Contour targets are affected by turbulence clutters in near-ground remote imaging scenes, leading to large matching errors. To address this problem, we propose a shape point set matching recognition method based on an oriented shape context and an edge continuity constraint. In the proposed method, directional features are embedded into a traditional shape context to construct a feature operator with a scale and rotation invariance. Further, inspired by the priori of edge continuity between the template and target shapes, we add the edge continuity constraint condition of the contour shape into the target matching energy cost function to improve the accuracy of shape matching. The experimental results of shape matching in a synthetic turbulence clutter scene and a real remote imaging scene show that compared with the traditional method, the proposed method can reduce the target matching error by about 6% in clutter scenes and reduce computational complexity.

In order to solve the problems of traditional atmospheric transmissometer, such as fixed transmitting-receiving baseline, limited sampling space, and poor applicability of transmittance model, a variable baseline atmospheric visibility measurement system is designed in this work. The laser emission unit of the system is fixed, while the optical receiving unit is movable, so the atmospheric transmittance can be obtained at different baseline lengths. By measuring the multi-point atmospheric transmittance and using the least square fitting, the atmospheric extinction coefficient and the atmospheric visibility can be obtained. Simulation experiments of the proposed system and the traditional transmissometer are carried out under the atmospheric visibility conditions of 200, 800, and 2000 m. The results show that the root mean square error of atmospheric extinction coefficient measured by the proposed system is less than that of the traditional transmissometer, which effectively reduces the influence of system error and random error on the measurement results. The effectiveness and reliability of the system are verified by the external field experiment in the atmosphere environment simulation chamber.

Aiming at the problem of traditional wavelet function in processing laser gyroscope output signal, a new wavelet threshold denoising method with parameter threshold function, adaptive determination of optimal decomposition layer number and optimal threshold is proposed. First, a new adaptive thresholding function is proposed. Then, the wavelet proportional energy entropy is calculated based on the principle of maximum energy entropy, and the optimal number of decomposition levels of the wavelet is adaptively determined, and the combination method of SURE (Stein Unbiased Risk Estimator) unbiased estimation principle and Newton iteration method is used to determine the optimal threshold of signal change with time adaptively. Finally, the experimental verification is carried out by using the measured data and Allan variance analysis. Experimental results show that both static laser gyroscope signal and dynamic laser strapdown imu signal, the improved adaptive wavelet noise reduction method of the noise reduction result is better than that of the traditional wavelet thresholding method and the standard Kalman filtering method, and the method processed signal higher precision, smaller mean square error and smaller noise coefficient, which effectively restrain the interference of noise of laser gyroscope output signal.

High-risk work site environments are complex and dangerous and responsible for many fall accidents and casualties. To detect the fall behavior of workers, a human fall detection method using a Kinect sensor was proposed. Based on depth images obtained using a Kinect, we extracted body joint points information and determined whether a human body fell by calculating the changes of the relative position entropy and speed of the joint points. Through comparative experiments, a set of skeleton joint points with the highest fall recognition rate were determined: head, shoulders, knees, and center points. Experimental data show that the method can detect fall behaviors more quickly and accurately compared with the conventional methods.

The high-speed polarization state rotation associated with the polarization multiplexing coherent optical communication system link causes channel damage. Further, the feedback delay associated with the dynamic equalization algorithm module of the coherent receiver in the actual system results in insufficient polarization state tracking performance. In this study, a tracking and prediction algorithm for polarization state rotation is proposed based on complementary Stokes vectors to resolve the aforementioned problems. The proposed algorithm initially transforms the measured polarization rotation matrix of the Jones space and its inverse matrix into the Stokes space, obtains a pair of complementary vectors, and tracks and predicts the motion trajectories of the complementary vectors in Stokes space. Finally, the compensation of the polarization state rotation of the link is realized. The simulation results show that the squared error of the predicted Jones matrix can be reduced by 10% compared with that in the original scheme by tracking the complementary vector when the equalization feedback delay is 5 frames. Furthermore, the polarization rotation speed tolerance of the system increases from 1.3 MHz to 1.5 MHz when using the proposed algorithm.

In order to solve the problem of holding-time-aware routing and spectrum allocation (HTA-RSA) in software defined elastic optical networks (SD-EON), multi-path routing (MPR), traffic grooming (TG), and adaptive modulation (AM) are combined to establish an integer linear programming model with the optimization objective of minimizing the spectrum resource occupation, and a holding-time aware multipath routing and spectrum allocation (HMRSA-TG) algorithm based on TG is proposed. For both immediate reservation allocation (IR) and advance reservation allocation (AR), the single path single service allocation method is used to establish the service connection. If it fails, the single path multi sub service allocation method is used. If it is still unsuccessful, the multipath multi sub service allocation mode is tried. In order to minimize the spectrum resource occupation and release the spectrum resource as soon as possible, when establishing the service connection, the allocation method with the least spectrum resource is preferred. When the spectrum resources are the same, the allocation method with the minimum total occupied time slots is preferred. Simulation results show that this algorithm can reduce the blocking rate and improve the spectrum utilization.

The DK46+092-DK53+300 sections of the Jingxiong intercity railway airport tunnel are located in the area with obvious land subsidence. In order to understand the safety situation of the tunnel during construction and later operation in a more rapid and intuitive way, it is necessary to monitor the health status of the tunnel structure. In this paper, based on the fiber grating sensing principle, the circumferential strain sensing of the tunnel, the relative displacement sensing of the deformation joint, and the layered settlement monitoring around the tunnel are carried out. The layout and installation processes of the sensor elements are introduced in detail, and the automatic and remote control of the health monitoring of the large-section tunnel structure is realized. The initial monitoring results show the changes of the strain, axial force, and bending moment of the tunnel during the concrete pouring and curing period and backfilling period. The automation and long-term monitoring of fiber Bragg grating are beneficial to the real-time monitoring and early warning of the tunnel structure.

This paper proposes a practical design method for an optical phase anti-counterfeiting mask based on the analysis of the characteristics of traditional optical phase-coding technology. A two-dimensional (2D) barcode is used to encode text or image information for anti-counterfeiting into a 2D barcode, and then the 2D barcode is encoded into an optical phase anti-counterfeiting mask based on the traditional phase-coding technology. After decoding the anti-counterfeiting mask with a lower quantization order, accurate encoding information of the original 2D barcode can be successfully restored using image morphology-related algorithms, and the 2D barcode is decoded to obtain the original text and image. The proposed design method not only effectively solves the physical implementation problems of traditional optical phase-coding methods but also exhibits the advantages of high security, low cost, and good anti-counterfeiting performance, which provides an effective technical approach to promote market-oriented applications of new-generation optical anti-counterfeiting masks.

Link performance of a hybrid radio frequency/free-space optical (RF/FSO) airborne communication system using the three-node cooperative architecture based on selection combination diversity is analyzed in this study. Using this architecture, FSO and RF links are simulated using the Exponentiated Weibull atmospheric turbulence distribution model under the mean aperture effect and Nakagami-m fading channel model, respectively. Closed form expressions for end-to-end performance indicators of this hybrid system are derived. The effects of turbulence intensities, modulation modes, and diversity communication schemes on the outrage probability (OP) and average bit error rate (BER) are analyzed using a simulation. The simulation results show that the hybrid RF/FSO airborne communication exhibits better BER and OP performances than the single FSO link system. Moreover, it is observed that low-order M-PSK modulation can effectively improve the impact of atmospheric turbulence on hybrid RF/FSO airborne communication system. When signal-to-noise ratio is high, the cooperative diversity communication scheme improves the BER performance of the system better than the low-order modulation scheme.

The surface-bonded fiber Bragg grating (FBG) sensor consists of three parts: fiber, middle layer, and matrix. By analyzing the ratio of the elastic modulus of the colloid to the optical fiber, the influences of the elastic modulus, Poisson''s ratio, length and other factors of the colloid on the average strain transfer rate from the matrix to the optical fiber are explored. Compared with the average strain transfer rate without considering the elastic modulus ratio. Experimental results show that when considering the elastic modulus ratio, the average strain transfer rate increases with the increase of elastic modulus and length of colloid, decreases with the increase of thickness and Poisson''s ratio of colloid, and first increases and then decreases with the increase of colloid width. The research results are more in line with the actual application.

Chaos synchronization using semiconductor lasers achieves high-speed physical-layer key distribution, but the chaos synchronization time of lasers limits the rate of key distribution. Consequently, the factors affecting the chaos resynchronization time in an open-loop injection-locked synchronization system of the vertical-cavity surface-emitting laser (VCSEL) have been numerically studied. Moreover, the experimental results demonstrate that the chaos resynchronization time can be reduced in three ways: increasing the bias current of the laser and the differential gain coefficient, or reducing the photon and carrier lifetime to shorten the relaxation oscillation period; reducing the linewidth enhancement factor that can reduce the complexity of laser chaos; and increasing the injection intensity and reducing the frequency detuning, which can achieve strong injection locking. Based on chaos synchronization, the results have theoretical reference significance for improving the key distribution rate.

In view of the high complexity of the current facial landmark detection algorithm network model, which is not conducive to deployment on devices with limited computing resources, this paper proposes a high-precision and lightweight facial landmark detection algorithm based on the idea of knowledge distillation. This algorithm improves the Bottleneck module of residual network(ResNet50) and introduces packet deconvolution to obtain a lightweight student network. At the same time, a pixel-wise loss function and a pair-wise loss function are proposed. By aligning the output feature maps and intermediate feature maps of the teacher network and the student network, the prior knowledge of the teacher network is transferred to the student network, thereby improving the detection accuracy of the student network. Experiments show that the student network obtained by this algorithm has only 2.81M parameter amount and 10.20MB model size, the frames per second on the GTX1080 graphics card is 162frames and the normalized mean error on 300W and WFLW datasets are 3.60% and 5.50%, respectively.

To improve the positioning accuracy of positioning systems, a time of arrival (TOA) estimation algorithm based on a preamble four-pulse signal differential matched filter is proposed. Using the two-pulse and four-pulse signals to evaluate the differential matched filter, the TOA estimation accuracy of preamble pulse signals is improved. Based on the number of pulses and a signal-to-noise ratio (SNR), the root mean square error of the differential matched filter output is compared, it is concluded that the TOA estimation accuracy of four-pulse signals is better than that of single-pulse signals. When the SNR is 20 dB, the TOA estimation accuracy of the four-pulse signals can reach 3.8947 ns, which is much lesser than the maximum time error accuracy of 25 ns specified by the International Civil Aviation Organization. Real-time data received by an ADS-B receiver installed at the terminal of Tianjin Airport and simulation data under the same conditions are used to verify the accuracy and stability of the TOA estimation of proposed algorithm.

This study proposes an improved rail bearing platform measurement method based on a binocular line-structured light sensor to alleviate the problems pertaining to the existing rail bearing platform detection methods. During the measurement, the relative position of the two cameras in the binocular sensor and rail bearing platform remains unchanged. Scanning of the rail bearing platform is performed by controlling the line laser movement using the driving device built in the sensor to obtain the point cloud data, which improves the data acquisition effect and measurement accuracy of the embedded sleeve position of the rail bearing platform. Concerning point cloud data processing, a method for point cloud data segmentation and extraction based on the Spearman rank correlation coefficient is proposed. Automatic, noncontact measurement of five key geometric parameters of rail bearing platform is conducted. The experimental results show that the accuracy of the proposed measurement method is up to 0.3 mm, which can fulfill the requirements of track plate detection.

In order to achieve the non-contact surface roughness measurement of objects with steep contours, we usually use confocal imaging to layer the objects and thus to reconstruct the three-dimensional surface contours of objects. Meanwhile, a Gaussian filter is used to extract the roughness contours from the three-dimensional surface contours. However, the boundary data are missed during the process of filtering and simultaneously the usual simplified extension of two end data of original contours leads to contour distortion. This paper introduces a new type of method for boundary area correction. This correction method can be also useful for parts with large surface radian changes and can be used to accurately extract the roughness contours of objects. Confocal imaging measurements are performed on two sets of actual roughness samples with overall smooth and steep contours. For samples with overall smooth contours, the root mean square error (RMSE) and average roughness obtained by the conventional method are 0.080 and 2.86 μm, respectively, and the error relative to the sample roughness value of 2.94 μm is 2.72%. In contrast, after boundary area correction, the obtained RMSE and average roughness are 0.090 and 2.85 μm, respectively, and the error relative to the sample roughness value is 3.06%. The roughness of the sample with an overall sharp contour is 3.2 μm, and the RMSE and average roughness obtained by the conventional method are 0.120 and 3.31 μm, respectively. The error relative to the sample roughness value is 3.48%, and after boundary area correction, the RMSE and average roughness are 0.045 and 3.19 μm, respectively. The error relative to the sample roughness value is 0.31%. The research results confirm that this method can accurately measure the surface roughness of objects with overall steep contours and can provide a certain reference to the development of laser confocal roughness measurement equipment.

Limited by the camera''s field of view, the truck contour dimension measurement based on machine vision cannot obtain a complete body image at one time. Therefore, image stitching technology is introduced on the basis of traditional machine vision measurement, and a dynamic non-contact measurement method of truck size is designed, which can be used for feature extraction, image registration and fusion, and external contour dimension measurement of sequence truck images without stopping and contacting. Simulation results show that the average measurement error of this method is 0.83%--1.87%, which meets the requirement of GB21861-2014.

In order to improve the surface hardness and wear resistance of 42CrMo steel, Ni60 reinforced coatings containing the nano-WC powder mass fractions of 0, 10%, 20%, 30%, and 40% were prepared on the surface of substrate by semiconductor laser in this paper. The microstructure and phase composition of samples were analyzed by OM, SEM, EDS, and XRD. The mechanical property and friction and wear property were tested using a digital microhardness tester and a high temperature friction and wear tester. The results show that the nano-WC reinforced Ni60 coating surface is well-formed. The microstructure of the enhanced coating is strip, dendritic, fishbone, block, and granular. The phase is dominated by austenitic Ni-Fe, part of nano-WC remains, part of W2C new phase is formed. A series of complex compounds, such as Cr23C6, M6C, Cr7C3, CrB, and NiW, are generated in the coating. The maximum microhardness of the nano-WC reinforced coating is 1256HV0.2, which is about 50% higher than that of the Ni60 alloy coating. The minimum wear volume of reinforced coating is 1.29mm 3, which is only 1/7 of Ni60 alloy coating; the average friction coefficient of the reinforced coating is as low as 0.275, while that of Ni60 alloy coating is 0.530, which decreases by about 48%. Friction and wear studies show that the wear mechanism of nano-WC reinforced coating is mainly adhesive wear, accompanying with slight abrasive wear.

The GCr15 high carbon steel powder prepared by plasma rotating electrode was used as the experimental raw material and prepared by selective laser melting (SLM). The effects of laser power, scanning speed, and volume energy density on the formability of GCr15 and the structure transformation after forming during SLM forming process were studied. Experimental results show that the laser power, scanning speed, volume energy density, and relative density are in a linear relationship within the adjustable range of parameters. It can be seen from the energy density curve that the power has a greater effect on the relative density than the scanning speed. In the case of low power, the relationship between the power and the relative density will be distorted. At the same time, the microstructure of GCr15 bearing steel prepared by selective laser melting is small and uniform mainly consisting of coarse needle-like martensite and retained austenite. With the increase of energy density, the content of retained austenite increases.

In order to explore the microstructure and properties of NiCoCrAlY coating under different laser scanning speed, the NiCoCrAlY coating was melted and deposited on the IN718 surface by laser cladding technology. The forming condition, microstructure, hardness, friction and wear properties of the coating were analyzed, and the dynamic relationship among scanning speed, microstructure and coating properties was established. The results show that the NiCoCrAlY coating has a good shape at different scanning speeds, and the solidification structure is columnar dendrite and equiaxed dendrite which is perpendicular to the solid-liquid interface and grows directionally and epitaxially. With the increase of scanning speed, the coating temperature gradient increases, the solidification rate increases, the grain structure is refined, and the coating microhardness increases slightly. At the same time, with the increase of the scanning speed, the average friction coefficient and wear rate of the coating first decrease and then increase. The results show that the wear resistance of the coating obtained at 12 mm/s scanning speed is better.

In this paper, using pulsed laser and continuous laser as the heat source of the selective laser melting process, the effects of different laser average powers and pulse duty cycles on the density, surface roughness, and microstructure of Ti6Al4V titanium alloy samples are studied. Experimental results show that compared with continuous laser, the use of pulsed laser with a duty cycle of 60%--70% can significantly improve the surface quality of the part. The surface roughness is as low as 3.6 μm, and the sample grain width is reduced from (1.14±0.23) μm to (0.85±0.18) μm, and can effectively eliminate the warpage caused by the accumulation of thermal stress during continuous laser processing.

Spiral micro-structured fiber Bragg grating (FBG) coated with nanorod Pt-WO3 hydrogen sensor was fabricated. Femtosecond laser was employed to fabricate spiral micro-structured on fiber cladding of FBG. WO3 nanorods were synthesized by hydrothermal method. Pt (acca)2 precursor was decomposed and Pt-WO3 nanorod particles were synthesized. The molar ratio of the two metals was controlled at Pt∶W=1∶5, the nanorod Pt-WO3 was coated on the surface of micro-structured cladding of FBG. The sensitivity of the double spiral micro-structured FBG sensors is about 2.5 times than that of standard FBG sensors. The response time of the sensor under 1% hydrogen concentration is 15 s to 30 s The sensor has good application prospects in the field of hydrogen sensing.

In order to further study the hardness and wear resistance of laser cladding Ni-Al/Al2O3-13%TiO2 cermet coating, a YLS-2000 fiber laser was used to prepare Ni-Al coating and Ni-Al/Al2O3-13%TiO2 cermet coating on a 45 steel substrate .The metallographic microscope, scanning electron microscope, electronic differential system energy spectrum analysis, X-ray diffraction and other systems were used to study the microstructure, phase composition, and element distribution of the coating. HXD-1000TB Vickers hardness tester was used to measure the micro-hardness distribution of the coating section, and the wear test was performed by using the M-2000 abrasion tester. The Ni-Al / Al2O3-13%TiO2 cermet coating has good macro-forming quality and no cracks. The maximum cross-section hardness of the coating is about twice that of the Ni-Al coating and about four times that of the substrate. Its wear volume is about 1/8 of that of the 45 steel substrate, which is 30% lower than that of Ni-Al coating. The structure of Ni-Al/Al2O3-13%TiO2 cermet coating is more uniform and dense, and its hardness and wear resistance are significantly improved compared to Ni-Al coating and matrix material. This research has certain reference significance for the overall performance analysis of cermet materials.

In this study, a method based on machine vision is proposed for the rapid nondestructive detection of laser surface modification in copper-chromium alloy. Surface morphology images of the specimen are collected, and the visual salient regions are segmented from the background by applying the adaptive thresholding method are extracted. Additionally, based on geometric moments, the characteristics of the connected domain with spatial transformation invariance. According to the laser energy input, four basic modification states are defined, and a support vector machine is trained to determine the modification quality. Writing scripts in MATLAB language, the results show that it takes about 45 s for feature extraction and model training. Moreover, the recognition speed is about 5×10 6 pixel/s, and the recognition accuracy is about 97.0%. Based on the detection results, the corresponding process parameters can be optimized. Furthermore, the method is not sensitive to light and other detection environment factors, thereby achieving the requirement of rapid and nondestructive detection of laser surface modification quality, which has a certain significance for the optimization of process parameters.

A series of Dy 3+, Sm 3+ co-doped KAlSiO4 phosphor materials were prepared by the high temperature solid phase method. The experimental results show that the doping of a small amount of Dy 3+ and Sm 3+ does not change the crystal structure of KAlSiO4. When KAlSiO4∶1% Dy 3+, w% Sm 3+ is excited at the characteristic excitation wavelength of Dy 3+, there occurs a resonant non-radiative energy transfer from Dy 3+ to Sm 3+ in samples. Meanwhile, the color coordinate shift is very small and there exists a red shift at 528 nm and a blue shift at 713 nm. In contrast, when KAlSiO4∶1.5% Sm 3+, v% Dy 3+ is excited at the characteristic excitation wavelength of Sm 3+, the emission spectrum is very similar to that of KAlSiO4∶1.5% Sm 3+ and there are no characteristic emission peaks of Dy 3+. However, the luminous intensity of Sm 3+ at 651 nm is increased by 6.5 times, which indicates that there does not exist energy return from Sm 3+ to Dy 3+ and the doping of Dy 3+ promotes crystal lattice matching and greatly enhances the luminous intensity of Sm 3+. Theoretical calculations show that the maximum energy transfer efficiency from Dy 3+ to Sm 3+ reaches up to 52% and the energy transfer interaction is electric quadrupole-quadrupole interaction. The color coordinates of phosphors are all around (0.41, 0.51) and located in the yellow-green area. The internal quantum yield under 386 nm excitation gradually increases from 25.8% to 42.6%.

Organic-inorganic hybrid perovskite light-emitting diodes (PeLEDs) is a new type of light-emitting device, it have many advantages, including a wide range of raw material sources, simple device preparation, and high carrier mobility, making it one of the research hotspot in the field of displays and luminescence. Despite this, PeLEDs do have disadvantages, such as poor luminescence stability and small, uniform luminous areas, and there is no unified measurement method for testing PeLED quantum efficiency. In light of this, we propose a new type of PeLED quantum conversion efficiency measurement system. Using a small-sized integrating sphere combined with a spectrum measurement system to collect the PeLED light emission, the quantum conversion efficiency is determined. Standard GaN light-emitting diode data is used to calibrate the center wavelength, brightness, and radiance of the system. Finally, this system is used to measure the performance of actual PeLED devices. Experimental results show that the PeLED external quantum efficiency is the highest (0.089%) at a voltage of 3.2V, and the error determined from the reference did not exceed 6%.

In this study, we designed a triple liquid lens array based on the electrowetting-on-dielectric effect to correct the wavefront errors caused by the piston, tilt, and defocus. A electrowetting-on-dielectric triple liquid lens array model is constructed herein according to the electrowetting-on-dielectric theory. The simulation of the surface shape of the liquid interface changes with the voltage. The wavefront compensation capability of the triple liquid lens array on the piston, defocus, and tilt errors are analyzed. The simulation results showed that the three-liquid lens array can realize the correction and the compensation of different types of wavefront errors. The peak-to-valley value is reduced from 1.838λ before the compensation to 0.285λ after the compensation. The root mean square value is reduced from 0.424λ before compensation to 0.053λ after the compensation. The Strehl ratio is 0.161 before the compensation to 0.917 after the compensation. The related research results show that the triple liquid lens array has broad application prospects in the field without mechanical wavefront correction.

Off-axis aspheric surfaces are widely used in modern optical systems and generally require specific auxiliary optical elements to be detected. Accordingly, this study proposes a reverse iterative non-zero detection method that can be used to detect the same type of off-axis aspheric surfaces without auxiliary optical elements. First, we design a detection optical path and established a reverse iteration method to eliminate non-zero errors. Next, we analyz and compensated the system, adjustment, and random errors, as well as their processing methods. Finally, through a simulation, we obtain the RMS value of the surface shape of the off-axis aspheric surface using reverse iteration as 0.133λ, which is consistent with the actual surface shape of the simulation. The residual error of the simulation fitting is within 10 -5λ. In conclusion, the reverse iterative non-zero detection method is a high-precision and universal non-zero detection method for off-axis aspheric surfaces.

The Kretschmann module comprises a prism and metal film, and a substrate module comprises two metal films and a glass sheet. When the two modules are close to each other, a double-sided metal-cladding waveguide structure with a nano air gap and an organic film as the waveguide layer will be formed. The resonance angle of the guide mode resonance excited in the double-sided metal-cladding waveguide structure is linearly related to the thickness of the nano air gap. When the reflectivity curve of one of the modules is selected as the detection signal, the thickness of the nano air gap can be measured by measuring the change in the resonance angle. Numerical simulation calculation results show that this structure can measure the air gap in the range of 0--100 nm, and the measurement resolution can reach 1 nm.

The color rendering index (CRI) is an important evaluation parameter of white organic light-emitting diodes (WOLEDs). We fabricated a series of devices by vacuum evaporation to obtain WOLEDs with high CRI. The exciplex formed by NPB∶TPBi(1∶1) as a blue emission layer can reduce the difficulty and cost of fabrication of WOLEDs. Comparing this to a device with an exciplex emitting layer (3 nm), the device with the double-exciplex emitting layers (1.5 nm×2) helps to balance the exciton distribution and improves the CRI. Furthermore, the thickness of the spacer is changed to adjust the Dexter energy transmission of the exciton. When the thickness of the spacer layer 1 (Spacer 1) is 2 nm, the maximum power efficiency of the warm white light device B2 is 16.11 lm/W, the CRI is as high as 95 under a driving voltage of 5 V, and its correlated color temperature is 2322 K.

In order to improve the classification accuracy of EEG signals, a classification method based on an artificial bee colony algorithm and back propagation (BP) neural network is implemented. In order to improve the poor global search abilities and sensitivity to initial weights of BP neural networks, the global search factor is used to enhance an artificial bee colony algorithm search formula, which is proficient in exploration but required further development. A crossover operation is used to improve the global search capacity of the artificial bee colony algorithm. This enhanced algorithm is further used to optimize the sensitivity of the BP neural network to initial weights, enabling classification of EEG signals. The experiment results show that the proposed algorithm produces a highly accurate EEG signal classification of 91.5% with an accelerated convergence speed.

Based on the multivariate function Taylor formula and optimal control principle, first, using the 10.65 GHz vertical polarization data of observed brightness temperature from FY-3C microwave radiation imager and simulated brightness temperature from community radiative transfer model (CRTM), the linear retrievals model between the microwave land surface emissivity and two (four) influencing factors are constructed in the central part of the Taklimakan Desert (retrieval area) in January. Second, considering the observed brightness temperature as a reference, the land surface emissivity obtained by two kinds of linear retrieval models are provided to CRTM model to simulate brightness temperature, it is found that the average deviations of the simulated brightness temperatures are reduced to 56.36% and 49.37% of the original simulated brightness temperature, respectively. Finally, in the whole Taklimakan Desert (test area), the time and space independence tests of two kinds of linear retrieval models are carried out by selecting Jan 18, which is used for retrieval date, and Jan 29, which is not used for retrieval date. The results show that the simulated brightness temperatures of the land surface emissivity obtained by two kinds of linear retrieval models are still closer to the observation than the original simulated brightness temperature, and the average deviations are also significantly reduced. The two linear retrieval models are reasonable and universal for the retrieval of land surface emissivity in the desert area in January, and the linear retrieval model with 4 factors is better than 2 factors.

The growth of moso bamboo shoots is closely related to the yield and carbon sequestration ability of moso bamboo. The studies on the relationship between volume and biomass as well as the changing rule are beneficial to our understanding of the growth characteristics of moso bamboo shoots. Three-dimensional point cloud data of moso bamboo shoots are first obtained by the ground LiDAR technology. Then, the three-dimensional model of moso bamboo shoot is constructed and its volume is calculated. A mathematical model is finally established to convert the volume of moso bamboo shoot into its biomass. The test results show that there exists a high correlation between the volume calculated from the three-dimensional model and that computed by the Simalian''s formula. Through the sample test, the accuracy of the conversion model between volume and biomass of moso bamboo shoot reaches 84.24%. The above studies show that the ground LiDAR can provide volume parameters for the rapid biomass measurement of moso bamboo shoot.

The collision avoidance positioning algorithm is very important for unmanned aerial vehicle (UAV) group safety. Aiming at the advantages of wide rage and strong anti-interference ability of ultraviolet communication, a collision avoidance location algorithm for UAV group based on wireless ultraviolet communication is proposed. First, a non-line-of-sight (NLOS) communication model is constructed, and a wireless ultraviolet ranging algorithm based on the received signal strength is proposed. Second, a wireless UV beacon communication model is constructed, and the 3D positioning of the UAV is realized through a four-node positioning algorithm. Finally, a vector sharing method is used to achieve effective collision avoidance between multiple UAVs. Simulation results show that when the distance between two UAVs is 200 m, the range accuracy can reach 1.1 m; when there are more than six reference nodes, the 3D spatial positioning accuracy tends to be stable at approximately 97%. Therefore, the vector sharing method can effectively realize the collision avoidance of UAV group.

Although polycrystalline materials sintered from nonlinear crystal grains are macroscopically isotropic, the random distribution of grain orientation makes it possible that coherent enhancement of nonlinear polarization occurs when laser interacts with them. Meanwhile, the statistical average value of nonlinear conversion efficiency is proportional to the interaction length. Thus it is called random quasi-phase matching (RQPM). RQPM in polycrystalline materials has a distinct advantage in bandwidth over birefringence phase matching (BPM) and quasi-phase matching (QPM), thus polycrystalline materials are of great significance in frequency conversion for broadband femtosecond lasers. Recently, difference frequency generation (DFG), second harmonic generation (SHG), efficient optical parametric oscillation (OPO), and so on, have been realized based on RQPM in polycrystalline materials, which offers a new low-cost option for supercontinuum and broadband optical frequency combs. This paper summarizes the history and status of the technology and theories of RQPM, discusses the latest achievements on ultra-broadband frequency conversion, introduces the processing and modelling methods of polycrystalline materials, and gives an outlook on the development of RQPM. It is expected that this review can give references to domestic researchers in the fields of ultrafast lasers, nonlinear frequency conversion, etc.

Brillouin optical time domain reflection (BOTDR) technique is a kind of simultaneous sensing technology for temperature and strain that has numerous applications and huge potentials. Compared with other sensing technologies, BOTDR has the following advantages: high accuracy, convenient layout, large dynamic range, and long measurement distance. This study introduces the principle of BOTDR and illustrates its main performance indexes. Additionally, new developments and key advances in BOTDR sensing for decades are reviewed, including improvement of spatial resolution, expansion of measurement distance, improvement of measurement accuracy, reduction of measurement time, as well as the solution of temperature and strain cross-sensitivity. Moreover, the examples of BOTDR application are introduced from the structural health monitoring of infrastructure and the pre-warning of geological disaster, and their characteristics are discussed. A typical BOTDR is advanced, and the developing trend in future will be characterized by the improvement of software, field-engineering application, and combination of multiple platforms.

With the further integration of various emerging information technologies and power grids, various wireless optical technology schemes relying on and serving smart power have been put forward and formed a preliminary scale. In this work, the main classification and frontier development of the smart power wireless optical technology are described from the aspects of the channel characteristics and transmission schemes of the fusion of power line communication and visible light communication, hybrid radio frequency power visible light communication, power wireless optical indoor positioning and relay, high voltage line wireless light monitoring, and so on. Then, combined with a number of prototype experiments, this paper introduces the levels of main technical indicators of various smart power wireless optical technologies in terms of the transmission rate, coverage, positioning accuracy, energy consumption, and so on. Finally, the major challenges and potential solutions of the smart power wireless optical technology are provided.

As a red emitting material, GaN∶Eu 3+ is very promising to be applied in GaN-based monolithic integrated full-color display devices. The current research focus is how to further control and optimize the luminescence characteristics of GaN∶Eu 3+ materials, and promote them to the practical stage. In this paper, the research progresses of optimizationing luminescence performance of GaN∶Eu 3+ materials from growth control, Mg 2+, Zn 2+, and Si 4+ co-doping control, and other rare earth element co-doping control, etc., are reviewed, the application potential of these methods is compared, the future work focus of GaN∶Eu 3+ materials is pointed out, and the trend of future development is prospected.

In this paper, we propose an iterative focusing method based on a weighted Gerchberg-Saxton (GSW) algorithm using an optical transmission matrix. The process of solving the modulation phase by using the transfer matrix is abstracted as a phase recovery problem, and the transmission matrix and mean square optimization operator are used as transformation operators of the scattering system to iteratively optimize the modulation phase. Simulations and experiments confirm that the proposed method has a more significant multi-point focusing effect than the phase conjugation method and the mean square optimization operator. The proposed method provides a new idea for light field energy regulation.

Aiming at the individual differences of human eye, it is important to establish a lens optical model that is consistent to human eye data in China and implement the corresponding digital processing technology. According to the three-dimensional(3D) digital model of the lens, 3D printing technology can print the lens model with simple steps and low cost. Based on the measured corneal parameters, intraocular distances, refractive index of each medium, and eye aberration, the lens optical model is reconstructed. We establish a 1 mm-thick gradient refractive index lens model with polymethylmethacrylate (PMMA) and polylactic acid (PLA) as materials, and a 1 mm-thick single refractive index lens model with photosensitive resin as the material. The single refractive index lens model is printed by stereo lithography appearance (SLA) technology and the gradient refractive index lens model is printed by fused deposition molding (FDM) technology. The results show that the gradient refractive index lens model printed by FDM technology has serious step effects. The single refractive index lens model printed by SLA technology has a stress of 87.9 nm/mm. The difference between the focal length of the lens model and the theoretical value is 4.98% and the roughness of the surface is about 120 nm.