range of 92.8%-97.6% can be achieved using only a single linearly polarized light incident at the Brewster angle. Compared with the existing laser multibeam method, the proposed method has considerable cost advantages.

The cladding power stripper (CPS) can remove cladding light to ensure the high beam quality and stability of the high power fiber laser system. It is one of the important core devices for the stable operation of a high power fiber laser system. This paper uses a new bidirectional low-high-low CPS based on the segmented corrosion method. The local maximum temperature of CPS is 31.2 ℃, the temperature increase rate is as low as 3.5 ℃/kW, and the stripping efficiency is 20.1 dB when the input power is 2051 W without active cooling. The bidirectional design of CPS can gradually strip the backlight in the fiber cladding, and further, improve the safety and reliability of the fiber laser system. This research can provide important device support for high power fiber laser systems.

In this study, the effects of welding speed on the microstructure, microhardness, and mechanical properties of laser welded 1700MS ultra-high strength steels were investigated. Experimental results suggest that the welding process involved martensite tempering transformation, leading to a large number of granular tempered martensite in the sub-critical heat-affected zone (SCHAZ). The size and quantity reduced significantly as the distance from the fusion zone's center (FZ) increased. Due to the tempered martensite, the welded joint had a serious decrement in hardness. With a softening degree of 52.71%, the maximum and minimum hardnesses were 609 HV and 321 HV, respectively. Because of the softening, the structure became uneven with a soft zone (heat-affected zone) in the center and hard zones (FZ and base metal) on the sides. This could cause a decrement in the mechanical properties of the welded joint during the stress process. As a result, increasing the welding speed can reduce the tempering degree and width of SCHAZ, thus improving the mechanical properties of the joints.

We propose a dual laser simultaneous etching and cleaning technique to solve the issues of residual glue (blockage), over-etching, sidewall damage, and tedious subsequent processing of blind holes in copper clad laminates by nanosecond laser etching. First-order blind hole etching experiments were conducted on copper clad laminates using nanosecond and nanosecond-matched picosecond lasers. Furthermore, a blind hole with a 122.24 μm diameter, a (37.02 ± 0.04) μm depth (37.00 μm processing requirement), a 0.16 μm bottom roughness, and a 0.25 μm surface roughness on the side walls was etched without shrinkage on a 49.00 μm-thick copper clad plate using the nanosecond-matched picosecond laser. The results indicate a significant improvement in the processing accuracy and quality of the dual laser etching and cleaning process for the copper clad plates, thereby obtaining high-quality blind holes. In conclusion, the nanosecond-matched picosecond laser shows superior etching depth (accuracy), cleanliness, taper, and roughness compared to the nanosecond laser.

The surface oxidation of titanium alloy is widely used to improve wear and corrosion resistance and interfacial compatibility. In this study, a surface heat source with a Gaussian distribution was employed to simulate the temperature field changes during the surface oxide layer preparation on a titanium alloy (Ti6Al4V) using an infrared laser. First, the simulation results of the temperature distributions on the titanium alloy surface and thickness with 500 W laser power (39.8 W/mm2 power density) and 15 mm/s scanning speed were compared with the experimental results, verifying further the effectiveness of the finite element model. Next, the verified model was used to study the influence of the laser power, scanning rate, and repeated scanning interval on the temperature field. The simulation results reveal that the line energy increased when the laser power was increased and the scanning rate was decreased. Consequently, the temperature field on the surface and along the thickness increased as a whole. Under the same line energy, a higher surface temperature and a similar internal temperature could be obtained under both high energy and scanning speed because of the energy accumulation on the titanium alloy surface. Moreover, the maximum surface temperature of the titanium alloy increased with the scanning interval reduction.

In order to further improve the performance of blue laser, the influence of the combination of p-type waveguide layer and active region on the performance of InGaN-based edge-emitting blue laser is studied in detail based on the experimental sample structure. Simulation software named PICS3D is used to simulate these blue lasers and to compare their electrical and optical characteristics including light output power-current-voltage characteristic curve, band structures, carrier current density distributions, and stimulated recombination rates. The results show that by using the novel structure of In-composition graded p-type waveguide and the first two quantum barriers, and the last quantum barrier uses the AlGaN material, the blue laser diode can restrain the electron leakage, increase the hole injection and stimulated recombination rate, and thus improve the performance of blue laser diodes. Under 1.5 A injection current, the light output power can reach 2.69 W, which is 47.8% higher than the standard structure.

Fast Fourier transform is a widely used method for signal processing in laser Doppler velocimetry systems. However, spectral leakage and fence effects occur in asynchronous sampling, and its processing accuracy is low. A hybrid convolution window based on the Nuttall window function and five-term maximum-sidelobe-decay window function is proposed to improve the detection accuracy of the six-spectral line interpolation correction algorithm. The hybrid convolution window can prevent the main lobe from becoming wide while ensuring good side lobe characteristics. The improved six-spectral line interpolation can effectively suppress the negative influence of the fence effect in the parameter estimation process and improve the analysis accuracy. The cubic B-spline interpolation is proposed to fit the interpolation coefficients to eliminate higher-order equations, and a frequency correction equation for the improved six-spectral line interpolation is derived. A dual-beam backscattering differential laser Doppler velocimetry platform is developed. The simulation data and measured signals demonstrate that the proposed algorithm exhibits good frequency and velocity measurement accuracy in the low signal-to-noise ratio environment.

The femtosecond laser processing technology primarily uses the laser focus to eliminate the microzone of the material. The exact processing of diverse functional microstructures is possible when combined with the precision design of the processing route and fine laser parameter control. However, during processing, the material's surface is not always in an ideal plane, which changes the distance between the laser focus and the material's surface. This results in the material's surface receiving a laser focal spot of varying sizes, which causes the microstructure of femtosecond laser processing to be uneven and, ultimately, does not meet the requirements of some applications. To address this problem, two calibration methods based on sub-region plane fitting and two-dimensional interpolation are proposed. First, the surface topography of the material is approximately described by a small number of sampling points in the area to be processed. Based on this, the processing path's height coordinates are adjusted to ensure that the processing impact is not adversely affected by the relative distance between the laser focus and the material surface during femtosecond laser processing. The experimental results demonstrate that these two calibration techniques are efficient ways to address the issue that non-flat surfaces make it challenging to achieve high-quality microstructure processing by femtosecond laser. They can ensure the uniformity and consistency of large-area microstructures processed by femtosecond laser.

Laser welding of B340LA high-strength steel is crucial for lightweight designing and manufacturing of automobiles. In this study, Fe30 metal powder was employed as a filler to perform B340LA high-strength steel laser powder filling welding, and the effect of the butt gap, welding speed, and powder feeding rate on weld quality was investigated. Furthermore, a high-quality weld with smooth weld morphology and better weld strength compared to base metal was obtained under optimized process parameters. Moreover, the butt gap was the most important process parameter affecting surface clearance and collapse, and the concave amount of the weld profile increased as the butt gap increased. However, when the butt gap was 0.15 mm, the weld collapsed. Welding speed had little effect on weld surface reinforcement and collapse. As the welding speed increased, the weld morphology became flat, and no collapse was observed. Furthermore, the powder feeding rate significantly influenced the tensile strength. As the powder feeding increased, the microstructure of the weldments was refined at a wide range, and the tensile strength increased. When the powder feeding rate was less than 8.27 g/min, the fracture of the welded joint occurred at the weld. However, when the powder feeding rate was ≥8.27 g/min, the welded joint broke at the base metal, and the strength of the welded joint was higher than that of the base metal. The research results enrich the basic theory of laser welding and provide technical support for B340LA high-strength steel laser welding of vehicles.

To address the problem of As40Se60 delamination from the sulfur substrate, a simulation model with ZnS, ZnSe, and Ge as the connective layer and As2Se3 as the substrate is established using molecular dynamics simulation software. The changes in structural potential energy, total energy, and adsorption energy after vacuum annealing of the simulation model are analyzed. Moreover, ZnS, ZnSe, and Ge monolayer films of the same thickness were prepared in the coating experiments and subjected to the adhesion test. Simulation and experimental results show that ZnS film is prone to shedding, whereas Ge film and ZnSe film do not easily fall off. ZnS film is prone to depacking, but its adhesion to the substrate may be improved by reducing the film thickness and substrate coating temperature.

Microcavity optical frequency combs exhibit low power consumption, integration, and tunable comb spacing, and they have been widely used in many fields. The technology for processing silicon-on-insulator (SOI) materials is compatible with the existing complementary metal-oxide-semiconductor (CMOS) process, making it one of the most promising photonic platforms. In this study, a silicon-based micro-ring resonator with a ridge section was designed, and the effects of various geometric parameters on the dispersion of the micro-ring resonator were investigated. The thermal dynamic equation of the micro-ring resonator was numerically solved, and the effects of different parameters on the thermal dynamic influence of the micro-ring resonator were analyzed. The Lugiato-Lefever equation (LLE) model was solved numerically. Because the thermo-optic effect was ignored in the theoretical research on SOI microcavity optical frequency comb, the influence of the thermo-optic effect on the generation and evolution of the optical frequency comb was analyzed. The numerical results show that at 0?0.16 °C, the maximum power of the light field increases by 22% in the time domain, and the optical frequency comb broadens by 221 nm in the frequency domain. Finally, the output spectrum of the optical frequency comb under two kinds of thermo-optic effects was analyzed. The results show that the bandwidth of the optical frequency comb is expanded by 353 nm compared with that at 0?0.16 °C when the temperature range of the thermo-optic effect is 0?0.32 °C.

With the continuous demand for technological advances in nucleic acid detection for use in medical testing, point-of-care testing (POCT) has emerged as a research focus, presenting various challenges to overcome. To circumvent the disadvantages of POCT nucleic acid detection instruments that are currently in use, a straight-axis multi-channel optical detection system is proposed and designed, which facilitates both real-time, multi-channel as well as instant detection of nucleic acids . First, an optical path is built based on an orthogonal optical path design. Second, a new straight-axis multi-channel integration and switching device is designed to enable real-time switching between multiple fluorescence detection channels. Finally, the effectiveness of the optical path design is verified by simulation; this system is integrated into a self-designed polymerase chain reaction thermocycler, and a real-time fluorescence detection experiment is conducted using a new coronavirus standard. This system reaches a minimum coefficient of variation value of 0.02%. The minimum channel resolution is 0.49 mg/mL, and no channel crosstalk is observed. The system demonstrates good on-site detection capabilities, and functions cooperatively with the instrument to complete on-site detection from “sample in” to “result out”, offering a new perspective for POCT using multi-channel real-time fluorescence detection of nucleic acids.

Based on a sandwich structure and adiabatic coupler, a polarization-independent optical power splitter with a designable splitting ratio is designed to achieve power distribution for the 1550 nm wavelength optical signal with a designable splitting ratio. By adjusting the refractive index of the sandwiched middle layer material SiNx, the splitting ratios of the transverse electric (TE) and transverse magnetic (TM) polarization modes are made equal at the same wavelength, and a polarization-independence function is realized. Next, the designable splitting ratio function is obtained by varying the asymmetry of the waveguide gaps in the adiabatic coupler. The three-dimensional finite-difference time-domain method is used for modeling and simulations. The results reveal that the coupling length of the proposed device is only 7 μm. The device can achieve designable splitting ratios ranging from 0.50 to 0.95 and simultaneously support the TE and TM polarization modes. The insertion loss value is lower than 0.31 dB. A 100 nm bandwidth can be obtained when the tolerance of the splitting ratio is within ±0.01. The proposed approach is potentially applicable to future photonic integrated circuit systems.

Solar cells can be used as coarse sun sensors, and sun vectors can be determined for the entire sky by combining several coarse sun sensors of the same specification. The accuracy of the sun vector is determined based on the on-orbit performance of the coarse sun sensors. On the basis of a large amount of on-orbit data of TZ-1 (TianZhi-1) satellite over an extended period, this study analyzed the angle error between sun vectors determined using coarse sun sensors and differential sun sensor. The output of the coarse sensors was inverted, and the installation angle error and performance attenuation of the coarse sensors were analyzed. The Kelly cosine curve corresponding to the triple junction GaAs solar cell was fitted by combining the output of the multiple coarse sensors. The analysis results show that the installation error of the coarse sensor is slight, the obtained sun vector error is smaller than 5°, and the performance attenuation rate is approximately 0.0621 V/a. The proposed sensor can achieve the all-sky acquisition of the sun vector within a specific accuracy range.

It is crucial to determine the content and distribution of heavy metals in soil in a timely and accurate manner. Based on GaoFen-5 hyperspectral images, this study investigates a large-scale inversion of soil Cd content in Tongguan County. The competitive adaptive reweighting algorithm and genetic algorithm (CARS-GA) are coupled via feature coding and random mutation to accurately screen the characteristic bands of Cd and improve the inversion accuracy of the model. The characteristic bands of Cd are searched for, first based on the global search strategy and then local search. Under the two spectral enhancement methods of standard normal variate (SNV) and first differential (FD), the accuracy values of the partial least squares (PLSR) models established using the CARS-GA method and other band selection methods (correlation coefficient analysis method and CARS algorithm) are compared. Finally, the optimal model is selected and applied to the entire bare-land area of Tongguan County. The experimental results show that when the CARS-GA method is used for band selection, the accuracy values of the PLSR model constructed based on the two spectral transformation datasets are significantly higher than those constructed using the correlation coefficient analysis method and the CARS algorithm. During the FD spectral transformation, the coefficient of determination of the validation set increases by 0.288 and 0.093, respectively. In the SNV-transformed spectrum, the coefficient of determination of the validation set increases by 0.372 and 0.088, respectively. This study demonstrates that the band selection based on the CARS-GA algorithm can effectively enhance the robustness of the Cd-content estimation model, providing improved data support for environmental pollution assessment and ecological protection.

The use of few-mode optical fiber strong coupling mode division multiplexing technology is a major solution for large-capacity optical fiber communication systems, and digital signal processing can compensate for channel damage in the digital domain, providing flexibility for signal recovery and further improving transmission capacity. In this paper, the impairments which occur in the few-mode fiber system with strong mode coupling but not in single-mode fiber system are introduced. The recovery techniques for those impairments like multiple input multiple output (MIMO) equalizer, space-time coding (STC), interference cancellation, and maximum likelihood estimation as well as their principles and research results are also introduced. The shortcomings of those algorithms in terms of complexity, delay, and transmission rate are also discussed. The results show that MIMO equalization algorithm combined with STC has obvious advantages. It has important application significance in the high-capacity long-distance few-mode fiber communication system with strong mode coupling in the future.

Chalcogenide glasses have excellent mid- and far-infrared transmittance and extremely high nonlinear coefficients, and were seen as excellent candidate materials for realizing the mid-infrared supercontinuum generation. Recently, researchers at domestic and abroad have explored continuous optimization of supercontinuum output characteristics by adjusting the matrix materials, optimizing the structural parameters, and improving the pumping source. In this article, the development course of supercontinuum generation in chalcogenide fibers was reviewed. Moreover, the most recent progresses about the spectral broadening, output power, and coherence of supercontinuum generated in three kinds of chalcogenide glass fibers, including step-index, microstructure, and tapered fibers, were reviewed. Finally, the problems existing in the researches and the development trends were analyzed and prospected.

In recent years, fluorescent optical fiber sensors fabricated using novel fluorescent materials have been used widely in the marine environment, water quality monitoring, and blood analysis owing to their advantages of intense luminescence, high sensitivity, real-time monitoring, and simple operation. This paper discusses the most recent development of fluorescent optical fiber sensors in the fields of dissolved oxygen, pH, and carbon dioxide detection, and summarizes the detection mechanism, advantages and disadvantages, and main performance parameters of different types of fluorescent materials. Finally, future development direction for fluorescent optical fiber sensors is analyzed and prospected based on the problems and challenges encountered at present.

Femtosecond laser has been an important processing technique for micro/nano structures in recent years. It can modify and ablate materials, and is capable of machining high-precision three-dimensional structures in specific areas. Femtosecond laser machining has broad application prospects in micro/nano processing. In this paper, the general interaction process between femtosecond laser and metals is described, and the methods for the preparation of micro/nano structures are introduced, such as femtosecond laser direct writing, femtosecond laser induced surface periodic structure, and femtosecond laser composite chemistry method. Then, the applications of femtosecond laser for the preparation of micro/nano structures on metal surfaces in environmental engineering, aerospace, and biomedicine are discussed. Finally, the shortcomings and future research directions of preparation of micro/nano structures by femtosecond laser are summarized and prospected.

The mid-infrared band has broad applications, such as fundamental science, biomedicine, environmental testing, national defense, security, communications, and entertainment. As the core component of mid-infrared technology, a high-performance mid-infrared coherent radiation source with a wide spectral range, high energy, high conversion efficiency, miniaturization, and room-temperature operation has been a research focus in scientific research and application. There are many types of mid-infrared lasers. According to different generation principles, mid-infrared lasers are mainly divided into chemical lasers, gas lasers, and lasers based on rare earth or transition metal ion doping, quantum cascade semiconductor lasers, and lasers based on nonlinear frequency conversion. This paper focuses on the characteristics and development of these lasers and discusses their research prospects.

Laser rock-breaking technology has great potential in oil and gas exploration, mining, and related fields. However, most studies on laser rock breaking are in the theoretical and experimental exploration stages. High-energy laser drilling and rock breaking are complex and involve optics, material science, mechanics, and other disciplines. It is necessary to examine the physical and chemical changes, rock mechanical properties, laser parameters, and other issues during the interaction between the laser and rock. Before practical applications can be achieved, many challenges must be addressed. This paper summarizes the recent research results on the interaction mechanism between lasers and rocks. In the ongoing research on the mechanism of laser rock breaking, numerical simulations and experimental research are the main approaches. This paper also reviews the application research progress in laser rock breaking and analyzes the future development trends of laser rock breaking.

The pulse duration compression via stimulated Raman scattering (SRS) has important applications in high-power short-pulse laser generation due to its characteristics of high load, high compression ratio, and phase conjugation. In this paper, the research progress of SRS pulse duration compression is analyzed and summarized from the aspects of SRS compression mechanism, gain medium, and compression structure.

The aim of this study is to investigate the problem of redundant soil selenium content spectral data and high model complexity. Several selenium-containing soil samples were collected, and the selenium content and spectral information of the samples were obtained, The raw spectra were preprocessed using Savizkg-Golag multivariate scatter correction first-order differential (SG-MSC-FD), and the feature wavelengths were screened using stability competitive adaptive reweighted sampling (sCARS) and other algorithms to establish the partial least squares regression (PLSR), support vector machine (SVM), random forest (RF), soil selenium-content seagull optimization algorithm (SOA)-RF prediction models. The coefficient of regression (R2), root mean square error (RMSE) and relative predictive deviation (RPD) values of the models under different feature screenings were compared to determine the best combination model. The results show that the accuracy of the models under different feature filtering is improved. The sCARS algorithm extracts the least number of variables, accounting for only 0.49% of the full band, and the algorithm combined variable combination cluster analysis and genetic algorithm has the highest accuracy. The RF model exhibits better robustness than the SVM and PLSR models, and the inversion accuracy of the models significantly improves with parameter optimization of SOA-RF. In summary, the SOA-RF model with VCPA-GA feature extraction is the best prediction model (R2=0.92, RMSE is 0.08, RPD is 2.911), and it can achieve rapid and efficient inversion of soil selenium content.

Dual-comb spectroscopy is an important tool for performing high-resolution spectral analysis. However, its coherence depends on complex and huge frequency-locking and feedback systems. Thus, the implementation of this technique is expensive and the system is sensitive to environmental disturbances; consequently, the applications of this tool are limited. A dual-comb system based on an electro-optic frequency comb has the advantages of a simple device, frequency agility, high coherence, and conduciveness to field applications. However, its accuracy and real-time performance for concentration inversion in gas detection applications still need to be verified. Therefore, a highly coherent electro-optic dual-comb system was constructed in this study. The absorption spectra of CO and CO2 were measured by using a multipass gas cell. The results are consistent with the simulation data of the HITRAN database. The spectral resolution reaches 200 MHz, and the single refresh time is only 4 μs. The concentration uncertainty of CO2 absorption peaks is reduced to 2.86% by concentration inversion and multipeak fitting. In addition, the real-time performance of the system for monitoring the concentration of a gas mixture is verified through the rapid detection of the CO absorption spectrum. The system is expected to be applied to the real-time monitoring of the fault characteristic gases of power equipment.

When using near-infrared spectroscopy for detection, the spectral band contains significant noise and scattering, which affect the stability of the model. Based on the competitive adaptive reweighting (CARS) and mutual information (MI) algorithms, a partial least-squares (PLS) regression model was established to detect the soluble solid content (SSC) in apples. The diffuse reflectance spectrum data of 120 samples at 800?2400 nm were obtained using a spectrometer. After preprocessing, 96 samples were randomly selected as the calibration set for modeling, and 24 samples were selected as the prediction set for prediction using the Kennard-Stone (KS) algorithm. Next, the full-band PLS model, CARS-PLS model, and MI-PLS model were established for comparative analysis. The results show that the coefficient of determination R2 of the PLS model is 0.8511, the root-mean-square error of calibration (RMSEC) of the model and the root-mean-square error of prediction (RMSEP) are 0.9413 and 1.1915, respectively. The number of characteristic wavelength point variables screened by the CARS algorithm reduces from 303 to 12, a decrease of 96.03%. The coefficient of determination R2 of the PLS model is 0.8746, an increase of 2.76%. The RMSEC and RMSEP values are 0.864 and 0.9757, respectively. The MI-PLS model contains 56 characteristic wavelength points, and the selected wavelength accounts for 18.49% of the total wavelength. R2, RMSEC, and RMSEP are 0.9218, 0.6822, and 0.8235, respectively. Compared with CARS-PLS, the number of characteristic wavelengths of MI-PLS increases by 64.55%, and the coefficient of determination R2 increases by 0.0472. Therefore, the CARS and MI algorithms can overcome the problems of noise and scattering of spectral data and can be effectively used for screening characteristic bands. The established model is suitable for determining the SSC in apples.

Herein, a two-dimensional reconstruction method for circular combustion velocity fields based on tunable diode laser absorption spectroscopy is proposed to obtain the velocity distribution of a circular-cross-section nonuniform flow field. A physical model of laser spectral absorptivity and flow velocity distribution is established, and the region of interest is covered with multiple laser beams from different angular views. The spectral absorption coefficient distribution is reconstructed using an algebra reconstruction technique. The frequency shift in the absorption spectrum of water molecules is substituted to determine the velocity distribution of the flow field so that the velocity distribution in the circular and annular regions in polar coordinates can be reconstructed. For the velocity distribution reconstruction in the circular region, the average relative error is stable at 3.73% in the reconstruction verification with a signal-to-noise ratio of 15 dB. When the signal-to-noise ratio exceeds 35 dB, the average relative error of the reconstruction results is stable below 1.50%. The reconstruction results of the proposed method are thus stable for the velocity distribution reconstruction using different input models (bimodal and annular). The results reveal that the proposed reconstruction method can precisely reflect the velocity distribution of the flow field. Overall, the research results presented herein are significant for promoting the applications of laser absorption spectroscopy in the gas diagnosis of circular and annular exit engine flow fields.

To promote the application of laser-induced breakdown spectroscopy (LIBS) for detecting heavy metals in soil and improve the heavy-metal detection sensitivity, we investigate the enhancement effect of adding different proportions of NaCl powder to soil samples on the LIBS spectrum of Cd. The results show that adding NaCl to soil samples can significantly increase the intensity of the characteristic spectral lines of Cd. When NaCl doping mass fraction is 90%, detection limits of Cd 214.441 nm and Cd 228.802 nm decrease from 30.57 and 28.12 mg/kg to 1.526 and 2.501 mg/kg, respectively. The plasma temperature and electron density are calculated, and the results show that both gradually increase with an increase in the NaCl doping mass fraction. NaCl doping can effectively improve the coupling efficiency of the laser and soil, increase the ablation amount in soil, and thus, enhance the spectral intensity of Cd. The research results are significant for applying LIBS in detecting trace heavy metals.