The atmospheric environment seriously affects performance of the free space optical communication system. Considering the influence of weather environment, atmospheric turbulence and directivity error on laser communication, we establish a joint channel statistical model, and derive the performance parameters of free space optical communication system based on on-off keying modulation, such as average bit error rate, average channel capacity and outage probability and their closed expressions, using Meijer-G function. The performance parameters of the system are simulated and analyzed under different M turbulences, different normalized pointing errors and visibilities of 5 km and 20 km. The results show that the smaller the directivity error, the greater the influence of turbulence on the performance parameters of the communication systems; the bigger the directivity error, the more likely for a best beam divergence angle existing to make the communication system achieve the best performance.

The visibility of output stripes from a fiber interferometer is affected by the polarization fading caused by the birefringence effect of a single-mode fiber. To solve this problem, we propose a simple depolarization fading method. This method can also realize the space point detection of an optical fiber interferometer sensor. A sensor probe with a built-in Faraday rotator which is with a rotation angle of 45° is designed, and a Faraday rotating mirror with a rotation angle of 45° is used. They are added in the two ends of a Michelson fiber interferometer. In this paper, the interferometer system is theoretically calculated and analyzed, and the visibility measurement experiment of the interferometer is carried out when the external environment and the polarization controller are changed. The results show that this method can effectively overcome the polarization fading of the fiber interferometer when we conduct the point detection in the outside world, and it can obtain the interference stability with variation less than 0.9%.

A photonic crystal fiber sensing system based on optical-borne microwave interference is built to solve the problem that the current photonic crystal fiber sensor is sensitive to inter-mode interference and difficult to package. The system interference occurs between the microwave envelopes of the optical carriers, the light does not interfere, and the polarization fading, dispersion, and inter-mode interference of the optical waves have a little effect on the signal quality. Therefore, the system does not require special processing for the photonic crystal fiber, with low requirements of the processing accuracy. Strain and high temperature sensing experiments are carried out on the system. The strain test results show that the visibility of interference fringe in microwave domain can reach 20 dB, the strain measurement sensitivity at 8 GHz is 6.3 kHz/με, and the resolution of the microstrain measurement is 1.59 με. The temperature experimental results show that temperature measurement sensitivity of system is 76.04 kHz/℃ from room temperature to 800 ℃, and the theoretical temperature measurement resolution is 0.13 ℃. Temperature experiments using multiple sets of length probes prove that the system has good temperature sensitivity and stability.

A processing method of scattering points with the equidistant V-shaped grooves is studied, which is used for the plastic fiber array. A blade carving technique is presented using gravity micro-pressure. The relationship between the light scattering rate of the scattering point and the weight mass providing gravity is analyzed theoretically. The results show that the light scattering rate of V-groove scattering points increases with the increase of the weight mass, in the form of 3/2 power exponent. The uniform luminescence model with isometric scattering points is established. According to the condition of each scattering point in machining, the formula of weight mass for machining is deduced theoretically. Experiments verify the relationship between the light scattering rate of V-groove scattering points and weight quality, and the relation curve between them is obtained. Using the parameters obtained from the formula of weight mass, a single side luminescent plastic fiber with equidistant scattering points is fabricated, and its luminance uniformity is higher than 85%. The 180 mm×101 mm backlight plate of plastic fiber array with isometric scattering points is fabricated, and its brightness uniformity is 90.9%. The experimental results show the feasibility of preparing the V-groove scattering points for plastic fiber array by gravity micro-pressure blade carving.

A method that combines projected fringe profilometry with independent component analysis (ICA) is proposed to realize the three-dimensional profile measurement of high-reflective surfaces. The reflection model and characteristics of reflection light from high-reflective surfaces are analyzed. The reflection light is mainly composed of specular and diffuse components. Considering the polarization property of the specular light, we put a polarizer before the CCD camera to eliminate the specular light primarily. Then, the polarization images at different angles can be captured by rotating the polarizer, and the separation of specular and diffuse components can be realized by using the reflection model combined with ICA. Finally, the images of diffuse components can be applied to the three-dimensional reconstruction. A smooth aluminum alloy sheet is measured, and the feasibility of the proposed method is verified.

The calibration of the phase measuring deflectometry (PMD) system is an important factor affecting the accuracy. Aiming at the difficulty of the calibration of posture relationship between the screen and camera in PMD system, a new system calibration method is proposed. By constructing retro-reflectors on the screen, a photogrammetry system is introduced as the medium of transformation between the screen coordinate system and the camera coordinate system. Therefore, a high precision calibration of geometric parameters is achieved. The calibration accuracy is verified using a stereo PMD system. The experimental results show that the reconstruction surface flatness is less than 1 μm, which demonstrates that the proposed method is feasible and effective.

The concentration of SO2 gas in the atmosphere is very low, and therefore, the emitted fluorescent signal is weak, directly impacting the detection accuracy of SO2 gas concentration. Owing to these issues, the optical path for traditional fluorescence collection is long, hindering the development of the miniaturization of instrument. To improve the collection efficiency of fluorescence signals and the detection accuracy of the instrument by shortening the traditional optical path, we used the ZEMAX software to design an optimized trace SO2 fluorescence signal collection optical path for a random divergent distribution of fluorescence. We then compared the results from this path with those from the traditional fluorescence collection optical path. Simulation results show that the collection efficiency of optimized fluorescence collection optical path is approximately 22.6%, which is 4 times that of the traditional fluorescence collection optical path. The distance from the image-based main point of the lens group to the optimal collection point is reduced by 29.17%. The optimized optical path in this paper is beneficial for further improvements in the miniaturization and detection accuracy of the existing atmospheric trace sulfur detection instrument.

Herein, to address the problems of low efficiency and accuracy, long time consumption, and high labor intensity of the contacting measurement on static clearance of high-speed locomotive train, a new two-dimensional scanning sensor of static clearance of high-speed train is developed based on the rotating clustered-ray measurement principle. Static clearance can be efficiently and automatically measured by installing the proposed sensor on a moving guide rail. The sensor is calibrated using a high-precision marble plane, and a coordinate system for the measurement system is established. Sensor measurement results are converted to three-dimensional coordinates in the orbital coordinate system via external calibrations. Thus, the static clearance measurement data of high-speed train can be obtained. Experimental results show that the accuracy of this new sensor is more than 1 mm, which satisfies the requirement of static clearance measurement.

The finite element simulation is used to investigate two different Z-shaped scanning paths parallel to the long and short sides. Considering the effects of heat conduction, heat convection, heat radiation, and temperature on the thermal properties of alloy powder materials, the finite element model of the transient selective laser melting (SLM) temperature field is established. Then, the established model is compared with the experimentally measured residual stress data and metallographic diagram. It is determined that in the SLM process, the temperature field formed by short-side scanning is more uniform; the temperature standard deviation, the temperature gradient, the residual stress, and the porosity of the formed part are smaller than those in the long-side scanning. During the scanning process, the temperature gradient at the boundary point of the scanning region is greater than that of the scanning region, and the residual stress peak appears at the boundary of the formed part. By preheating the substrate, the temperature field can be more uniform, and both the standard deviation and the gradient of the temperature field can be reduced. Therefore, the residual stress and the porosity of the formed part are reduced, and the forming quality is improved. The investigation of the influence of scanning path on the temperature field provides the reference for the improvement of the SLM technique.

VITA MARK II, a commonly used dental glass ceramic material, is typically milled using a 5-W infrared femtosecond laser. The effects of ultra-fast laser process parameters on milling efficiency and milling effects are systematically studied, and the 20-W infrared femtosecond laser prepared for future test prototype is estimated using the experimental results of 5-W infrared femtosecond laser. The experimental results show that the milling efficiency of the 5-W infrared femtosecond laser on VITA MARK II ceramics is 0.0409 mm 3/s when the laser repetition frequency is 100 kHz, the scanning speed is 200 mm/s, and the scanning interval is 0.01 mm. The roughness of VITA MARK II ceramics treated by femtosecond laser is ranged within 3--5 μm, the margin gap is approximately 50 μm, and the slope quantity is within 100 μm. The laser cutting threshold of VITA MARK II dental glass ceramics is 0.72 J/cm 2. It is estimated that the milling efficiency of 20-W infrared femtosecond laser on VITA MARK II ceramics would be 0.1558 mm 3/s. Therefore, this experiment demonstrates the feasibility and effectiveness of laser cutting dental glass ceramics, providing a reference for the construction of the test prototype.

Numerical simulations on 316L stainless steel is conducted using selective laser melting (SLM) technology,and the effects of the placement angle of the printed parts in the horizontal plane and the inclination angle in the vertical plane on the thermal behavior of the SLM process are investigated. By adopting the short straight-line scanning strategy, the research results show that for a bar with dimensions of 50 mm × 5 mm × 10 mm, when the angle between the longer side of the bar and the scraper is 45°, the deformation generated by thermal stress is the smallest. In the vertical plane, the corresponding deformation generated when the angle between the bar and the vertical direction is 15° is the smallest as well. The deformations on the substrate prior and subsequent to the removal exist a considerable difference, which amounted to approximately 70%.

In this study, a novel loading set, the set of loading region based on embedded surface, is implemented using the ABAQUS finite element package. When determining the parameters and operations, a comparison is made among the current loading sets, validating the effects of these on the resulting solution. According to our investigations, the loading set based on embedded surface possesses high efficiency. This technique has the ability to predict loads with precision, increasing the efficiency of the loading set under conditions where target elements are of high quality.

In this study, impact toughness samples of GH4169 are prepared by selective laser melting (SLM), and the microstructures of these samples are observed. The results show that in the preferred range of the SLM process parameters, the samples form a uniform orientation of the solidified columnar grain refinement arrangement. For a power of P=260 W and scanning speed of ν=0.9 m/s, the impact toughness of the GH4169 samples at room temperature is 43.9 J/cm 2, and with the increase of laser power and scanning speed, the impact toughness continuously decreases, and the fracture of the impact sample has obvious transgranular characteristics.

The 1.6 mm thick advanced high strength steel QP1180 was welded by an IPG YLS-6000 fiber laser. The effects of different heat inputs (14-36 J/mm) on the microstructure and properties of laser welded joints were investigated. The results show that the full penetration welded joint was obtained when the heat input reached 21 J/mm and above, and the width of fusion zone increased with the increase of heat input. There was a softened zone in the welded joints, but the degree of softening was low (≤10.1%). The softened zone was bound by the strengthening phase on both sides, leading to the fracture in the base metal, and the strength was equivalent to that of the base metal. In the Erichsen test, when the heat input was 21-36 J / mm, the cracking positions of the welding samples were perpendicular to the weld failure. The Erichsen values of three fully penetration welded joints all reached 70% of the base metal. The laser welding heat input range of 21-36 J/mm can ensure the full penetration weld seam performance meets the requirements of industrial applications.

In this study, via the retinal functional imaging device, not only the structural information of the retina is imaged, but also the functional information such as the retinal oxygen saturation and vessel diameter is imaged and measured noninvasively and quantitatively. By comparing quantitatively the functional imaging results of diabetes patients and healthy controls, significantly elevated arterial oxygen saturation and arterial-venous oxygen saturation difference are found in diabetes patients. The area of the foveal avascular zone is also significantly increased in diabetes patients. The result also shows that there are significant differences between the average diameters of arteries and veins both in diabetes patients and healthy controls, and the arterial diameter is always larger than the venous diameter. The study demonstrates that by using the retinal functional imaging method, the clinical changes of retinal oxygen metabolism as well as the perfusion rate in diabetes patients can be detected, which helps doctors to better observe and evaluate the pathological changes of the retinal microvessels in diabetes patients. In addition, the retinal functional imaging technique has the application potential for the early diagnosis and prognostic evaluation of ophthalmic complications associated with diabetes.

Interaction of two Airy-Gaussian beams in a one-dimensional nonlocal nonlinear defected lattice is numerically studied, and the effects of the nonlinear non-local properties, lattice properties, beam properties, beam incidence angle, and phase difference between the two beams on the experimental results are discussed. It is found that the interaction of two Airy-Gaussian beams under different conditions forms lattice solitons, quasi-breaths, and even lattice solitons. In most cases, the quasi-breaths are observed, and their spatial size and period are affected by nonlocal nonlinearity, lattice defects, and light self-acceleration. When phase difference exists between the two incident Airy-Gaussian beams, the interaction in the lattice will form a soliton pair, with one soliton transmitting vertically and the other soliton transmitting diagonally.

In order to meet the machine vision system’s demand on the zoom double telecentric system, we design a double telecentric lens that can achieve continuous zoom. The system magnification is from -0.50× to -0.20×, and the observable diameter range of the object field of view is from 22 mm to 55 mm. The designed system meets the design requirements of low distortion ( less than 0.1% for all multiplications ), high resolution (higher than 0.30 at 77.5 lp/mm), and high telecentricity (less than 0.1° for all multiplications), and has the advantages of being insensitive to object surface and image plane displacement as well as continuous zoom detection. Two methods to solve the variable cam curve are introduced and used to verify each other. The verification indicates the accuracy of the cam curve data, which plays an important role in the subsequent production and processing of the variable magnification system.

This paper proposes to use the trust region dogleg method to solve the high nonlinearity problem of post finishing of general aspheric optical components. Firstly, based on the low-order body representation and the homogeneous transformation method, a forward kinematic model suitable for any aspherical surface shape and arbitrary path is established. Then, a strong nonlinear forward kinematic model is established based on the trust region dogleg method. The numerical optimization method is used to obtain the corresponding inverse kinematics numerical results. Finally, the inverse kinematics numerical solution results are processed to obtain the control values of each axis for post processing. For an off-axis aspheric surface with an initial surface shape of root mean square 0.037λ, after four rounds of finishing with a raster line path planning and five rounds of finishing with a spiral path planning, the surface shape of the processed component converges to root mean square 0.012λ, and the total convergence efficiency reaches 67.57%, indicating that the proposed post-processing method is correct and can be used for aspheric processing.

Slow tool servo (STS) diamond turning technology is an effective method to process freeform surface optical elements. However, in the process of slow tool servo turning, the machining accuracy is affected by the sagittal height and caliber of the surface. Aiming at this situation, by studying the linearization error trend of the constant-angle and constant-arc methods in STS diamond turning, a tool path generation optimization method combining the constant-arc and constant-angle methods is proposed. In order to realize the reasonable planning of the tool path, joint point selection of the new tool path is optimized. The simulation is applied to the sinusoidal grid surface with MATLAB, and the result shows that the tool path optimization method can effectively improve the surface accuracy.

In order to manufacture high-precision plastic diffraction microlenses, this paper proposes to select the process parameters in a wide range by Taguchi method, determine the process parameters that significantly affect the molding precision of microstructure through the signal-to-noise ratio, and obtain the optimal parameter combination through multi-objective optimization by weighted comprehensive scoring method. The results show that the holding pressure, mold temperature, and holding time have a significant impact on the microstructure molding precision. In order to improve the precision of diffraction microstructure, the main source of diffraction microlens injection molding error is analyzed and the error compensation model is established. The experimental results show that the diffraction microstructure of the injection molding has a height error of 5.69% and a period error of 6.16%, and the injection molding precision of the diffraction microstructure is significantly improved.

A plasma refractive index nanosensor based on Fano resonance is designed, which is composed of the metal-insulator-metal waveguide with a stub coupled with a split-square resonator. Analysis of transmission characteristics of the sensor's structure is performed using the finite element method, and the influences of the structural parameters on the sensing characteristics of the sensor are studied. The calculated results show that the structure can excite the Fano resonance, and the resonance peak wavelength and line type can be adjusted by changing the key parameters. By adjusting the structural parameters, the sensitivity of the structure is up to 1125.7 nm/RIU and the figure of merit is 30.01. The results indicate that the proposed structure can be applied to optical integrated circuits, especially in nanometer biosensors.

Distributed optical fiber acoustic sensing (DAS) technology based on coherent Rayleigh scattering can obtain the vibration and sound field information along the optical fiber in real time. Recently, DAS has received extensive attention from scholars in many fields, due to its unique advantages such as large sensing range and high time-and-space resolution. In this paper, the fundamental sensing mechanism of DAS is introduced. The research progress on key scientific and technological issues, such as coherent fading suppression, response bandwidth enhancement, and spatial resolution optimization, is briefly reviewed. The application progress of DAS in perimeter security, rail transportation, and other fields is also described. Finally, the potential future research directions are discussed and speculated.

Coaxial powder feeding nozzle, as one of key components in laser metal additive manufacturing system equipment, directly affects the forming accuracy and performance of parts. Because of its importance, a variety of new powder delivery nozzles have been developed by scholars at home and abroad. In this paper, the research on coaxial powder feeding nozzles is briefly summarized from two different powder feeding methods of "powder feeding by light outside" and "powder feeding by light inside", whether the laser beam and powder beam can vary focal length or not is analyzed, the characteristics of coaxial powder feeding nozzles are pointed out, and the development of the coaxial powder feeding nozzles in the future is provided.

Laser metal additive manufacturing, which is referred to a near-net-shaping process, builds metal parts by rapid melting, solidification and layer-wise cladding. The large temperature gradient in laser additive manufacturing process causes the thermal stress, thermal deformation, metallurgical defects and microstructure degradation of the part; therefore, the detection, analysis and control of the temperature fields are always the key problems of metal additive manufacturing. The review is presented of detection, analysis and control technologies of the temperature fields in additive manufacturing at home and abroad, including the finite element simulation, the in-process detection based on the infrared camera and pyrometer, the closed-loop control and the substrate preheating control. The advantages and disadvantages of the present techniques of detection, analysis and control of the temperature fields are compared, and the future trend is analyzed.

Time-frequency synchronization technology based on optical fiber transmission has advantages of high accuracy, high stability and low loss. In recent years, optical fiber time-frequency synchronization technology developed rapidly, with the emergence of new methods, new technologies and new applications, and it has strong military application needs and civil promotion prospects too. It is extremely necessary to review its development status and objectively examine its future development trend. On the basis of defining the principle and technical characteristics of optical fiber time-frequency synchronization technology, the current status of optical fiber time synchronization, frequency synchronization and networked synchronization technologies are introduced, the key points in the construction of ground-based time-frequency network are proposed. The problem of restricting the practicality of optical fiber time-frequency synchronization technology is analyzed. It is considered that ultra-long-distance and high precision transmission on commercial networks is the difficulty of restricting optical fiber time-frequency synchronization technology and the key problem to be solved in the future research.

As a new green and efficient paint stripping technology, laser paint stripping has broad application prospects in the field of manufacturing and maintenance, and is gradually replacing the traditional methods to become the most advanced approach. We introduce the principle of laser paint stripping technology, review the research progress based on different lasers at home and abroad, and look forward the development prospect of laser paint removal technology.

2 μm single-frequency pulse laser is the key light source of lidar for the detection of the atmospheric wind field and CO2 concentration. In the paper, the research progress of the continuous-wave 2 μm single-frequency laser, pulsed high-repetition-frequency laser and pulsed low-repetition-frequency laser are summarized respectively, according to different application requirements. Their technical characteristics are analyzed as well. The development tendency of the pulsed single-frequency 2 μm all-solid-state laser is prospected.

As an important branch in the field of distributed optical fiber sensing, optical frequency domain reflectometer (OFDR)has the advantages of high sensitivity and high spatial resolution, and is the research hotspot in the field of distributed optical fiber sensing in recent years. The principle and key technologies of OFDR are introduced and the recent progress of optical frequency domain reflectometer is systematically reviewed from two aspects of high spatial performance and remote frequency domain reflectometer. Then, the latest applications of OFDR in different fields are analyzed and the characteristics of different OFDRs are summarized.

Vortex beams carry orbital angular momentum (OAM), and have wide application prospects in optical manipulation, optical communication, and quantum optics. To produce ultrashort vortex pulses, we combine vortex beams with the time domain control technique. The method is very important in physical experiments performed under extreme strong field conditions and the researches about ultrafast nonlinear spectroscopy and precision laser material processing. In this paper, the research progress on ultrashort vortex pulse generation methods at home and abroad in recent years is summarized. The main methods for generating ultrashort vortex pulses are reviewed, and the advantages and disadvantages of each method are compared and analyzed.

In order to enable imaging spectrometer to be used in a complex vibration environment and a wide temperature range (5-35 ℃), we designed a short-wave infrared imaging spectrometer based on an optical system of convex gratings using Offner-type concentric structure. Patran & Nastran was used to conduce modal analysis, static load analysis, and thermal response analysis with respect to the optical-mechanical structure of the instrument to verify the rationality of structure design. Further, the generalized inverse matrix method was used to process the results obtained based on static load response analysis to obtain the surface deformation and rigid body displacement data with respect to optical element of the instrument. Under temperature of 0-40 ℃ and an acceleration load of 4 g, the root mean square (RMS) with respect to the optical surface deformation is less than 34 nm, the relative position change between the mirrors is less than 0.05 mm, and the eccentricity of mirrors is less than 0.05 mm, satisfying the requirements for the surface shape and rigid body displacement tolerance of the instrument. The vibration tests denote that the first mode of the imaging spectrometer is 559 Hz, which is considerably higher than that of general ambient excitation. The stiffness of the imaging spectrometer also satisfies the application requirement. The temperature experiments denote that the extreme wavelength drift is 0.306 pixel in a wide temperature range and that the extreme spectral bandwidth change is 0.493Δ, in which Δ is full width at half-maximum (FWHM). Furthermore, the environmental adaptability of the structural design is verified via engineering analyses and experiments, resulting in important practical value for instrument engineering.

The laser induced breakdown spectrum (LIBS) is used to excite and detect the different positions at liquid steel surface, and normalization pretreatment is performed for the spectral data. The four representative factors are screened out by principal component analysis and used as input information. Aiming at the four elements of Mn, Ni, Cr, and Si in liquid steel, the calibration model is trained and established, and the optimal parameter value is selected by Cat-fish particle swarm optimization (PSO) algorithm. Finally, the test set is used for verifying the prediction effect of the model. The experimental results show that the determination coefficient R2 of Cat-fish PSO-support vector regression (SVR) is greater than 0.95, the mean value of relative standard deviation RSD is 3.53%, and the root-mean-square error RMSE can be controlled within 1.5%. The proposed model is superior to the ordinary SVR prediction model, and it can detect the element content quickly and accurately. This study provides an optimization algorithm for the on-line and accurate quantitative analysis of liquid steel elements by LIBS, which has high reference value.

In this study, a micro-ultraviolet spectrometer with an IV-type optical system is designed, fabricated, and analyzed. The micro-ultraviolet spectrometer is effectively validated for online real-time analysis applications. The main parameters of the prototype include a wavelength range of 200-400 nm, resolution of 0.31 nm, wavelength accuracy of ±0.1 nm, and a signal-to-noise ratio of 507∶1. The experimental results of a 12-h system stability test suggest that the spectral fluctuation is less than 0.47%, confirming the long-term stability of the spectrometer. Finally, the performance of the spectrometer is verified by measuring SO2 gas at 25 ℃. Based on the theory of differential absorption spectroscopy, a differential absorption cross section calculation of a standard gas is performed. The test results show that the inversion mass concentration of the spectrometer test data has a fluctuation of less than 1%, linearity error of less than 0.6%, and maximum indication error of -0.56 mg/m 3 upon testing an SO2 mass concentration of 20-100 mg/m 3 for 24 h.

In this study, we propose a nondestructive method based on hyperspectral imaging technology to determine the bloodstain age. The spectral images of the bloodstains on a white ceramic tile, white paper, and white cotton cloth with different aging times can be obtained using a hyperspectral imager and can be characterized in the spectral range of 550-800 nm. Further, the bloodstain age is predicted using an artificial neural network model. The results indicate that the regression coefficients of the aging time of bloodstains for the three samples are larger than 0.9930 within 30 h under the laboratory conditions. The average root mean square error of prediction (RMSEP) is 18.29 min, and the median relative error δM is 8.05%. Thus, the proposed method is observed to be effective for estimating the aging time of the bloodstains in a short time (<30 h).