In this study, a microwave photon up and down-conversion signal generation scheme is proposed to realize phase tuning. The main component of this scheme is a polarization multiplexing dual-drive Mach-Zehnder modulator (PDM-DMZM). In the proposed scheme, up and down-conversion signals switching can be realized by adjusting the direct current bias point of the modulator. Further, the phase is continuously tuned by adjusting the polarization controller. The proposed scheme can be extended to a multichannel independent phase tuning system. Simulation results show that the radio frequency signal with a frequency of 10GHz can be converted into a down-conversion signal (1GHz) and an up-conversion signal (19GHz). Its phase can be continuously tuned in the range of 0°--360° and generated under different phases. The maximum power fluctuation of the signal is less than 0.3dB, the spurious signal suppression ratio can be maintained above 20dB, the maximum input frequency of the system can be adjusted from 0.5 to 65.0GHz, and the frequency of the generated phase-shifted signal can range from several GHz to 130GHz.

Based on the histological characteristics, a three-dimensional model of the vein and its surrounding tissues was constructed. The light distribution of the irradiated vein was simulated by diffusion approximation theory, the biological thermal equation was solved by finite element method to obtain the temperature distribution throughout the tissue, and the damage caused by laser irradiation was calculated according to the Arrhenius equation. The photothermal response of a radial fiber and a radial 2ring fiber was compared. The effects of laser power, pull-back speed, linear endovenous energy density and venous diameter on the therapeutic effect of the radial 2ring optical fiber were discussed. The results show that the temperature of the tissue irradiated by the radial 2ring fiber is lower than that by the radial fiber, and the adhesion between the fiber and vascular wall could be reduced. When the tissue is irradiated by the same linear endovenous energy density, it is more secure in the lower laser power treatment. The larger the vein diameter, the higher the linear endovenous energy density is required to achieve the therapeutic effect. The proposed model is helpful to better understand the action mechanism of the endovenous laser ablation.

As a new type of model animal, zebrafish is more and more widely used in the brain-related researches. However, there is a lack of high-resolution imaging technologies for the in vivo characterization of the brain of zebrafish from its infancy (>7 days old) to adulthood. In this study, optical coherence tomography (OCT) is used to give in vivo imaging of zebrafish brains after hatching 21, 45 and 100 d. The results show that the imaging depth and resolution of OCT are both enough to visualize the whole brain of zebrafish from three age groups, and the brain structural features of OCT images match well with the sectional staining results. Both the 2D and 3D OCT results quantitatively show that the zebrafish brain increases significantly in 80 d, however due to tissue atrophy, the sectional staining results can not accurately or quantitatively evaluate the brain''s development. This study shows that OCT can be used as a tool for efficient in vivo imaging and used for the brain''s development research based on zebrafish.

The dual phase lagging (DPL) non-Fourier heat transfer model can reflect the transient interaction process between pulsed laser and biological tissues. However, in many literatures where the DPL model is used to study the heat conduction mechanism of biological tissues, there exist both Fourier and non-Fourier boundary conditions and thus many induced conclusions are contradictory. In this paper, the control equation based on the DPL non-Fourier model is adopted and the Fourier and non-Fourier boundary conditions are derived. Meanwhile, the analytical solutions under the above conditions are obtained by integral transformation and Laplace transformation. The biological tissues are taken as an example and the calculation results show that as for the non-Fourier control equation, the predicted temperature distribution in tissues based on the non-Fourier boundary condition is in accordance with the energy conservation law, while the result based on the Fourier boundary condition is not. The conclusions on the temperature rising amplitude and temperature rising rate are opposite for the two kinds of boundary conditions. Moreover, the thermal damage predicted under the Fourier boundary conditions is overly conservative and obviously lower than that under the non-Fourier boundary conditions. Finally, from the point view of energy conservation, the DPL non-Fourier boundary condition is just the DPL energy conservation equation of boundary, while the Fourier boundary condition is the energy conservation equation of the Fourier model. The Fourier control equation of bio-heat conduction should be matched with the Fourier boundary conditions, while the non-Fourier control equation of bio-heat conduction should be matched with the non-Fourier boundary conditions.

In this work, using the model of random phasor sums, the intensity probability density distribution of the signal of an optical coherence tomography (OCT) structure is described, the probability density distribution of the amplitude difference signal is derived, and the threshold model of the dynamic and static regions of the difference image is theoretically determined. A set of swept source optical coherence tomography systems that can scan and image the microvascular of the human skin is used to generate binarized images through a threshold model, combining the existing cross-correlation images based on volume data and binarized images in the laboratory. Results show that the proposed model can reduce the speckle noise and obtain clear structural information.

In order to reasonably select corneal contact lenses of different materials, based on the principle of geometric optical imaging, a corneal imaging model based on contact lenses is established, and the influences of contact lenses with different refractive indexes on corneal imaging quality are analyzed. By using the idea of reverse optical imaging, a paraxial optical system for detecting imaging quality is designed, the corneal contact lenses of different materials and thicknesses are added respectively, and the influences of corneal contact lenses of different materials on the imaging quality are quantitatively analyzed. The effective focal length of the optical system is 18.36 mm, the total length is 36.49 mm, the image height is 2.48 mm, the modulation transfer function value is close to limit diffraction, and the distortion of the full field-of-view is less than 0.1%. ZEMAX simulation results show that the material of the contact lens is PMMA and the thickness is 0.05 mm, which can meet the imaging and wearing requirements of contact devices in augmented reality techniques.

In the biomedical field, to reduce the cost and dependence on advanced devices and to realize multi-dimensional image analysis for unlabeled samples, including spectra and structures, a multispectral microimaging system with multi-channel LEDs was independently developed based on narrow-band LED light source technology. The spectral resolution of the system was 20nm over 420--680nm, with spatial resolution better than 2μm and an imaging range of 520μm × 416μm under 13× magnification. To verify feasibility of the system for clinicopathological analysis, multispectral images of mouse skin squamous cell carcinomas were collected, for both in situ and normal skin tissues. Excitingly, cell structure was clearly observed using the multispectral image system. Spectral information extracted from the image sequence shows that reflectance of the cancerous nucleus has significant difference with that of the normal nucleus in the visible band, allowing the two types of cells to be effectively distinguished. These results indicate that LED illumination-based multispectral imaging systems are promising alternatives to replace traditional, expensive, and complex multispectral imaging systems and play an important role in pathological analysis.

Aiming at the problems of high mobile positioning complexity, low positioning accuracy, and unreasonable positioning for users in large indoor places, a visible light and inertial navigation fusion positioning algorithm based on the hidden Markov model is proposed in this work. First, the indoor parking lot map and positioning fingerprint in the off-line database construction stage are established, the visible light receiving signal strength of each reference node and the distance and angle between the nodes are collected, and a hidden Markov model is established. Then, in the online positioning stage, the candidate set of state transfer is reduced according to the user''s maximum moving speed, and the visible light signal and motion information are obtained. Finally, an improved Viterbi algorithm is used for user trajectory matching and positioning. Simulation results show that the proposed algorithm can accurately predict the user''s trajectory in an indoor parking lot of 2500m 2, the prediction accuracy of the reference node is about 85%, and the average positioning error is about 3.35 m. Compared with other four positioning algorithms, the positioning trajectory of the proposed algorithm is more continuous and smooth with higher accuracy.

This study proposes and experimentally demonstrates a novel image rejection microwave photonic mixer structure based on a dual-driven Mach-Zehnder modulator (DDMZM) and stimulated Brillouin scattering (SBS) narrow-band photonic filtering. In this structure, the radio frequency (RF) and local oscillator (LO) signals are input to the RF ports of the DDMZM on the upper and lower arms, respectively. The optical sideband caused by the RF and LO signals satisfies the equivalent phase modulation relation by bias voltage control; hence, the in-band interference intermediate frequency (IF) signals generated by the frequency beating of the RF and LO optical sidebands can be rejected. Furthermore, with the narrow-band photonic filtering characteristic of the SBS loss spectrum, a useful IF signal is generated by converting the equivalent phase modulation to the intensity modulation relation between the useful RF and LO optical sidebands. The experimental results show that the image rejection ratio(IRR) of this mixer can reach 43dB. The IRR performance of the system can be maintained at a 35dB--40dB level in the operating frequency band of the 6--20GHz RF signal and the 0.5--1.5GHz IF signal.

Based on the chaos polarization system of external optical feedback injection vertical cavity surface emitting laser (VCSEL) and the theory of linear electro-optic modulation, a reconfigurable opto-electronic chaotic logic gate is proposed and its physical model is given in this paper. First, the parameter space, such as applied electric field and optical feedback intensity, is determined when VCSEL output light is chaotic state. Then, the external electric field is modulated as the gating factor, the optical feedback intensity is modulated as the logic input, and the logic output is demodulated by threshold mechanism. When the logic input and gating factor satisfy different logic operation relations, the system can switch different chaotic logic gates flexibly, such as AND, NAND, OR, NOR, XOR, and XNOR.

A modulated grating Y-branch (MG-Y) tunable semiconductor laser can achieve fast tuning in a wide wavelength range and is expected to become one of the most promising light sources in fiber optic sensing applications. In order to meet the demand for fine wavelength quasi-continuous tuning in fiber optic sensing applications, this paper proposes an automated test technique for MG-Y lasers based on spline interpolation. This scheme makes full use of the tuning characteristics of the MG-Y laser. A smooth tuning path covering the range of 40 nm is obtained by coarse scanning of the currents in the reflection areas of the left (IRR) and right (ILR) gratings. After the deduplication and stitching of the linear tuning sections corresponding to each IRR and ILR pair, fast interpolation retrieval can be realized. Through the double calibration of current of the semiconductor optical amplifier and current in the phase region, the flat laser powers at different output wavelengths are realized. Using this automated calibration technique, a wavelength-current look-up table covering 1527 nm to 1567 nm and with a wavelength interval of 8 pm is constructed. The look-up table has smooth current tuning paths and the power fluctuation is less than 0.2 dBm, which can be used in fiber optic sensing applications requiring fast spectrum acquisition.

Multimode fiber is a thick scattering medium. When the target image is projected onto the multimode optical fiber, multimode coupling will occur, thereby generating speckle images at the output of the fiber. In this work, multimode optical fiber imaging is restored based on deep learning, and the distortion of thick scattering media imaging is solved. DenseUnet is used and the speckle image is used as the input of the model for reconstructing the target image. The DenseUnet model employs a fusion mechanism to deepen the network depth, thus, improving the reconstruction accuracy and realizing good robustness. The experimental results reveal that DenseUnet can be used to reconstruct speckle images produced by multimode optical fibers with different lengths.

Based on the mode selective coupler (MSC) in a cavity, a Q-switched pulsed erbium-doped fiber laser with switchable output modes is reported in this work. Through the joint action of the Bragg grating and MSC, the output wavelength selection and the conversion between different modes are realized. Because the MSC has mode separation characteristics and the laser cavity has a dual-branch output configuration, the laser output can be switched between different modes by adjusting the cavity loss. The dual wavelength Q-switched pulse output with linear polarization modes (LP01 mode and LP11 mode) is successfully observed. The laser with switchable output modes can be used in communication, particle trapping, and other fields.

A local oscillation laser seed source with narrow linewidth and large tuning bandwidth is one of the core components of space coherent optical communication systems. Using the narrow linewidth seed source in combination with external electro-optical modulation and narrowband grating filtering, narrow line width and high tuning bandwidth can be achieved, but the fiber Bragg grating controlled by temperature is difficult to adapt to the high-speed Doppler frequency shift between moving platforms. In this paper, a closed-loop system of a fiber Bragg grating controlled by piezoelectric ceramics in combination with the gradient descent algorithm is used to realize the relative locking of the fiber grating and the injected laser wavelength. The proposed scheme can adapt to spatial Doppler shift above 40 MHz/s.

We have developed a nanosecond pulse width Q-switched stretched 532-nm Nd∶YAG green laser based on a multipass cavity (MPC). The pulse widths were stretched from an adjustable regime of 110--260 ns to 460--600 ns by changing from single-pass to multipass operation at a pulse repetition rate of 10 kHz. At a typical pulse width of 460 ns, an average output power of 6.5 W at 532 nm was successfully achieved. The 532 nm output power and pulse width versus input power at 1064 nm were simulated. The simulated results were shown to be consistent with experimental data. Such nanosecond pulse lasers are interesting for both industrial and scientific applications, such as laser damage experiments for the development of new materials.

This paper proposes a multichannel single-pulse laser energy monitoring methodology to realize real-time monitoring of the laser pulse energy at different laser transmitter positions. The sample laser pulse is coupled with an all-in-one optical fiber bundle and imaged onto a CMOS photosensitive surface through an achromatic lens. A software is used to enable real-time identification and calculation of the grayscale values in the CMOS image for each laser pulse. The grayscale value is adjusted to obtain the laser pulse energy. Using the proposed methodology, a long-term and simultaneous monitoring of single-pulse energy of 1064, 532, and 589nm lasers as well as amplified spontaneous emission (ASE) fluorescence in the 1--110km diurnal atmospheric lidar can be achieved. The efficiency of the secondary harmonic generation, conversion efficiency of the pulsed dye laser, and ASE ratio can be obtained based on the measurements of the laser pulse energy. This methodology can be advantageous for the laser system, which monitors the multichannel single-pulse energy.

Based on the characteristics of resonance-domain grating, a high performance polarizer for near-infrared communication band is designed and fabricated using commercial silicon-on-insulator(SOI). In the wavelength range of 1.460μm to 1.625μm, an all-dielectric resonance-domain grating with a period of 0.98μm is designed by use of finite difference time domain method. The maximum extinction ratio of the grating is up to 55dB. According to the results of the design, the polarization grating is experimentally fabricated by electron beam lithography and the polarization performance of grating is measured. Experimental results show that the transmission of transverse magnetic polarized light of grating exceeds 80%, the extinction ratio of the polarization grating is more than 20dB, and the maximum value can reach up to 32dB, agreeing well with the simulation results. Compared with the polarization characteristics of the traditional sub-wavelength metal grating whose period requires less than a quarter of the incident light wavelength, the polarization grating exhibits good polarization performance with near wavelength grating period, reducing the difficulty of lithography in fabrication. Moreover, the polarizer is fabricated based on commercial SOI, which is compatible with the existing mature semiconductor technology and has strong integration and practicability.

The passive mode-locked erbium-doped fiber laser based on nonlinear optical loop mirror operating in the dissipative soliton resonance (DSR) region is reported. Square wave pulse output is obtained in the abnormal and normal dispersion regimes respectively. At anomalous dispersion regime, the net cavity dispersion is calculated to be -0.32ps 2. Stable square pluses with maximum temporal pulse duration of 33ns are obtained when the pump power is adjusted to 481.2mW. Correspondingly, the single pulse energy is 12.4nJ. Subsequently, a 7m long dispersion compensating fiber is employed to compensate the cavity dispersion to make the laser system work at the normal dispersion regime and the net cavity dispersion is 2.85ps 2. Under the same pump power, the maximum temporal duration of the square pulses is 34.3ns and the single pulse energy is 9.42nJ. It is shown that DSR square pulses can be generated at both anomalous and normal dispersion regimes under the conditions of balanced cavity parameters. Additionally, the influence of the pump power on the time domain width and single pulse energy of square wave pulse is also studied. The results show that the time domain width and single pulse energy of square wave pulse change linearly with the increase of pump power.

In this study, we propose a linear polarized fiber laser based on the radiation mode of a 45°-tilted fiber grating (45°-TFG). The laser is constructed using a ring resonator structure and a fiber Bragg grating, and an all-fiber single-polarized laser output based on the radiation mode of the TFG is realized for the first time. The experimental results show that when the input pump light power is greater than 24 mW, a stable laser output can be achieved. The central wavelength of the output laser is 1553.45 nm, that of a 3-dB bandwidth is 0.05 nm, degree of polarization is up to 99.8%, and slope efficiency of the laser system is 10.79%. Simultaneously, with the help of the temperature sensitivity of the fiber Bragg grating, the central wavelength of the output can be continuously tuned from 1553.21 nm to 1554.03 nm, and the tuning sensitivity is 11.37 pm/℃.

The laser strapdown inertial measurement unit(LSIMU) is greatly interfered by measurement noise in the working environment, especially the small laser gyroscope, which cannot accurately identify the angular velocity of the earth''s rotation. As a result, the strapdown inertial navigation system cannot accurately and quickly perform initial alignment on the moving base. To solve this problem, an initial alignment algorithm of LSIMU moving base based on wavelet Kalman cascade filter is proposed in this paper. The results of simulation and comparison experiments show that compared with other initial alignment algorithms, this algorithm can effectively improve the initial alignment accuracy, reduce the attitude angle alignment error. The initial alignment accuracy of the global positioning system assisted laser strapdown inertial navigation system increases from 10'' to 5'' with an minimum variance, which can make the alignment error more stable and fast convergence.

In this paper, the titanium (Ti)/hydroxyapatite (HA) powders collection experiment was designed using the unseparated powders width value as the component evaluation standard to overcome the problem of deviation between the actual composition and the designed composition after the two powders are mixed and sprayed in the laser cladding process. Based on the response surface method, the mathematical model between the width of the unseparated powders and process parameters of the laser was established. Through the calculation of the extreme value of the regression model and determination of the reasonable process parameters, the powders composition deviation in the laser deposition process was inhibited. The experimental results reveal that defocusing distance has the most significant influence on the Ti/HA powder separation, followed by the scanning speed and powder feeding rate. The unseparated powders width initially increases and then decreases with the increase of defocusing distance; meanwhile, it decreases with the increase of the scanning speed. Moreover, when the defocusing distance is -3 mm to -1.5 mm and the scanning speed is 0 to 4 mm·s -1, the width value of the unseparated powders is large, and the process parameters in this range help to improve the inaccurate composition raio of Ti/HA biomedical materilas.

The application of amorphous alloy materials is limited by the behavior of small molding size and serious crystallization. With pure zirconium as the substrate, we herein adopted the selective laser melting technology to fabricate a 15 mm×15 mm×15 mm bulk Zr50Ti5Cu27Ni10Al8 amorphous alloy. The sample''s microstructure was analyzed. Moreover, the thermal effect of the preparation process of the bulk amorphous alloy was simulated using ANSYS finite element software. The research results show that the formed amorphous alloy sample is mainly composed of amorphous phase. Crystallization occurs in the superposition area of the heat affected zone because of the accumulation of structural relaxation and crystal embryos. The crystalline phase is Al5Ni3Zr2. This study provides a possibly effective method for preparing bulk amorphous alloy by laser additive manufacturing.

This paper investigates the low-cycle fatigue performance of boron-modified TC4 titanium alloy deposited via laser melting at different strain amplitudes. The results reveal that the low-cycle fatigue performance of boron-modified TC4 titanium alloy deposited via laser melting is comparable to that of annealed forging when subjected to a strain amplitude of 0.8%--1.0%. A comparison of the microstructure and low-cycle fatigue performance of the boron-modified laser melting deposited TC4 in solid solution-aging state with the annealed TC4 forging is performed. It is found that as the strain amplitude is above 1.0%, the basket-shaped microstructure of the solid solution-aged boron-modified TC4 titanium alloy deposited via laser melting exhibits better resistance to crack propagation compared with the double phase microstructure of TC4 annealed forgings. Moreover, the solid solution-aged boron-modified TC4 titanium alloy obtained via laser melting deposition exhibits different degrees of cyclic softening behavior at different strain amplitudes. Finally, the morphologies of the low-cycle fatigue fractures of solid solution-aged boron-modified TC4 titanium alloy obtained via laser melting deposition are observed under a scanning electron microscope, and crack propagation during low-cycle fatigue failure is studied here.

The gas-solid-liquid three-phase model based on the volume-average method was used to study the influence of process parameters upon the chromium element distribution and its uniformity in laser-cladded 316L stainless steel on 45 steel. First, the chromium elemental distribution in cladding layer was characterized by average concentration of chromium element and the evolution of chromium element distribution during the cladding process was analyzed; secondly, the simulated and experimental Cr distributions along y direction were compared to verify the model''s reliability. Then, a simulation was performed by set the orthogonal-process parameters to obtain the relationship between the process parameters and the distribution of chromium element in the cladding layer. Finally, according to the simulation results, the flow behavior of the molten pool was analyzed to obtain the relationship between the process parameters and the uniformity of chromium element in the cladding layer along the x direction. The result shows that the powder-feeding rate has the greatest influence on chromium content in the cladding layer, followed by laser power and scanning speed in sequence. The powder-feeding rate is positively related to the average concentration of Cr, whereas the laser power is negatively related to this concentration. The solidification and flow rates of the molten pool have an important impact upon the uniformity of the chromium element distribution in the cladding layer. A cladding layer with a more uniform elemental distribution can be obtained by appropriately increasing the laser power and reducing the scanning speed.

Owing to its excellent shape memory effect, nitinol is a smart material that has been widely used in fields such as aerospace, medicine, and electronics. Nitinol components with complex shapes and desirable properties can be produced by selective laser melting, which overcomes the limitations of traditional manufacturing. Selective laser melting enables the shapes, properties, and functionalities of the components to achieve controllable changes in time and space dimensions, which is one of the popular research topics in “4D printing”. In this study, the research progress and technology status of nitinol formed by selective laser melting are briefly reviewed. Various influence factors on the transformation temperatures, shape memory effect, and superelasticity of nitinol are investigated, in which the influence factors are related to forming process, heat treatments, etc. Moreover, the suitable process parameters of nitinol formed by selective laser melting are summarized. Finally, a prospect for future development of deposition of nitinol by selective laser melting is presented. This study provides a reference for “4D printing” of nitinol formed by selective laser melting.

TA2/TA15 gradient material was prepared using the laser direct deposition technique. The microstructural evolution and bending properties of this material were investigated, and the stress-strain behaviors of the gradient-transition zone with different compositions were discussed by finite-element simulation. The results show that when the alloy composition transitions from TA15 of bottom to TA2, the microstructure gradually changes from an α+β basket-weave phase to a single-α phase, the types of alloy elements and β-phase volume fraction gradually decrease, and the α-phase volume fraction gradually increases. The microhardness and bending strength increase with the increase of Al-element content and the bending strength gradually increases from 964 MPa to 2156 MPa. The finite element stress field simulation results show that the top is subjected to compressive stress and the bottom is subjected to tensile stress during bending deformation of the specimen. Compared with the TA15 sample, the decrease of Al content will reduce the bending strength of the gradient material but greatly improve the plastic ability and achieve the uniform stress transition. Among all the samples, GZ-3 has the best comprehensive properties.

The Gaussian pulsed laser line etching energy density distribution model is constructed, and the effects of laser power and number of pulses on the point/line size of diamond surface produced by chemical vapor deposition (CVD) are studied. The diffusion mechanism of energy on material surfaces and the compositions of etched surfaces are obtained. On this basis, the laser surface etching is conducted. The results show that the etching profile is approximately a Gaussian one under the action of single Gaussian pulse, which indirectly proves that the energy of laser beam acting on the material surface shows a Gaussian distribution and the etching surface is composed of diamond, graphite and hybrid materials. Moreover, both the pulse point etching depth and width increase as laser power and number of pulses increase. The laser power has a great influence on the line etching degree of the CVD diamond surface. When the power value increases by 12W, the etching width and side sweep depth increase by 23.32μm and 346.04μm, respectively. In contrast, the laser scanning speed has a relatively small influence on the line etching degree of the CVD diamond surface. When the scanning speed increases by 49.8mm·s -1, the etching width and side sweep depth decrease by 6.35μm and 70μm, respectively. The etching results under the conditions of power of 3W, scanning speed of 50mm·s -1 and scanning spacing of 2μm indicate that the etching depth is 9.71μm and the surface roughness is 1.10μm.

Abstract As for the high-precision micro-hole formation in FR-4 copper clad laminate, the traditional mechanical drilling process is cumbersome and the degree of precision is low. The femtosecond laser is used to perform the single factor test and the orthogonal test on the copper clad laminate. The inlet diameter, outlet diameter and taper are used as the evaluation indexes to discuss the influence of the process parameters on the quality of micro-holes. The results show that the single pulse energy has the greatest impact on the quality of micro-holes and the repetition rate has the least influence. The optimal process parameter combination is set as single pulse energy of 29μJ, repetition rate of 92kHz, pulse number of 2112, and defocusing amount of 0.01mm. After these optimal process parameters are adopted, high-quality and high-precision drilling of FR-4 copper clad laminate can be performed to realize the rapid and efficient production of printed circuit boards.

In this paper, a method for volume error calibration of a coordinate measuring machine (CMM) is proposed, which is based on the inverse-distance weighting (IDW) algorithm. The volume errors of the CMM spatial measurement points are firstly obtained using the laser tracing multi-station measurement technique combined with the Levenberg-Marquardt (L-M) algorithm. Subsequently the IDW algorithm is used to spatially interpolate the volume errors of the measurement points and thus the volume error of any point in the whole measurement space of CMM is obtained. The experimental results show that the IDW algorithm has low requirements for measurement paths, high interpolation accuracy, and an error coincidence degree of higher than 96% for volume error in each direction. The research results provide a reference for the selection of the optimal measurement position for workpieces in the measurement space.

Here, a distributed optical fiber temperature sensor is embedded in a lithium-ion battery to realize real-time distributed in-situ monitoring of the temperature field in the battery and the evaluating and forewarning of its operating health. The distribution state and evolution of the temperature field in lithium-ion batteries under different operating environments are analyzed theoretically according to the structure design model of the batteries. Accordingly, the characteristic temperature points (positive taps, negative taps, and center point) are selected to optimize the layout location of sensors for the accurate measurement of the temperature field and the optimization of the cost performance. Hence, the number of sensors used, the difficulty of the layout process and the cost of demodulation equipment can be reduced. Distributed cascaded fiber Bragg grating temperature sensors are employed in the experiment. The experimental results show that the temperature of each characteristic point slowly increases with the ambient temperature, while the central temperature point exhibits a rapid temperature increase, which are consistent with the theoretical results. The proposed method provides a technical reference and an implementation scheme for the in-situ monitoring of the health status of the integrated components of large-scale lithium-ion batteries in the future.

The influences of mid-spatial frequency surface errors on the illumination field uniformity and the penumbra width of off-axis illumination are analyzed herein. The analytical relationship between peak-valley (PV) values of the errors and the coherence factor on the line spread function (LSF) distribution under the dipole illumination is derived, and the effect of the mid-spatial frequency error on the LSF of the relay lens group of the photolithography illumination is numerically analyzed. Mid-spatial error describes the reduced uniformity of the illumination field and the increased penumbra width. Using actual manufactured surface errors in conjunction with commercial optical design software to simulate the relay lens group in the photolithography illumination, theoretical accuracy is verified. Therefore, this simulation method can be used at the design stage using the actual manufactured profile, which can provide a reference for optical designs.

A new structured light stripe centerline extraction algorithm is proposed. This algorithm can stably extract the stripe centerline under different interference environments and has the ability to repair broken lines. Using the unsupervised feature of the density clustering algorithm, even if there is a broken line or noise interference, it can still quickly cluster the set of candidate pixels on the centerline, greatly reducing the search range. Then, after experimental data analysis, it is found that the centerline of different scenes also has the features of high brightness and tend to be continuous. The energy function is defined by the Euclidean distance between pixels and the brightness value to model the feature, and the shortest path search algorithm is iteratively converged to accurately extract the centerline. The experimental results show that in three strongly disturbed structured light images, the algorithm extracts the centerline with a root mean square error of 0.4 pixel, the processing speed is 12.48 times faster than the image seam algorithm with the same strong anti-interference ability. The proposed algorithm greatly improves the anti-interference ability while maintaining fast operation speed and high accuracy, and effectively reduces the restrictions of using structured light measurement in industry.

To estimate the accurate disparity in weak texture region and fine structure region when the light field camera is used for three-dimensional measurement, a model of the light field depth estimation based on deep learning technology is proposed. Moreover, the relationship between the disparity and corresponding depth is also established. The proposed method is applied to a variety of complex scenes, and the experimental results show that the proposed method can accurately estimate the disparity information in the weak texture region and fine structure region, and leading to a good reconstruction of three-dimensional structure. The processing time of the proposed method is compressed to the order of 1s, which is 1 to 2 orders of magnitude lower than the traditional methods based on cost optimization.

The core of nonlinear laser ultrasonic crack detection technology involves the use of a mechanical/photo-thermal loading method to induce loading on cracks, thereby enabling periodic opening and closing of these cracks. The crack closure mechanism has rarely been investigated. To address this issue, in the heated laser irradiation area, the time domain laser ultrasonic method is used to study the closing response of real micro-cracks. The local plastic/elastic microscopic changes induced by the crack closure are also investigated. Analysis of the changes in the peak-peak value and arrival time of each ultrasonic mode in different crack closing states yield pertinent information about the crack closure process. The results reveal that the change process of the signal peak-peak value and arrival time is related to the time of crack closure, and the sequence of crack closure corresponds to the crack width.

In the multi-view triangulation with known image observation values and camera internal and external parameters, due to the existence of observation noise, the midpoint method and the L2 back projection standard method have insufficient triangulation accuracy and efficiency, respectively. Therefore, this paper proposes an inverse depth adaptive weihting based multi-view triangulation method. First, by constructing an inverse depth model of the three-dimensional points to be estimated in a multi-view environment, the corresponding weights to the observation errors are assigned under different viewpoints. Then an unbiased estimation model of the approximate angle error for the multi-view triangulation is determined. Finally, a fixed-point iteration is carried out to quickly solve the cost function. Experimental results both on simulation and real datasets show that the proposed method can obtain a better balance between accuracy and efficiency for multi-view triangulation, and the reconstruction accuracy and the number of iterations under different noise conditions are robust.

There is growing demand for ensuring accuracy with respect to the assembly of new aircraft. The commonly used digital-measurement auxiliary assembly system cannot meet this demand. In this study, a new multidevice hybrid docking measurement method is proposed based on the iGPS laser measurement system. Further, a position measurement model, position solution model, and docking path solution model are established based on the aforementioned method. After guiding the global docking, the iGPS laser measurement system triggers the local multidata fusion measurement system to detect the local position. The local position solution model can be used to obtain the angle error and position error between the joint ear pieces. The docking path can be optimized after considering the compensation error, improving the docking accuracy. The experimental results indicate that the position accuracy after considering the compensation error is 5.8×10 -2mm and that the angle accuracy is 9°×10 3, indicating that the proposed method meets the actual docking accuracy requirements.

Vertical stratification of the atmospheric boundary layer can hinder or change the vertical and horizontal transmission of energy, momentum, moisture, and trace substances. Therefore, the boundary layer height is particularly important for atmospheric research. The continuous changes in boundary layer height throughout the day in time cannot be obtained based on the sounding data. Further, the aerosol content gradient at the top of the boundary layer is not obvious, so the boundary layer height cannot be accurately given. In this paper, based on the water vapor mixing ratio data of Raman lidar, the boundary layer height is inverted by the slope method and the Dougls-Peucker (DP) algorithm, and the results are compared with the sounding data. The results show that the two are in good agreement.

In order to develop a Rayleigh-Mie Doppler lidar system for detecting mid-to-high wind fields, a set of 532 nm Rayleigh-Mie Doppler lidar verification system based on triple Fabry-Perot interferometer (FPI) was previously built and the actual comparison test was conducted. Using the verification system, the FPI transmission calibration experiment was carried out firstly, and the actual transmission curves of triple FPI were obtained by using the nonlinear fitting method. The spectral width of FPI-1, FPI-2, and FPI-L were 1.20 GHz, 1.22 GHz, and 1.18 GHz respectively, the peak transmission were 0.817, 0.807, and 0.768 respectively, and the peak intervals of FPI-1 & FPI-2 and FPI-1 & FPI-L were 3.91 GHz and 1.25 GHz respectively. Furthermore, the actual wind speed detection sensitivity of the system was given when both of the Mie and Rayleigh scattering signals were incident. Secondly, continuous observation experiment of radial wind speed and comparative observation experiment of horizontal wind field were carried out. The experimental results show that in the single radial wind speed measurement, the system has the capable of detecting wind field at a height of about 10 km and 16 km in the daytime and night respectively with the time resolution of 2 min and spatial resolution of 75 m. In the height range of 2.7 km to 10 km in the daytime and 1.5 km to 10 km in the night, the data of the horizontal wind field measured by the verification system coincide with those measured by the balloon. In the night, 70.8% of the horizontal wind speed and direction data deviation is less than 2 m/s and 10°, and 95% of the data deviation is less than 5 m/s and 15°, which fully verifies the accuracy of the system wind field measurement results.

Dielectric spectral technique is the technique to analyze microstructural changes by means of macroscopic dielectric parameters. Compared with microwave ones, terahertz dielectric spectra contain rich fingerprint information and can reflect multiple motion modes within materials. In this paper, the dielectric spectra in the terahertz spectral band of natural rubber after thermal aging are investigated and the corresponding changes in the molecular structures are further analyzed. The research results show that both the real and imaginary parts of terahertz dielectric constants of samples possess definite change laws, which is corresponding to the microstructural changes during aging of materials. In addition, the acquired terahertz dielectric spectral data is fitted to obtain the corresponding dielectric constant at zero frequency, dielectric constant at optical frequency and dielectric strength. From the standpoint of overall structures of molecules, the relationship of the polar structures and intermolecular network structures during aging with the decomposition and crosslink of molecule chains is analyzed. The research conclusion indicates that terahertz dielectric spectra have potential application value in non-destructive detection of aging materials.