In this study, we investigated the single-path and multipath conversions of ultracold bosonic heteronuclear tetra-atomic molecules using the generalized stimulated Raman adiabatic passage technique. First, we established a mean-field model and obtained the corresponding dark state solutions and two-photon resonance conditions. Next, we compared the molecule conversion dynamics of the single-path and multipath cases and found that constructive interference effects existed in the multipath cases; this could increase the molecular conversion rate. In particular, for the three-path scheme, the interference effect was obvious and the conversion rate was high. We further studied the influence of external field parameters on the conversion rate of the multipath scheme by varying the pulse intensity and found that the influence had two sides: constructive and destructive interference, respectively, which increased and decreased the conversion rate of molecules.

Integrated optical filters based on guided-mode resonant gratings have potential applications in optical fiber communications. However, the output spectrum of a single guided-mode resonant grating is generally Lorentzian, which hinders the use of this type of structure in wavelength division multiplexing systems. Traditional methods generally use multiple resonator cascades to achieve a flat-top filter response. However, the entire structure is considerably large and the manufacturing process is complicated. Therefore, based on the output spectral response, a cascaded double-layer guided-mode resonant gratings structure of the flat-top and steep-edge type is proposed in this study. First, the physical model of the device is established. The physical mechanism is to combine the guided mode resonance effect with the Fabry-Perot resonance effect, and then use the physical model to analyze and design the filter structure. The center wavelength of the filter is observed to be 1550 nm, and its 3 dB bandwidth can be increased to 20 nm.

The Talbot effect from the spherical wave illuminating on two-dimensional (2D) grating is investigated theoretically and experimentally. First, the complex amplitude distribution of the light field in the Fresnel diffraction region after the spherical wave is illuminating on the grating is analyzed. Second, the imaging conditions of the Talbot image and fractional Talbot image are discussed. The imaging position and imaging period are determined by the distance from the light source to the grating and the distance from the grating to the observation surface, and the Talbot distance of the spherical wave incident grating is equal to the product of its periodic magnification and the Talbot distance of the plane wave incident grating. Experimental results are consistent with the theoretical results, and the clear Talbot image and fractional Talbot image can be observed at specific location. By changing the distance from the light source plane to the grating, the Talbot image changes according to a specific law. Because the grating period is less than twice the aperture side length and based on the divergent characteristics of the spherical wave itself, the pixel overlap phenomenon appears in the fractional Talbot image. According to the degree of overlap, the overlapped image can be divided into two types (discrete point distribution and checkerboard distribution) of fractional Talbot images. The research in this paper can promote the application of the Talbot effect in optical measurement and array lighting.

Based on the mode coupling theory of a tilted fiber grating (TFBG), the spectral characteristics of a TFBG under different ambient refractive indexes are studied by the Optigrating software. The results show that when the ambient refractive index is less than the refractive index of the cladding mode, both the core mode and the cladding mode of the TFBG exist; in contrast, when the ambient refractive index is larger than or equal to the refractive index of the cladding mode, only the core mode exists and the cladding mode disappears. The experimental results of this TFBG in distilled water, anhydrous ethanol, safflower oil, peanut oil and soybean oil are consistent with the corresponding simulation results. These research results have certain guiding significance for the real-time leakage monitoring of pipelines full of liquids with larger refractive indexes.

In this article, first, the advantages of laser communication links are introduced. Then, end-to-end learning based on generative adversarial network improves the real-time and global optimization of the communication system. Finally, because of the lack of robustness in the system caused by the training set cannot contain all situations during the training process of the offline learning mode of the system, a self-organizing incremental learning method is introduced to improve online incremental training of the end-to-end system. Experiment results show that by implementing the self-organizing incremental learning method, the end-to-end communication system can simulate the channel effect efficiently, and it greatly improved the real-time optimization and robustness of the system.

Optical fiber speech sensors have the advantages of anti-electromagnetic interference, high sensitivity, and long sensing distance. However, there are often much noise when using them for speech detection, which greatly affects the quality of speech signals. To reduce the influence of noise on the speech signal, a multiwindow spectrum estimation spectrum subtraction method based on endpoint detection for the optical fiber speech sensor system is proposed in this paper. Through endpoint detection, it is determined whether the signal is a speech frame to realize the estimation of the average noise amplitude. The constructed linear Sagnac optical fiber speech sensing experiment results show that compared with traditional spectral subtraction and multiwindow spectrum estimation spectrum subtraction methods, the method has a better suppression effect on background noise, and the signal-to-noise ratio of the speech signal can be increased by 2?3 dB.

To improve limitations of bandwidth capacity of optical fiber communication system in practical engineering applications, a photonic crystal fiber core structure which is capable of transmitting fundamental and high-order modes is proposed based on space division multiplexing technology. The effective refractive index curves of the corresponding modes under different structural parameters are obtained using the finite-difference imaginary-distance beam propagation method. An asymmetric dual-core photonic crystal fiber mode converter is designed by matching the effective refractive index curves of the two modes. It demonstrates that such an LP01-to-LP02 mode converter can be achieved at the wavelength of 1550 nm. In a wider frequency range, the mode coupling efficiency is above 90%, and the coupling length is about 178.5 μm. The device diameter is 47.6 μm, and the structural design is flexible and controllable, which can meet the needs of future large-capacity communication systems.

Based on the working principle of the parallel Vernier effect, a sensitization method to achieve the Vernier effect by superimposing the spectrum is proposed. The Fabry-Perot (F-P) temperature sensing interferometer is used to obtain the measured reflection spectrum. The reflection spectrum of the reference interferometer obtained using the F-P interference principle is superimposed during data processing to achieve the Vernier effect. In the range between 30 ℃ and 55 ℃, the temperature sensitivity of 5.0380 nm/℃ was achieved. Controllable temperature sensitivity can be achieved by changing the cavity length of the reference interferometer. Besides, the dip point of the Vernier envelope for measurement can be placed at any desired wavelength by changing the initial phase of the reference interferometer's incident light. A sensing interferometer with cavity length of 118.60 μm and a reference interferometer with cavity length of 96.60 μm were designed and prepared to conduct a temperature sensitization experiment based on the parallel Vernier effect. The measurement sensitivity of 2.7984 nm/℃ was obtained, which is consistent with the temperature sensitivity achieved by superimposing the F-P reflection spectrum with the same cavity length. The relative error is only 0.57%. Thus, the proposed method is feasible and effective. Besides, it solves the problem that the reference interferometer is vulnerable to the external environment.

The flat-top beam output is realized through special treatment of the cone area of the optical fiber signal combiner and output fiber and the torsion treatment of the output fiber. The experimental results show that the beam intensity distribution of 4 × 1 signal combiners with a 20/130 μm (the core diameter is 20 μm, the cladding diameter is 130 μm) fiber input and 100/120/360 μm (the core diameter is 100 μm, the cladding diameter is 360 μm, the diameter of the low refractive index layer between the core and cladding is 120 μm) fiber or 200/220/360 μm fiber output is not a flat-top distribution; the strength distribution is relatively scattered. More fiber mode will be excited by twisting the output fiber. Then, a 200/220/360 μm fiber was spliced between the cone area and output fiber. The intensity distribution of 4 × 1 signal combiner is uniform and has a flat-top distribution, and presents distribution in a 4.88 mm range close to the beam waist. The calculation results show that the flatness of the beam in that range is below 0.1. It also shows that the signal combiner can handle a signal power of more than 2 kW.

In this study, a soil pressure sensor based on additive manufacturing (AM) technology and fiber Bragg grating (FBG) is designed. The calibration experiment results indicate that the sensitivity, minimum resolution, and measurement range of FBG soil pressure sensor are 0.2 pm/kPa, 5 kPa, and 1000 kPa, respectively, and that the sensitivity of the sensor can be adjusted as per requirement using AM parameters (filling density, filling material) to reduce measurement errors. The experimental results of the indoor model box show that, the sensor can effectively measure the internal pressure of soil during test loading and that measurement range is wide. The resolution and range can be customized according to real-world conditions, which provide a new approach for internal pressure monitoring of the soil.

To study the communication performance of non-line-of-sight (NLOS) ultraviolet (UV) communication in foggy environments, we propose a new attenuation model and a simplified calculation method of asymmetric factors. These solve the problems that the common fog attenuation model is not suitable for ultraviolet atmospheric channel attenuation and the calculation of multiple scattering transmission model is complex. A single-input-multiple-output (SIMO) ultraviolet communication system is established using the diversity receiving technology. First, a UV attenuation model is developed based on the Mie scattering theory to calculate the UV attenuation parameters of two fog types at different concentrations. Second, the asymmetric factor of a droplet size is established to simplify the calculation. Finally, the equal-gain combining technique is used to combine the diversity received signals. The performance of the SIMO UV communication system is analyzed by the Monte Carlo method and compared with that of the SISO UV communication system. The results show that diversity reception can effectively improve the performance of ultraviolet communication on foggy days: on thick, medium and thin fog days, and the maximum communication distance of the SIMO communication system is about 5, 10, and 10 m longer than that of a SISO communication system, respectively. When the bit error rate of the SISO ultraviolet communication system is 10-3, the bit error rate of the SIMO communication system is reduced to about 10-5.

The monitoring requirements of temperature, strain, and other physical parameters during the assembling, cooling, and operation of low-temperature and high-temperature superconducting magnets are introduced. The working principles of fiber-optic sensing technologies based on the fiber Bragg grating, Brillouin scattering, Raman scattering, and Rayleigh scattering are also introduced. The research progress of the above optical fiber sensing technologies in temperature and strain measurement of low-temperature and high-temperature superconducting magnets is reviewed. The existing problems in the above researches are summarized, and the future research is prospected. This review is helpful for researchers in the field of superconducting magnet, especially in the field of superconducting magnet stability, to understand the application progress of optical fiber sensing technology in superconducting magnet stability improvement intuitively, clearly, and comprehensively.

Due to the variability of the underwater environment, individual nodes in the underwater wireless optical communication sensor network cannot meet the requirements of line-of-sight transmission. In order to restore effective communication between nodes, this paper proposes a relay routing algorithm based on relay cooperative transmission method, and the bit error rate of the mixture exponential-generalized Gamma model is used as the relay selection metric. In order to ensure that the selected relay node can solve the link failure problem in the sensor network under the condition of low energy. In terms of relay selection, consider the power threshold when the node communicates successfully. The simulation results show that the relay cooperative routing algorithm for reconstructing the transmission link can guarantee low bit error rate and maximize the network lifecycle simultaneously.

To explore the influence of a double-vortex optical interference pattern on the precision of micromeasurement, a method to measure the characteristics of the self-interference pattern of an optical vortex is proposed based on the principle of double-vortex optical interference. In this paper, the factors affecting the interference image of two vortex beams are analyzed, and an optical system is designed and built to measure the characteristics of the double-vortex optical interference pattern with shear interferometry. By collecting the interference images after different displacements of the objects in the system under the same conditions and analyzing the effect of the positions of two vortex beams and the number of topological charges on the interference image with the method of image correlation processing, a conclusion can be drawn from the measured deviation of a double-vortex optical interferogram that the pixel positions of the two phase singularities are (351, 251) and (151, 251) and the topological charge is 1 as the minimum when the fringe angle and width are 0° and 0.1714 mm, respectively, from comparing the results with the theoretical value. It means that the double-vortex optical interference images with low topological charge and phase singularities located in the center of the image and the alignment direction orthogonal to the fringe direction are more suitable for micromeasurement.

In order to improve the ability of the star sensor to detect the limit magnitude, a complex double-Gaussian structure optical lens is designed through selection of models and parameter calculation in this paper. After optimized by ZEMAX software, a refraction optical lens without vareing composed of 12 spherical lenses is finally obtained. The lens has an entry pupil diameter of 125 mm, a system focal length of 200 mm, a full field angle 2ω of 14.84°, and a spectrum range of 500-800 nm. The design results at a temperature of 20 ℃ show that the root mean square dispersion spot radius is less than 3.5, the full field optical design modulation transfer function (MTF) is more than 0.7 at 60 lp/mm, the energy concentration in 3×3 pixels is more than 90%, the distortion is less than 1%, and the maximum magnification chromatic aberration is 1.6. After processing and adjustment, the lowest laboratory static MTF of the measured optical system at 60 lp/mm is 0.324.

The optical axis of a transmission optical system cannot be found directly. To solve this problem, an optical axis calibration method based on the characteristics of optical nodes is proposed. The method is used to investigate the characteristics of a node and an equivalent node, by observing the focal plane image point displacement change, the location of the node to calibrate the optical axis of the system is determined. Furthermore, based on this method, the bidirectional exchange standard double autocollimation optical axis calibration device of parallel light pipe is designed, including imaging thrusting at the receiving end type structure design, which can effectively avoid the influence of the wavefront error. Finally, the feasibility of the proposed method is verified. Experiment results show that the proposed method has high optical axis calibration accuracy and wide adaptability. The optical axis calibration accuracy of the lens optical system is 7.7", which provides an auxiliary means for testing and adjusting lens optical systems in space optics and national defense fields.

This study proposes a surface defect detection method based on the scattering field distribution fitting approximation to accurately detect different sizes of optical element surfaces, especially small-size defects, with typical optical element surface defects-pits and scratches-as the research target. Experimental results show that the method can rapidly and effectively detect small-size defects on optical element surfaces and the relative error between fitting calculation results and the original size of a sample is basically less than 5%, which verifies the effectiveness of the method. In addition, the method addresses the problems of low accuracy and complex structure of existing measurement methods and introduces a new idea for accurately detecting microsized defects on optical element surfaces.

Rotor-stator axial clearance measurement requires small-size sensing probe, large measurement range, and high measurement accuracy. However, existing measurement methods cannot meet these requirements. Considering the characteristics of rotor-stator axial clearance variation, we propose a measurement method based on frequency-swept interferometry and develop a corresponding high-speed real-time online measurement prototype. The prototype combined large-bandwidth high-speed frequency sweeping and periodical Doppler error smoothing to achieve a large measurement range and a high measurement accuracy and used a single-mode optical fiber to realize the small-size probe. To test the prototype performance, we built a simulation experiment platform for the proposed rotor-stator axial clearance measurement. Dynamic clearance experimental results showed that the measurement range of the prototype was 20 mm, and the measurement accuracy was 0.08% of the full range at 15000 r/min. The proposed prototype represents a new measurement technique for rotor-stator axial clearance measurement and provides an important reference for improving measurements.

In the process of laser frequency scanning interferometry ranging, the target vibration introduces Doppler shift in the ranging interference signals which results in the spectral broadening of the signal and the amplification effect of ranging errors. To reduce the effect of vibration on ranging results, we proposed a ranging error compensation method based on laser self-mixing vibration measurement. This method compensates the phase modulation of the target vibration on the ranging interference signal by synchronously measuring the phase change of the self-mixing interference signal, and meanwhile the frequency resampling method is used to correct the laser frequency modulation nonlinearity. Finally, the feasibility of the proposed method is verified by simulation and experiment. In the experiment, when the measured target amplitude was 7102.1 nm, the measured vibration standard deviation was 7.9 nm, the range measurement standard deviation before compensation was 3270.6 μm, and the range measurement standard deviation after compensation was reduced to 21.4 μm,which was close to the case of no vibration, indicating that the amplification problem of ranging errors caused by target vibration was effectively solved.

The traditional method for measuring sound velocity in seawater is developed on the basis of the piezoelectric effect. This traditional method is prone to errors because of its uncertain starting points when measuring the propagation time and distance. To address these problems, this study proposes an approach for measuring underwater sound velocity based on the acousto-optic effect between optical frequency comb and ultrasonic pulse. We introduce the acousto-optic effect with a clear interaction point between sound and laser. A dual Michelson interferometer system is built to measure the optical pulse markers generated when the ultrasonic pulse passes through two measuring arms. We measure the ultrasonic propagation time and distance using the cross-correlation technique. The traceability of the method is clear, however, the accuracy of the method has room for improvement. The experimental results show that the experimental system can achieve high precision measurement of underwater speed, and the measurement uncertainty is 0.023 m/s. It can be used as a new calibration device for measuring underwater sound velocity.

Aiming at the problem of low signal sampling rate and signal processing speed of linear frequency modulation continuous wave displacement sensor, this paper designs a fiber optic displacement sensor with a Fabry?Perot interferometer structure based on STM32H743 chip. The optical fiber displacement sensor uses sawtooth wave to modulate the frequency of the laser, and selects STM32H743 as the core processor to improve the signal acquisition and processing speed. Its main frequency is 400 MHz, and the analog to digital converter maximum conversion rate is 4.5 MHz. Combined with frequency modulated continuous wave laser interferometry, the displacement of stainless steel pipe with fixed cavity length and moving target is measured. Experimental results show that in the 200?400 mm measurement experiment, the standard deviation of the measurement result of 1 mm/s is less than 3.3 nm, and the linear fitting coefficient in the range of 600 mm is above 0.99998, which has a good application prospect in the field of displacement measurement.

The precision of phase extraction directly affects that of interferometry. The traditional fixed-step or equal-step length phase extraction algorithm must carry out phase calibration for the test system, but phase shift error is often introduced due to inaccurate phase calibration, which affects the precision of phase extraction. Therefore, this paper proposes a random two-step phase shift algorithm of K-order two-dimensional polynomial fitting background light (PFBL) to solve phase. This algorithm does not need to carry out phase calibration, and can solve the measured phase with only two frames of phase-shift interferogram when phase shift quantity, background light, modulation system and phase are unknown. When order number K value is greater than or equal to 2, it is determined by the simulation of K-order two-dimensional polynomial, the accuracy of the proposed algorithm for phase can be higher. At the same time, the algorithm robustness is analyzed by comparing the calculation accuracy of Gram-Schmidt orthogonalization (GS) two step phase-shift algorithm with the PFBL method. The results show that the PFBL method has good robustness in the interferogram phase shift, non-uniform illumination and noise, and the calculation accuracy of the PFBL method is obviously better than that of GS algorithm.

To obtain a better transmitter layout and enable the system to achieve higher positioning accuracy, we propose an iGPS transmitter layout optimization method based on an immune optimization algorithm. According to the system's measurement principle, we obtain the measurement uncertainty model of the system. Besides, we establish the affinity function and utilize the immune optimization algorithm for optimizing the transmitter layout. Finally, we verify the results through the simulation. The simulation analysis shows that the proposed method can significantly optimize the transmitter layout and improve the system's measurement accuracy. Thus, the immune optimization algorithm has a better global optimization effect than the genetic algorithm and can obtain better placement of transmitters.

By changing the repetition rate, energy-flux density of focusing spot and scanning speed of a femtosecond laser, the effect of laser processing parameters on the removal rate of a diamond coating was investigated. Based on the observation results by the white-light interferometer combined with the numerical fitting method, the material removal rate function model was established. The analysis of experimental results shows that the accumulated laser energy within the coating surface per unit time remained stable at different repetition rates, and the material removal rate did not change significantly. The ablation intensity as well as the material removal rate raises with the increase of energy-flux density of focusing spot. The processing results under different laser scanning speeds are different, and the material removal rates exhibit a variance trend of first increasing and then decreasing with the increase of scanning speed.

In this paper, TC4 titanium alloys were prepared by laser melting deposition using different scanning strategies. The effects of scanning strategy on the microstructure and properties of TC4 titanium alloys were studied using optical microscopy, X-ray diffraction (XRD), scanning electron microscopy, and electronic universal material testing machine. In particular, the evolution and distribution of residual stress in the XOZ plane of the TC4 alloys were analyzed in detail using XRD. Results indicate that the scanning strategy affected the morphology of the basket microstructure, which in turn affected the mechanical properties of the TC4 alloys. The tensile and yield strengths of the TC4 specimen under the roundabout scanning strategy were the maximum (1251.7 MPa and 1250.0 MPa, respectively), while the tensile and yield strengths of the TC4 specimen under the unidirectional scanning strategy were the minimum (991.5 MPa and 1010.9 MPa, respectively). The residual stress varied substantially under different scanning strategies, with the test results of the partition roundabout scanning being distributed more uniformly. The order of the overall stress level of the specimens obtained using different scanning strategies was partition roundabout, reciprocating, roundabout, and unidirectional scanning.

We report an all-fiber dissipative soliton passively mode-locked Er-doped fiber laser. By adjusting the pump power and the polarization states, we can obtain the two-soliton and three-soliton bound state dissipative solitons further. Utilizing anomalous dispersion fiber to compress the pulse duration of wide-bandwidth two-soliton bound dissipative solitons, compressed pulse width is fitted to 96 fs by hyperbolic secant, and the calculated time-bandwidth product is 0.324, indicating the near transform-limited pulse. The broadband spectrum is obtained thanks to the dispersion management in the cavity and high modulation depth (20%) of carbon nanotube (CNT) saturable absorber. On this basis, the dissipative soliton with the spectral width of 35 nm (center wavelength is 1.57 μm) is obtained, which is also the widest spectrum based on the dissipative soliton produced by CNT.

Copper has extremely high thermal conductivity and laser reflectivity. Hence, incomplete fusion and undercut problems commonly occur on the copper side during the laser welding of copper and steel. Herein, the laser welding process of T2 copper and SUS304 austenitic stainless steel was performed under two laser deflection angles using the 4-kW fiber laser. The deflection of the laser beam on the steel side can significantly increase the amount of copper in the weld, suppress weld forming defections, promote the mixing of the weld microstructure, optimize the connection form of the weld joint, and promote the smooth transition of components at the copper side interface. Consequently, reliable weld joints can be obtained.

In this study, an L-shaped model was designed to simulate the constraining structure of the laser additive strip sidewall of a valve seat to construct the constrained structure. The basic laser additive simulation model considers the changes in laser absorptivity, latent heat of phase change of the material, and heat exchange between the additive process and the external environment. Results show the existence of a competitive relationship between the laser energy density change and the energy input of the laser in space. When the effect of increasing the laser power and power density on the temperature rise is greater than the effect of increasing the speed and reducing the energy in the space on the temperature drop, the temperature of the additive layer increases. Because of the influence of the substrate structure asymmetry and the heat transfer and dissipation in the laser additive process, the depth of fusion between the additive layer and the bottom surface of the substrate is greater than the depth of fusion with the side surface and the cross section of the additive layer has a stepped-crescent shape. Furthermore, because of the combined effects of the hysteresis of heat conduction and rapid heating and cooling of the laser, with the increase in laser power and scanning speed, the cross-sectional profile of the additive layer gradually switches from a crescent to a platform shape.

Based on the rigorous full vector diffraction theory, the influence of misalignment on the beam focusing characteristics of large aperture off-axis parabolic mirror (OAP) are analyzed in detail. The results show that the shape of the diffraction focal spot does not change after the translation or revolving of OAP around the z″ axis, but the center position of the focal spot shifts. The quantitative relationship between OAP’s three-dimensional translation and rotation deviation around z″ axis is obtained by using Rayleigh criterion. When OAP’s rotation deviation around x″ or y″ axis occurs, the appearance of astigmatism and coma will cause the shape of diffractive focal spot to change, and the peak intensity of the focal spot is greatly reduced. The relationship between the maximum rotation deviation angle and OAP off-axis parameters and beam parameters is discussed in detail. Therefore, understanding the influence mechanism and variation relationship of misalignment on beam focusing characteristics can provide a reliable theoretical basis for precise adjustment of OAP.

The injection angles of Yb∶YAG slab are calculated and the configuration of laser amplification is optimized. The advantages of the reflective image transfer system are compared and analyzed, and the spherical aberration of the image transfer system is calculated. The results show that the spherical aberration is significantly decreased by the reflective image transfer system, which improves the beam quality of the amplified laser. Based on single Yb∶YAG slab, a three-passes master oscillator power amplifier system is developed at room temperature. By using the reflective image transfer system and matching the near-filed intensity between pump laser and seed laser, an output power of 7.13 kW and a beam quality of 2 times diffraction limit are achieved without the active optical correction system.

To improve the service life of 45 steel shaft parts, we aim to study optimum process parameters of laser cladding Ni60AA coating on 45 steel shaft surface. The cladding process test of shaft surface was carried out with multi-pass spiral lap technology, namely, a Ni60AA alloy cladding layer was prepared on a 45 steel substrate. Based on the single variable method, the single factor cladding experiments were carried out on three process parameters, namely laser power, powder feeding rate and shaft speed. The thickness of cladding layer, dilution ratio and micro-hardness were selected as the evaluation indexes of coating quality. Based on the single factor experiment, the orthogonal experiment of three-factor and three-level was completed. The multi-objective comprehensive optimization of the process parameters was finished by the weight matrix method, and the microstructure and micro-hardness of the optimized cladding coating were analyzed. At the same time, friction and wear experiments were carried out at different working temperatures, and the friction coefficient,wear rate and wear scar morphology were analyzed and the feasibility of process optimization is verified. Powder feeding rate has the largest comprehensive influence ability, followed by laser power and shaft speed. The optimal parameters are laser power of 1400 W, powder feeding rate of 16.3 g/min, and shaft speed of 2.3 r/min. The thickness and micro-hardness of the cladding coating were increased by 3.49% and 2.8% respectively compared with those before optimization. When the test temperature is 35, 80 and 125 ℃, the average friction coefficient of the cladding coating is 28.5%, 21.1% and 11.8% lower than that of 45 steel and the wear rate of the cladding coating is 87.6%, 86.6% and 80.9% less than that of the substrate. Ni60AA cladding coating with high forming quality and significantly improved hardness and wear resistance can be obtained by optimizing the laser cladding process parameters.

The scheme of an external semiconductor laser with built-in microstructure fiber is designed and studied to achieve fiber-side lighting. This scheme solves the problems associated with traditional direct down liquid crystal modules: these require a large number of light-emitting diode chips, and the volume of the built-in semiconductor laser scheme is too large. The effects of different depths, radii, and the number of microstructures on the optical field are simulated and analyzed. Light field with a peak illumination of 32650 lx, a horizontal viewing angle of 85°, and a vertical viewing angle of 84°33′35″ is obtained. These values meet the requirements of the liquid crystal display (LCD) industry for achieving a peak backlight illumination of 10000 lx, a horizontal viewing angle of 60°, and a vertical viewing angle of 50°. The proposed scheme provides a new method for applying semiconductor lasers in the field of LCD display.

In a high-power optical cutting system, the laser is focused by the optical system to generate heat, which causes the optical system components to undergo thermal deformation and change in refractive index, which changes the focal length of the lens and affects the processing effect. COMSOL software is used to model the optical system in a multi-physics field, the shape of the mirror and the change of refractive index under the action of continuous laser and quasi-continuous laser are obtained by simulation. The heated data of the lens is imported into ZEMAX for beam tracing, and the axial offset of the focal point of the optical system is calculated by simulation. The higher the power, the greater the focal shift; the larger the pulse width, the smaller the focal shift; the higher the repetition frequency, the smaller the focal shift. Finally, the focus shift is compensated by introducing the convection coefficient, and the position of the focus can be controlled by changing the convection coefficient. This research solves the problem of difficult measurement of the axial focus offset during high-power laser processing and provides a theoretical basis for the focus control of high-power laser cutting equipment.

In order to increase the photo-generated carrier density of the photoconductive switche, prolong the service life of the device, reduce the energy requirement of the light source, and realize the miniaturization of the device, we establish a mathematical model of the total internal reflection photoconductive switch based on the semi-insulating 4H-SiC material. The conditions of total internal reflection and the factors that affect photoconductive switches absorption efficiency and uniformity are analyzed. The non-sequential mode in ZEMAX is used to establish a total internal reflection photoconductive switch model, and the ray tracing method is adopted for analysis. A high-efficiency total internal reflection photoconductive semiconductor switches optical system is designed. The results show that the optical system can achieve high absorption efficiency while ensuring high uniformity. The absorption efficiency can reach 90.78% and the absorption uniformity can reach 74.56%.

Based on the background of multitarget detection in the lidar field, a multibeam formation method for a silicon-based optical waveguide phased array is proposed and the working mechanism of the optical waveguide phased array is introduced. Based on the principle of beam deflection, the total aperture array is divided into several continuous subapertures by the subaperture method. After passing through each subaperture, the beam will be subjected to different phase modulation. Finally, various beams that can be deflected through different angles are formed at the exit end. According to the target threat degree, the number of array elements of the subaperture is adjusted and the multiple beams are divided uniformly or non-uniformly. Then, the energy of each beam can be reasonably distributed. Simulation results show that the far-field diffraction pattern appears at the desired angle, verifying the feasibility and effectiveness of the proposed method. Besides, the proposed method can significantly increase the number of targets detected by a phased array lidar and reduce the scanning time.

In this study, the Raman scattering of copper phthalocyanine is enhanced by adopting a millimeter-scale oscillating metallic optical waveguide structure. Different from the traditional surface-enhanced Raman spectroscopy (SERS) technology that creates hot spots by designing complex nanostructures of precious metals, we increase the distance between the upper and lower surface metal cladding layers of the metal optical waveguide, which can increase the thickness of the guided wave layer coupling of light energy into guided wave layer, thereby enhancing the interaction between light and matter. Although increasing the thickness of the guiding layer has the risk of a single-mode field strength drop, the advantages are obvious. First, the high mode density facilitated the coupling of incident light energy with the waveguide layer. Second, the excitation light could be incident nearly perpendicular to the waveguide surface, thereby simplifying the optical setup. Finally, the polarization-independent characteristics of the thick waveguide structure contributed to the Raman enhancement.

In order to simultaneously improve the light extraction efficiency and internal quantum efficiency of GaN light emitting diodes(LEDs), GaN LEDs are integrated with quasi-symmetric optical waveguide (including grating, Ag thin layer and SiO2 layer) and the GaN LED structure is optimized and analyzed based on the finite difference time domain (FDTD) method. The simulation results show that the surface plasma polaritons are excited by the light emitted from the active region in the Ag thin layer which produces the Purcell effect with the active region and thus the internal quantum efficiency is significantly improved. In addition, the existence of the high transmission grating makes the light extraction efficiency of LED significantly improved. Moreover, with the grating layer, the refractive index quasi-symmetrical waveguide structure is formed on both sides of the Ag thin layer, which further improves the light extraction efficiency of surface plasma polaritons and makes the uniform electric field distribution on both sides of the Ag thin layer.

To improve the accuracy of reference phase estimation in the continuous-variable quantum key distribution, a scheme of reference phase estimation is proposed, which is based on the least square method. Utilizing the second-order correlation characteristics of slow phase drift and the least-square estimation theory, the phase measurement results for a group of reference pulses are fitted by a quadratic polynomial at the receiver to suppress the effect of phase noise. The simulation results show that the least square phase estimation algorithm, compared with the block-averaging estimation algorithm, is better adapted to phase drift variation, so that the mean square error of reference phase estimation can be reduced and the secret key rate of the practical system can be improved significantly.

The measurement-device-independent quantum key distribution (MDI-QKD) system can resist any attacks on the side channel of the single-photon detector. In order to further optimize the multi-party MDI-QKD protocol, this paper investigates the multi-party MDI-QKD protocol based on W states, and introduces the detector quality factor (ratio of dark count Y0 to detection efficiency ηd) as an analog parameter to simulate and analyze the factors influencing bit error rate and key generation rate. The simulation results show that the increase of any one among the three variables of channel-transmission loss, fiber-channel distance and detector quality factor enhances the bit error rate and reduces the key generation rate.

Perovskite light-emitting diodes show great potential in the fields such as display, lighting, and imaging because of their high efficiency, high color purity, low fabrication cost, and widely tunable light emission spectra. Starting from the basic structure and working mechanism of perovskite light-emitting diodes, this review focuses on the main technical means to improve the fluorescence quantum yield, light extraction efficiency, carrier injection efficiency, and reliability of perovskite light-emitting diode devices. The development process of the key parameter improvement method for the blue, green, red, and near-infrared perovskite light-emitting diodes is systematically explained, and the latest research progress of lead-free perovskite light-emitting diodes is briefly introduced. The technology development trend of light-emitting diodes is discussed, and the methods and ideas to further improve the performance and reliability of perovskite light-emitting diodes are prospected.

Convex grating is the core of Offner structure imaging spectrometers. To improve the imaging quality of a spectrometer and realize remote sensing detection, it is key to use convex grating with high diffraction efficiency and high resolution. The diffraction efficiency of convex gratings is analysed by strictly coupled wave theory. In this study, we present the research status of convex grating and discuss the main methods for designing and manufacturing convex blazed grating, including electron beam direct writing, X-ray lithography, mechanical etching, and holographic ion beam etching. Owing to the advantages of holographic ion beam etching, such as low cost, controllable groove type, and ghost-free, we introduce in detail the fabrication of convex grating via holographic ion beam etching and present related studies. Based on the investigation and analysis, we aim to optimize and improve the uniformity of the light intensity distribution of holographic exposure, the adjustable rotation axis of swing-etching device, and the process parameters of ion beam etching to produce a practical convex-blazed grating.

Due to the periodic nonlinear error, the measurement accuracy of heterodyne laser interferometer is difficult to improve. In this regard, this paper first analyzes the sources of nonlinear errors in heterodyne laser interferometers, including frequency aliasing, polarization aliasing, and ghost ghosting. Second, it discusses nonlinear error compensation and suppression techniques, including interference signal processing, traditional structure improvement, space separation of polarized light, and phase modulation dual-homodyne interference, and then introduces the measurement technology of nonlinear error, including interference signal processing measurement, dual-phase differential detection, and Fabry-Perot interferometer detection. Finally, it summarizes and prospects the compensation, suppression, and measurement technology of nonlinear error, which provides reference for research in related fields.

Laser-induced liquid micro-jet technology is a medical method that uses lasers to induce cavitation bubbles used to generate micro-jets, so as to cut target tissues in a narrow chamber. It has advantages of low thermal damage, high precision, minimal invasiveness, and a high degree of choice for elastic tissues such as membranes and blood vessels. The mechanism of laser-induced micro-jet generation and the structure of a typical micro-jet system are introduced. Its application and research progress in medical field are reviewed. The key issues that restrict the clinical application of laser-induced micro-jet technology are summarized, and its application potential in medical application is prospected.

Connecting rod cracking processing is a key technology for connecting rod processing, which contains many advantages, such as fewer processing procedures, which can minimize equipment investment; the material loss is low, which can achieve the effect of energy saving and material saving; and the products have higher quality and improve the carrying capacity of connecting rods. Its core technologies include three types, the first is connecting rod cracking groove processing, the second is the directional splitting connecting rod, and the last is fixed torque assembly bolts. The main processing method of connecting rod cracking groove processing is laser processing. This article mainly introduces the principle and characteristics of laser processing connecting rod cracking tank and the development status, and characteristics and prospects of laser processing connecting rod cracking tank equipment at home and abroad. The characteristics of laser processing connecting rod cracking tank are mainly high precision and high efficiency. At present, domestic and foreign laser processing connecting rod cracking tank equipment is developing in the direction of improving processing efficiency and reducing costs.

To confirm the applicability of polarization spectroscopy to complex Sm atoms, we employed two-color two-step resonance excitation and photoionization detection techniques to study the spectra of even-parity highly excited states of an Sm atom. First, through two-step excitation, an Sm atom in the ground state 4f66s27F0 was excited to the even-parity excited states (angular momentum quantum numbers, J=0?2), and photoionization was used for detection. The spectra were compared and analyzed under different polarization combinations, and the total angular momentum quantum numbers J of the three even-parity highly excited states were determined using the polarization selection rule. Finally, by changing the angle of the vibration directions of the two linear polarized lights, we established the relationship between the photoionization signal and the angle, which verifies the applicability of polarization spectroscopy to Sm atoms.

In this work, we studied film thickness error in an electron beam evaporator with revolving structure. Using the noncosine film-thickness distribution theory, we propose a method for analyzing the film thickness error, in which the film is formed on the dome structure, and characterize the thickness error distribution using a mathematical method. Analysis shows that the film thickness error is the function of the location of film deposition, which is related not only to the mechanical configuration between evaporation source and substrate but also to the thin-film manufacturing parameters. Results reveal that the film thickness error comes from the deviation of the electron beam evaporation source from the axis of the revolving dome. We prepared a three-layer thin film on a 2700-mm-diameter coating machine. The film thickness error was retrieved using the spectral method. The results are consistent with the theoretical results of thickness error distribution.

Multi-viewpoint optical positioning system is an effective solution to make up for the disadvantages of light occlusion in optical positioning because it can reduce the blind area in the operation and obtain a larger field of vision. In this paper, multi-viewpoints optical positioning algorithm based on the optimal reconstruction accuracy is proposed to solve the problem of light occlusion in optical positioning. First, the proposed algorithm analyzes the number of optical positioning markers in each viewpoint to confirm the light occlusion of each viewpoint and surgical instrument. Then, according to parallel stereo vision measurement accuracy analysis model, the influence of the multi-viewpoints structure and the position relation between the marker and the camera on the measurement accuracy is analyzed. Finally, the viewpoint pair with the best reconstruction accuracy and no occlusion is selected surgical instruments. Experimental results indicate that the proposed algorithm can achieve accurate positioning and real-time tracking of surgical instruments when there is a certain view occlusion.