In order to evaluate the operational environment adaptability and comprehensive support capability of lidar in civil airport, experimental data was monitored in a typical plateau airport by using a wind lidar which is made in China. By considering the factors such as historical weather data in the same place, the weather condition of sunny, cloudy, overcast, fog and rainy days, the lidar's wind data was analyzed, and then the typical wind feature in a plateau airport was revealed. The comprehensive support capability of a wind lidar was also tested at the same time. The results show that, lidar's performance of catching wind field is different under different weather condition. In sunny, cloudy, and overcast days, its performance is better, and its horizontal and vertical sounding range is up to 6623m and 2895m, respectively. Moreover, the lidar can accurately discover the wind field's typical feature that is changeable in timing and spacing. This study provides a reference for the application of radar in civil aviation.
In order to the evaluate the non-ideal fabrication on the performance of our Si/SiO2-InP microcavity, a simulation based on the finite difference time domain method was used. From the perspective of process defects and process errors, the effects of non-ideal process conditions on the performance of Si/SiO2-InP micro-pillar cavities were simulated. The simulation results suggest the robustness against processing imperfection and the application feasibility of the hybrid Si/SiO2-InP micropillar cavities as 1.55μm quantum dot single photon sources to be applied in silica-fiber-based quantum information processing.
Wireless power transmission (WPT) technology includes two technical approaches: Micro-wave wireless power transmission (MWPT) and laser wireless power transmission (LWPT). In this paper, the basic concepts of LWPT technology was introduced. And the development history and current situation of LWPT technology at home and abroad were summarized. The main research contents of LWPT technology and the development direction and possible application of LWPT technology were reviewed. Comparing the situation at home and abroad, domestic LWPT research is still in the early stages of theory and application, and more investment is needed to promote its development.
In order to systematically research the factors affecting coupling efficiency, the coupling model of semiconductor laser and single-mode fiber was established and an automatic coupling platform was built by means of simulation and experiment. Theoretical analysis and experimental verification were carried out, and the relationship between coupling efficiency of the model and displacement sensitivity of each direction and the relationship between coupling efficiency and tolerance of each direction in the actual coupling process were obtained. The results show that, coupling efficiency is most sensitive to horizontal displacement, followed by angular rotation and longitudinal displacement. The maximum coupling efficiency of simulation and experiment is 64.29% and 51.46% respectively. The error of simulation and experiment is within a reasonable range, thus the results are highly credible. The results are helpful to improve the packaging coupling efficiency of practical photoelectric devices.
In order to generate radially polarized beams, a method of polarization shaping of linearly polarized beams outside the cavity by a combined half-wave-plates and a combined linear polarizer was put forward. In order to detect the performance of the generating system, the polarization distribution of the output beam was detected by the rotary polarizer method, and its polarization purity was calculated by the classical stokes parameters measurement method. Finally, based on the Mach-Zehnder interference principle, the linear polarization phase relationship of the symmetric region of the radially polarized beams was detected. The results show that when the combined linearly polarizer is divided into four segments, the radially polarized beams with a polarization purity of 80.5% is obtained, and the linear polarization phase difference of the symmetric region is π. The result is helpful to produce the radially polarized light with high purity at low cost.
Low-level jet is of great significance to aviation security and severe weather warning and forecast. In ordar to study the structual features of low-level jet, the wind lidar data from xining airport from 2017-11-30 to 2017-12-01 were analyzed in detail. Results show that the low-level jet velocity decreased after the first increased with height, the strength and thickness decreased with time, and the jet axis height increased with time. There appeared a cold advection in the center of the jet, and its intensity drops with the jetdecreases. The rushing wind turn along with height at the top of the jet, and the turbulence is strong. The jet structure was damaged at 01:30, and the turbulent intensity reached the maximum. After 21:00, the turbulence cluster appeared in the low-level jet, and the wind speed fluctuation was obvious. The turbulence cluster scale first increased and then decreased. The results showed that the wind lidar has a very good detection effect on the structural characteristics of low-level jet as well as the internal intensity and pulsation of low-level jet.
A strong low-level wind shear can cause a super low-level go around, which is a great threat to aircraft safety. In order to improve the ability of safeguard flight safety, the detailed structure and genesis mechanism of the wind shear event were studied using lidar, wind profile radar and other data of Xining Airport on 2018-04-26. The results indicate that microburst is the main cause of the low-level wind shear. The direct reason for the formation of low-level wind shear is the thunderstorm high divergent airflow and the ambient wind which is superposed in the same direction. The dry cold air subsided quickly from an altitude of 2.0km to the near ground and formed a thunderstorm high pressure, and then became an outflow that formed a divergent flow at a horizontal scale of about 3.0km, triggering low-level wind shear. This low-level wind shear lasted about 8min, of which poses the greatest threat to flight safety is at the initial generation of downburst. The time for updraft quickly turning to downdraft at 0.4km~2.0km height is about 4min ahead of the occurrence of low-level wind shear. The research is significant to use wind lidar to improve the ability of flight safety support.
To reduce the deviation of the datum marks and the docking positions of tested workpieces owing to variations in their placements or the use of different clamping methods during assembly processes, a real-time monitoring system of three-dimensional (3-D) strain field was designed based on fiber Bragg grating (FBG). The correspondence between the 3-D strain field and the 3-D spatial coordinates of the workpiece was established, and the calculation method of the workpiece deformation offset was derived. Two FBG sensors were placed in a perpendicular to each other on the workpiece in the form of an FBG strain gauge group to monitor the strain field changes of the workpiece in real time. Numerical analyses were performed to study the workpiece deformations caused by pressure. In addition, the same pressure was applied at different positions of the workpiece and caused the surface of the workpiece to be deformed. Accordingly, the slope of the strain line becomes dense near the edge or at the clamping position, while the slope of the gradient distribution becomes larger than it would be if there were no force. The experimental FBG sensor response is shown to be consistent with the response characteristics of the applied force at the vertical and axial FBG sensors. The absolute error of the simulation analysis is 0.72mm. The absolute error of the strain detection is 0.52mm. Comparing the simulation results, strain detection results, and the visual detection results, the sample deviation of 0.19mm was observed. It can be seen that by establishing the relationship between the 3-D strain field and the workpiece deformation offset, the deformation offset compensation can be realized and the precision assembly is assisted. This system plays an important role in the digital precision of the assembly of large-sized workpieces.
Quantum emitters serve as the building blocks of quantum network, connecting quantum computing, quantum communication and quantum metrology. Semiconductor quantum dots (QDs) are widely considered as the best candidate for quantum emitters. By a decade of effort, the controllability, purity, brightness, indistinguishability, and coherence of QD emitters are greatly improved so that they are much closer to the application level. In this paper, the scientific and technological development of quantum emitters based on QDs were reviewed. Firstly, QD-based single photon sources have achieved indistinguishability of near unity, high purity, and high extraction efficiency. Secondly, QD-based entangled photon emitters have achieved high bit rate, high entanglement fidelity by improvements such as eliminating fine structure splitting. Thirdly, remarkable development has been made towards on-chip integration of QD emitters into planar circuits and nano-photonic systems. It turns out that quantum emitters based on semiconductor QDs are greatly potential to be applied in quantum information processing systems in the near future.
In order to realize the on-line measurement of a birefringence fiber (BF) loop mirror (Bi-FLM) strain sensor with a short BF, the theoretical on-line measurements expression of a Bi-FLM strain sensor using a set of adjacent wave-valley and wave-peak wavelengths was deduced. The adjacent wave-valley and wave-peak wavelengths were near 1550nm and the BF initial conditions were used to calculate strain. The maximum error and minimum error of strain calculated by three different wavelengths combination were 0.0296% and -0.0003%, respectively. The result shows that the calculated strains are basically consistent with the given strains. The method doesn't need human judgment. So it is helpful to realize on-line measurement by computer. The method is unrelated to the monitoring point. So the Bi-FLM sensor isn't calibrated. In addition, the method requires less information and only needs 0.5 period of interference waveform. So it is helpful to realize the on-line measurement of a Bi-FLM sensor with a short BF.
In order to study the magneto-optical image(MOI) characteristics of cross-weld defects, cross butt laser welding was performed on the medium carbon steel plate to obtain test samples with both transverse and longitudinal cracks. The test sample was excited by constant magnetic field and alternating magnetic field. Magneto-optical imaging sensor was used to collect magneto-optical images of welding defects under magnetic excitation from different angles. The defect characteristics of magneto-optical image were then analyzed. The results show that the magneto-optical imaging technology under multi-direction excitation can obviously detect multi-angle welding defects, and can effectively avoid the missing detection phenomenon of curve cracks in welding defect detection. The resolution of the same crack image is increased by 40pixel~50pixel under the excitation of the alternating magnetic field, which can locate the defect more accurately. This study provides a basis for improving the detection rate of welding defects.
In order to study the monitoring and early warning capabilities of laser wind radar in aviation meteorological support. A typical wind-shear weather evolution at Xining Plateau Airport was analyzed on 2019-04-10, by using multiple modes measure data of laser wind radar, and then compared with the existing data of wind measurement equipment and the data reported by the crew at the airport. The results show that during the wind shear detection process, the laser wind radar can clearly detect the structure, position, height, and movement direction of the wind shear. The laser wind radar can achieve the early warning of wind shear about 10min ahead of the self-view data. The results of the Lidar monitoring of the wind shear process are in good agreement with the results reported by the unit. These conclusions have certain reference and guidance significance for civil aviation airports using laser wind radar to forecast wind shear weather and ensure flight safety.
In order to break the limitation of high Young's modulus of quartz material on the sensitivity improvement of fiber optic sensor in uniform radial direction, a doped double-core photonic crystal fiber sensing structure was proposed. The circular air holes were arranged on the fiber cladding to form hexagonal lattice. Polymethyl methacrylate was doped into the base-material area surrounded by the air holes on one side of the double-core photonic crystal fiber. The influence of cross-section parameters on sound pressure sensitivity under uniform stress was analyzed by COMSOL and the optimal structure was obtained. At the kPa level, the free spectral width is about 13nm. At the MPa level, the free spectral width is about 2.5465nm. The results show that the sensitivity of x polarized sound pressure is 0.15942nm/kPa at 1550μm. Compared with the Sagnac PCF pressure sensor, the size of this sensor is smaller, and the sensitivity at uniform radial direction is increased about 46.6 times. This work contributes to the design of the next generation underwater sound pressure sensor.
In order to measure the roughness parameters of metal and insulating surface, the oblique incidence roughness measurement system based on laser scattering was adopted. Using a semiconductor laser source, the scattering spot of roughness surface was photographed by complementary metal-oxide-semiconductor transistor industrial camera. The correspondence between the speckle characteristic parameters and roughness was then analyzed. According the theoretical and experimental study, the monotonic relation between the characteristic parameters and the roughness was verified. By using MATLAB to design graphical user interface, the function of one-key roughness measurement was realized. The results show that the system's structure is simple, and the error between the measurement result and stylus measurement result is less than 8% (the insulation surface is less than 5%), so the roughness of different materials can be measured. This result is helpful to the study of roughness measurement of object surface.
During the detection of laser spot center, in order to improve the calculation efficiency under the premise of ensuring the location accuracy of the spot center, an improved template matching algorithm was used for theoretical analysis and experimental verification. The results show that: In the case of no exposure, the average calculation time of the adaptive region of interest (ROI) is 897s, while the average calculation time of the traditional template matching algorithm is 3388s. In the presence of exposure, the average calculation time of the adaptive ROI is 921s, and the average calculation time of the traditional template matching algorithm is 3389s. The improved adaptive algorithm has achieved excellent performance in the experimental test of laser spot positioning, which shows that it can improve the calculation efficiency under the premise of ensuring accuracy.
In order to solve the problem of inaccurate results and high false alarm rate when using hyperspectral image for anomaly detection, an anomaly detection algorithm based on spectral angle background purification was proposed. With this algorithm, which is based on the local RX algorithm, the the anomalous components in the background pixels between the inner and outer windows could be separated according to the spectral angular distance. The purified background pixels were then obtained, following which the anomaly detection could be performed. In order to verify the effectiveness of the algorithm, two sets of airborne visible infrared imaging spectrometer real hyperspectral data were selected for simulation experiments. The corresponding data was then compared with that of the classical global RX and local RX algorithms. The results show that, the area under the curve of the two sets of data is respectively increased by 0.0317 and 0.0053 compared with that of the local RX algorithm. These results provide a reference for the next research direction.
In order to reveal the distribution of temperature field, the absorption and transfer of energy, and the formation mechanism of heat affected zone during laser cutting carbon fiber reinforced plastics, the carbon fiber reinforced plastics was chosen as the research object, and the multiphysics model of laser cutting carbon fiber reinforced plastics was established. The temperature field distribution during laser cutting and the influence of laser parameters on carbon fiber reinforced plastics temperature and heat affected zone were calculated. The 3-D temperature field distribution during laser cutting carbon fiber reinforced plastics was then obtained. The results show that the surface temperature field of carbon fiber reinforced plastics is approximately elliptical during laser cutting.The energy transfer and diffusion in carbon fiber reinforced plastics are mainly along the direction of carbon fiber laying. When the laser power is 20W, the spot radius is 100μm, and the laser with a cutting speed of 50mm/s is cut perpendicular to the carbon fiber laying direction, the carbon fiber temperature at the laser spot is much lower than the temperature of the resin layer. With the increase of spot radius and laser power, the maximum temperature in carbon fiber reinforced plastics increases gradually, and the heat affected zone gradually increases. With the increase of cutting speed, the maximum temperature in carbon fiber reinforced plastics gradually decreases, and the heat affected zone gradually becomes smaller. This study provides theoretical guidance for understanding the thermal damage mechanism of laser cutting carbon fiber reinforced plastics and the high quality and efficient processing of materials.
In order to evaluate the effect of laser interference under non-cooperative conditions, a new method was proposed to evaluate the effect of laser interference by using "cat-eye" echo intensity by the forming principle of "cat-eye effect". The influence of laser incidence angle, laser jamming power, and distance on the echo power of "cat-eye" was analyzed. The relationship between the power of "cat-eye" echo and the laser jamming effect of the photoelectric imaging system was obtained. The results show that the echo power of the "cat-eye" was mostly affected by the laser interference distance and the interference laser incidence angle, and the echo power and interference duration decreased significantly when the distance of the echo detector from the laser source exceeded 50m while jamming anti-tank missiles. It was feasible to apply the principle of "cat-eye" effect to evaluate the effect of laser directional jamming in real time. The conclusion had certain reference significance for laser directional jamming equipment.
In order to improve the performance of TC11 titanium alloy surface, the strong laser irradiation treatment was used, and then the influence of laser pulse energy density on TC11 titanium alloy surface morphology and performance was studied. The results show that after the laser irradiation by strong laser pulse of 1J/cm2, the surface of the alloy begins to melt, and with the increase of pulse energy density, the outer diameter of the molten hole in the alloy surface becomes larger. After laser irradiation, a micropore with outside diameter of about 1.5μm formed at the surface of the alloy, whose constituent elements were mainly Mg, O, S and C. The microhardness of TC11 alloy was significantly increased after pulse irradiation. When the pulse energy density increases, the microhardness of the alloy increases, and the anti-oxidation performance of the alloy sample is obviously improved. The oxides formed on the surface of the alloy consist of two types: Granule and lamellar. The oxide is mainly composed of Al2O3 and Cr2O3. The study is helpful to improve the surface properties of TC11 titanium alloy.
Picosecond pulse light source is the core device of a quantum key distribution system. In order to realize the localization of picosecond pulse light source, a gigahertz picosecond pulse laser module was developed based on domestic chips. The module was fabricated by using proportion integration division algorithm to control the temperature so that the wavelength drifts within 0.01nm. The external positive intrinsic negative tube was used to detect the light power, and the driving current of the laser diode was adjusted by feedback. In the meantime, experiments were carried out to verify the theoretical results. The results show that the constant current source and short pulse circuit are controlled accurately by domestic microcontroller to drive the laser diode. The output light pulse frequency can reach 1.25GHz, and the pulse width is about 50ps. When the optical power is -3dB, the spectral width is less than 0.2nm, and the output light wavelength and power is stable. The picosecond pulse laser module of localization can meet the requirements of quantum key distribution system for light source stability.
In order to study the relationships of the intensity and distribution of electromagnetic pulses (EMP) with laser parameters, target materials and configuration, the ultra-small B-dot antenna inside the target chamber was used to measure the electromagnetic pulses generated during the strong laser shooting metal copper targets. The pulse intensities in different radiation directions were analyzed. At the same time, electromagnetic radiation in the cases where the target support rod was an insulator and a conductor were discussed. The electromagnetic pulse shows a maximum value of 20V in the normal direction and 22V for the conductive rod, which indicates that EMP induced by strong laser targets has a strong polarized direction and can produce stronger electromagnetic radiation in the case of conductive target rods. The conclusion of this experiment is helpful for revealing the transmission polarization characteristics of EMP generated by laser target interaction in the target chamber and the relationship between its intensity and the conductivity of the target rod.
In order to collect the real-time strain distribution of complex surface shapes, and provide data support for the health assessment of complex surface structures, the strain field detection system for complex surface was designed with fiber-optic sensor network. The system consisted of a fiber laser, a coupler, a demodulator, and a fiber sensing array. The method was compared with the optical scanning detection data, and the theoretical analysis and simulation calculation of the strain distribution were carried out under many different conditions. The strain distribution of the device under test with a variety of different force conditions was simulated and analyzed. The results show that the strain distribution is related to the applied position, size and surface structure. A 5.0mm aluminum plate was tested and compared with simulation data in the experiment. Four groups of fiber grating sensors were placed on the surface to be measured in an orthogonal structure arrangement. The test results show that the maximum wavelength offsets are 1.324nm, 2.547nm, and 1.643nm, and the corresponding shift offsets are 0.244mm, 0.523mm, and 0.347mm, respectively. Compared with the calibration data of laser scanning method, the offset of this method is relatively less than 10%. The test data can reflect the trend of surface shape change, and it meets the design requirements.