An enhanced cable force sensor based on fiber Bragg grating (FBG) is proposed. The base of the sensor is a cylindrical ring-shaped elastic body, three groups of Hui word beams are arranged on the ring at 120° intervals, and 6 FBGs are pasted sequentially on the Hui word beams in three groups. Moreover, an FBG is pasted on the sensor substrate for comparative experiments. Finite element analysis is used to study the strain distribution characteristics of the elastomer, and the difference in the wavelength drift of the three groups of FBG is used as the output signal of the sensor to realize the measurement of anchor cable stress and temperature-compensation. The pressure test results show that the sensitivity of the output signal of FBG on the matrix is 0.75 pm/kN, while that of the output signal of FBG on the Hui word beam is 33.53 pm/kN. The sensitization effect is remarkable, and the sensor has good linearity and temperature-compensation ability.

The ideal indoor visible light communication (VLC) channel transmission model is typically unsuitable for an actual irregular indoor environment. To address this issue, this study investigates the irregular reflection of visible light from irregular scenes and establishes a more realistic VLC channel model; further, based on this model, it develops a genetic algorithm-optimized back propagation (BP) neural network positioning (GA-BP) algorithm to overcome the poor performance of the BP neural network in handling nonlinear systems. Herein, by simulating the reflection element normal vector information of the actual channel model in irregular scenes, the direction of light reflection can be determined, enabling the receiver to collect more accurate optical power values. In an irregular indoor environment with dimensions of 5 m × 5 m × 5 m, the simulations reveal that the total optical power received by the system fluctuates within a range of 0.0141-0.0639 W; additionally, compared with the BP neural network, the GA-BP algorithm achieves a significantly reduced positioning error of 2.32 cm, along with an average positioning time of 0.0625 s.

Flexible optical transmitters can define the modulation format of a signal according to the requirements of different application scenarios, further optimizing the transmission performance of an optical signal. A flexible high-order quadrature amplitude modulation (QAM) optical transmitter scheme based on a dual-parallel Mach-Zehnder modulator (MZM) and a single MZM cascade is proposed in this paper. The principle and method of generating and adaptive-switching circular 16QAM, four-amplitude-four-phase 16QAM, circular 32QAM, and four-amplitude-eight-phase 32QAM optical signals are theoretically analyzed. In the virtual path identifier (VPI) simulation environment, the generation and transmission performance of the above four signals under 5 Gbaud and 10 Gbaud modulation rates are verified. The results show that the transmitter supports free switching between 8/16/32QAM signals by configuring the drive signal (binary or quaternary) and the direct-current bias voltage of the transmitter. Furthermore, the four generated signals have a good signal-to-noise ratio after transmission through a specific length of a single-mode fiber.

The influence of bending loss on distributed fiber Raman temperature measurement demodulation is studied, the demodulation concept of the single-channel and dual-channel demodulation algorithms is theoretically investigated, and tests are used to confirm the viability of the two demodulation algorithms for temperature demodulation of multibend loss fibers. The experimental results suggest that the temperature demodulation of the fiber with bending loss may be achieved using the two demodulation algorithms. However, the single-channel demodulation algorithm’s accuracy and volatility are superior to the two-channel demodulation algorithm for the fiber close to the point of bending loss.

To meet the transmission demand of radio-frequency (RF) signals, a radio-over-fiber (RoF) transmission link was designed based on an intensity-modulation/direct-detection scheme, employing high-linearity directly modulated semiconductor lasers, array waveguide gratings, and analog photodetectors. This link achieves low crosstalk, low harmonic distortion, and a variable link gain. Directly modulated semiconductors and control circuits, an analog RF transmitter, and receiver modules are designed and fabricated. Experimental results indicate that the link gain can be tuned in the range of -30-10 dB, the second harmonic suppression ratio exceeds 50 dB, the crosstalk among channels is lower than 60 dB, and the phase difference is within ±5°. For different input RF powers, the link gain can be tuned online to improve the noise figure or to reduce the nonlinear distortions of the RoF link. This design and prototype can be used for L-band RF signal transmission.

Aiming at the issue that the air refractive index measurement accuracy with the Edlén equation is limited by the sensors' accuracies and the integral interference fringe number is difficult to determine using laser interferometry with a length fixed vacuum cavity, an air refractive index measurement method combining laser single-frequency interferometry and PTF sensing is proposed. We design a sinusoidal phase modulated laser single-frequency interferometer with one length-fixed vacuum cavity for measuring the air refractive index. A pre-estimated value of air refractive index is obtained to determine the integral interference fringe number using the environmental parameters obtained by the low precision sensors. Then, the PGC-Arctan algorithm is adopted to accurately demodulate the phase of the interference signal to obtain the fractional interference fringe. Therefore, real-time large-range and high-accuracy measurements of air refractive index can be realized. The experimental setup is built, and the measurement results of the proposed method are compared with the findings of the Edlén equation. The experimental findings show that the measurement results of the two methods are in good agreement. The standard deviations of the differences between the measurement results of the two methods in 12 min and 1 h are 1.5 × 10-8 and 2.3 × 10-8, respectively. Experimental results indicate that the proposed method can be applied to the real-time compensation of air refractive index in laser interferometric precision displacement measurement.

When Moiré tomography is applied to measure the temperature of complex flow fields, a partition reconstruction method is used to minimize the influence of species composition on the results obtained, which is essential to ensure measurement accuracy. Considering the complexity of flow field structures, a boundary searching algorithm is proposed in this study to automatically divide the regions of the measured high-temperature complex flow fields. A propane-air flame and an argon arc plasma are used to verify the feasibility of the proposed algorithm. The results show that this algorithm can simultaneously improve the calculation efficiency and accuracy of boundary search in the divided flow field regions. This study provides a foundation for widening the range of applications of Moiré tomography.

To address the problem that the pose measurement system will increase the weight of the measured object, a visual pose measuring system based on grid-structured light is developed. First, grid-structured light is used to obtain the 3D point cloud on the surface of an object. A grid-structured-light calibration algorithm based on a 2D target is proposed. Based on the coplanarity of the target and the structured light, the grid-structured light and a camera can be calibrated simultaneously. To verify the accuracy of the point cloud obtained by the grid-structured light, structured-light calibration and point-cloud accuracy measuring experiments are conducted. The results show that the point cloud accuracy is above 0.04 mm. Moreover, the point-cloud registration algorithm for pose measurement is studied. The sample consensus initial alignment (SAC-IA) algorithm is used for coarse registration because it provides a good initial position for fine point-cloud registration. The improved iterative closet point (ICP) algorithm is used for fine registration and random sample consensus (RANSAC) algorithm and a normal vector threshold are introduced to filter matching points. The distance from the point to the surface is used as the error function to perform pose measurements. Registration algorithm comparison and pose measurement experiments are conducted. The results prove that when the measured object is in rotational motion, the maximum error of the system does not exceed 0.25° and in translational motion, the maximum error does not exceed 0.35 mm.

Laser distance measurement devices used for the space calibration and positioning of manipulators are easily affected by factors such as the work environment owing to their insufficient ranging accuracies. This leads to inaccurate measurements and shortcomings in the space calibration and positioning of manipulators. This article presents a phase laser ranging system based on the all-phase Fourier transform (apFFT). The proposed system uses the apFFT algorithm for phase discrimination and obtains the real-time measured distance. Compared with the Fourier-transform-based traditional phase laser ranging method, the proposed method can effectively suppress the spectrum leakage caused by various factors in practical applications. The experimental results reveal that the system exhibits good stability and can suppress spectrum leakage. Furthermore, the average positioning accuracy of the proposed system can reach 1 mm, which satisfies the requirements of actual industrial manufacturing.

The VNbMoTaW refractory high entropy alloy was prepared using selective laser melting. The effect of laser melting parameters on the surface forming quality, microstructure, and mechanical properties of VNbMoTaW refractory high entropy alloy specimens were investigated. The results show that the surface quality of the specimens can be effectively improved when a higher power and lower scanning speed are used, where porosity and cracks are the main defects in the preparation of the VNbMoTaW refractory high entropy alloy using selective laser melting. The VNbMoTaW refractory alloy mainly comprises columnar and cellular crystals, the bottom and central areas are mostly columnar crystals, while the sides and top of the melt pool are mainly cellular crystals. The maximum ultimate compressive strength of VNbMoTaW can reach 2154 MPa, which is 69.6% higher than that of alloys prepared using arc melting.

Extreme high-speed laser cladding (EHLA) technology can break through the efficiency bottleneck of coating production and provide an effective way to prepare high-quality coatings. TiC/Inconel 625 composite coatings were prepared on 45 steel substrates using EHLA and conventional laser cladding (CLA) technologies, and the microstructure, phase composition, corrosion resistance, and friction and wear properties of the coatings were characterized. Results show that the microstructure of the two coatings exhibits the same growth pattern, from cellular or primary columnar crystal to equiaxed crystal. For the EHLA coating technology, a cladding speed of 98.2 m/min accelerates the cooling rate of the solidified microstructure, thereby refining the dendrite. The average particle size is less than 1 μm, contributing to the improvement of the corrosion resistance of the coating. The addition of TiC promotes the formation of interdendritic carbide, thereby playing the role of precipitation strengthening, and forming dense passivation on the coating surface. The friction coefficient of the EHLA coating technology is lower than that of the CLA coating technology, showing good friction and wear performance.

For the mode-selection and wavelength control of rare-earth crystal infrared lasers, two-sided mirror resonator based on grating-coupling is proposed in this paper. The single laser mode output and wavelength control of yttrium-scandium-gallium-garnet (Er∶YSGG) crystals are realized by utilizing the high reflectivity, frequency selectivity and angle tuning properties of the periodic surface of the grating. The experimental results show that when the grating angle varies from 21.1°-21.6°, the Er∶YSGG laser exhibited single-mode operation, and its wavelength is switched from 2796.8 nm to 2824.4 nm. The obtained laser output power is 4.3 mW. The grating two-sided mirror cavity provides a simple and effective technical solution for the single-mode output of the rare-earth crystal infrared laser.

Vertical cavity surface emitting lasers (VCSEL) have the advantages of low cost, high rate, low power consumption, and easy integration, making them widely used in fields such as short-range data communication. With the increasing requirements of lifetime and failure rate as well as the growing demand of device applications, the reliability of VCSEL has received a lot of attention. It has been found that the main cause of VCSEL failure is related to the formation and expansion of dislocations. In this paper, the causes of dislocation formation in VCSEL are analyzed, and the dynamic characteristics and intrinsic mechanism of dislocation expansion are systematically introduced to contribute to the reliability of the devices.

To improve the photoelectric performance of an ultraviolet laser and reduce the threshold current obtained for standard structures, AlGaN-based ultraviolet laser diodes with an Al-composition graded quantum barrier layer (QBs) and an Al-composition graded n-type waveguide layer (n-WG) are proposed. A standard structure is extracted and modified from an experimental sample. Three different new structures and the standard structure are constructed and numerically investigated using PICS3D simulation software. A comparison of the L-I-V characteristic curves, band structures, carrier current density distribution, and other properties of the four structures demonstrates that ultraviolet laser diodes with an Al-composition graded QBs and Al-composition graded n-WG exhibit improved performance. Under 800 mA injection current, the optical output power can reach 775 mW, which is 35.7% higher than that obtained for the standard structure; the threshold current decreases to 62.3 mA, which is 73.6% lower than that obtained for the standard structure.

We propose a 2-μm-band high optical signal-to-noise-ratio (OSNR) hybrid compound-resonating-cavity (CRC) single-longitudinal-mode (SLM) thulium-doped fiber laser (TDFL). The hybrid CRC consists of an asymmetric linear compound-four-cavity (AL-CFC) made of three uniform fiber Bragg gratings (FBGs) and two optical couplers (OCs), as well as a dual-coupler-ring (DCR) cavity made of two OCs. Based on the Vernier effect, the AL-CFC can select the SLM from dense longitudinal modes, and the DCR is used as a narrow-band filter to further stabilize the operation of SLM lasing over a long term. A 1567-nm laser diode amplified by a high-power erbium-doped fiber amplifier is used as a pump source. Under a pump power of 2.80 W, a stable SLM laser output is achieved at a center wavelength of 2049.160 nm with an output power of 15.47 mW and an OSNR as high as 75.65 dB. The fluctuations of the wavelength and power are respectively lower than 0.005 nm and 0.85 dB within a measurement time of 200 min. The SLM operation becomes stable within 10 min. The pump threshold and slope efficiency are 1.75 W and 1.43%, respectively. The proposed TDFL has potential for applications in free-space optical communication, laser radar, and optical sensing.

The effects of key process parameters (laser power, scanning speed, and laser energy density) on the defects of 316L stainless steel samples are studied by experimental observation and numerical simulation. The results show that porosity is the main reason for the decrease in density. The generation of different types of pores is closely related to the process parameters, especially the laser energy density. Insufficient laser energy input (E3), especially insufficient molten pool width, is the key cause of unfused porosity. The formation of keyhole is mainly caused by high temperature and deep size of molten pool due to high laser energy input (E≥93.056 J/mm3). It is difficult to eliminate stomata completely, but reasonable control to avoid excessive laser energy input is beneficial to reduce stomata size. By adjusting the process parameters reasonably, the density can reach 99.62%.

The study aimed to examine the relationship between the process parameters of the high-temperature nickel-based alloy additive manufacturing process and the cladding morphology and quality. First, an Inconel718 laser cladding model was established on the surface of 45# steel by using ANSYS analysis software, APDL programming, and life and death unit technology. By comparing the size of the molten pool obtained by numerical simulation and experimental results, the accuracy of the model was verified to reduce subsequent test cost. Second, taking the quality of the cladding layer (forming coefficient) as the index, a regression equation was established by using the regression orthogonal experimental design, and the order of influence of the process parameters on the quality of the cladding layer was studied, followed by laser power, powder feeding rate, and scanning speed. Our results showed insignificant effect of the interaction on the quality of the cladding layer. However, the laser power and powder feeding rate exhibited the most significant impact on the quality of the cladding layer. Therefore, a single factor test is designed to analyze the influence of laser power and powder feeding on the hardness, dilution rate, and cladding morphology of the cladding layer. Through the analysis of variance, the optimal solution to the test is predicted to be as follows: laser power 1200 W, scanning speed 23 mm/s, powder feeding rate 20 g/min. These findings are consistent with the results obtained in the experiment. Moreover, the optimal parameters are verified by multi-pass lap experiments , and the structure is dense and fine. The cladding layer was found to have a good metallurgical bond with the substrate, which has a certain guiding effect on the follow-up practical production work.

This paper investigates the effect of the interval remelting process on the forming quality of three-dimensional printing Ti-6Al-4V (TC4) samples. To improve the internal defects and hence the efficiency of forming samples with thick layers (150 μm), the optimized process mode of "surface remelting + internal interval remelting" was applied. Comparison tests with samples formed without remelting showed that interval remelting and layer-by-layer remelting significantly improved the surface quality of the samples, with little difference between the results of both processes. The tensile strength, yield strength, and elongation of the samples remelted with a one layer interval were 97.84 MPa, 45.96 MPa, and 0.9% higher, respectively, than those of the samples formed without remelting. The fracture morphologies showed river-cleavage and dimple fractures, with slightly more holes in the one-interval remelted sample than in the layer-by-layer remelted sample. The mechanical property improvements of both samples were very similar. Meanwhile, the microstructure of the sample was related to the laser interval remelting process. The one-interval remelted sample gave a uniform and dense surface and the highest microhardness (442.1 HV0.3) among the samples.

As the most desirable technology of additive manufacturing, selective laser melting is capable to fabricate sophisticated structures with high-precision, however, absence of standards in design for additive manufacturing leads to disadvantages in batch production. As a result, this paper summarizes a few design criteria for parts built by selective laser melting, including deformation control, redundant powder discharge, support detachment, scanning strategy, equipment processing capability, machining allowances, etc. In addition, stress shrinkage and regular stress distribution during parts building are discussed in details. This research provides a basis for designers to design parts and optimize models.

Laser rescaling is an effective way to reduce the surface corrosion of marine steel. The differences in laser rescaling parameters will result in differences in the descaling effect and corrosion performance. Therefore, it is necessary to examine the change in the corrosion performance after laser rescaling. This study used EH36 marine steel as the research object and examined the influence of parameters, such as laser energy density and scanning speed, on the corrosion resistance and changes in surface morphology and elemental composition. Additionally, the mechanism of the influence of laser parameters on corrosion performance was evaluated, and on this basis, the optimal laser rescaling process for corrosion resistance was determined. Results shows that the corrosion resistance of EH36 steel first increased and then decreased with the increase of laser energy density and scanning speed. The oxygen content of the surface met the corrosion resistance requirements under the optimal parameters. When the laser energy density was 3.820 J/cm2, the excessive laser energy ablated the substrate. The grain size of the metal substrate decreased. Grain refinement and the density of active sites at the grain boundaries became higher, which facilitated the dissolution of the metal and reduced the stability of the corrosion products on the metal surface, thereby reducing the corrosion resistance. The surface of EH36 steel treated with a laser energy density of 2.546 J/cm2 and scanning speed of 3000 mm/s exhibited optimal corrosion resistance, with a 57% decrease in corrosion current density compared to the original steel.

In this study, the functionalization of a tapered optical fiber using graphene oxide is monitored in real time by a chaotic correlation fiber loop ringdown system, and hemoglobin sensing is achieved experimentally with the functionalized graphene oxide tapered optical fiber as the sensor element. The functionalization of the tapered optical fiber surface using graphene oxide can be divided into hydroxylation, silanization, and graphene-oxide deposition. The effect of transmission loss is analyzed during functionalization according to the change in the ringdown time. The functionalized tapered optical fiber is tested via scanning electron microscopy. Moreover, the sensitivity of hemoglobin sensing is evaluated using different concentrations of graphene oxide in the functionalization process. The experimental results show that the functionalized tapered optical fiber exhibits a considerable increase in sensitivity by an order of magnitude compared with the unfunctionalized tapered optical fiber. The sensitivity of the functionalized tapered optical fiber is influenced by the concentration of graphene oxide during functionalization; sensitivity increases with concentration. These results can potentially be applied in the field of biosensing.

The microscope objective is the key component of the nano-laser direct writing processing system, and the development trend in industry involves a large object-side field of view under a large numerical aperture (NA) and adapting to the change of the refractive index of the photoresist for two-photon polymerization (TPP). This paper compares the indicators of the microscope objective used in current TPP effect research, excavates the relationship between the object-side field of view, NA, and number of lenses, and proposes the objective synthetic sensitivity index (Iss). Combined with the Iss, a microscope objective with a wavelength range of 500-800 nm, NA>1.3, and an object-side field of view of 1.0 mm is designed. The resultant design of the objective lens involves a modulation transfer function curve close to the diffraction limit and a root mean square of wave aberration less than 0.07λ and uses the internal focusing method to adapt to the change of photoresist refraction for TPP. Tolerance analysis demonstrates that the design results are feasible.

The sensitivity of infrared optical imaging systems is closely related to the transmittance of optical windows, and Ge windows are commonly used windows in infrared optical systems. Fabrication of subwavelength structures on Ge windows can enhance the antireflection performance so as to improve the optical transmittance, and the Ge windows are usually convex shaped to get a larger field angle. However, based on current methods, it is difficult and complicated to fabricate subwavelength structures on curved windows. To solve this problem, this study presented an efficient and high-quality way to fabricate subwavelength antireflection structures on the convex Ge window based on soft ultraviolet nanoimprint lithography (soft UV-NIL). The parameters of the subwavelength antireflection structures were optimized based on the finite-difference time-domain method first. The subwavelength structures were fabricated on the convex Ge window by soft UV-NIL. Test result shows that the average single-side transmittance of the convex Ge window is raised from 65.81% to 78.68% in the region of 3.55-5.55 μm, and specifically, from 65.85% to 83.13% at the wavelength of 4.4 μm. As a result, the broadband antireflection performance in mid-infrared is realized.

This study aimed to investigate the changes in stress distribution of each compound eye during optical precision molding of curved compound eye lens. This paper built a finite element model using MSC.Marc to present a simulation study of the molding and holding stages of the glass lens under different process parameters. For this, the effect of temperature, molding velocity, and molding pressure on the stress of each compound eye, as well as the molding pressure and displacement curves, were obtained. Our findings for spherical preforms with a large deformation showed that the constant velocity molding condition increased downward displacement, leading to excessive external forces that prevent stress relaxation. The holding stage was further studied to obtain the pattern of effect of different holding forces on the filling effect and stress distribution in the compound eye.

A self-rotating solar reflection lighting system for tunnel lighting is proposed. Based on the principle of integrating the optical center of the lighting system and the outgoing system, the optical characteristics of the system are analyzed and a high-lighting reflection lighting system is designed that is conducive to the overall package. The analysis shows that when the system is tracking sunlight in all directions, the optical center remains unchanged. By setting the direction of sunlight projection, the installation positions in the system can be adjusted to realize full coverage of the tunnel entrance for sunlight lighting, which demonstrates the feasibility of the system for strengthening lighting at the tunnel entrance. Experimental tests show that the maximum utilization rate of sunlight by the system is 60%, and the lighting distance is 120 m long, which indicates a technology with the highest light energy utilization at the same transmission distance as that in direct sunlight lighting. The research and application of this technology can promote low-carbon, energy conservation, and environmental protection technology for highway tunnel lighting that demand high light energy, as well as promote the "carbon peak, carbon neutral" and sustainable development of road traffic.

For the demands of light weight and small size, wide field of view (FOV), high resolution, and real-time imaging of the unmanned aerial vehicle (UAV) optical payload, we designed an optical system suitable for the UAV camera using a folding cascade optical structure. The basic components of this system are a front monocentric folding objective and a relay imager. The front monocentric folding objective captures a spherical intermediate image with a wide FOV that is located in the monocentric sphere of the front monocentric folding objective. The relay imager array completes field subdivision, fine correction of residual aberration, and a high resolution relay image on the spherical intermediate image. After optimization, we obtained a folding cascade optical camera system with a full FOV angle of 109.6°, an instantaneous FOV of 7.8", and a tube length of only 107 mm. In the full FOV, the root mean square radii of ray tracing points on the image plane are all less than 1.1 μm. At the spatial frequency of 230 lp/mm, the values of the modulation transfer function are greater than 0.4, and the image quality of the system is close to the diffraction limit. The folding cascade structure UAV airborne camera optical system has a wide FOV, high resolution and compact structure, and can be used in the field of UAV remote sensing. While obtaining a high resolution optical image in a wide FOV, it can also realize the miniaturization and weight reduction of the optical system, which has broad application prospects.

To satisfy the strict requirements of semiconductor lasers in terms of wavelength stability, phase noise, and other indicators in precision measurements and similar applications, an analysis method based on the combination of system transfer function theory derivation analysis and simulation verification is proposed. We designed a semiconductor laser diode drive circuit with a smaller wavelength drift and ultra-low noise. For an alternating current small-signal model and alternating current path, we theoretically analyzed the correlation between the circuit parameters and system stability. The circuit design was optimized by introducing a noise-suppression network. Using Tina-TI simulations, the drive circuit loop noise is effectively suppressed, and the system stability improves to a bandwidth below 2 MHz. Experimental results reveal that the effective value of alternating current noise is approximately 224 nA and 1.9×10-6 for the direct current ripple between 3 kHz and 2 MHz in 2.5 h. When the 1 h optical power integration time is 1 s, the stability is 1.177×10-5. These results verify the theoretical model and simulation analysis. Notably, this approach provides a universal guideline for analyzing and designing ultra-low noise current drivers for semiconductor laser diodes.

Because of the application requirements of high image quality, full-color display, and the simple and compact structure of a helmet-mounted display system, a dual-free-form prism structure is proposed. A dual-channel helmet-mounted display optical system is designed using the off-axis folding/reflection principle. Furthermore, a dual-prism model is constructed using the custom constraint function, and the off-axis non-rotational symmetry system is optimized using the rectangular array pupil sampling algorithm, which is combined with vector aberration theory. In the design of the projection and transmission dual-channel system, which has a working wavelength of 400-700 nm, the diameter and distance of the pupil are 8.5 mm and 21 mm, respectively, and the volume is 41.5 mm×31.5 mm×14.1 mm. The field of view of the projection channel is 45°, and the full field of view modulation transfer function value is greater than 0.3 at 61 lp/mm. The transmission channel field of view is 52°, and the full field of view modulation transfer function value is greater than 0.4 at 30 cycle/(°). The dynamic image quality analysis of the dual-channel system is conducted, and the analysis results show that the image quality received by the human eye is unaffected by the attitude of the eyeball within the range of the diameter of the pupil. This dual-prism structure provides a reference design direction for the next generation of the dual-channel helmet-mounted display system.

In the new generation of infrared countermeasure technology, it is necessary to couple the infrared high peak power laser into the infrared energy transmission fiber for transmission. Aiming at the problems existing in fiber coupling of infrared wide-band and high peak power laser, this paper designs an achromatic coupling optical system in which the fiber end cap participates in focusing. It can couple 2.1-4.6 μm infrared lasers with high peak power, and the fiber end cap can improve the damage threshold of the fiber end face. Then, the achromatic coupling optical system is designed in detail, and the best three piece achromatic glass combination ZNS/MGF2/IRG206 is selected for design. Finally, when the focal length of the coupling system is 35 mm, the coupling efficiency for 2.1-4.6 μm band reaches 92.74%. Further analysis shows that the optimal focal length range of the coupling optical system is 35-47 mm, and when the focal length is 40 mm, the maximum tolerance of optical fiber alignment is 60 μm.

The present study aimed to design a temperature control system and a new control scheme to precisely control the temperature of the fast steering mirror. The temperature control system considered the single chip microcomputer as the core control element, and the thermoelectric cooler as the executive element. The system used a nonlinear proportional-integral-derivative active disturbance rejection control algorithm based on wavelet denoising to control the temperature. The control parameters were tuned through particle swarm optimization algorithm based on Sigmoid personalized inertia weight. The simulation and experimental results show the effectiveness of the control scheme in suppressing the startup temperature drift of the fast reflector. It is found that the temperature control accuracy reaches ±0.02 ℃ in the temperature control range of 15 ℃-28 ℃, which can be stabilized at the preset temperature within 142 s. In addition, the results show that the designed temperature control system has fast response speed, high-control accuracy, strong robustness, and good performance of application value.

Traditional optical decoys have complex compositions and high loading requirements. In this study, optical decoys with simple microstructures with higher reflection performance were designed. First, the TracePro optical simulation software was used to simulate the reflectivity of the glass bead structure, truncated angular cone structure, and cubic angular cone structure, and the structure that best meets the requirements of high reflectivity of optical bait was selected. Then, the microstructure size of the optical decoy were determined by the reflection simulation of the microstructure of the unit with different sizes. Finally, the effect of incident angle deflection in reflectivity was simulated to determine whether the reflector meets the requirements of the optical bait. Results show that the cubic cone reflection structure is more suitable for the design of optical decoys.

In this paper, a T-type nonreciprocal two-channel filter composed of straight waveguide and rectangular resonator is designed based on non-magnetic two-dimensional photonic crystal. The rectangular resonator has the characteristics of local multi-frequency electromagnetic wave and the electromagnetic wave propagation direction is adjustable, and the structure size of the straight waveguide determines the carrying capacity of the electromagnetic waves with different symmetries. Nonreciprocal two-channel filtering function is realized using the characteristics of the rectangular resonator and straight waveguide. The experimental results show that, in the case of forward transmission, the filter achieves filter transmission with central wavelengths of 1534 nm and 1574 nm, and 16 nm and 8 nm bandwidth, respectively, corresponding to the insertion loss of 0.4 dB and 0.36 dB, respectively, and inter-channel isolation of 33 dB and 22 dB. In the case of backward input, the mismatch of the electromagnetic wave symmetry mode causes no transmission, which shows that the designed dual-channel nonreciprocal filter has a good filtering effect and contributes to the development of the future all-optical communication integration field.

The bonding process will affect the actual performance of the phase corrector. However, its mirror surface is often damaged during the development process. In this paper, the characteristics of the correction surface shape and the damage to the mirror after the bonding process are analyzed, and it is inferred that the excessive difference in the thermal expansion coefficient between the mirror glass and the connecting column head material causes excessive residual stress in the corresponding position of the correction surface after high-temperature curing. A numerical model is established to simulate the thermal stress of the joints, and it is used to select a stud material with a thermal expansion coefficient similar to that of mirror glass and an adhesive with a lower curing temperature to reduce the residual stress. The stigma material is replaced with 3Cr13, which has a thermal expansion coefficient that matches the glass material (K9). The experimental results show that the static surface shape of the phase corrector has been significantly improved after high-temperature curing, and the correction surface has not been damaged after multiple experiments.

Accurate forecasting of photovoltaic power can effectively promote safe and efficient generation and utilization of photovoltaic power. Accordingly, an ultra-short-term photovoltaic power prediction method combining singular spectrum decomposition (SSD), double-attention mechanism, and bidirectional gating logic unit (BiGRU) time-series modeling is proposed to address the insufficient forecasting accuracy of existing methods. First, SSD is used to reduce the randomness and volatility of photovoltaic signals. A BiGRU network is then adopted to model the time series of the decomposed signals. Additionally, an attention module is designed to simultaneously learn the importance (weight) of the feature and time series by weighting the features extracted by the BiGRU network. The final forecast of photovoltaic power is obtained via the decision-making layer. The experimental results demonstrate that the SSD and attention mechanism can improve the accuracy of forecasts obtained from the deep time-series model. The proposed method is superior to several other conventional methods and is highly practical for different seasons and weather conditions.

The satellite time service technology is limited by the measurement accuracy of the classical radio signal, and the time service accuracy can only reach the ns level. In this paper, a satellite time service scheme based on microwave-optical wave-entangled signals is proposed. The advantages of long-distance transmission of microwave signals and single-photon detection of optical wave signals are effectively combined using a cavity electro-opto-mechanical converter. The phase difference is calculated using a phase-conjugating processor to obtain accurate time-difference information. Through theoretical analysis and simulations, it is demonstrated that even if the quantum signal is in low entanglement, the proposed scheme can improve the satellite time service accuracy to the ps level.

A symmetric side cavity coupling sensing structure based on two-dimensional photonic crystals is proposed for voltage and magnetic field strength sensing. In the complete photonic crystal, defects are introduced through the translation and size change of air holes, and two photonic crystal microcavities, H0 cavity and improved H1 cavity, are formed respectively; The H0 cavity and the improved H1 cavity are coupled with the W1 waveguide respectively, and the symmetrical structure is made along the W1 waveguide; The microcavity is filled with liquid crystal and magnetic fluid as sensitive materials, and the electro-optical effect of liquid crystal and the magneto-optical effect of magnetic fluid are used to form the sensing region of voltage and magnetic field intensity. Due to the photon localization characteristics of photonic crystals, two relatively independent transmission peaks are formed in the transmission spectrum of the side cavity coupling structure. The changes of voltage and magnetic field intensity are indirectly measured by measuring the wavelength offset of the two transmission peaks. The sensing characteristics are numerically studied under anisotropic perfectly matched layer boundary conditions using the finite-difference time-domain method. The simulation results reveal that the voltage sensitivity can reach 0.65 nm/V in the voltage range of 14-32 V and 1.86 nm/V in the voltage range of 32-50 V. In addition, the sensor demonstrates a refractive index sensitivity and quality factor of 296 nm/RIU and 3350 in the voltage range of 14-50 V and 251 nm/RIU and 2722 in the magnetic field strength range of 10-40 mT, respectively. And the magnetic field strength sensitivity is 13.06 nm/mT in the magnetic field strength range of 10-40 mT.

In order to detect gadolinium nitrate with high sensitivity, a fiber ring cavity laser sensor based on micro-nano fiber interferometer is studied in this paper. A kind of micro-nano fiber interferometer with double cone structure is prepared. The strong evanescent field of micro-nano fiber can interact effectively with the external environment or surrounding medium, and the evanescent field increases with the decreasing of the diameter of fiber biconical structure. The sensitivity of refractive index sensing is also significantly improved. The experimental results show that when the diameter of micro-nano fiber is 20 μm, the refractive index sensitivity of the sensor is 1925 nm/RIU; for the mass concentration of gadolinium nitrate solution, the sensitivity of the sensor is as high as 0.172 nm/(mg·mL-1). In addition, the fiber ring laser sensor has the advantages of high sensitivity and compact structure, and has a broad application prospect in biological modification and chemical sensing.

The accurate monitoring of fiber Bragg gratings (FBG) during high stress changes and long-term service of unidirectional composites is important for the application of prestressed carbon fiber composite (CFRP) plate. The coupling of external-mounted bare-gate, externally-mounted substrate, and embedded bare-gate FBG sensors with CFRP plate is tested for the temperature sensing accuracy of the three coupling methods, and the process of stress loading up to 1000 MPa is monitored based on the prestressed CFRP plate reinforcement system. The experimental results show that all three coupling methods have good temperature sensing characteristics, but the stress sensing characteristics are significantly different from the temperature sensing characteristics. Among them, the embedded bare-gate sensor has the highest monitoring accuracy, and the linearity, hysteresis, and repeatability of its stress sensing are 0.9999, 0.25%, and 3.20% respectively, which can be applied to the reinforcement engineering of prestressed CFRP plate.

The noise caused by the coupling capacitance between the adjacent electrodes of an electrical impedance tomography sensor was measured to help solve the problem that traditional sensors need to be rebuilt and installed according to the change in the outer diameter of the detected pipeline. A portable differential electrode sensor with an adjustable electrode to the distance between the axes of the pipeline (electrode spacing) was designed for these measurements. The control module adjusts the electrode spacing so that a single sensor can be used for pipe measurements with an outer diameter ranging from 60 mm to 100 mm in the dynamic range. The differential electrode structure allowed the sensor to fix the radial electrode of appropriate length and eliminated the measurement noise caused by some parasitic devices in the sensor. The experimental results show that the new sensor can detect pipes with different diameters, and the differential electrode improves the imaging quality of multiphase flow.

Optical chiral metasurfaces are 2D or quasi-2D photonic devices composed of subwavelength-scale units, which combine novel physics and cutting-edge nanofabrication development, can generate extremely strong optical chirality, and have broad application prospects, including chiral sensing, chiral particles separation, and active control. This paper introduces the fundamental mechanisms of chiral metasurfaces, summarizes domestic and foreign state-of-the-art studies from the perspectives of metallic and dielectric materials, and focuses on the circular dichroism and near-field chiral responses. This paper also addresses the application areas of chiral metasurfaces.

Majorana fermions (MF) obey non-Abelian statistics and have potential applications in topological quantum computation and quantum information processing. Several types of hybrid devices that can possibly host MFs in low-latitude condensed matter systems have been proposed in the last decade, including hybrid semiconductor nanowire/superconductor devices, iron chains on the superconducting surface, hybrid iron-based superconductor, and topological insulator/superconductor structures, with the analogous Majorana signals have been observed in the above hybrid system with different electrical means. And the proposal that there may be Majorana fermions in topological insulators has attracted much attention. Although a mass of theoretical schemes have been proposed consecutively, and similar Majorana signatures have been experimentally demonstrated, no conclusive evidence of the existence of MFs in low-latitude condensed matter systems is available and MFs-based topological quantum computing is difficult to achieve. In this review, we introduce several schemes for detecting MFs in low-latitude condensed matter systems, as well as elaborate on the different electrical means for probing MFs. Most MFs detection schemes focus on electronic transport properties recently, and in order to obtain more conclusive evidence of MFs, it is necessary to propose alternative methods for detecting MFs. Alternative setups or proposals for detecting MFs are thus required to obtain definitive signatures of MFs. We introduced an all-optical pump-probe technology accompanying hybrid micro- and nano-systems, and proposed a series of all-optical methods for detecting MFs, benefiting from recent progress in nanotechnology. Moreover, we also review the optical detection of MFs and MFs-induced coherent optical propagation. Finally, we anticipate quantum computation using MFs in solid-state quantum devices.

Integrated radar-communication refers to waveform fusion based on hardware sharing to simultaneously perform radar and communication functions using one signal. Consequently, the system performance can be optimized, and the frequency-spectrum resources can be saved. In this paper, a systematic overview of the integrated radar-communication waveform is provided. Specifically, the technical connotation and development stage of the radar-communication integration are presented, the application potential of linear frequency modulation (LFM) signal in the integrated system is analyzed. And the research progresses of LFM-integrated waveform design, high-frequency broadband LFM signal, and LFM-integrated waveform optical generation and processing are summarized. Studies have shown that microwave photons play an important role in the future of integrated radar-communication systems, and radar-communication integration is a system integrating optical and electrical technologies and linking analog and digital technologies.

Satellite-to-ground laser communication (SGL) can address the spectrum limitation of traditional microwave communication and satisfy the increasing communication demand of satellite ground links. The adaptive optics (AO) system is an integral part of SGL, and it can effectively suppress the impacts of atmospheric turbulence and improve link stability and reliability. This paper introduces typical optical ground-station AO systems at home and abroad and its primary parameters. Based on the research results of AO in laser communication, the development trend followed by the AO system, including its improved wavefront detection ability, enhanced correction capability, stabilized and reliable operating performance, and improved automatic operation, is summarized. This study provides a reference for AO system development in SGL to ensure better availability of SGL link.

With the development of intelligent and connected vehicles, in-vehicle networks, as information sharing platforms between sensors, processors, and actuators in automobiles, are gradually moving in the direction of simplified architecture and higher bandwidth. In this paper, the bandwidth demand trend of in-vehicle network is analyzed through the introduction of the principle and bandwidth demand of several major new in-vehicle sensors on intelligent and connected vehicles. At the same time, based on the review of the network architecture and topologies of traditional in-vehicle networks, as well as the current progress of in-vehicle networks, we point out the bandwidth bottleneck faced by the in-vehicle networks under the trend of automotive intelligence, and optical fiber transmission is the development direction of future in-vehicle networks. Finally, through the analysis of the requirements of in-vehicle networks for optical fiber and the investigation of the latest research progress of plastic optical fiber transmission technology, the article shows that the in-vehicle optical fiber transmission is worthy of further research urgently.

In order to measure the concentrated solar radiation flux distribution of curved surface absorbers, based on segmented-jointed approaches, a measurement method for the solar flux density distribution on the curved surfaces is proposed according to the characteristics of the surface radiation transfer. By dividing and extracting the hemispherical shell, a hollow water-cooled strip spherical arc Lambertian target is designed and processed. Using image space coordinate transformation and surface radiation transfer calculation, the entire spherical shell surface is obtained by splicing multiple sub-images. The measurement method is experimentally verified on an indoor solar simulator using a CCD camera to assemble a test system. The results show that the uncertainty of this method is 5.12%. The distribution of solar flux density along the circumferential and zenith angles of the hemispherical surface is uneven, and the peak energy flux density appears at the outer edge of the surface vertex, which is significantly different from the focal plane energy flux density distribution.

The Mueller matrix describes the influence of an object on the polarization of optical waves. It has various information about the object surface. In this paper, the scattering field and the scattering Mueller matrix of two-dimensional random rough surfaces are analyzed using the Kirchhoff approximation method. The scattering Mueller matrices of copper, iron, nickel, glass, and lithium niobate are numerically simulated using the incidence angle, and the relative roughness is changed. With the increase of the incident angle, the m01, m10, m22, and m33 parameters of metals and dielectrics vary by less than 30% and greater than 80%, respectively. The m00, m11, m22, and m33 parameters of metals and dielectrics vary by more than 60% and less than 20%, respectively. Further, the m23 and m32 parameters of metals are increased as the incident angle increases, and are decreased as the relative roughness increases, whereas the m23 and m32 parameters of the dielectric are always 0. The differences can be used for identifying metal and dielectric and provide some reference to the measurement of object surface roughness.

A complex “frequency-doubling-comparison-phase-shifting” circuit is often required for the generation of frequency-doubling signals for harmonic detection in the existing tunable diode laser absorption spectroscopy-wavelength modulation spectroscopy (TDLAS-WMS). Thus, an innovative signal generation method is proposed in this paper. In this method, a field programmable gate array (FPGA), as a main controller, controls a high-speed digital-to-analog (D/A) converter to generate a sawtooth scanning signal and sine modulation signal, which are used to drive a laser for wavelength modulation scanning after the signals are combined. Simultaneously, a square signal, which is frequency-multiplying and strictly in-phase with the sine wave, is also generated based on the phase information for demodulation of the gas absorption signal. Based on this method, the system scheme, high-speed D/A conversion circuit, and FPGA control flow are designed, and the generation of the sinusoidal signal and its frequency-doubled square wave signal with a delay is verified experimentally. When the system is applied to a gas detection, an absorption signal related to the concentration is successfully detected, and the detection amplitude is improved to some degree, which verifies the effectiveness of the proposed method.

This study proposes a quantitative analysis method combining sensitivity dimensionality reduction and Bayesian optimization algorithm support vector regression (BOA-SVR) to improve quantitative analysis accuracy of soil elements. The X-ray fluorescence (XRF) spectrum of the soil is obtained using a portable XRF analyzer, and the background is subtracted by iterative discrete wavelet transform. Furthermore, the calculated net peak area of each element is used as the model input feature. The influence of different input feature sets on the prediction accuracy is studied using sensitivity analysis to achieve feature dimensionality reduction. The samples are divided into training and test sets, and prediction accuracy of the model is evaluated using the root mean square error and coefficient of determination. Based on Cu and As elements, the prediction results of the BOA-SVR model under full feature input, the BOA-SVR model after feature dimension reduction, and the single-parameter partial least squares model are compared. The experimental results show that BOA-SVR model after feature dimension reduction achieves the best prediction result in both Cu and As elements.

The inspection and identification of human biological tissues, such as nails, play an essential role in investigating several criminal cases. To quickly and nondestructively identify nail tissues extracted from crime scenes, this paper proposes a nondestructive identification and gender characterization method of human nails based on molecular spectroscopic analysis and machine learning. We establish various classification prediction models by collecting 120 infrared spectroscopy data of different gender nail samples of the same age group. Using principal component analysis technology, dimensionality reduction is used to extract 3 principal components, and the samples are interactively verified. The recognition effects of Fisher discriminant function, multilayer perceptron, and back propagation (BP) neural network model are also compared. The experimental results show that the classification and recognition rate of the multilayer perceptron model can reach 91.4%, which is better than the Fisher discriminant analysis model. The BP neural network model based on the particle swarm optimization algorithm has the best classification effect, with a recognition rate of 97.7%.

A local field enhancement structure with dual-band of near infrared and terahertz is designed, which consists of a micron-scale rectangular groove structure and a nano-scale double disk structure. The terahertz resonance enhancement is realized by using the micron-scale rectangular groove structure, and the nanoscale double disk structure is combined with it to achieve optical capture in the near infrared band. The structure is simulated and analyzed by the finite difference time domain method. Research results show that the dual-band local field enhancement structure has a resonance peak at 0.63 THz and strong local field enhancement, and the maximum electric field enhancement is 1800. When the incident light intensity in the near infrared band is 1 mW/μm2, the depth of the potential well reaches 30 kBT, which can achieve stable trapping of particles. The results have a certain reference significance for the detection of THz vibration spectrum of biological macromolecules.

Fe/MgO nanocomposite films are prepared using pulsed laser deposition, and the effects of pulse number on the structure, composition, and optical properties of the composite films are studied in this paper. X-ray diffraction analysis shows that a diffraction peak with a crystal plane orientation of (211) appears when the pulse number of the deposited Fe nanoparticles is greater than 500, confirming the existence of Fe, Mg, and O elements in the composite film; part of the Fe nanoparticles in MgO film is oxidized, thus existing in the elemental and oxidized states (content ratio of ~3∶2). High-resolution transmission electron microscopy analysis shows that when the pulse number is 100, Fe nanoparticles with an average particle size of ~2.73 nm are uniformly distributed in an ellipsoid shape in the MgO film, and the average spacing between Fe nanoparticles is ~1.75 nm. Ellipsometry analysis shows that the refractive index and dispersion sensitivity of the Fe/MgO nanocomposite films increases as the pulse number increasing when the wavelength is less than 365 nm. Ultraviolet-visible spectral analysis shows that Fe/MgO nanocomposite films exhibit an obvious ultraviolet narrow-band antireflection phenomenon in the wavelength range of 190-235 nm compared with pure MgO films;the transmittance of the composite film at 197 nm is ~69.4%.

TiO2 and SiO2 are selected as high and low refractive index materials, and the sapphire substrate wide cutoff high Q factor band pass filter is designed by traditional design method (the long wave and short wave pass film systems are plated on both sides of the substrate, with the thickness of 1.67 μm and 8.67 μm, respectively). In order to avoid the problem of large variation of filter one-sided shape caused by large difference of film thickness, the membrane system on both sides of the substrate is rearranged. After optimization, the number of film layers on both sides is 49 and 50, and the thickness of film layer is 5.73 μm and 4.22 μm, respectively. The thin films are plated by electron beam evaporation physical vapor deposition and the transmittance of the samples is measured by spectrophotometer. The experimental results show that the average transmittance of the sample in the passband (521-596 nm) is 96.59%, the average transmittance in the cutoff region is 0.076%, the rectangularity of the passband is 0.95, and the steepness of the transition zone on both sides of the passband is 0.89%. It has the characteristics of high Q factor filter. In addition, the experimental curve is in good agreement with the design curve, which verifies the effectiveness of optimizing the structure of the two-sided membrane system.

Infrared optical coatings deposited on the As40Se60 chalcogenide glass have the disadvantage of poor adhesion. The firmness of the coating has been a major research object to solve the problem of coating adhesion. First, the appropriate film source materials were chosen, and the design and optimization of the film system were completed. The single factor experiment was carried out with the deposition temperature as the influencing factor, and the deposition process and residual stress of the ZnS connection layer were examined. The method without an ion source was used to reduce the residual stress of the connection layer and improve film adhesion. Finally, the problem of coating adhesion at higher temperatures was solved. An infrared antireflective coating with an 8-12 μm wavelength was developed, and the deposition process was applied to practical production. The average transmittance and reflectance of the prepared film were 98% and 0.6%, respectively. The adhesion, high and low temperature, and humidity experiment met the requirements of the GJB2845—1995 standard.

This paper investigates a spectral optimization simulation method based on multi-channel light-emitting diodes (LEDs). According to the principle of linear superposition of spectra, each color LED spectrum is imported into the program, and the model is programmed to output the best combination of color rendering index, luminous efficacy, and color tolerance under the specified color temperature conditions to guide the dimming and color adjustment applications of multi-channel LED lighting products. The experimental results show that the warm white LEDs mixed with RGB (Red, Green, Blue) light have the best combination of photometric chromaticity parameters in the color temperature range of 3000-5000 K, and the cool white LEDs mixed with RGB light have the best effect in the range of 5000-8000 K. The visual efficacy and non-visual efficacy of each optimal spectral combination solution are discussed, and the optimal solution of the spectrum is experimentally verified.