High power pulse laser has important applications in precision welding and laser cleaning. Peak power increasing can be realized by beam combining of multiple pulse lasers, and the pulse synchronization accuracy significantly determines the performance of the beam combination laser. Therefore, we propose a pulse synchronization method based on programmable time modulation circuit with a maximum time delay of 256 ns and a resolution of less than 1 ns. It has been proved that the incoherent beam combination with 97% efficiency can be achieved by using this method for three independent sub-module lasers. When the synchronization is error less than or equal to 4 ns, the pulse repetition frequency and full width at half maximum can be adjusted in the range of 40?1000 kHz and 19?660 ns.

The transient absorption properties of Rydberg atoms driven by two pulsed laser fields are investigated herein on the basis of the theory of density matrix equation, which describes the interaction of photon and material. It is found that owing to the weak coupling field, the probe absorption first increases to the maximum value and then decreases monotonically to zero with time. The maximum value of the probe absorption increases with an increase in Rabi frequency until the largest value is obtained. Then, it decreases gradually and the absorption with time presents the character of oscillation at the same time. When the coupling field's Rabi frequency is appropriate, the phenomenon of negative absorption occurs. The analysis of the evolution of population and the coherent term with time reveals that the coherent term caused by the influence of the coupling and probe field results in a negative absorption.

In recent years, the partially coherent beam carrying the twisted phase has received extensive attention due to its unique properties. A new partially coherent vector beam endowed with a twisted phase and a special spatial correlation structure is introduced, which is radially polarized twisted rectangular multi-Gaussian Schell-model beam. The cross-spectral density matrix elements of such beam passing through the ABCD optical system were derived, and the evolution properties, such as the normalized intensity distribution, the spectral degree of coherence (SDOC), and the spectral degree of polarization (SDOP) were investigated in detail. Numerical results show that the intensity distribution of the radially polarized rectangular multi-Gauss Schell-model beam without the twist phase gradually evolves from the hollow ring profile in the source plane into the rectangular flat-top profile in the focal plane. In comparison, the twisted phase carried by the radially polarized twisted rectangular multi-Gaussian Schell-model beam will not only induce the rotation of the beam spot, but also cause a series of changes in the SDOC and SDOP of the beam during the propagation process. The research results provide some theoretical guidance for the control of new vector structured beams with twisted phases, and have potential applications in beam shaping, optical micro-manipulation, and free space optical communications.

In this paper, Bi2O2Se/TiO2 heterostructures different mass fractions were synthesized by one-step hydrothermal method and characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and the ultraviolet detector based on Bi2O2Se/TiO2 heterojunction was prepared. The experimental results show that the photodetection performance of Bi2O2Se/TiO2 heterojunction detector is the best when the mass fraction of Bi2O2Se is 60% under 365 nm ultraviolet light. The photocurrent of Bi2O2Se/TiO2 heterojunction is 7 times that of TiO2 detector and higher than that of Bi2O2Se detector. The response time is about 30 ms, which is 1/6 of that of TiO2 detector. The responsivity and detectivity are 10-3 A/W and 1.08×107 cm·Hz1/2/W, respectively, which are also one order of magnitude higher than that of TiO2 detector. This is mainly because the heterojunction formed by the combination of Bi2O2Se and TiO2 promotes the separation of photogenerated electrons and holes.

Two types of weak grating sensors with different packaging methods were developed using the weak grating strain monitoring technology. The strain of the steel beam after loading is measured and compared with the distributed optical fiber sensor. The experimental results show that the strain monitoring results obtained using weak grating agree well with those obtained using distributed optical fiber and theoretical calculation. The error between the calculated deflection of the steel beam and measured and theoretical values of the dial indicator is within 10%. The horizontal static load test results of an offshore steel pipe pile show that the deformation of the pile is mainly within the range of 60 m below the sea level. The deflection of steel pipe piles increases with the increase of load and decreases with the increase in pile depth. After 50 m buried depth, the steel pipe pile is almost no longer affected by horizontal thrust, and the deflection value is 0. In the horizontal static load test, the average error between the monitored deflection and actual deflection is 16 mm. Through the indoor model and practical engineering application, the feasibility and accuracy of weak grating in steel structure monitoring are proved, which provides technical support for similar projects.

Full width at half maximum (FWHM) is an important factor affecting the performance of the sensor. In order to improve the quality factor of the surface plasmon resonance sensor, a grating-assisted ultra-narrow band multispectral plasmon resonance sensor structure is proposed in this paper. The structure is composed of periodically alternating SiO2 and Au rectangular nanorods and is placed on the SiO2/Al2O3 thin film layer. The full vector finite element method is used to simulate the optical transmission and sensing characteristics, and the effects of structural parameters and polarization state of incident light on FWHM and sensing characteristics are analyzed. The simulation results show that in the wavelength range of 800-1100 nm, there are two dips formed by plasma resonance and dielectric grating in the transmission spectrum of the structure. The corresponding FWHM can reach 0.35 nm and 0.59 nm, respectively. The refractive index sensitivity is 525.7 nm /RIU and 475.7 nm /RIU, respectively. The figure of merit is 1502.00 RIU-1 and 806.27 RIU-1, respectively, which had potential applications in biological detection, drug screening, membrane biology and other fields.

In order to accurately identify the types of intrusion signals in the distributed optical fiber early warning system, this paper proposes an optical fiber intrusion signal feature extraction and recognition algorithm based on Fourier decomposition method (FDM) and permutation entropy noise reduction method. First, the FDM is used to decompose the fiber intrusion signal into a number of intrinsic frequency band functions (FIBF). Then, the permutation entropy of each FIBF component is calculated, the sensitivity of permutation entropy to noise is used to screen qualified FIBF, and the signal is reconstructed. Finally, the approximate entropy and energy of the reconstructed signal are calculated and a two-dimensional feature vector is constructed, which is sent to the support vector machine for training and recognizes the fiber intrusion signal. Experimental results show that the algorithm can effectively identify three types of optical fiber intrusion signals: tapping, trot and passing, with an average recognition accuracy of 93.33%.

Low-density parity-check code is a kind of linear block code, which has received much attention in recent years. At present, the min-sum (MS) algorithm, which is widely used, has a lot of decoding loss, and it belongs to flood scheduling, so the decoding convergence speed is slow. In this paper, the MS decoding algorithm that introduced shuffled strategy and improved variable node update (shuffled-VNU-MS) is proposed. When the improved algorithm updates check node information of current column in this iteration, it can use the latest variable node information of the previous sequence, and the variable node information is averaged by the weighted factor. The simulation results show that when the code length is 256, the code rate is 0.5, and the bit error rate is 10-5, shuffled-VNU-MS algorithm increases the coding gain by about 0.92 dB compared with the MS algorithm. When the signal to noise ratio is 0, compared with the MS algorithm, shuffled-VNU-MS algorithm can improve the decoding convergence speed by about 52%.

In visible light communication (VLC) systems, the amplitude of the modulated transmit signal must be nonnegative to drive light-emitting diodes to illuminate, resulting in a very different achievable rate formula of VLC system compared to that of a traditional radio frequency system. Therefore, the traditional precoding matrix design method for maximizing the achievable rate is no longer applicable. In terms of the issue, this study proposes a precoding matrix design method for multiple input multiple output VLC systems. First, it is based on the strict Karush-Kuhn-Tucker conditions to achieve the eigen-channel power allocation expression. Then, the water-filling algorithm ensures that the subchannels with better performance are allocated higher power. The method can achieve the optimal achievable rate with low complexity characteristics by constraining the order of eigen-channel power values. The simulation results show that the achievable rate index of the method is significantly improved, compared with the existing precoding matrix design methods.

Herein, an optical fiber temperature sensor based on a random laser was proposed and implemented. The Rayleigh scattering of the single-mode fiber and the reflection of fiber Bragg grating (FBG) were employed to provide the optical feedback of the laser and achieve a random laser output. Results show that the central wavelength and threshold power of the output laser are 1550.52 nm and 30 mW, respectively. When the pump power is considerably higher than the threshold power, the laser output remains stable. When the temperature of FBG range varies from 30 °C to 90 °C, the output wavelengths of the random laser will shift accordingly, and there is a good linear relationship between temperature and wavelength. The temperature sensitivities of the sensor are 10.5 pm/℃ and 10.4 pm/℃ during heating and cooling, respectively. This type of optical fiber sensor based on random lasers is expected to show diverse application prospects in the temperature sensing field.

To improve the indoor visible light positioning accuracy, we proposed a visible light fingerprint positioning method using the least squares support vector machine (LSSVM) optimized by the beetle antenna search (BAS) algorithm. First, the signal strength characteristics of the LED light intensity were used to build the fingerprint database. Next, the BAS algorithm was applied to optimize the hyperparameters of the least square support vector machine to improve accuracy and reduce time cost. Finally, we obtained the mapping relationship between the position coordinates and signal strength characteristics to achieve positioning. The experimental results show that the BAS-LSSVM positioning method can achieve a good positioning effect, with the positioning error of 97.0%, test points being less than 0.10 m, and the average positioning error of all test points being 0.031 m.

The beacon spot position detection technology is widely used in the field of vision-based optical communication coarse alignment, and its detection algorithm directly affects the accuracy of acquisition and positioning. Aiming at the defect that the algorithm of searching beacon spot based on threshold segmentation is easy to be affected by background strong light, a real-time acquisition and positioning system of unmanned aerial vehicle optical communication based on deep learning algorithm is established in this paper. First, the YOLOv4 (You only look once, v4) network is improved, four simplified modules and one up-sampling module are designed using the feature map channel splicing method that can enhance the extraction of shallow feature information, which greatly improves the speed of the network. Then, the improved network, the original YOLOv4 network and its simplified network are trained on PASCAL VOC data set. Finally, collect and train the beacon spot data set, and run the improved YOLOv4 network on the unmanned aerial vehicle to output the beacon spot position of the camera video frame. Based on proportion integration differentiation algorithm, the gimbal is adjusted for position closed-loop control, so as to realize real-time acquisition and positioning for optical communication. Experimental results show that the accuracy rate of the improved YOLOv4 network on the beacon spot test set is 99.6%, the recall rate is 99.8%, and the frame rate on the NVIDIA Jetson Xavier NX embedded computer platform is 42 frame/s, which meets the requirements of real-time acquisition and positioning for unmanned aerial vehicle optical communication.

To solve the complexity problem in the design of radar signals with low probability of interception, this paper proposes a novel compound modulation signal, namely the Costas/CTPC compound signal of inter-pulse Costas frequency coding and intra-pulse chaotic two-phase code (CTPC). The introduction of CTPC increases the randomness of the signal phase. The composition of the composite modulation signal is analyzed theoretically. After parameter optimization, the autocorrelation function, cross-correlation function, power spectral density, and ambiguity function of Costas/CTPC signal are analyzed through simulation. The simulation results show that this signal has better autocorrelation performance than Costas, Costas/Bark, LFM/Bark, and Costas/LFM signals. It also has good anti-jamming and low-interception performances. Therefore, it is very suitable for radar systems with low-interception probability.

For solving the problems of poor initial value selection sensitivity and weak convergence performance while using fast independent component analysis (FastICA) algorithm to extract co-frequency aliased signals, a double relaxation factors modified FastICA (DLM-FastICA) algorithm is proposed. Firstly, the double relaxation factor is introduced into Newton iteration method, and the optimal weight separation matrix is obtained by adjusting the combination coefficient of separation matrix adaptively, then the sensitivity of FastICA algorithm to the initial value is improved; furthermore, the extraction signal is obtained via fast convergence characteristics of modified FastICA (M-FastICA), and the separation accuracy and convergence speed of the algorithm are improved. The simulation results show that the similarity coefficient between the extracted signal and the source signal reaches 0.9, meanwhile compared to the original algorithm, the iteration times are reduced by nearly 40%, so the proposed algorithm has faster and more stable extraction performance.

Aiming at the low signal detection performance of the order successive interference cancellation (OSIC) algorithm in the nonlinear detection of multiple input multiple output (MIMO) systems, the paper proposes a dynamic adjusted OSIC (D-OSIC) detection algorithm. In order to solve the problem of early error propagation, the maximum likelihood (ML) is used to select the best symbol which could improve the detection performance of the ML-D-OSIC algorithm. The number of elimination layers is dynamically adjusted due to the traversal capacity. Compared with the hybrid iterative algorithm, the complexity of the algorithm is reduced. The simulation results show that ML-D-OSIC algorithm is superior to the OSIC algorithm in signal detection performance. The detection performance improves with the difference of predefined threshold, offset and weight. The complexity is much lower than that of ML algorithm.

Herein, a multi-wavelength defect detection system based on the theory of integral scattering detection is proposed. This system uses three light sources with wavelengths of 635 nm, 525 nm, and 405 nm and employs a photomultiplier tube as the photodetector. Two samples of high-transmittance quartz glass sheets with standard size defects,one with a width and a depth of 20 μm and the other with a width and a depth of 25 μm,are evaluated. The powers of the light source are 50 mW and 80 mW, respectively. Experimental results show that the highest scatter rate is achieved using the 405 nm light source. Therefore, the detection ability of the 405 nm light source is stronger than those of the 635 nm and 525 nm light sources. The findings of this study provide a reference for detecting small defects and achieving defect depth information.

Laser ranging technology is crucial for the monitoring and early warning of space debris. To improve the monitoring capability of the 1.2 m telescope laser ranging platform of the Yunnan Observatory of the Chinese Academy of Sciences for space debris, the daytime laser ranging technology and method for space debris monitoring were studied. First, the feasibility of using the existing 1.2 m telescope laser ranging platform of the Yunnan Observatory to perform daytime space debris laser ranging was analyzed. Then, the key problems associated with space debris laser ranging during daytime were analyzed and solutions were proposed. Based on a daytime space debris laser ranging experiment, some space debris laser ranging data were obtained. The cross section of the measured space debris radar ranges from 9.0 m2 to 20.0 m2, the perigee ranges from 400 km to 900 km, and the apogee ranges from 500 km to 900 km. Results show that the space debris laser ranging platform of the Yunnan Observatory can perform space debris laser ranging during daytime, which can provide technical support for subsequent research on space debris laser ranging.

Particle swarm optimization (PSO) algorithm has good global optimization ability . However, PSO has some disadvantages such as the tendency to easily fall into local extremes, slow convergence speed, and low convergence accuracy at the late stage of the algorithm. Therefore, this study optimizes the traditional PSO algorithm, affording a simplified version and introducing random disturbances to facilitate the falling out of local extremes, thus enhancing its performance on global optimization. Moreover, a hybrid algorithm for the inverse design of photonic devices is proposed by combining PSO and the greedy algorithm with the gradient descent method to evaluate automatic switching between algorithms. Compared with the traditional PSO algorithm, the proposed hybrid algorithm shows better performance on global optimization with a faster convergence speed, higher accuracy, and superior design efficiency. A 1∶1 optical splitter is inversely designed using the proposed hybrid algorithm. At a bandwidth of 120 nm, the range of insertion loss at the output of the device is 0.125 dB?0.197 dB. Moreover, the device is manufacturable robustness.

The microstructure and phase composition of 304 stainless steel fabricated by laser cladding are studied by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results show that the cladding layer is mainly composed of austenite (γ) phase and FeCr (σ) phase, and the atomic ratio of Fe to Cr in the σ-phase is close to 1∶1. The γ-phase is in the form of fine and dense dendrites, while the σ phase is mainly in the form of long strips with a width of about 200 nm and locates in the dendritic interstices. During the rapid solidification of the cladding layer, the σ phase precipitates from the inter-dendritic eutectic ferrite (δ). A large amount of γ/δ interfaces formed by the inter-dendritic eutectic can effectively reduce the difficulty of nucleation of the σ-phase, and the enrichment of the inter-dendritic Cr element can promote the formation and coarsening of the σ-phase. Therefore, compared with the σ-phase precipitated in the solid solution process of stainless steel, the σ-phase precipitated in the laser cladding process has short formation time and large size.

The circular micro-pits are prepared on the surface of titanium alloys by the laser surface texturing technology. The tribological properties of micro-textured samples at room and high temperatures are investigated by the HT-1000 high temperature friction and wear tester. The effect of high temperature environment on the wear resistance and wear mechanism of micro-textured samples is discussed by analyzing the friction coefficient, wear amount, three-dimensional profile and morphology of wear marks. The results show that the tribological properties of laser textured samples are better than those of titanium alloys at room temperature and high temperature. Under the high temperature wear conditions, the micro-textured samples show a lower friction coefficient (0.27), smaller wear amount (1.26 mg), and narrower and shallower wear scar profiles. The wear mechanism of the micro-textured specimens changes from abrasive wear and mild oxidation wear at room temperature to severe oxidation wear at high temperature. The micro-textured specimens show better wear resistance at high temperature due to the debris collection characteristics of micro-pits and the formation of continuous and compact smooth friction oxide layers on the micro-textured surface under the action of friction loads.

In this paper, the simulation model of ablation and phase change of SUS304 stainless steel targets irradiated by continuous laser or continuous/modulated composite laser is established. The temperature rise curve and phase change distribution of the steel target irradiated by the composite laser or the continuous laser are calculated and verified by experiments. The ablation process of steel target is described by the dynamic grid method, and the curves of the ablation and phase change depths versus time are obtained. The simulation results are compared with the experimental results, and the results of temperature rise, phase transition distribution and ablation are in well agreement. According to the simulation and experimental results, the perforation of the steel target under the above laser irradiation can be divided into two ways: vaporization perforation and melting perforation according to the power density. When the output power is the same, the speed under the 2.55 kW/0.85 kW composite laser is 41% faster than that under the 3.4 kW continuous laser for the 20 mm steel target. The mass transfer mode is the joint action of melting and vaporization stamping, and the molten material splashing phenomenon is obvious in the ablation process, which forms a certain degree of positive feedback to the temperature rise and the phase change and ablation process of the steel target.

As for laser polishing of metal materials, the main criterion of laser polishing is surface roughness. In this paper, the orthogonal experiment and the response surface method are used to design an experiment of surface roughness after laser polishing in order to study the effects of defocusing distance, laser power, repetition frequency, and scanning speed on surface roughness. First, four factors and three levels of orthogonal experiments are designed, and the range analysis and comparison are used for searching the best result. Then, the response surface method is used to design a Box-Behnken Design (BBD) experiment with four factors and three levels. The numerical model of surface roughness is established and the optimized laser polishing process parameters are obtained. The minimum surface roughness is 0.1178 μm using the range analysis of orthogonal experiment, slightly higher than the surface roughness of 0.1112 μm using the response surface method. Finally, the best process parameters of laser polishing are listed: defocusing distance is 3 mm, laser power is 29.825 W, repetition frequency is 91.451 kHz, and scanning speed is 1749.794 mm/s. Under the best process parameters, the surface roughness of TC4 alloys after laser micro-polishing is reduced from 0.3247 μm to 0.1112 μm. Good polishing quality and low surface roughness can be obtained by using suitable process parameters.

Unearthed bronzes are easily eroded by the external environment due to their perennial burial underground and different kinds of corrosion occur. The presence of "harmful rust" accelerates the corrosion of bronze substrates. Aiming at the common corrosion of loose green rust, the safe cleaning thresholds by the neodymium yttrium aluminum garnet (Nd∶YAG) laser cleaner in dry, wet, and agar gel states are investigated in this paper. The surface morphologies and compositions are characterized by the microscope, in situ Raman spectroscopy, and energy disperse spectroscopy (EDS). The results show that the cleaning threshold in wet state with short free running (SFR) pulse mode is 2.83?8.49 J/cm2. The high corrosion removal rate is obtained, which is conformed to the rule of the "no change in the appearance of cultural relics" and the "minimum intervention" in cultural relics protection.

With the industrial need of laser cleaning, new requirements are put forward for the cleanliness evaluation of material surfaces before and after cleaning. In this paper, the bidirectional reflection technology of surface roughness measurement is proposed to characterize the surface quality of materials, and the autocorrelation length (T) and the root mean square of surface roughness(σ) are taken as the key parameters to characterize the surface quality of samples. Based on the Beckmann-Kirchhorff integral scattering model and after a reasonable simplification on rough surfaces, we plot the ratio Is/I0 of the incident light intensity (I0) to the reflected light intensity (Is) versus the inverse square of wavelength (1/λ2). Under the simplified model, an ideal linear curve can be obtained in the vertical incident direction with a large g value. The parameter σg obtained by linear fitting can be used as the characterization value of surface cleanliness. In the experiment, a beam of white light (xenon lamp) is first used to irradiate the surface of the titanium alloy sheet TA15 sample at a vertical angle, and then the specular reflected light beam on the surface of the sample is collected. The experimental results confirm the correlation between the surface quality of the sample and the σg value. This method is a non-contact spectral detection method, which can realize high-speed scanning, is convenient and fast, and can be used to online judge the cleanliness after laser cleaning in practical work.

The MSC Marc software is used to establish the thermal-mechanical coupled finite element model to analyze the evolution of temperature and stress deformation during laser direct deposition. Considering the stress relaxation behavior of titanium alloy at high temperature, the material constitutive equation is modified through several iterations. At the same time, based on the thermocouple and laser displacement sensor, a transient real-time measurement device is developed to measure the temperature and deformation of titanium alloy thin-wall parts during the actual forming process. By comparing and analyzing the simulated and measured values of the modified model, the results show that the temperature error between the in-situ measurement results and the simulated results is only 7.9%, the deformation error is 19.6%, and the laws of the substrate deformation are consistent. The stress in the deposition layer is generally tensile, and the main stress direction is consistent with the deposition direction.

In this paper, Co-based WC composite coating was prepared by laser cladding on the surface of high speed steel (HSS) tools damaged for numerical control machine tools. The results show that the interface metallurgical bonding between HSS substrate and repair layer is good without obvious defects. The repair layer is mainly composed of a Co-based FCC crystal structure and three types of carbides. The microhardness is about (1625±63) HV, which is 364.3% higher than that of the HSS substrate. The average friction coefficient is 0.65. The wear surface is relatively intact compared with the HSS tool. Cutting experiments show that the HSS tool with the Co-WC repair layer has lower O content on the rake face and better cutting performance.

In this paper, taking laser cladding coating on drilling tool surface in extreme environment as the research object, aiming at the friction failure of its surface in acid and alkali environment, and the tribological law of laser cladding coating under different pH value lubrication conditions is explored. Metallurgical coatings are prepared by laser cladding technology, the microstructure of coatings is observed, and the tribological properties of coatings under the different pH value lubrication conditions are studied. The results show that the coating is density, element distribution is uniform, and present good metallurgical bonding to the substrate. The main wear mechanism under different pH value and lubricating mainly adhesive wear and oxidation wear, and pH value has less influence on the friction coefficient of coating. The coatings present serious falling layer phenomenon due to corrosion and friction together on the alkaline environment.

Objectified and quantified indicators in the diagnosis of tooth-marked tongue in traditional Chinese medicine (TCM) are lacking. Thus, an algorithm for identifying and detecting multiple objectified indicators of tooth-marked tongue was proposed to aid the clinical comprehensive detection of tooth-marked tongue in TCM. The regions of interest of the tooth marks were extracted from the obtained tongue image, and a region binarization pretreatment was performed. The Graham scan method was used to extract the characteristics of the tooth marks, and the support vector machine algorithm was used to classify and discriminate the presence or absence of tooth marks. The improved Douglas-Peucker algorithm was used to fit the edge curve of the tooth marks, and the minimum number of curves satisfying the conditions was set as the number of tooth marks. Finally, the degree of tooth marks was determined by combining the number and depth of tooth marks. The algorithm has a correct rate of 80.86% in judging the presence or absence of tooth marks, 80.00% in detecting the number of tooth marks, and 89.63% in detecting the degree of tooth marks. Experimental results show that the proposed algorithm can realize the comprehensive detection of tooth-marked tongue and provide the corresponding objective parameters to assist the clinical diagnosis and treatment of TCM.

In this article, the crosstalk characteristics of the few-mode optical parametric amplification (FMOPA) are studied, and the intra-mode and inter-mode four-wave mixing and their phase matching conditions in the few-mode fiber are described in detail. The time-independent nonlinear Schrodinger transmission equation in few-mode fibers is given, and the intermodal crosstalk of FMOPA is described by numerical solution method, and the corresponding semi-analytical solution is deduced. First, a new fiber structure is designed to transmit five modes in C-band (1530?1565 nm) with a bandwidth of 20 nm. Then, the mode field distributions of different modes are obtained with COMSOL simulation software, and the propagation constants and nonlinear coefficients between these modes are calculated with Matlab software. Finally, the maximum differential gain between different modes can be reduced to 0.7 dB over 150 m fiber length by properly adjusting the transmission power of each mode. The experimental results show that the crosstalk results obtained by the semi-analytical solution and the numerical solution method are highly consistent.

A method of fabricating the multi-layer subwavelength circular gratings is proposed, which is based on the high-order waveguide mode interference and continuous sample rotation. The waveguide mode interference field is simulated by the finite element method, and the coordinate rotation matrix and the numerical simulation method are used to study the total optical field after performing continuous rotating exposure to the sample. A 442-nm laser is selected as the excitation light and TE5 and TM51 are taken as the examples to study the optical field distribution of the multi-layer subwavelength circular gratings fabricated by the high-order waveguide mode interference. By the optical filed distribution, the period of the X-Y plane and the period and layers of the Z-axis of the multi-layer subwavelength circular gratings are analyzed, which can be adjusted by changing the thicknesses of the photoresists and the waveguide modes for interference exposure. Under the condition of the same thickness of photoresist, there are many high-order waveguide modes and the excitation angle corresponding to the same high-order waveguide mode can be effectively controlled by changing the thicknesses of photoresists. As a result, the multi-layer circular gratings with different parameters can be fabricated by selecting the photoresists of different thicknesses and the high-order waveguide modes used in exposure. The proposed method is a simple and effective way to fabricate the multi-layer subwavelength circular gratings and has a certain application prospect in the field of micro-nano optics.

A femtosecond fiber laser is extensively used in the field of precision micro-hole manufacturing because of its short pulse width, high instantaneous power, and nonselectivity for processing materials. This study proposes a high-precision trajectory adjustable beam scanning system, which uses a motor to control the angle of the deflection wedge group and the parallel plate group relative to the laser optical axis. Then, it narrows the spot through a focusing lens to achieve precise control of femtosecond laser rotation scanning. Moreover, it solves the current problems of high depth-to-diameter ratio and difficult inverted taper hole machining. The system is applied for processing the oil hole of the automobile fuel injector, and the aperture of the processing aperture is 25—800 μm, and the aperture error is ≤±2 μm. A micro-hole taper can be achieved at -5°—+5° in taper hole processing. Micro-hole machining with a depth-to-diameter ratio of 20∶1 is achieved.

A method that can be applied to two-dimensional surface shape weighted superposition is proposed, which can control the light distribution by designing free-form surfaces for extended LED light sources. Five sampling points are taken on the light source surface, which are used as five point light sources to generate five free-form surfaces, and each free-form surface data point is multiplied by a weight factor. The weighted free-form surfaces are superimposed, and the superimposed free-form surfaces are used as the initial outline. The particle swarm algorithm is used to further optimize the weight factor to obtain the optimal weight factor, and the five free-form surfaces are weighted and superposed using the optimal weight factor. The light distribution of the extended LED light source is adjusted by using the superimposed optimal free-form surface lens. The simulation result shows that this method enables the uniformity of the illuminance of the target surface to reach 75%, which is 15% higher than that generated by the initial lens on the target surface. This method has the advantages of fewer optimization variables, good surface continuity, and fast convergence speed.

In order to improve the light utilization rate of the existing outdoor basketball court lighting and reduce the glare value, this paper designs a deflected lighting scheme to reduce the light exposure to the outside of the field. Through optical analysis of different lighting schemes, the reasons for the low utilization rate of light are found, and the deflected light design is carried out to make the light illuminate the inside of the venue in a concentrated manner. DIALux is used for simulation analysis of the overall scheme: the overall illuminance uniformity reaches 0.85, and the measured glare value GR maximum is 29, which is far less than the outdoor stadium glare required value of 50. The uniformity and glare control can meet the needs of various competitions. The calculated light utilization rate of 75% is far greater than the 52% of the existing lighting scheme. Compared with the existing lighting scheme, the energy-saving effect is significant.

This study focuses on the design and simulation of the transmission far infrared microscopic imaging optical system matched with the cooled staring focal plane array detector that operates in the wavelength range of 50—70 μm and contains pixel number 64×64, each pixel is 120 μm×120 μm in size in order to make the far infrared detector obtain optoelectronic signals with a high signal-to-noise ratio. Stray light analysis predicts the negative effect caused by cold reflection, and a solution is proposed to address it. The simulation results show that when the designed optical system’s spatial resolution, numerical aperture, focal length, effective magnification, and central wavelength are 200 μm, 0.25, 14 mm, 10, and 61 μm, respectively, the modulation transfer function value reaches 0.305 at the characteristic frequency of 5 lp·mm-1, and the energy concentration of the surrounding circle of the system exceeds 80%. Meanwhile, the optical system’s produced object picture is easily distinguishable, indicating that it meets the functioning criteria of the focal plane array detector.

With the popularization of laser communication to the platforms with limited load capacity, laser communication system is developing towards lightweight and miniaturization. As a key role of laser communication, the design of scanning and acquisition unit is also need to be lightweight and miniaturized. In this paper, first, the double wedge prisms based scanning and acquisition unit abandons the conventional mechanical servo structure, which realizes beam deflection in large field of view by independently rotating the prisms around the common rotation axis. Then, the beam deflection model and the scanning pattern model of double wedge prisms are established by using non-paraxial ray tracing method, and the scanning mode of the double wedge prisms is analyzed, which provides a certain reference for the development of light and miniaturized laser communication optical transceivers. Finally, the design and application of a kind of light-weighted and miniaturized laser communication optical terminal is proposed and analyzed based on rotating double wedge prisms and quadrant detector multiplexing technology.

The performance of metamaterial absorbers can be affected by the incident angle of electromagnetic waves, and it is difficult to design metamaterial absorbers with wide-angle stability. The traditional method relies on artificial design and optimization, which limited by its difficulty and long cycle. According to the target design’s characteristics, we design a wide-angle and high-absorptivity metamaterial absorber based on the improved particle swarm optimization algorithm. Dynamic weights and Gaussian errors are added to resolve the problem of weak local search ability in the later stage of binary particle swarm optimization algorithm. To achieve wide-angle and high-absorptivity characteristics of the absorber, the improved binary particle swarm optimization algorithm is used to optimize the structure of discrete metal blocks coded with 0 and 1 on the surface of the absorber. The simulation results show that the designed metamaterial absorber has a high absorptivity of greater than 90% from 9.4-13.3 GHz, and perfect absorption, i.e., absorptivity exceeds 99%, is obtained in the broadband of 11.6-12.6 GHz. Moreover, the absorption remains above 80%, even for the incidence angles of up to 60° under both transverse electric and transverse magnetic polarizations. This design method overcomes the shortcomings of the traditional design method and demonstrates the unique advantages of on-demand design without human intervention in the design process. This technique has broad application prospects in related fields.

The core component of atomic sensors is the alkali-metal atomic vapor cell, such as the atomic electric field meter, atomic gyroscope, atomic magnetometer, and atomic clock. Integrating the optical path on the glass shell of the atomic vapor cell is one of the most effective ways to realize the miniaturization of atomic sensors. Herein, to solve the problems associated with discrete optical components and low laser utilization in atomic sensors, a type of metasurface that can separate and transmit lasers with different wavelengths was designed based on the generalized Snell's law and equivalent medium theory. By integrating this metasurface with an atomic vapor cell, it can conveniently detect and process the laser passing through the vapor cell. In addition, the proposed method can improve the integration and portability of atomic sensors and provide an achievable scheme for the miniaturization of atomic sensors. Simulation analysis using finite-difference time-domain (FDTD) was conducted to excite a cesium Rydberg atom via a two-photon method. The results show that the metasurface can cause the 510-nm coupling laser to have a deflection angle of 6° without affecting the propagating direction of the 852-nm probe laser, and the transmittance of the two lasers exceeds 96.3%.

During measurement, the laser self-mixing interference is susceptible to noise interference, which affects the measurement’s accuracy and stability. Consequently, based on the use of dual-beam feedback to improve the signal-to-noise ratio of self-mixing interference signals, this paper aims to further reduce the system noise by incorporating the dual-polarization differential detection technology of random polarization laser self-mixing interference. Experimental results show that combining dual-beam feedback with dual-polarization differential technology can increase the signal-to-noise ratio of self-mixing interference signals by 7 dB. Therefore, the proposed method and technique have good application value in self-mixing interferometry.

A special real mixed entanglement of triqubit pure states is proposed. Different from Greenberger-Horne-Zeilinger (GHZ) entanglement and W entanglement, it has the properties of GHZ entanglement and W entanglement at the same time. The mixed entangled states are constructed using two inequivalent sets composed of four non-superfluous basis vectors. A new measurement method, the total tangle, is introduced for quantifying total entanglement (including mixed entanglement) of the triqubit pure states. It is revealed that there is mixed entanglement in the final state in the experiment reported by Walther et. al., and the proportion of W entanglement is larger than that of GHz entanglement.

The evolution properties of geometric quantum discord (GQD) of the Heisenberg XXZ spin model in a non-Markovian environment are studied using the quantum state diffusion method. The influences of environmental correlation parameters γ, coupling constants in the xy plane Jxy, coupling constants in the z direction Jz, applied magnetic field B and Dzyaloshinskii-Moriya (DM) interactions on the GQD dynamics are analyzed. The results show that the shorter the γ is, the more obvious the non-Markovian characteristics of the environment are, the better it is to effectively improve the GQD; Jxy and Jz have different effects on the GQD when different initial states are selected; in the non-Markovian environment, increasing the magnetic field B can improve the GQD, while the DM interaction will lead to decaying oscillations of the GQD. It is worth mentioning that the GQD can be effectively induced from the entanglement-free initial state system.

Semi-quantum dialogue has a relatively strong practicality in quantum communications, and its partial users do not need to be equipped with expensive quantum devices. A four-party authenticated semi-quantum dialogue protocol based on the Brown states is proposed. Then, the proposed protocol is extended to multi-party using the generalized Brown states. Through security analysis, it is verified that the proposed protocol does not have the information leakage problem and can effectively resist the intercept-resend attack, man-in-the-middle attack, disturbance attack and Trojan horse attack. The analysis comparison with the similar protocols shows that the proposed protocol has high quantum communication efficiency.

Aiming at the problem of multi-directional strain measurement, we design a trifarious fiber Bragg grating (FBG) strain sensor based on a boss and a ring-shaped substrate structure. We realize the simultaneous measurement of the strain in three directions of the structure. Static contrast and vibration monitoring experiments with resistance strain gauges were conducted using the vibration testing machine and stainless steel plate. The results show that the static strain curves of the FBG sensor and strain gauge in three directions are the same. Additionally, the correlation coefficients are 0.98, 0.98, and 0.99, respectively. The results of vibration power spectrum analysis show that the FBG sensor and strain gauge can observe the first and second harmonics; the frequency error is 2.77% and 0.97%. Furthermore, the strain gauge can detect high harmonic signals. The sensor has many advantages, such as simple structure, small size, high accuracy, and accurate location, having a promising application future in multi-directional strain monitoring.

In 1981, Professor Caves first proposed the concept of "squeezed state" and indicated that the sensitivity of laser interference gravitational wave detection can be improved using the squeezed states of a light field. For the past forty years, the squeezed states of light have been successfully used in quantum precision measurements such as gravitational wave detection, displacement measurement, and phase measurement that beat the standard quantum limit. Two-mode squeezed and multi-party entangled states prepared based on single-mode squeezed states also play an important role in quantum information processing, such as quantum computation and quantum communication. This review briefly introduces the basic concepts, preparation, and detection methods of the squeezed states of light and their application progress in quantum precision measurement, quantum communication, and quantum computing.

The direct-detection optical fiber communication system has become the main solution for the future short-reach optical transmission links due to its simple structure and low cost. The field-signal recovery (FSR) technique is a critical technique to improve the capacity of the direct-detection system. This paper introduces a system structure, working principle and main research progress of Stokes vector receiver, carrier-assisted differential detection receiver and Kramers-Kronig (KK) receiver in direct detection optical fiber communication systems. The advantages and disadvantages of three commonly used FSR techniques are compared. The results show that compared with the other two techniques, and the KK receiver technology has obvious advantages. Finally, the important position of KK receiver in the future direct-detection optical fiber communication systems is clarified. Meanwhile, the key technical challenges faced by KK receiver are analyzed and the solutions for reference are given ultimately.

The 1 μm band ultrafast laser has a wide application prospect in material surface modification and material micromachining. Laser oscillation and amplification technology can enhance the mode selection ability of resonator, and laser gain and compensation device can increase the peak power of laser, and further reduce the pulse width of output laser. This paper mainly summarizes the latest research progress of ultrafast laser oscillator (pure passive mode-locking, soliton clamping, and Kerr lens mode locking) and ultrafast laser amplifier (chirp pulse amplification, pulse shaping, and nonlinear compression technique) of the 1 μm band period, and 1 μm ultrafast laser control devices and systems (laser gain medium, dispersion control device, high order transverse mode generation, and ultrafast laser intelligent control). Finally, the development prospect and trend of 1 μm band period ultrafast laser are prospected.

As one optimization technique for modulation format, constellation shaping technique greatly improves the flexibility, nonlinear compensation and error performance of traditional coding modulation scheme. It can achieve high spectral efficiency and signal transmission close to Shannon’s limit without increasing the transmission power and complexity of the system, which has been widely used in many fields. The research status and the latest advances in the fields of constellation shaping technology schemes are introduced, especially the type, method, architecture and other aspects. The basic principle, performance comparison and related applications of probabilistic shaping with arithmetic coding are mainly discussed and the current problems and future trends of probabilistic shaping techniques are summarized.

Infrared spectroscopy detection provides a reliable and stable method of analysis. Micro electro mechanical system (MEMS) Fabry-Perot (F-P) tunable filters are the core components of instruments, such as infrared spectrometers, mobile phone camera modules, portable high spectral imagers, and remote sensing devices. Traditional infrared analysis systems and spectrometers are bulky, power-consuming, and expensive. Due to their large size and power consumption, they are not suitable for miniaturized devices. Compared with traditional types of filters, MEMS F-P tunable filters have the advantages of small size, high resolution, easy integration, and low power consumption. This article summarizes the progress made in the research on MEMS F-P tunable filters in China and other countries in recent years and discusses their wavelength tuning range, spectral resolution and aperture size, and the complexity and cost of manufacturing. Finally, the future development trends and application prospects of MEMS F-P filters are prospected, and these provide a reference for future research on MEMS F-P tunable filters.

Electromagnetic metamaterial perfect absorbers have unique subwavelength structures, which can generate effective electromagnetic resonance with the incident electromagnetic wave, and achieve nearly 100% perfect absorption over a specific frequency range. Electromagnetic metamaterial perfect absorbers, especially the terahertz band perfect absorbers, have been widely concerned by researchers at home and abroad, and have made some progress. In this paper, the research progress of the terahertz band-based electromagnetic metamaterial perfect absorber is reviewed, the basic structural characteristics, performance, and theoretical model of the metamaterial absorber are described, and the future development trend and application prospect of them are briefly discussed.

Phase sensitive optical time-domain reflectometer (Φ-OTDR) transmits light pulses into the sensing optical fiber, and uses the method of analyzing the back Rayleigh scattered light or forward scattered light of the sensing fiber to identify and analyze intrusion disturbance events. Compared with other distributed optical fiber sensing technology, Φ-OTDR can perform long-distance distributed multi-point measurement with high accuracy and reliability. The study of Φ-OTDR has important application value. In this paper, the basic principle, structure, system performance, signal demodulation, and application of Φ-OTDR are introduced, and the extension Φ-OTDR technology is prospected.

The test quality of optical force accelerometer is isolated from the external environment, and the optical detection accuracy is excellent. It can detect ultrasensitive acceleration and is widely used in different navigation systems, ultraprecision microgravity detection, entertainment, and other fields. The optical accelerometer system comprises four modules: a loading module, an optical trapping module, a displacement detection module, and a cooling feedback module. From a practical standpoint, the existing technical methods of each module are combed and summarized in this research. The optical accelerometer will be developed in the future for simplifying and compacting each module, and its acceleration detection accuracy and reliability will be continuously improved during this process.

Parallel micro/nano lithography is essential for rapidly fabricating microstructures. This review briefly introduces the principle and advantages of parallel micro/nano lithography and then analyzes and discusses spatial light modulator (SLM)-based parallel micro/nano lithography. In terms of modulation to incident light, the principle and progress of SLM-based parallel micro/nano lithography (which is divided into two types, i.e., multifocus parallel lithography and projection parallel lithography) are reviewed. This review summarizes the current situation, existing problems, and future prospects of these two types of SLM-based parallel micro/nano lithography.

Maskless lithography has a wide range of applications in microstructure fabrication due to its advantages of no physical mask, low cost and suitability for mass production. Maskless digital lithography based on digital micromirror device (DMD) has the advantages of high resolution, good flexibility and high processing accuracy, which has become a research hotspot in the field of lithography in recent years. This paper reviews the research progress of DMD digital lithography, including DMD-based scanning lithography, stepping lithography and gray-scale lithography, and introduces the applications of the method in integrated circuit, micro-optics, three-dimensional printing and other fields, the paper also summarizes the current problems of DMD lithography and its future development trend.

In this paper, based on the law of conservation of electromagnetic energy, a model of equating the electromagnetic anisotropic medium to be the electromagnetic isotropic medium is established, and its correctness is verified. Under the condition of the electromagnetic wave length being comparable to the geometrical parameters of the cylinder,the equivalent permittivity of the cylinder of gypsum crystal in the elliptical Gaussian beam varies with its geometrical parameters, beam parameters and beam propagation direction are studied. The simulation results show that the equivalent permittivity fluctuated changes with the increase of the radius of the cylinder, and the change of the equivalent permittivity is very small with the increase of the length of the cylinder. In addition, the analytical expression of the scattered field of an anisotropic cylinder being irradiated by an electromagnetic wave beam with an arbitrary direction is presented. The simulation results show that the radius of the cylinder and the angle between the electromagnetic wave propagation direction and the symmetry axis of the cylinder have a great effect on the scattering, and the length of the cylinder, the distance between the beam and cylinder and the beam waist width etc. have little effects on scattering.

The method for identifying and classifying plastic express bags as the physical evidences commonly seen at crime scenes is proposed to promote the public security investigation. By means of X-ray fluorescence spectroscopy, the element types and contents of 60 plastic express bag samples with different origins and brands are tested. Meanwhile, the qualitative and semi-quantitative analysis is performed according to the spectral data, so that the 60 samples are preliminarily divided into 13 categories. Based on the within-cluster sum of squared errors (SSE), the relationship between SSE and number of clustersis explored, and the best number of clusters is determined to be 6. Besides, the 60 samples are clustered into 6 categories by using the K-means algorithm. Finally, the clustering results are analyzed through the Fisher discriminant analysis. As can be learned from the test, the accuracy of original classification and that after cross-validation classification of the 60 samples are 98.3% and 91.7%, respectively. This verifies that the method for identification and classification of plastic express bags is both accurate and scientific, which is based on K-means and SSE. The inspection and identification of classified plastic express bags as physical evidences through X-ray fluorescence spectroscopy, K-means and SSE are non-destructive, quick and effective, and the proposed model can give accurate and reliable results.

Aiming at the problem of secondary diffraction in aberration correction of an M-type Czerny-Turner spectrometer, we propose the anti-secondary diffraction condition for this optical structure under the coma-free condition. The main factors of secondary diffraction are analyzed and deduced theoretically. Combining the anti-secondary diffraction condition with the constraint coma-free condition, we built an M-type coma-free Czerny-Turner spectrometer. In order to verify the correctness of the theoretical analysis, the Zemax OpticStudio simulation software is used for a comparative experiment. The simulation results show that there is no secondary diffraction in the M-type optical path structure meeting the constraints, but there is secondary diffraction in the M-type optical path structure that does not meet the constraints, which is consistent with the theoretical analysis result. Under the condition that the incident slit width is 25 μm and the grating engraving line density is 600 line/mm, the spectral resolution of the optical system optimized by the software is better than 1 nm in the range of 200?500 nm.

Owing to the rapid development of organic-inorganic hybrid perovskite materials, they have been employed in many applications such as solar cells, light-emitting diodes, lasers, spintronic devices, and photodetectors. Triple-cation perovskite thin films exhibit higher conversion efficiency in solar cells than double-cation ones. Herein, a high-quality FA0.79MA0.16Cs0.05PbI2.52Br0.48 (FAMACsPbI2.52Br0.48) thin film is prepared on a Si substrate using the one-step spin method. The crystal structure, surface morphology, and optical properties of the prepared thin film are characterized using X-ray diffraction, scanning electron microscopy, and spectroscopic ellipsometry, respectively. Moreover, the optical constants of the thin films are described using the Tauc-Lorentz model. The second derivative of the corresponding dielectric function is also provided, with optical transitions located at 1.66, 2.21, 3.36 eV. Results show that the peak position of the photoelectric transition is mainly determined by X-site doping and the contribution of the A-site doping to the optical transitions is negligible. Finally, the optical properties of a FAMACsPbI2.52Br0.48 material-based perovskite solar cell are simulated using the finite-difference time-domain method. The optical properties of the solar cell are similar to those of triple-cation perovskites obtained via ellipsometry analysis. Furthermore, the solar cell based on the FAMACsPbI2.52Br0.48 triple-cation perovskite thin films can achieve a lighting efficiency exceeding 85%.

A spectrum optimization problem of maximizing the mesopic visual luminous efficiency of phosphor-coated white light-emitting diodes (LED) by exciting green and orange phosphors with a blue LED. The objective function is to maximize the average mesopic visual luminous efficiency at multiple brightness levels. The optimization model for correlated color temperature (CCT) is discrete and exhaustive, and it can only maximize the average mesopic visual luminous efficiency for varied brightness levels under a constant color temperature. A nonlinear constrained optimization model with a simple objective function is suggested in this study to attain the maximum mesopic visual luminous efficiency at varied brightness levels, and the CCT is considered an optimization parameter varying in a specific range. The experimental results show that the model can obtain the optimal LED spectrum, while meeting the requirements of color rendering index, color fidelity, and a given mesopic visual brightness level, and that it truly achieves the purpose of maximizing the medium visual luminous efficiency under the specified brightness level.

Aiming at the problems of color fading and chromaticity coordinate deviation in the existing railway signal in China, an idea of single lamp multi display light emitting diode (LED) mixed light intelligent signal is proposed in this paper. First, according to Grassmann's law and International Commission on illumination standard chromaticity system mixing principle, the RGB (Red, Green, Blue) three-color mixing modulation system is established. Then, the functional relationship between duty cycle, chromaticity coordinates and related color temperature is established, and the RGB three channel moon white, yellow and purple lights are adjusted by pulse width modulation. Finally, the design and construction of three channel mixed light modulation system with adjustable duty cycle are completed, and the simulation and experimental verification are carried out combined with the relative luminous flux attenuation data. The results show that the RGB three-color light system can accurately set the relevant chromaticity coordinates of each color light and realize the chromaticity adjustment under different conditions, so as to meet the needs of railway signal display.