Single photon detection technology is a very sensitive photoelectric detection technology that can detect the energy of a single photon. It is a weak signal detection technology widely used in laser ranging, quantum communication, laser radar 3D imaging, and other fields. Single photon avalanche diodes generally operate in Geiger mode, that is, the operating voltage is greater than the breakdown voltage. Photon detection efficiency refers to the probability that a photon incident on a device is converted into a macroscopic signal that can be detected. It is an important parameter to measure the detection ability of single photon avalanche diodes. InGaAs/InP single photon avalanche diodes can work in near infrared band, has the characteristics of high photon detection efficiency and good time jitter, in addition to small size, high stability, excellent anti-radiation performance, can realize large array imaging and other advantages, become one of the most promising near infrared single photon detectors. The planar back-illuminated InGaAs/InP single photon avalanche diodes designed in this paper adopt the absorption grading charge multiplication separation structure, in which the charge layer can control the electric field intensity of the multiplier layer to be high enough to produce avalanche breakdown, while the absorption layer electric field intensity is limited to a certain range to reduce the tunneling effect. The grading layer can reduce the accumulation of carriers at the heterogeneous interface. The P+ active region is formed by two Zn diffusion structures, the multiplication region is limited to the area below the deep diffusion. The shallow diffusion can effectively limit the edge electric field of the multiplication region without using the guard ring structure to avoid premature edge breakdown. The structure design and numerical simulation of InGaAs/InP single photon avalanche diodes are carried out by using TCAD software and selecting the appropriate physical model and parameters, and the corresponding electrical and optical parameters are obtained. Then aiming at the effect of avalanche breakdown probability on device photon detection efficiency, the relationship between the avalanche breakdown probability of the device and the difference between the two Zn diffusion depths, the lateral diffusion factor of Zn diffusion, the doping concentration of Zn, and the temperature parameters is emphatically studied. It is found that when the depth of deep diffusion is 2.3 μm, there is an optimal target value corresponding to the shallow diffusion depth. The deeper the shallow diffusion depth, the higher the breakdown probability of avalanche in the center of the multiplication region under the same overbias, and the higher the electric field intensity will also increase. However, when the difference between the two Zn diffusion depths is less than 0.6 μm, non-ideal breakdown will occur outside the multiplication region, resulting in an increase in the dark count of the device. The larger the lateral diffusion factor of Zn diffusion, the higher the breakdown probability of the avalanche at the center of the multiplication region, and the lower the breakdown probability of the avalanche at the edge of the multiplication region. With the same diffusion depth, the shallow diffusion Zn doping concentration has no significant effect on avalanche breakdown probability, but the higher the deep diffusion Zn doping concentration, the lower the avalanche breakdown probability under the same overbias. The study of the influence of temperature on avalanche breakdown probability shows that the device can obtain better performance at low temperature. The research work in this paper can guide the design of InGaAs/InP single photon avalanche diodes with higher photon detection efficiency and lower dark count. Moreover, relevant research can also provide a reference for selecting the optimal working point of the device to ensure the device works in the best state and realize the optimal application of the device.

Traditional Organ Photodetectors (OPDs) respond not enough in long-wave region, and it is difficult to support panchromatic detection from ultraviolet to infrared regions. In order to overcome the weak absorption ability, researchers adopted a ternary heterojunction structure and the material of complementary absorption spectra. Ternary polymer high-performance OPDs, with ultra-broad spectral response, in panchromatic range, have been reported by mixing the third component. However, there are still problems existing, such as low detection rate, insufficient photoelectric characteristics, and low spectral response uniformity, which are the current research focuses in OPDs.In order to realize panchromatic response to three primary colors, a ternary active layer with heterojunction structure was introduced to broaden spectra by mixing non-fullerene receptor ITIC in P3HT∶PCBM, which can improve detection performance by achieving mobility balance and surface morphology of active layer. In the proposed ternary active layer, polymer P3HT was used as the donor, while fullerene PC61BM and non-fullerene ITIC were adopted as acceptors. The influence of ITIC acceptor mass ratio on photoelectric performance of the detector was mainly studied.The optical characteristic analysis of proposed ternary OPDs indicates that the main material P3HT∶PC61BM film has good light absorption ability from 400 to 600 nm. Moreover, ITIC molecules have stronger absorption abilty in red light region, and main absorption peak is located at 702 nm. Ternary blend film produces a new absorption peak in the range of 600 nm to 750 nm. With gradual increase of ITIC ratio, the absorption ability of blend film in long-wave region enhances. By changing the ratio of PC61BM and ITIC, the absorption intensity of long-wave region can be effectively adjusted.In electrical characteristic, the J-V tests show that dark current density gradually reduces as dual acceptors increase Under red light, the bright current density increases first and then decreases with increasing of the mass ratio of ITIC. As the mass ratio of the active layer was 10∶8∶2, the red current density reached a maximum of 1.91×10-4 A·cm-2. Mixing ITIC into an active layer enhances photocurrent absorption in red light and carriers transport.ITIC influence on the electrical characteristics in the full spectrum was analyzed with External Quantum Efficiency (EQE) spectroscopy at different mass ratios. The EQE of ternary OPDs with ITIC extends to 800 nm, which is attributed to mixing ITIC to promote absorption in long-wave band. The effect on the charge dynamics process in active layer was investigated by fluorescence quenching experiment, to analyze charge transfer inside different mass ratios blend. Photoluminescence spectroscopy (PL) intensity of P3HT is greatly quenched in blended film, which indicates charge transfer existing between P3HT and ITIC. It improves the internal exciton dissociation efficiency and significantly increases photocurrent. By interaction experiments between dual acceptors PC61BM and ITIC, the photocurrent density of mixture is larger than that of single. Charge transfer can improve photocurrent introduction, which enhances light absorption ability and forms more efficient exciton dissociation surfaces.In summary, an appropriate ratio of non-fullerene ITIC mixed into P3HT:PC61BM bulk heterojunction structure can widen OPDs spectrum to 400~800 nm. As a mass ratio of P3HT:PC61BM:ITIC is 10∶8∶2, the EQE of ternary OPDs in three primary colors is up to 56%, 68% and 52%, respectively, and specific detection rate (D*) of three components are up to 1012 Jones in the range of 400~700 nm. Response spectra range is broadened from 600 nm to 800 nm. ITIC compensates absorption of binary blend film in long-wave range, achieves high and balanced carrier mobility ability. ITIC dissociates with original donor and acceptor, which improves light current. Moreover, ITIC also reduces dark current by promoting thin film crystallization and weakening bimolecular recombination.In conclusion, the proposed dual acceptors ternary organic photodetector with complementary absorption ranges, has high mobility of fullerene in active layer film and strong absorption non-fullerene in red and near-infrared light, which contributes to wide spectrum and high sensitivity OPDs.

The confocal unstable cavity has been widely used in chemical laser systems due to its large controllable mode volume, high transverse mode discrimination, near-diffraction limit plane wave output, and high power and high quality far-field spots. The guiding light emitted by the laser is reflected back and forth between the two mirrors of the confocal unstable cavity and interferes with each other. In theory, the beam that output from the confocal unstable cavity is multiple concentric rings. However, due to the influence of air disturbance, platform vibration and other factors, the gray level of the output interference concentric rings fluctuates, the light intensity is gradually weakened from inside to outside, and is in rapid dynamic change. These factors increase the difficulty of extracting the optical pupil position of the guiding light in the automatic optical path collimation. In order to solve the difficult problem of optical pupil position extraction in automatic optical path collimation, a method for optical pupil position extraction of unstable cavity laser is proposed in this paper. First, the original image is preprocessed using the bilateral filtering algorithm. After image preprocessing, calculate the image threshold. Multiplying the coefficient by the image threshold of the Otsu algorithm to get the final threshold of the image. After calculating the threshold, performing threshold segmentation on the image. After the binary image is obtained, the median filter is applied to the binary image to reduce the noise in the binary image and fill the small holes in the binary image. Each contour in the binary image is regarded as a separate connected region, and the contours of the binary image are extracted by using the idea of connected region detection. Then, the inner contour of the optical pupil image can be found from many contours by using the two contour attributes of the contour center and the number of points that make up the contour. After finding the inner contour of the optical pupil image, the Random sample consensus (RANSAC) ellipse fitting algorithm is used to fit the inner contour, which reduces the influence of the internal contour noise on the ellipse fitting results, so as to improve the robustness and accuracy of the optical pupil position extraction results. Since the RANSAC ellipse fitting algorithm needs to fit multiple ellipses, NVIDIA GPU is used to speed up the RANSAC ellipse fitting algorithm, and thousands of ellipses are fitted in the GPU core at the same time to improve the real-time performance of the algorithm. The optical pupil position extraction method proposed in this paper can meet the requirements of real-time, reduce the impact of internal contour noise on ellipse fitting, and improve the accuracy and robustness of optical pupil position extraction results. MATLAB is used to generate 100 frames of simulated optical pupil images with the known position, and then 40% random noise points with amplitude 0~13 are added to the inner contour of the simulated optical pupil image. The proposed method and the direct ellipse fitting method are used to fit the inner contour, to extract the position of the optical pupil image. The simulation results show that the proposed method has higher accuracy and robustness than the direct ellipse fitting method. Compared with the results of direct ellipse fitting, the average value of the extracted position deviation is 0.283 pixels smaller, the maximum value of the position deviation is 0.660 pixels smaller, and the root mean square value of the position deviation is 0.136 pixels smaller.

Low contrast and weak detail features of images collected in a low-light environment will seriously affect the accuracy and stability of machine vision detection. In recent years, the low-light image enhancement technology has made remarkable progress. However, the existing low-light image enhancement algorithms have some problems, such as image detail loss, low brightness, local exposure, insufficient visual naturalness, complex algorithm and high resource overhead. To solve the above problems, a low-light image enhancement algorithm based on extended atmospheric scattering model is proposed. Firstly, the maximum value of R, G and B color channels is calculated and the initial transmission map is obtained by gamma correction. Secondly, the main structure and fine structure of the initial transmission map were extracted, PCA (Principal Component Analysis) method was used to fuse the main structure transmission map and fine structure transmission map to obtain the optimized local consistency transmission map of texture detail removal. Then, the inverse atmospheric light value is calculated using the dark pixel of the bright channel. Finally, the LIEAS (Low-light Image Enhancement via Extend Atmospheric Scattering Model) model is solved to obtain the final enhanced image with natural color and good contrast. The enhanced model derived by the algorithm is similar to the Retinex enhanced model in form, but the difference is that there is an additional correction term in the LIEAS model, which can better suppress the excessive enhancement and detail loss in the image. The algorithm uses the image fusion method to optimize the transmission image and can reproduce the contour and texture details well. In order to evaluate the algorithm objectively, spatial frequency, average gradient, edge intensity and natural image quality evaluation are used as the image quality evaluation metrics. In order to verify the effectiveness of the algorithm, the parameter analysis experiment, model analysis experiment and performance comparison experiment are carried out respectively. In the parameter analysis experiment, firstly, the influence of the selection of gamma parameters on the enhanced image is analyzed. The subjective visual analysis and objective data analysis are carried out on the test results under different parameters, and a good gamma parameter value is obtained. Secondly, the influence of the selection of the maximum filtering window size of the bright channel on the solution of the inverse atmospheric light value and the enhanced image is analyzed. The test results under different window sizes are analyzed to obtain an appropriate window size. Then, the darkest pixel proportion of the bright channel in the solution of the inverse atmospheric light value is selected and analyzed. Finally, this paper verifies the advantages of the transmission map optimization method based on fusion technology. In the model analysis experiment, compared with Retinex model, spatial frequency and average gradient of the proposed algorithm are significantly improved, which also has prominent visual advantages, indicating that the correction term in the proposed algorithm can better suppress the excessive enhancement and detail loss of the enhanced image, and has good enhancement ability. At the same time, by changing the atmospheric light value in the model, the proposed algorithm can also be used in image dehazing, and the image dehazing can get a good effect from both subjective and objective aspects. In the performance verification experiment, three low-light image datasets were selected to test, and the performance of the proposed enhancement algorithm was compared with that of other eight algorithms from both subjective and objective aspects. Compared with the other eight algorithms, this algorithm has the advantages of bright background, high contrast, complete edge details, natural, vivid image, avoiding local overexposure and so on. The algorithm has more advantages in spatial frequency, average gradient, and edge intensity, which indicates that the algorithm has better performance in the aspects of image color richness and image sharpness. Both for the metric analysis of the whole image of the dataset and for the metric analysis of a single image, the proposed algorithm is very advantageous, and the model is simple and low complexity. Compared with the existing enhancement algorithms, the proposed algorithm has some advantages in detail information retention, contrast enhancement, image naturalness and local overexposure suppression.

Along with the development and progress of science and technology, the image quality will be affected by variation of orbit, attitude angle and other factors, as well as tracking speed errors, platform and moving parts jitter. All of these factors will cause image motion, which will lead to image resolution reduction, image blurring and image quality declined. Therefore, how to suppress the impact of dynamic image motion becomes the bottleneck of obtaining high-resolution images. At present, the existed researches basically analyze the factors of image motion from a separate application field. They do not present the generation and compensation technology of image motion of space-based optical system systematically and comprehensively. How to suppress the influence of dynamic image shift gradually has become the bottleneck of obtaining high-resolution and clear images. Compared to the conventional ground-based telescope, the space one can get away from the distortions of the Earth’s atmosphere. So less background noise, wider optical wavebands and higher imaging precision to the diffraction limit can be achieved. This paper analyzes the various factors that produce image shifts during the imaging process of the space-based space target optical system and on this basis, comprehensively analyzes and locates the factors that affect the quality of dynamic imaging. Aiming at the problem of unclear imaging caused by dynamic image movement in the process of space high-speed moving target tracking, the degradation mechanism is analyzed, and the satellite platform disturbance, moving base tracking stability, stray light, defocusing, and imaging distance within the integration time are analyzed in detail. The influence of factors such as changes on the dynamic MTF is given, and the mathematical model corresponding to each influencing factor is given. An image motion compensation scheme based on FSM is given, which has been verified by laboratory tests and can effectively reduce the impact of image motion. During the space camera's on-orbit working process, vibration caused by reaction wheel assembles; solar panels and lower frequency can be compensated and suppressed by attitude controllers. While vibration with a smaller amplitude and higher frequency will still convey through the platform to the sensor, resulting in subtle jitter and weakened attitude stability of the sensor. Due to the tiny unit pixel view angle of high resolution sensor, jitter will lead to the image point of the ground scene indistinct and imaging quality declined in exposure time. With the development of spacecraft attitude control method, sensing, optical system design and manufacturing level, how to suppress the influence of dynamic image shift gradually It has become the bottleneck of obtaining high-resolution and clear images. In order to realize high resolution imaging, the space-based space target optical imaging system has higher and higher requirements for the spatial resolution of the payload, and a wider and wider range of motion adaptation of the space moving target. This paper sketches the mechanism of image motion influence and image motion compensation technologies. On the basis of that, this paper classifies space-based imaging according to the applications, such as remote sensing, space astronomical observation, Mars exploration and space target detection. Furthermore, we introduce in detail the research progress of image motion influence and compensation in the fields of remote sensing, space astronomical observation, Mars exploration and space target detection. This paper provides the research progress of image motion influence and compensation in the fields of domestic and international in recent years. Through analyzing the research, we can further improve our understanding of the development direction of space optical technology, and provide new methods and approaches for the development of space optical technology and equipment.

Near-Eye Displays (NEDs) are considered as a next-generation display platform. They have shown great application potential in communication, education, healthcare, and so on. As an important NED technique, retinal projection display has attracted much attention for its advantages of large depth of field, wide viewing angle, and simple structure. Traditional retinal projection display can alleviate the Vergence-Accommodation Conflict (VAC) problem to a certain extent. But, this kind of system has problems such as bulky, limited exit pupil area, and inability to evoke monocular accommodation information. For this reason, a variety of retinal projection display technologies based on Holographic Optical Elements (HOE) have been proposed. However, the HOE is an optical element based on diffraction, such systems usually need to use a laser as the light source. Lasers are expensive, have speckle problems, and have potential safety hazards to the eyes.To address these issues, a 3D retinal projection display based on doublet HOEs has been proposed in this paper. The performance of traditional retinal projection display system is improved by using a cheap and safe LED light source and HOEs. A retinal projection display system based on doublet HOEs is made. The display experiments prove the effectiveness of the system.The doublet HOEs are used to compensate for the chromatic dispersion of HOE, which reduces the image blur, and increases the display sharpness. The doublet HOEs compose of a reflective holographic grating and a reflective holographic lens. The reflective holographic grating is made by the interference exposure of two parallel beams. The reflective holographic lens is made by the interference exposure of a parallel beam and a divergent spherical wave. The aperture of the holographic grating and holographic lens is both 30 mm×45 mm. The focal length of the holographic lens is 90 mm. The diffraction efficiencies of the holographic grating and lens are 61% and 58% respectively. The display effects of single HOE and doublet HOEs system are tested by using USAF1951 resolution plate as display target. The results show that the horizontal resolution of the system increases from 2.6 lp/mm to 11.6 lp/mm, and the vertical resolution increases from 2.06 lp/mm to 11.6 lp/mm. These indicate that the doublet HOEs can effectively compensate for the dispersion caused by the diffraction of HOE illuminated by a broadband light source. The doublet HOEs structure can be used to expand the application of HOE in the near eye display system illuminated by incoherent light sources.Combined with the doublet HOEs, LED array, and high performance digital micro-mirror device, a 3D retinal projection display system with full parallax and dense viewpoints is realized by using time division multiplexing and angular multiplexing technology. The LED array is used to generate a viewpoint array corresponding to different viewing angle. By injecting corresponding parallax images for each viewpoint in time sequence, the proposed experimental system realizes the true 3D display with monocular focusing depth cues within the depth range of 0.45 m to 2 m. The display range can cover the sensitive range of human eye with VAC which is from 0.5 m to 2 m. It can alleviate the visual fatigue caused by the VAC problem effectively. The pupil area of the system is expanded from one viewpoint to 7 mm×7 mm, solved the limitation of small exit pupil of retinal projection system. The imaging experiments of 3D scene with three different depth planes are designed to quantitatively characterize the focusing and defocusing effect of images by evaluating the image contrast in different planes. The results further prove the 3D imaging effects of the proposed retinal projection display system.The proposed system uses HOEs to replace the bulky glass lenses, which makes the system structure simple and compact. It also uses the incoherent LED array to replace the laser as the lighting source, which avoids speckle noise and potential safety hazards, and has good application prospects.

Underwater lidar technology has become an important tool for ocean exploration and underwater operations. So far, all of the reported underwater lidars are based on the pulsed Time-Of-Flight(TOF) method for ranging, which is characterized by high pulse peak power and relatively long detection distance. However, TOF lidar is large in size, high in power consumption, and small in dynamic range, and there will be interference between different TOF lidars. Hence they are not suitable for compact platforms such as Autonomous Underwater Vehicles(AUV) swarms. In addition, back scattering presents a great challenge to underwater pulsed lidar, which limits the sensitivity and dynamic range of the detector. Strong back scattering of suspended solids in water can completely submerge the real signal, leading to false target detection. Underwater Frequency Modulated Continuous Wave (FMCW) lidar has a greater dynamic range than TOF radar and can output a continuous spectral signal proportional to distance. Because the signal of the coherent detection is amplified by the local oscillator, FMCW lidar requires low laser output power and can be realized with low power diode laser, which can significantly reduce the size, weight and power of the lidar system. So far most reported studies on FMCW lidar are concentrated on near-infared wavelength such as 1 μm, 1.55 μm. However, there have been no reports of underwater FMCW lidar using blue or green lasers so far.The implementation of FMCW lidar is faced with two challenges, one is to obtain a single-mode tunable narrow linewidth laser, the other is to eliminate the nonlinear effect of laser frequency modulation. Because the light absorption loss of water will lead to the signal attenuation and shorten the detection distance, it is necessary to select the blue-green laser located in the seawater “transmission window” with a small attenuation coefficient. A commercial 405 nm Blue FP laser diode and a 30% reflector are used to construct an External Cavity Diode Laser(ECDL). The blue ECDL exhibits a coherence much longer than 10 meters in fiber, and a continuous frequency sweep range of 1.5 GHz by direct modulation of the injection current. Modulation nonlinearity of the FMCW laser can broaden the FFT spectrum of the measured signal and reduce the ranging accuracy. To overcome this problem, an FMCW ranging method based on equal optical frequency resampling is adopted. The system consists of both a fiber interferometer and a free space interferometer. The optical fiber interferometer uses 10 m delay optical fiber to monitor the frequency change with time, and the free space interferometer is used to obtain the beat frequency signal containing the distance information of the target to be measured. Theoretical analysis and experimental verification were carried out. The underwater ranging was conducted by adding Mg(OH)2 powder in the water tank to adjust the attenuation coefficient to simulate the seawater environment. An FMCW laser ranging system with dual interferometers is built, and the extremum point of the beat signal of the fiber optic interferometer is extracted to sample the beat signal of the free space Interferometer. It is verified that the beat signal spectrum broadening problem due to the laser′s frequency modulation nonlinearity is well corrected. Using the resampling method, the distance is measured at eight equally spaced positions, and a reflector is placed at these positions in turn as the detection target. The results show that the measurement range of the target is linear with the actual range, and a detection range of 5 meters is realized with only 9.5 mW laser output power, and the maximum error is 0.051 m. In order to obtain the measurement error of the FMCW ranging system, ten groups of data are measured at the same position. Through calculation, the average measurement error of the ranging system is 0.027 m. Our work demonstrates that a low power commercial blue laser diode can be used to construct a single frequency ECDL laser, and it can be directly frequency modulated to perform accurate underwater FMCW laser ranging. This lidar architecture characterizes by small size, low power and weight, which promises an effective laser ranging sensor for compact AUV swarm.

The attosecond light source can reveal the macroscopic properties of matter from the microscopic field, so it is widely used in the fields of materials, medicine, atomic and molecular physics, and quantum physics. The common laser for generating attosecond light sources is the Ti∶Sapphire laser with a central wavelength of 800 nm. However, the average power is limited due to the thermal effect limitation. With the deepening of the application of attosecond light sources, high power with a high repetition rate driving laser if highly demanded. In order to achieve the driving laser with short pulse duration, high repetition rate and high pulse energy, Yb-doped lasers, such as Yb∶KGW, Yb∶YAG have been developed rapidly in recent years. However, the pulse duration of the Yb-doped laser is much longer, and it needs to be compressed by a post-compression method in order to obtain few-cycle laser pulses. Noble gas filled hollow core fibers are widely employed for pulse compression, but it is difficult to compress the 515 nm pulses obtained by frequency doubling to a nearly single cycle. Therefore, this paper simulates the compression obtaining few cycle pulses based on the time-domain generalized nonlinear Schr?dinger equation satisfied when the pulses are transmitted in a hollow core fiber. The light source in the calculation process refers to the PH2-2mJ-SP laser of Light Conversion Company, the center wavelength is 1 030 nm, the repetition rate is 10 kHz, and the pulse energy is 2mJ. In the simulation, the input pulse with a center wavelength of 515 nm, a pulse energy of 1 mJ, and a pulse duration of 250 fs is employed, which peak power is 4×109 W. In order to achieve controlled spectral broadening with minimum loss in the hollow core fiber, the peak power of the pulse should first be less than the photoionization threshold intensity of the noble gas, which limits the minimum core radius to 50 μm. Besides, the peak power should be lower than the self-focusing threshold in order to avoid self-focusing when the pulse is transmitted in a hollow core fiber, which limits the maximum pressure of the noble gas. For the argon and krypton to be investigated, the maximum pressures are 10 bar and 3.5 bar, respectively. Considering the loss coefficient when the pulse is transmitted in the hollow core fiber, and the broadening factor required to broaden the pulse spectrum to an octave, a preliminary length of 2.5 m and a core radius of 125 um can be determined for the hollow core fiber. On this basis, the frequency spectrum and time domain broadening of the pulses under various gas pressure and propagation length are simulated. Finally, the pulse spectrum can be broadened to an octave. Considering the influence of the broadening factor and transmission efficiency, the length of the hollow core fiber is finally selected as 2.5 m when the argon and krypton are filled at their maximum pressures. After compensating the dispersions, the pulses of 2.91 fs and 2.62 fs can be obtained in argon and krypton, respectively, which are less than two optical cycles. But at this time, the compressed pulses still have some high-order dispersion that cannot be compensated. Thus, we employed the multi-stage compression method, which avoids introducing too much high-order dispersion. The first stage compression is referenced to the work of HARITON V et al., who successfully compressed a 515 nm, 250 fs pulse to 38 fs in their experiments using a multi-pass cavity. The second stage uses a hollow core fiber. Under the appropriate gas pressure, transmission length, and dispersion compensation, the pulse is compressed to ~ 2 fs, which is close to a single cycle, with significantly reduced high-order dispersion than that from single stage compression.

The installation of pavement meteorological sensors in high-risk road sections and real-time warning of passing vehicles can effectively reduce the accident rate and improve the highway transportation efficiency. The pavement meteorological sensor can be divided into contact type and non-contact type according to the installation mode. The contact sensor needs to be drilled and installed on the subgrade, which has poor flexibility and is easy to be damaged due to the rolling of vehicles. The non-contact sensor adopts remote sensing technology, which can measure a variety of pavement meteorological data. Its installation does not need to damage the pavement, which is convenient for large-scale promotion and use, and has a broad application prospect.The road slippery state is closely related to traffic safety. To solve the problems of low life, inconvenient installation, and easy damage to the subgrade of the traditional contact pavement meteorological sensor, this paper uses 1 310 nm and 1 430 nm lasers as the detection light source, combined with infrared temperature measurement assistance, to study a non-contact pavement meteorological sensor method. In this method, the reflectivity of water and ice medium film at two characteristic wavelengths is obtained by measuring the backscattered light intensity formed by the light source under different road conditions. The pavement meteorological information can be obtained by solving and analyzing the reflectivity. First of all, based on Lambert Beer's law and according to the analysis of the laser beam propagation path, a theoretical model for measuring the thickness of seeper and icing is proposed. The model contains two parameters, which are related to the type of detection material and the road water absorption, respectively. Among them, the parameters related to the measurement material are constants, which can be obtained through experimental calibration, while the parameters related to the road surface are variables, which need to be measured at the road surface site, it is obtained by the automatic calibration method of the zero point of the relative reflectivity; then, according to the demand analysis, a pavement weather sensor with practical significance is designed, and the relevant detection system is built; finally, the meteorological state of the pavement and the thickness of seeper and icing are measured on the asphalt pavement and stone pavement with the self-designed sensor. In the identification of pavement status, the mixed identification logic of relative reflectance and infrared temperature signal is used to realize reliable identification of various pavement statuses, including dry, wet, seeper, icing, and frost. For the measurement of thickness parameters, the reflectance zero point is used to automatically identify and calibrate the measurement model parameters, so that accurate measurement can be achieved under different road conditions without on-site calibration, effectively solving the problem of baseline drift when measuring at different angles on different roads.A non-contact pavement meteorological sensor based on dual wavelength laser detection is proposed. The sensor has the advantages of simple structure, long detection distance and low cost. In terms of measurement method, five pavement meteorological states can be accurately judged through mixed logic judgment; by using the automatic calibration method of reflectivity zero point, the measurement of seeper and icing thickness is realized. The experiment shows that the measurement accuracy of this method reaches 0.2 mm, the measuring range reaches 3 mm, and it can adapt to the pavement with different water absorption, achieve the measurement capability similar to that of foreign advanced equipment, and solve the problem that other methods usually require manual on-site calibration, which has good practical value.

Recently, with the growing problem of environmental pollution, a large number of emerging environmental purification technologies, especially the photocatalytic oxidation technique based on semiconducting metal oxide nanostructures, have been rapidly developed for the applications in degradation of organic pollutants from water and atmospheric environments. In the process of development, scientists around the world have recognized that the improvement in the visible light response, the separation efficiency of photogenerated charge carriers and the light stability of the catalysts are the key factors to promote the large-scale application of the photocatalytic oxidation technique. For this purpose, a series of new high-performance nanostructured composite photocatalysts have been continuously developed and investigated, but the process complexity and synthesis cost are gradually increasing. Also, it is difficult to realize the band structure regulation of the semiconductors and well-match energy levels between different semiconductors. These problems need to be solved urgently. At the same time, with the future demand for high selectivity of new technologies (such as selective sensing, selective gas separation, selective carbon dioxide reduction), the selective photocatalytic degradation of organic pollutants will also become a development direction in this field. In this study, a series of photocatalysts including pure ZnO, Mn-doped ZnO (Mn:ZnO), Mn2O3 coupled ZnO (ZnO/Mn2O3) and Mn2O3 coupled Mn-doped ZnO (Mn:ZnO/Mn2O3) are successfully prepared by a modified polymer network gel method, and the characteristics of the catalysts for photocatalytic degradation of Rhodamine B (RhB) and Methylene Blue (MB) dyes under simulated sunlight irradiation are investigated. The phase compositions, microstructures, surface chemical states as well as optical and optoelectronic properties are analyzed through some material characterization approaches in detail. The results of X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-emmett-teller (BET) specific surface area shows that the particle sizes of Mn:ZnO and Mn:ZnO/Mn2O3 are decreased and the particle dispersibility are improved after trace (0.1 mol%) Mn doping and then coupling trace (0.2 mol%) Mn2O3,increasing BET specific surface area. Correspondingly, this results in the decrease of crystalline quality and the increase of crystal defects. Ultraviolet-visible (UV-vis) light absorption spectra indicates that the light absorption capacities of the composite photocatalysts in the visible region are significantly improved compared with pure ZnO and doped ZnO samples. Photoluminescence (PL) spectra suggests that trace Mn doping and trace Mn2O3 coupling jointly facilitate the separation of photogenerated electron-hole pairs. Combined with X-ray photoelectron spectroscopy (XPS), it is found that the enhanced visible light absorption capability and photogenerated electron-hole pair separation rate originates from the increase of oxygen vacancies on the catalyst surface and the formation of type II heterojunction structure between Mn:ZnO and Mn2O3. Therefore, Mn:ZnO/Mn2O3 exhibits the robust and superior photocatalytic activity for degradation of RhB dye under simulated sunlight irradiation. However, because of the narrow band gap (Eg ≈ 1.4 eV) of Mn2O3 and its higher valence band position than the redox potential of hydroxyl radical (·OH), the oxidation potential of photogenerated holes is too low to generate ·OH with the stronger oxidizing power. This results in the lower RhB and MB dyes photodegradation efficiencies of the ZnO/Mn2O3 photocatalysts. In addition, Mn:ZnO/Mn2O3 exhibits a selective photodegradation behavior towards RhB and MB dyes, that is, a significantly lower photodegradation efficiency for the easily degradable MB. Such a selective photocatalytic property is attributed to the difference between active species during the photocatalytic reactions and the relationship between the Zero Charge Point (ZPC) of the catalyst and the pH of the initial dye solution. In the photocatalytic processes, the strong oxidizing species (·O2-, ·OH and h+) on the surfaces of the catalysts for the photodegradation of RhB dye are more than those (·OH and h+) for the photodegradation of MB dye. The ZPC value of Mn:ZnO/Mn2O3 closes to the pH value of the weakly acidic RhB (pH=6.3~6.6) rather than MB (pH=6.0) dye aqueous solution, resulting in a higher adsorption ratio of cationic RhB dye molecules on the catalyst surface.

Excessive bacterial load will not only cause delayed wound healing and local or systemic inflammatory reaction, but also threaten the life safety of patients in severe cases. Therefore, a new method that can detect wound bacteria quickly and directly is needed. Traditional bacterial detection methods are mainly visual observation of clinical symptoms (including fever, redness and swelling, pus exudate, etc.) and microbial swab sampling, but these two methods are usually subjective and time-consuming. The results of the same clinical symptom observed by doctors with different experiences may be different, and in some cases the infection may not show obvious symptoms. Therefore, it is often subjective to judge the infection by observing the clinical symptoms with naked eyes and may cause misdiagnosis. Swab sampling is often plagued by false negative, and different sampling methods and selection of sampling areas will affect the results of sampling and culture. False negative areas or missed areas may contain a large number of bacteria. The missing of a large number of bacteria in these areas may lead to repeated wound healing, causing great pain to patients and great burden on the medical and health system. In addition, longer culture time is also a pain point for swab sampling, because it may cause inaccurate culture results and miss the best treatment opportunity. Relevant studies have found that bacteria can emit fluorescence by themselves under the excitation of 405 nm light source, without using contrast agents. The purpose of this study is to design a fluorescence detection imaging device based on the principle of spontaneous fluorescence of bacteria, which provides a fast and direct new method for wound bacteria detection. In this study, a bacterial fluorescence imaging system is developed. The light source module of the system consists of two LED with a central wavelength of 405 nm and LED driver modules. After calibration and parameter setting, the light source driver works in constant current mode to ensure stable operation of the light source. When the light source shines on the wound bacteria, it can stimulate the spontaneous fluorescence of bacteria almost in a moment. The customized dual band filter is used to receive bacterial fluorescence and filter out the interference of reflected light from the light source. The transmission band of the filter is selected according to the results of the three-dimensional fluorescence spectrum of bacteria. In the dark environment, the smartphone imaging mode is set to night mode, the shutter speed is set to 3 s, the automatic white balance is set, and each sample is collected five times to reduce experimental error. Porphyrin fluorescence images are converted into three-dimensional intensity images to verify the imaging uniformity of the device. The fluorescence region is detected by region extraction algorithm, and the bacterial fluorescence is quantified. The signal area is extracted by using the Hough circle detection and edge contour extraction method as well as the mask method obtained by using the binary function. The gray value of all pixels in the signal area is traversed and the average value is calculated, which is taken as the quantitative result of the relative fluorescence intensity of bacteria. Finally, a linear rule between the fluorescence intensity and the concentration is obtained by linear fitting of the quantitative result. The experimental results of three-dimensional fluorescence spectrum of bacteria provide an important basis for the selection of excitation and emission bands in this study. It can be seen from the porphyrin three-dimensional intensity map that, except for the projection points of the two light sources, the uniformity of the signal area is good. This indicates that the two LED light sources used in the device can uniformly excite the fluorescent signal area, and the fluorescent image with good quality can be obtained without using the whole row of ring LEDs as light, which greatly reduces the power consumption and heat generation of the system. The result of image processing proves that regular and irregular signal regions can be extracted with the device. The regular region extraction algorithm can accurately extract the fluorescent signal region, avoid the fluorescent interference of the culture dish wall, and effectively improve the calculation accuracy of the relative signal strength. The gradient concentration of Escherichia coli and Staphylococcus aureus shows that there is a good linear relationship between the bacterial fluorescence intensity and the bacterial quantity under the experimental bacterial concentration. Combined with the bacterial plate counting experiment, the minimum detection limit of the system is 105 CFU/mL, which indicates that the system can effectively detect the infection of wounds. Through linear fitting of the calculation results, it can be obtained that there is a linear relationship between bacterial fluorescence intensity and concentration, and the minimum detection limit of the system can be calculated according to the linear relationship. The device provides a new means for the bacterial detection of the wound, with high detection sensitivity to meet the bacterial load identification of the infected wound. There is no need for swab sampling and fluorescent labeling, and the detection procedure is simple and easy to operate. The extraction of signal region can clearly and intuitively show the location of bacteria, which can provide effective reference information for wound debridement and targeted drug administration. This study only conducts quantitative detection of bacteria in vitro, and further measurement of bacteria in vivo is needed. In addition, future efforts should include the development of a smartphone app that integrates existing processing algorithms to further simplify the process and enable rapid in vivo detection of wound bacteria.

In this paper, based on the normalized saturable nonlinear fractional Schr?dinger equation with linear potential, the transmission and control of solitons in linear defocusing two-channels PT-symmetric waveguide with fractional diffraction and saturable nonlinearity are studied. The equation can be numerically solved by the modified squared-operator iteration method to obtain soliton modes. The Fourier collocation method is used to judge the linear stability of soliton, and the split-step Fourier method is used to simulate the transmission of soliton in the PT (Parity-Time) -symmetric waveguide. According to the requirements of PT-symmetric, the refractive index distribution of two-channels PT-symmetric waveguide is even symmetric and the gain/loss distribution is odd symmetric. In addition, the refractive index of two channels is smaller than that of substrate, so it has the defocusing property. The results show that the PT-symmetric waveguide can support the stable double gray solitons modes in the defocusing saturable nonlinearity. The real part of double gray solitons is even symmetric and the imaginary part is odd symmetric due to the effect of PT-symmetric waveguide. The Lévy index and gain/loss coefficient of PT-symmetric waveguide have little effect on the shape of double gray solitons modes. But the saturable nonlinear coefficient has a great influence on the soliton modes. With the increase of saturable nonlinear coefficient, the background intensity of double gray solitons increases. The Lévy index, gain/loss coefficient, and saturable nonlinear coefficient can affect the transverse energy flow density of solitons. With the increase of Lévy index, gain/loss coefficient, and saturable nonlinear coefficient, the transverse energy flow density of solitons changes more sharply, but it is close to 0 infinitely at the position of waveguide channel. This means that the energies on the left and right of channels reach a balance, thus the double gray solitons are formed. At the same time, the propagation constant also has an effect on the double gray solitons. With the increase of the absolute value of propagation constant, the background intensity of the solitons increases, the gray value decreases and the power increases. Through linear stability analysis, the stable double gray solitons can be obtained at a low gain/loss level. The double gray solitons can transmit stably forward in the waveguide, keeping the width and intensity of original mode unchanged. The width of solitons increases with the increase of saturable nonlinear coefficient and propagation constant.In the focusing saturable nonlinearity, the two-channels PT-symmetric waveguide can control the transmission of bright soliton beams. When it inputs from the center of waveguide, the beam is transmitted as a respirator. With the increase of saturable nonlinear coefficient, the frequency of respirator decreases, the width of beam widens, and the peak intensity decreases. When it doesn't input from the center of waveguide, the beam occurs oscillation with the initial input position as the boundary. This is because the refractive index in the center is the largest, decreasing gradually away from the center between the two-channels PT-symmetric waveguide. This structure is similar to that of gradient index fiber, which has linear focusing effect on beam. When the input is not in the center, under the focusing effect of waveguide, the beams propagate toward the center, through the center to the other, and then reflect back. Thus, the propagation of beam occurs oscillation between two channels. With the increase of saturable nonlinear coefficient, the oscillation frequency of beam increases and the width widens. In addition, the increase of the absolute value of potential good depth in PT-symmetric waveguide will lead to the increase of oscillation frequency and peak intensity of beam. These results can provide some theoretical reference for the application of two-channels PT-symmetric waveguide in all optical control.

In the traditional sequential extraction of late exponentials method, the selection of the correlation function fitting window is the key to the bimodal particle size inversion by dynamic light scattering. The inversion results depend on the selection of the correlation function fitting window of the bimodal data, and the particle sizes retrieved by different fitting windows are different. Based on the traditional sequential extraction of late exponentials method, this paper analyzes the attenuation rate of the correlation function of bimodal particle samples and the difference of particle information distribution at different decay times, and proposes a new improved algorithm named attenuation characteristics sequential extraction of late exponentials method. By analyzing the absolute value of the difference between the derivative of the electric field correlation function and the derivative of the equivalent average particle size reconstruction electric field correlation function, the method defines it as the relative attenuation characteristics of the correlation function, and based on the relative attenuation characteristics of this correlation function, the starting point of the fitting window for the small particle correlation function, the interval point and the ending point of the fitting window for the large particle correlation function are defined respectively. These following three reference points are the selection criterion of the fitting window for the correlation function. Firstly, the interval point of the fitting window of the correlation function of large and small particles is defined as the delay time corresponding to the minimum value of the relative attenuation characteristics, the interval point corresponds to the starting point of the fitting window of large particles, and the previous delay time of the interval point corresponds to the termination point of the fitting window of small particles. Secondly, the starting point of the fitting window of the correlation function of small particles is defined as: the minimum delay time corresponding to the maximum value of the vertical coordinate of the relative decay characteristic graph of 0.003 times before the termination point of the fitting window of small particles. Thirdly, the termination point of the fitting window of the correlation function of large particles is defined as: the maximum value of the vertical coordinate of the relative decay characteristic graph of 0.02 times after the starting point of the fitting window of large particles the maximum delay time of the vertical coordinate value. Through the above steps, the problem of inaccurate positioning of the fitting window is solved, and the blindness of fitting window selection is reduced, thus improving the accuracy of the particle size inversion results. The inversion of the simulated data (95 nm/285 nm, 100 nm/400 nm, 105 nm/630 nm, equivalent average particle size of 140.9 nm; 48 nm/144 nm, 50 nm/200 nm, 50 nm/300 nm, equivalent average particle size of 70.6 nm) and the experimental data (60 nm/220 nm, 65 nm/450 nm) was performed by using the improved algorithm, simulated data was performed, in which for the 95 nm/285 nm simulated bimodal particles, the relative error of particle size for large particles was reduced by 11.7%~52.4%, and the relative error of particle size for small particles was reduced by 9.9%~95.1%; the relative error of peak position for large particles was reduced by 4.0%~19.3%, and the relative error of peak position for small particles was reduced by 23.9%~94.5%; the root mean square error of the correlation function was reduced by 36.5%~76.1%. For the 60 nm/220 nm measured bimodal data, the relative error of particle size of large particles was reduced by 2.1% and that of small particles was reduced by 1.7%; the relative error of peak position of large particles was reduced by 1% and that of small particles was reduced by 10.2%, and the root mean square error of the correlation function was reduced by 89.2%. The calculated results of both simulated and measured data show that the inversion results of the improved algorithm significantly reduce the relative error of particle size, relative error of peak position and root mean square error of correlation function. The proposed attenuation characteristics sequential extraction of late exponentials method is better than the traditional sequential extraction of late exponentials method.

When light passes through scattering media, such as biological tissues and multimode fibers, the wavefront of the beam is disturbed due to multiple scattering and distortion. This phenomenon is usually seen as an obstacle to biomedical imaging, telecommunications, and photodynamic therapy. As an effective method, iterative wavefront shaping is capable of manipulating the incident wavefront and compensating the wavefront distortion due to multiple scattering. Recent advances in iterative wavefront shaping techniques have made it possible to manipulate the light focusing and transport in scattering media. To improve the optimization performance, various optimization algorithms and improved strategies have been utilized. However, an improved strategy that is suitable for various algorithms has not been demonstrated yet. Here, a novel guided mutation strategy is proposed to improve optimization efficiency for light focusing through scattering medium. Not limited to a specific algorithm, guided mutation strategy is extended to various feedback-based wavefront shaping algorithms. In this study, single point focusing is firstly conducted in a feedback wavefront shaping system based on multiple classical optimization algorithms, including genetic algorithm, particle swarm algorithm, ant colony algorithm and simulated annealing algorithm. To validate the effectiveness of the guided mutation strategy in improving the focusing efficiency, the guided mutation strategy is introduced on the basis of the above four algorithms. The focusing efficiency is characterized by the enhancement factor after optimization and the number of iteration cycles when the maximum enhancement factor is reached as made by regular algorithms. Through numerical simulation and experimental verification, the guided mutation strategy greatly improves the focusing efficiency of the four classical optimization algorithms. The enhancement factor increases by more than 25%, the number of iteration cycles is reduced by more than 63%. When the input modes numbers increases, the benefits of the guided mutation strategy will become more significant. To further verify the universality of the guided mutation strategy, numerical simulation analysis of single point focusing with binary modulation and multi-point focusing with multi-objective genetic algorithm are also carried out. The results show that, similar to the single point focusing with phase modulation, the guided mutation strategy can effectively enhance the focusing efficiency with binary modulation and multi-objective optimization. This investigation of binary and multi-objective optimization further demonstrate that guided mutation strategy can be applied to widely applications, such as binary amplitude optimization system and multi-point uniform focusing. Overall, this study provides a more efficient focusing strategy for various classical algorithms and regulation methods of feedback wavefront shaping. For both phase modulation and binary amplitude modulation, considerable improvements in optimization effect and rate have been obtained with the introduce of guided mutation strategy. Because of the effectiveness and universality of the guided mutation strategy, it will be beneficial for applications ranging from controlling the transmission of light through disordered media to optical manipulation behind them. And this research will have potential application value in the field of fiber laser, two-photon microscopy and optogenetics.

As an important part of the original fingerprint identification under the optical screen, the infrared cut-off filter needs to be plated on a large-diameter and ultra-thin substrate in order to connect the subsequent processing process and facilitate mass production. The substrate surface type has very high requirements. In recent years, many scholars have done a lot of experimental research on the issues related to the uniformity of sputtering coating film thickness, but there are few references on the related research on the uniformity control of ultra-thin and large-area substrates. In the traditional method of coating double-sided film layers, in the process of using ultra-thin and large-diameter substrates, only one side can be plated first, and then the substrate can be taken out and turned over to coat the other side. This operation is inefficient and the risk of substrate chipping is high and the film uniformity is poor, which will cause uneven stress distribution in the film layer, resulting in the bending of the substrate, which can not meet the actual use requirements. In this paper, two materials, SiO2 and Nb2O5, are used as the research objects, and the influence on the film thickness uniformity is analyzed from three aspects: the distribution of the magnetic field intensity of the target material, the public-rotation system, and the shielding angle of the substrate fixture. According to the experimental results, the relative strength of the target magnetic field has a certain relationship with the uniform distribution of the relative thickness of the film, and the relative thickness of the film will also increase when the relative strength of the magnetic field is larger. The revolution system can greatly improve the film thickness uniformity. In this paper, the film thickness uniformity under three rotational speed ratios of 1∶2, 2∶1, and 5∶4 is studied. When the rotational speed ratio is 5∶4, the film thickness is uniform,and the uniformity is the best. The film uniformity of SiO2 increases from 17.31% when only rotating to 3.86%, and the film uniformity of Nb2O5 increases from 15.99% when only rotating to 3.41%. After calculation, the coating efficiency and target utilization rate increase by 12.3% and 17.6% respectively. Since the equipment has a public rotation system, the edge of the substrate fixture will block the effective coating area. In this paper, five blocking angles of 0°, 20°, 35°, 55°, and 70° are studied. Among them, SiO2 single-layer film is thin at a 20° blocking angle, and has the best thickness uniformity, which is 0.62%. The uniformity of 0°, 35°, 55°, and 70° is 1.42%, 5.43%, 7.52%, and 8.58%, respectively. The thickness of Nb2O5 single-layer film is uniform at 20° blocking angle, and the best performance is 0.71%. The uniformity of 0°, 35°, 55°, and 70° is 1.55%, 3.64%, 7.56%, and 10.81%, respectively. Considering factors such as substrate loading and uniformity, a 20° blocking angle is selected for the preparation of the infrared cut-off filter. The filter is made of D263T substrate with a diameter of 20.32 cm and a thickness of 0.07 mm. In order to balance the influence of the film stress on the upper and lower surfaces on the surface shape of the substrate as much as possible, the Essential Meclord software is used to adopt the design of a symmetrical film system. The physical thicknesses of the upper and lower surfaces are 3 944.27 nm and 4 366.19 nm, respectively. After measurement of the prepared samples, the wavelengths at the transmittance of 50% are 572.6 nm and 572.5 nm, the transmittance at the 450~550 nm band are 97.59%, 98.14%, and the transmittance at the 590~1 100 nm band is 0.042%, 0.048%, which all meet the design and practical application requirements. The sample uniformity can reach 0.13% and 0.142%, and the warpage degree of the substrate is 0.085 mm, which meets the requirements. How to obtain a film with a larger effective coating area and better film thickness uniformity on the magnetron sputtering equipment is the key research direction for the next step.

Gallium oxide (Ga2O3) is a wide bandgap (4.8 eV) semiconductor oxide with the advantages of high transparency and excellent chemical and thermal stability. Therefore, Ga2O3 thin film has a wide range of applications in metal oxide field effect transistors, photodetectors and so on. However, the large bandgap of Ga2O3 is unfavorable to the conductivity, which limits the application of Ga2O3 film in optoelectronic devices. The optical and electrical properties of Ga2O3 can be significantly improved by elemental doping, thereby enhancing device performance. The lattice deformation of Ti-doped Ga2O3 (TGO) is small due to the close matching of the Shannon ion radii (0.060 5 nm, 0.042 nm) of Ti4+ in octahedral and tetrahedral coordination with Ga3+ (0.062 nm, 0.047 nm). The reported plasma-enhanced atomic layer deposition at 120 ℃ for the preparation of TGO films requires four precursors: triethyl gallium, oxygen plasma, titanium tetraisopropoxide (TTIP) and H2O. Using H2O as an oxidizer requires long purging times after water vapor exposure and brings in hydroxyl (-OH) impurities at deposition temperatures below 150 ℃. Compared with H2O, O3 has stronger oxidability and higher volatility and does not introduce impurities. In order to avoid the problems caused by using H2O as precursor. TiO2, Ga2O3 and TGO films are prepared by thermal atomic layer deposition using Trimethylgallium (TMG) and Tetrakis-dimethyl-amido Titanium (TDMAT) as precursor sources and O3 as reaction gas at 250 ℃. The Ti-doped Ga2O3 concentration is adjusted by designing the Ga2O3/TiO2 cycle ratio. TGO thin films form sandwich structure through different cycles (9, 6 and 3) of Ga2O3 and 1 cycle of TiO2. The growth rates of Ga2O3 and TiO2 measured by spectroscopic ellipsometry are 0.037 nm/cycle and 0.08 nm/cycle, respectively. The growth rate of TGO film is lower than the theoretical calculated value due to the delayed growth of Ga2O3 nucleation caused by the decrease of surface reactive site density after TiO2 growth. The results of X-ray photoelectron spectroscopy show that the concentration of Ti in the film increases with the decrease of Ga2O3/TiO2 cycle ratio, the binding energy of O 1s, Ga 2p and Ti 2p shifts to the lower, which is attributed to the replacement of some sites of Ga by Ti atoms, indicating that Ti elements are successfully doped into Ga2O3 films. The core level spectra of TiO2 and Ga2O3 show the presence of Ti4+ and Ga3+ ions in the films. In the O 1s core level spectra of TGO films, Ga-O bonding decreases with increasing Ti-O bonding content, indicating the formation of Ga2O3-TiO2 composites in the TGO films. The absence of diffraction peaks in the grazing incidence X-ray diffraction spectra indicates that the deposited Ga2O3 and TGO films are amorphous. The surface root mean square roughness of 0.377 nm is observed by atomic force microscopy, indicating that the surface of the film is flat and smooth. This is attributed to the layer-by-layer growth of atomic layer deposition with the advantage of atomic-level thickness control. The TGO films exhibit high transparency in the visible region and strongly absorb ultraviolet light. With the increase of Ti doping concentration, the refractive index of TGO films increases from 1.75 to 1.99 due to chemical changes, the transmittance decreases due to the increase of extinction coefficient in the ultraviolet region, the absorption edge appears red-shifted and the optical bandgap decreases from 4.9 eV to 4.3 eV. The reduced band gap of TGO films can extend the sensitive region of optoelectronic devices to longer wavelengths. The optical band gap of thin films measured by spectrophotometric and X-ray photoelectron spectroscopy shows consistent results. The comprehensive analysis shows that Ti doping has a significant impact on the optical properties of Ga2O3.

Microchannel Plate (MCP) is a high-gain electron multiplier that consists of a channel-type array of millions of single-channel electron multipliers tightly spaced parallel to each other. MCP is widely used in low-light night vision technology, time-of-flight mass spectrometry, and other fields due to its advantages of high electronic gain, high spatial resolution, high temporal resolution, and extremely low background noise. Traditional MCP is constructed of lead-silicate glass and is created by the processes of stretching, stacking, fusing, slicing, etching, and hydrogen reduction. After hydrogen reduction chemical treatment, a conductive layer and a Secondary Electron Emission (SEE) layer are formed. When MCP works, a DC high voltage is applied at both ends. When electrons or photons enter the channel, they collide with the SEE layer to excite secondary electrons, and then accelerate to bombard the tube wall under the action of an electric field to produce more electrons, resulting in the amplification of the input signal. However, because of the complicated manufacturing process of traditional MCP, its performance is difficult to improve. In recent years, Atomic Layer Deposition (ALD) has given a straightforward solution to the aforementioned issues. ALD is a thin film deposition technology capable of producing very thin conformal films. By exposing the substrate surface to alternate gases for successive surface reactions, the thickness and composition of the film are regulated at the atomic level. ALD can also deposit homogenous nano-films on substrates with high aspect ratio structures at the same time. Based on the benefits of ALD discussed above, the researchers recommend depositing a conductive layer and a SEE layer inside the channel to improve the performance of traditional MCP. Using ALD to functionalize the MCP can remove the functional layer from the glass substrate, allowing for variable modification of the conductive layer and emission layer based on individual demands, therefore simplifying the production process, and improving MCP performance. The MCP conductive layer is responsible for conducting current and supplementing electrons in SEE layer. If the resistivity of the conductive layer is too large, the electron charge of the SEE layer can not be replenished in time, causing the MCP to saturate ahead of time and lower its electrical gain. If the resistivity is too small, the current going through the MCP will be too strong, resulting in a thermal effect and MCP damage. At the moment, the conductive layer films produced by ALD are mainly ZnO∶Al2O3(AZO), W∶Al2O3, and Mo∶Al2O3 composite materials. However, there are several issues with these conductive layer film materials. Because MCP requires a high-voltage environment, but the performance of AZO thin film is unstable and easily broken down under high voltage, and the precursors of W and Mo are costly and very poisonous, there are issues such as safety and economy in industrial mass production. As a result, it is critical to design a novel conductive layer composite film to address both safety and economic concerns. Al2O3 is a typical dielectric material with a high dielectric constant and resistance. TiO2 has excellent electrical characteristics as well as chemical stability. Simultaneously, the precursors of Al2O3, Al(CH3)3 (TMA), and the precursor of TiO2, Ti(N(CH3)2)4 (TDMAT), have the benefits of cheap cost, non-toxic, and innocuous reaction by-products. In this paper, we propose TiO2∶Al2O3 nanocomposite films as the conductive layer of MCP. Based on the bulk resistance of the MCP, we first calculated the sheet resistance requirements of the conductive layer and found that for a channel with an aperture of 10 μm, a center distance of 12 μm, an aspect ratio of 48∶1, a diameter of 25 mm and a diameter of 20.5 mm in the active area for MCP, when the bulk resistance value is 100~300 MΩ, the sheet resistance value range of the conductive layer should be 1.73×1013~5.20×1013 Ω/□. On borosilicate glass substrates, we used ALD to deposit TiO2∶Al2O3 nanocomposite films with varying TiO2 cycle percentages. The square resistance of TiO2∶Al2O3 nanocomposite films is found to be within the required range of the square resistance of the conductive layer when the TiO2 cycle percentage is between 30.27%~37.06%. A 20 nm Al2O3 transition layer and a 100 nm TiO2∶Al2O3 nanocomposite film are designed and prepared on a p-type single-sided polished monocrystalline silicon (100) substrate. The thickness of the film is measured by SEM to be 122 nm, and the surface is flat and smooth. Finally, the conductive layer of TiO2∶Al2O3 nanocomposite film in the MCP is prepared. The measured bulk resistance is 212.81 MΩ@1 000 V, and the gain is 18 357@1 000 V. To summarize, the TiO2∶Al2O3 nanocomposite film we developed can well meet the requirements of the MCP conductive layer and has the advantages of low cost, high voltage resistance, low corrosivity, and high safety, providing a new material choice for the development of ALD-MCP.

The Fiber Bragg Grating (FBG) vibration sensor based on the cantilever beam structure has strong lateral anti-interference ability, high stability, and simple structure. It is particularly suitable for one-dimensional acceleration measurement. And its working range and resolution are determined by its resonant frequency and sensitivity, however, because the resonant frequency and sensitivity of cantilever beam type sensors are mutually restricted, it is difficult for the current generation of cantilever beam type sensors to simultaneously meet the requirements of wide measurement bandwidth and high sensitivity. To satisfy this demand, a novel FBG accelerometer based on F-beam is developed. The FBG can be sensitized by the neutral layer far away from the cantilever beam, and suspended and fastened at both ends to successfully prevent the chirp effect of FBG.Firstly, the amplitude-frequency characteristics of the damped mass-spring system with one degree of freedom are studied. The flatness of the amplitude-frequency response curve varies with the change of the damping ratio. Without damping, the sensor's working bandwidth is narrow. By adding damping materials such as silicone oil, the sensor can have a larger working bandwidth. Generally, the damping ratio is 0.7. After that, the resonant frequency and sensitivity formulas of the sensor are derived, and its mathematical model is established according to these formulas. With the sensitivity formula as the objective function, and its size parameters and the resonant frequency formula as the constraint conditions, the sequential quadratic programming program is established by MATLAB to optimize the solution, and the sensor's size parameters that satisfy the operating band range and have high sensitivity are obtained. Imported 3D model of this sensor created by SOLIDWORKS into ANSYS software, where the material properties are adjusted, the mesh division is finished, and fixed constraints are given to the sensor base to produce the sensor's first-order and third-order modal vibration patterns. The modal analysis results verify the correctness of the theoretical analysis and show that the sensor has a good transverse anti-interference ability. And then, set the simulation conditions such as sweep frequency range to analyze the harmonic response of the sensor. By modifying the damping ratio, the simulated amplitude-frequency response curves under the conditions of two damping ratios are obtained to simulate the amplitude-frequency response of the sensor without silicone oil and filled with silicone oil. The simulated amplitude-frequency response curve at the maximum amplitude position is basically consistent with the theoretical curve. Finally, based on the theoretical and simulation results, two sensors were fabricated, one of which was directly encapsulated as sensor 1 and the other was encapsulated with silicone oil as sensor 2, and the amplitude and frequency response tests, sensitivity tests and transverse immunity tests were conducted on sensor 1 and sensor 2. In order to determine the sensor's amplitude-frequency response, the trigger signal's amplitude is fixed swept between 10 Hz and 240 Hz. Next, the sensor's minimum detection frequency is tested by continuously varying the excitation frequency between 0 Hz and 2 Hz, and the detection performance of the sensor under various excitation conditions is tested by setting various excitation conditions. In the sensitivity test experiment, fixed the excitation frequency and adjusted the acceleration to measure the sensor's sensitivity. In the lateral immunity test experiment, fixed the excitation frequency and acceleration, change the measurement direction to test the sensor's lateral immunity.The experimental indicates that the experimental results of sensor 1 and sensor 2 are basically consistent with the theoretical and the simulated amplitude-frequency curve. The resonant frequency of sensor 1 is about 168 Hz, the measurement bandwidth is 1.5~50 Hz, the sensitivity coefficient is 159.84 pm/g, the transverse immunity is 9.88%, and the error between the theoretical and actual values of resonant frequency and sensitivity is 0.93% and 3.29% respectively. The error may be caused by the low processing accuracy of the sensor in the production process and the immature fiber pre-stretching process. The measurement bandwidth of sensor 2 filled with silicone oil is 1.5~100 Hz, the sensitivity coefficient is 133.57 pm/g, and the lateral interference immunity is 8.1%. This two FBG sensors can well reflect the external sinusoidal excitation in their corresponding operating bands and have good detection performance. By filling silicone oil, the working frequency band can be effectively expanded, the sensitivity can be stabilized, the transverse interference immunity can be improved, and the measurement error can be reduced.

With the development of petroleum and natural gas resources, pipeline transportation has become one of the main transportation modes. Pipeline leakage caused by various external factors during transportation affects the safe running of the pipeline. The development of optical fiber sensing technology has brought a new solution for pipeline leakage monitoring. Most of the existing research are carried out by numerical simulation work, lacking experimental demonstration, and only studied the temperature field distribution in the soil area after pipeline leakage, without taking the impact of the difference in soil internal physical properties on the temperature change into account. In addition, the accuracy of the monitoring of small leaks still can't satisfy the monitoring requirements. And the conventional fiber arrangement is only suitable for monitoring the temperature along the line, when the surface of the object to be measured is large and the monitoring requires a higher spatial resolution, the one-dimensional laying method is difficult to achieve the required resolution, it needs to be optimized.Based on the advantages of high spatial resolution of optical frequency domain reflectometry technology, in this paper, we mainly focus on oil and gas pipeline monitoring wiring problem and build a sandbox model with a small proportion. On the basis of one-dimensional tiled line monitoring, a new way of laying optical fiber for sinusoidal surface monitoring is proposed. Using optical frequency domain reflectometry technology with high spatial resolution as a supporting tool, the superiority of sinusoidal layout is verified. The results show that the measurement effect of buried optical fiber with a sinusoidal layout is better than that of a conventional one-dimensional tiled layout because of its wider measurement range. We analyzed the effect of sinusoidal period and longitudinal length on temperature monitoring, these two factors have a greater effect on the monitored maximum temperature, which means the larger the sine period and vertical length, the lower the highest temperature detected. Therefore, if there is no precision requirement, the optical fiber can be arranged long and sparse. Otherwise, it needs to be even tighter. Through the combination of experiments and numerical simulations, it is obtained that the maximum thermal influence radius of the tiny heat source is 7 cm, and this result can further guide to optimize the arrangement of optical fiber. In addition, the relationship between soil thermal conductivity, soil bulk density, and water content is obtained by the variable method. The relationship between soil bulk density and soil thermal conductivity is basically linear, the relationship between soil thermal conductivity and water content is not a specific linear increasing or decreasing trend, it varies in a parabolic-like form with the influence of external factors. Water content also affects the vertical distribution of the soil temperature field. When the water content is below the threshold, as it increases the rate of soil heat transfer in the vertical direction becomes faster, the temperature around the heat source increases faster, the maximum temperature monitored becomes larger, the high temperature influence range becomes larger, and the degree of heat diffusion increases significantly. We have studied the effect of heat source temperature on soil heat transfer, and found that as the heat source temperature increases, the heat diffusion range becomes larger, the high temperature influence range becomes larger, and the distance of temperature transfer in the vertical direction becomes farther. The influence law of these factors on soil heat transfer provides a reference for pipeline leakage monitoring, which can further guide the fiber arrangement. Meanwhile, it also verifies the feasibility of optical frequency domain reflectometry distributed optical fiber technology can accurately measure soil temperature field and also provides guidance for other distributed temperature measurement technologies in the layout of buried optical fibers.

Laser chaotic communication system is widely used in the field of secure communication due to its unique advantages such as strong randomness, quasi-noise, and high bandwidth of chaotic signals. At present, laser chaotic synchronization communication generally depends on the laser internal nonlinear effect or photoelectric oscillator. Still, it is difficult to achieve high-quality synchronization communication because of the difficulty of hardware parameters matching between the transmitter and the receiver. Aiming at this shortcoming, some scholars have proposed to use the powerful nonlinear fitting ability of a neural network to model the receiver of a chaotic optical communication system, to realize high-quality synchronization communication. This paper proposes to use the long short-term memory neural network for the mathematical modeling of the chaotic optical transmitter. It successfully solves the problems of complex hardware systems and low synchronization coefficients in traditional chaotic optical communication and provides a reference for point-to-multipoint chaotic communication.This paper presents the design of a laser chaotic synchronization communication system based on long short-term memory neural network, and uses a cross-prediction algorithm to optimize the network model. In the off-line training stage, a large number of chaotic encrypted signals generated by the transmitter are used as input variables of the neural network, and the real chaotic carrier sequence is further selected by the cross-prediction algorithm as output variables of the neural network. To enable the long short-term memory neural network to accurately predict the output variables according to the input variables, each training iteration of the network will update its node state until the ideal loss value is reached. In the test stage, the node state of the neural network has been determined. When the input variable is received, the system will automatically map the predicted carrier sequence, and the received encrypted signal can be directly subtracted from the predicted carrier sequence to decrypt useful information. The scheme achieves a high synchronization coefficient and achieves high-quality chaotic synchronization communication.The simulation result consists of three parts. The first is the quality of decrypted information at the receiver end. After modeling and training of laser chaotic system by long short-term memory neural network, the system has good prediction effect and high-quality chaotic synchronization. The synchronization coefficient between the real target carrier and the predicted carrier is more than 99.9%, and the root means the square error is as low as 10-3. The noisy information is demodulated directly from the encrypted information minus the chaotic carrier predicted by the neural network, and the bit error rate is as low as 10-10. It is far lower than the hard decision threshold of the forward error correlation standard, which is 3.8×10-3. To verify the universality of the system, the simulation of optical feedback and photoelectric feedback synchronization communication system has the same level of communication quality. Secondly, the influence of the number of network nodes, the information coupling coefficient, and the signal-to-noise ratio on the chaotic synchronization communication performance is studied in the optical feedback chaotic synchronization communication system. The results show that when the coupling coefficient is 0.08, the signal-to-noise ratio is 30 dB unchanged, and the number of nodes is between 200 and 800, the system has good bit error rate performance, and the maximum is only 10-10. When the number of nodes is 300, the synchronization coefficient reaches the peak value of 0.999 93. When the number of nodes reaches 1 000~1 200, the neural network appears overfitting state, and the information appears with certain distortion. This paper further studies the effect of nodes in the range of 40~240 on system performance. In the case of a few nodes, the synchronization coefficients of the system are all above 0.999 8, the bit error rate is far lower than the hard decision threshold of forward error correlations standard, and the bit error rate is lower than 10-8 magnitude. When the number of network nodes is 240, the maximum synchronization coefficient is 0.999 96. For the coupling coefficient, the number of nodes is kept at 200 and the signal-to-noise ratio is unchanged at 30 dB. When the coupling coefficient is large and reaches 0.04~0.12, the bit error rate of the system can reach a relatively low level stably, all of which are lower than 10-6, and the system communication quality is good. At the same time, when the coupling coefficient reaches 0.11, the maximum synchronization coefficient of the system is 0.999 95. For the signal-to-noise ratio, keep the network nodes 200, the coupling coefficient 0.08 unchanged, the signal-to-noise ratio between 5~40 dB, and the system synchronization coefficient can reach above 0.999 8. When the signal-to-noise ratio reaches 15 dB, the bit error rate reaches the order of 10-6, far lower than the hard decision threshold of the forward error correlations standard. When the signal-to-noise ratio is 25 dB, the synchronization coefficient reaches the peak value, which is 0.999 966. Finally, to verify the actual availability of the system, the grayscale image of 256×256 is successfully transmitted in the optical feedback system. In addition, the system security is analyzed from three aspects: brute force search, plaintext attack, and ciphertext attack. The results show that the system can resist many attacks and has high security.The proposed laser chaotic synchronization communication based on long short-term memory neural network and the network structure optimization by cross-prediction algorithm achieves high-quality chaotic synchronization communication in both optical feedback and photoelectric oscillator system. This scheme successfully solves the problems of complex hardware systems and low synchronization coefficients in traditional chaotic optical communication. Then, the influence of long short-term memory neural network nodes, coupling coefficient, and signal-to-noise ratio on the communication performance of the system is studied. When there are more nodes or the coupling coefficient is low, the decryption information will appear with a certain distortion. Finally, the feasibility of this scheme is further verified by image transmission. As a whole, the synchronization coefficient of the system can be as high as 0.999 966, and the bit error rate is as low as 10-10, which realizes high-quality chaotic synchronization communication. The advantages of this scheme are as follows. First, long short-term memory neural network, with its long-term dependence on learning time series and strong robustness, enables this scheme to achieve high-quality synchronous communication in both optical feedback and photoelectric feedback systems and has certain universality. Second, in the chaotic synchronous communication system based on long short-term memory neural network in this paper, the system performance obtained by the state of a few nodes and multiple nodes is outstanding. Choosing the state of a few nodes can greatly reduce the time loss and save the time cost of training neural networks. Third, the long short-term memory neural network scheme proposed in this paper successfully solves the problem of hardware parameter matching between the two receivers in traditional chaotic optical communication and has the advantages of convenience and security, which provides a thought for the subsequent research of chaotic optical communication.

Real-time health monitoring of the bridge is of great significance. Compared with traditional piezoelectric sensors, Fiber Bragg grating has the advantages of high sensitivity, strong wavelength division multiplexing ability, and strong anti-interference ability. It has been widely used in real-time monitoring of various large structures in recent years. Aiming at the selection of bridge acceleration sensor, this paper proposes a double fiber grating acceleration sensor based on arc cycloid hinge, and analyzes the resonant frequency and sensitivity of the sensor by establishing a mechanical model. The analysis results show that under the condition of different hinge thicknesses, the height of the proof mass and the length of the minor axis of the semi-ellipse have a great influence on the resonant frequency and sensitivity of the sensor. As h and e2 increase, the mass of the mass block increases, the sensitivity of the sensor increases, and the resonance frequency decreases. As the thickness t of the hinge becomes larger, the resonant frequency becomes larger, and the sensitivity of the sensor becomes smaller. When t is in the range of 1 mm to 3 mm, as c becomes larger, both the sensor sensitivity and the resonant frequency become smaller. According to the bridge in-situ calibration requirements, this paper uses MATLAB to optimize the parameters of the sensor structure. Then use ANSYS to conduct static stress analysis, modal analysis and harmonic response analysis. The modal analysis shows that the first 4 modal frequencies of the sensor model are 471.06 Hz, 2 878.1 Hz, 3 226.7 Hz, 9 208.4 Hz and 13 763 Hz. The static stress analysis shows that the strain produced by the sensor under the acceleration of gravity is 1.4 μm. The harmonic response analysis shows that the resonance frequency of the acceleration sensor model is 474 Hz. After the software simulation, the actual sensor is made and calibrated. When performing resonance frequency calibration, the signal generator sets the signal voltage to 1 V, starts the vibration test from 10 Hz, ends at 650 Hz, and records the wavelength change. The sensor has the largest wavelength variation near the vibration frequency of 460 Hz, and the wavelength variation is relatively stable at 10~250 Hz, that is, the resonance frequency is 460 Hz. When performing sensor sensitivity calibration, set the constant frequency of 30 Hz and 60 Hz on the vibration table as the test frequency of the simulated bridge site. During the 30 Hz test, the voltage value increases from 0.2 V to 0.9 V with a step size of 0.1 V. During the 60 Hz test, the voltage value increases from 0.2 V to 0.7 V with a step size of 0.1 V. When the frequency is 30 Hz, the sensitivity of the dual FBG of the sensor is 43.14 pm/g, and the fitting coefficient is 0.995 7; the sensitivity of the single FBG1 of the sensor is 21.74 pm/g, and the fitting coefficient is 0.997 7. When the frequency is 60 Hz, the sensitivity of dual FBG is 43.21 pm/g, and the fitting coefficient is 0.992 8; the sensitivity of single FBG1 sensor is 21.81 pm/g, and the fitting coefficient is 0.998 9. Set the vibration frequency of the vibration table to 50 Hz, and the input voltage of the signal generator to 0.3 V. The test direction of the acceleration sensor is installed perpendicular to the vibration direction of the hinge, and when the sensor performs vibration sensing perpendicular to the vibration direction of the hinge, the sensitivity of the sensor is 2.456 pm/g, which is much smaller than the sensitivity of the vibration direction of the hinge. The lateral interference degree of the sensor is about 5.7%, which proves that the acceleration sensor has a good lateral anti-interference ability. The calibration experiment results show that the arc cycloid hinge structure FBG acceleration sensor designed and manufactured in this paper has a smaller volume and a higher integration level compared with other FBG acceleration sensors under the premise that the parameters meet the bridge acceleration monitoring. Using a combined elliptical and rectangular mass structure, dual fiber gratings can be engraved on an optical fiber to facilitate wavelength data collection. The experiment proves that the acceleration sensor designed in this paper can be used for acceleration sensing on the bridge.

The laser interferometer and the optical encoder are commonly used for high-precision displacement measurement, which is significant for equipment manufacturing. The former can realize sub-micron measurement by counting and subdividing interference fringes. However, it has the disadvantages of strict requirements for the measurement environment and difficult integration directly into the equipment, which greatly limit its applications in industrial measurement and control. Compared with the laser interferometer, the encoder has been widely integrated with the CNC machine as a core measurement component due to its advantages of low cost, small size, and simple optical structure. Grating lithography has been successfully employed to fabricate the gratings of optical encoders. However, some inherent problems exist in this fabricating process, such as low production, long production cycle, and harsh production conditions. Furthermore, the optical encoder manufactured by the grating lithography requires a combination of a light source and a reading head. When the encoder has worked for a long period of time, the light source will dissipate a large amount of heat, resulting in a drastic change in the internal temperature of the encoder. The drastic temperature change will cause the thermal deformation error of the encoder substrate to influence its measurement precision. Due to the advantages of high efficiency, low cost, and simple process requirements, we have introduced additive manufacturing with perovskite quantum dots to fabricate a novel linear encoder named quantum dot encoder, which prints the perovskite quantum dot coding patterns on the substrate via additive manufacturing. Then, machine vision is applied to process the continuous, regular and winding quantum dot code pattern in real time to achieve displacement measurement. As a novel linear encoder, its measurement precision is significant for its wide applications. In order to further improve the measurement precision of the quantum dot encoder, a displacement measurement method based on triangular wave skeleton extraction of coding patterns is proposed in this paper. First, considering the winding and continuous shapes of coding patterns of the quantum dot encoder, the boundary tracking method with variable steps is proposed to detect the edges of coding patterns in real time. The detection path of this method is always kept around the edge of the coding patterns, so only a few pixels need to be traversed to detect the edges. Then, triangular wave fitting is carried out on the middle lines of coding patterns to obtain the triangular wave skeletons of coding patterns, so as to improve the measurement stability and the subdivision linearity of displacement. Finally, because of the advantages of simple structure, fast convergence, easy deployment, and good approximationperformance for nonlinear functions, a Radial Basis Function (RBF) neural network is used to compensate for the nonlinear errors emerging in the quantum dot encoder. A laser interferometer is used as a baseline for linear displacement measurement. We compared the three waveforms to fit the measured signal, which are triangle wave, sine wave and square wave. The experimental results show that the triangle wave can well fit the measured signal with a high amplitude and a low error rate. To validate the RBF neural network on the measurement error compensation of the quantum dot encoder, a BP network, an LSTM network and an RBF neural network are individually used to compensate for the measured displacement data while other experimental conditions remain unchanged. The experimental results show that the RBF neural network is superior to the other two neural networks in error compensation performance. To analyze the effect of three different steps in the proposed displacement measurement method, an ablation experiment is conducted. The experimental results show that the boundary tracking step with variable steps for coding pattern detection greatly accelerates the speed of boundary tracking. Compared with our previous work, the operation efficiency has increased by 108.86%. The coding pattern skeleton extraction method based on triangle wave fitting reduces the impact of environmental noise on the measurement precision, resulting in a reduction of the repetitive displacement error from ±8.695 μm to ±0.870 μm. The error compensation method based on the RBF neural network effectively compensates the nonlinear error of the quantum dot encoder, and improves the RMSE, maximum error, variance and confidence interval. Comparison experimental results indicate that the proposed method is more robust and achieves better measurement accuracy than the existing methods.

With the development of modern manufacturing and testing technology, micro-vibration detection technology for rough metal surface plays an important role in many fields, including material analysis, nondestructive testing, and mechanical system dynamic analysis. The piezoelectric transducer has been widely used in detecting the micro-vibration on rough metal surface, but it is not available to be used on hot or corrosive surface, and hardly to achieve in-line detection for the limited working distance. Several interferometers have been developed for distant detection of micro-vibration, which work well on mirror surface in the laboratory, however, those interferometers can hardly be used to detect micro-vibration of rough metal surface due to the environmental noise and wavefront mismatch.A micro-vibration detection system based on differential two-wave mixing interference is proposed to meet the requirements of non-contact measurement for micro-vibration on rough metal surface. It provides a simple and elegant solution to these problems arising in the above interferometers, which results from the replacement of a conventional beam splitter with a dynamic holographic grating continuously recorded in a photorefractive crystal. The dynamic holographic grating is modulated by the interference fringe and presents the same distribution, but the change of dynamic holographic grating is available only when the time constant of photorefractive crystal is larger than the change frequency of the interference pattern, which contributes to the fact that the proposed system has the ability of low-frequency noise suppression in non-laboratory environment. The dynamic holographic grating in the photorefractive crystal adapts the reference wavefront to the signal beam, which enables the vibration measurement on rough surface of metal. To reduce the fluctuation of the beam intensity, electric noise, and single measurement error, the proposed system adopts two nonlinear Bi12SiO20 (BSO) photorefractive crystals to demodulate the vibration signals in the system. Two BSO photorefractive crystals are applied with high voltage of opposite polarity to obtain the dual-path signals with opposite polarity, by adopting differential processing to the dual-path signals, the noise insensitive to voltage polarity can be suppressed and the sensitivity to vibration can be improved. Simulation analysis is carried out to verify the feasibility of the proposed detection system, the simulation results show that the dynamic holographic grating is non-shifted or shifted by half of the grating period with respect to the interference fringes when the two BSO photorefractive crystals are applied with high voltage of positive or negative respectively, which contributes to the dual-path output beam intensity with an opposite polarity. By comparing the time domain diagram of vibration signal and output beam intensity in simulation, the capability of the proposed system to measure micro-vibration is affirmed. By calculating the amplitude of the output beam intensity corresponding to vibration signals of different amplitudes, the relationship between them can be achieved, from which an approximate linear relationship between the output beam intensity amplitude and the vibration signals amplitude can be known. To evaluate the noise suppression capability of the proposed system, Gaussian noise and high frequency noise is added to the laser intensity, the simulation result shows the added noise is effectively suppressed by the proposed system. A prototype has been built to further validate the feasibility of the proposed system. The vibration measurement experiment of a copper sheet connected to the piezoelectric transducer is carried out, and the measurement result of the proposed system is compared with the voltage applied to the piezoelectric transducer and the commercial laser vibrometer, the time domain diagram of them has an excellent consistency. Compared with the traditional single-path system, the sensitivity of the proposed system is doubled, the noise is suppressed, and the signal-to-noise ratio is increased from 27.47 dB to 30.83 dB. The relationship between the output voltage amplitude of the proposed system and the measured vibration amplitude can be obtained by applying various voltage amplitude to the piezoelectric transducer, which indicates that the proposed system has an exceptional linearity (the nonlinear error is 2.41% when the vibration amplitude is smaller than 40 nm). The vibration measurement with a frequency of 200 kHz is carried out to evaluate the capability of the proposed system for detecting the high frequency vibration, which is better than the maximum measuring frequency of commercial laser vibrometer (20 kHz). To verify the stability of the system proposed in this paper, the repeatability experiment was conducted, in which the copper sheet was measured 20 times and the measurement interval was 5 min, the relative residual error of each measured amplitude and average amplitude is calculated, the result of experiment shows that the peak to peak value and RMS value of the relative residual error in the proposed system are 4.11% and 1.42% respectively, which is better than the 8.69% and 3.07% in the traditional single-path system. The proposed detection system has high bandwidth and sensitivity with strong noise suppression ability, which provides an effective and feasible method for micro-vibration measurement of rough metal surface in an industrial environment.

Due to the advantages of fast response, multiple factors metering and easy implementation, the measurement method of light-screen array has been widely used in the measurement of external ballistic flight parameters of barrel rapid-fire weapons. Compared with the separated light-screen array, the integrated light-screen array measurement model has the advantages of simplified parameters, simple model and easy to use. Aiming at the integrated light-screen array measurement model, the structure-related design parameters of the integrated light-screen array measurement model are extracted and the error propagation formula is derived to analyze the influence of different parameters on the measurement error of the projectile flight parameters. Then the simulation model is established in MATLAB according to the analysis result, and the influence law of the vertical angle α, the horizontal angle β, the target distance s and the height difference h on the flight velocity and coordinate measurement errors of the projectile is analyzed. The simulation results show that the vertical angle α mainly affect the projectile ordinate measuring error. and with the increase of α, the ordinate measuring error decreases and the decreasing trend gradually weakens. The horizontal angle β mainly affect the projectile abscissa measuring error, and with the increase of β, the abscissa measuring error decreases and the decreasing trend gradually weakens. The ordinate measuring error, abscissa measuring error and velocity measuring error of the projectile are all affected by the target distance s. The measurement errors gradually decrease with the increase of s and the decreasing trend is gradually weakened. Then the optimization method of structural parameters is given. By increasing angle of light screen structure, the effective target surface detection area will be reduced, and the value range of the optimized vertical angle α and horizontal angle β is from 20° to 30°. Since large target distance is not conducive to transportation, field layout and use, it is more appropriate to choose an optimized target distance s range of 1.5~2.5 m and the height difference is 0 m. According to the error distribution law of projectile flight parameters under the influence of various parameters, typical values are assigned to each parameter in the optimized integrated light-screen array measurement model that the distance between front target and back target s=2 m, height difference h=0 m. The accurate angles of the light-screen are obtained by the calibration experiment using the method of plane fitting that vertical angle α=24.94°and horizontal angle β=24.61°. Then the measurement error distribution of projectile velocity and coordinates in the range of 1 m×1 m rectangular target surface are obtained. The results showed that the measurement error of the projectile is no more than 1.50 mm in horizontal coordinate and no more than 2.10 mm in vertical coordinate. The velocity measurement error is not large, which is 728.70 mm/s. Finally, the live verification test is carried out. Due to the influence of external field environmental factors, the measurement error obtained by the test is slightly larger than the simulation result. The live test results show that the measurement of projectile flight parameters is consistent with the simulation analysis. The maximum error of abscissa measurement is not more than 3.1 mm, the maximum error of ordinate measurement is not more than 4.8 mm, and the maximum error of velocity measurement is not more than 1.1 m/s. The results of the method presented in this paper can provide theoretical basis for the measurement error analysis and theoretical support for the engineering design of light-screen array measurement equipment, and also provide a reference for improving the flight parameter measurement accuracy of barrel weapon projectile.

Artificially designed photonics devices have promising applications in various fields of modern optics. The design of conventional photonics devices is usually based on a known physical model, and then the structure is optimized by numerical simulation methods. Since the device structure relies heavily on the a priori model, the degree of freedom of the conventional optimized design is limited. In recent years, with the increasing demand for high-performance photonic devices, inverse design methods with higher design degrees of freedom have been rapidly developed. Currently, the most widely used inverse design method is the gradient descent algorithm, which can achieve fast iterative approximation of the target by using the gradient information of the objective function on the variables. For problems where the gradient is difficult to solve or uncertain, genetic algorithms or particle swarm algorithms can generally be used, which find the global optimal solution by simulating the evolutionary process of organisms and foraging of populations, respectively, and thus do not require gradient information. In recent years, with the rapid development of artificial intelligence, neural network-based machine learning algorithms have attracted widespread attention in various scientific fields. Neural network algorithms are flexible in regulation and can be combined with a variety of algorithms, but the models lack universality and require corresponding data sets for different physical models. It can be seen that different inverse design methods have different advantages and limitations, so for different design problems, the physical model needs to be evaluated and a suitable inverse design method needs to be selected. Compared with traditional parametric design methods, inverse design methods can yield more complex and diverse device structures with superior performance. In addition to using a single inverse design method, the combination of multiple methods is also beneficial to improve the computational efficiency. For example, combining deep learning with genetic algorithms not only improves the computational speed of genetic algorithms, but also makes use of the gradient-free feature of genetic algorithms to find the global optimal solution. The inverse design method breaks the design limitations of traditional methods and can achieve efficient parameter optimization in the full parameter space, thus making it easier to obtain device structures with extremely high performance. This paper summarizes the common methods for inverse design of optoelectronic devices and gives specific applications of inverse design in various optoelectronic fields. With the continuous development of computer science, the inverse design of photonic devices has shown unparalleled potential. Compared with traditional design methods, intelligent inverse design methods are more efficient and offer greater freedom, providing new solutions for achieving high-performance photonic devices. In various fields of photonics, the inverse design approach allows a higher degree of freedom in optical field modulation and enables the design of various high-performance photonic devices from a demand perspective.

Micro-nano structured functional surface is a hot topic in surface engineering research, and sub-wavelength structures have better anti-reflective properties. Geometric parameters of micro-nano structure on silicon surface are calculated by using equivalent medium theory. Then the above optical model structure is established based on finite element simulation and the optical properties are simulated using COMSOL Multiphysics commercial software to study the effect of reflection reduction in the long-wave infrared (8~12 μm) range, and the effects of surface morphology and structural feature size on the transmittance are analyzed separately. According to the simulation results, it is concluded that the period of the micro-structure dominates its surface transmittance change. Under the condition that other structural parameters are consistent, changing the height can increase the transmittance in a small range. The transmittance of trapezoidal micron structure is higher than that of conical and square cylindrical; there is no obvious effect of reflection reduction of nanostructure in infrared band. The effects of period, microstructure height and duty cycle on the surface tension of zone-melted silicon are studied by analyzing the theoretical model of wettability, and it is found that the change trend of static contact angle of microstructure surface is positively correlated with height, and negatively correlated with cycle and duty cycle. The micron structures with a period of 6 μm are formed by the Radical Plasma Source (RPS) etching technique at an etching gas flow rate of CF4∶O2∶Ar = 400∶200∶20, a microwave power of 2 000 W, an operating air pressure of 125 Pa, and an etching time of 150 s. On this basis, the dot, stripe and cone nanostructures are fabricated by low-energy ion beam etching (LE-IBE) with ion beam incidence angles of 60°, 60° and 75°, incidence energies of 400 eV, 600 eV and 400 eV, ion beam currents of 50 mA and etching times of 60 min, respectively; finally, the antireflective and self-cleaning nanocomposite structures are fabricated on the zoned silicon surface. The final micro- and nanocomposite structures with anti-reflection and self-cleaning functions are prepared on the fused silicon surface.The surface morphology of the fabricated micro- and nanocomposite structures with different morphologies of period 6 μm is examined using an Atomic Force Microscope (AFM).The optical and hydrophobic properties of the fabricated silicon surface micro- and nanocomposite structures are characterized using a Thermo Scientific Nicolet iS20 Fourier infrared spectrometer and a JC2000D2A contact angle meter, respectively, with a transmittance of 78% and a static contact angle of 125.77°. In addition, further analysis of the resulting structure shows that the transmittance of the micro-nano composite structure in the long-wave band is slightly larger than that of the micro-structure, and the nanostructure with lower height has no significant effect in the infrared band to reduce the reflection, while the micron structure achieves the dominant role in the infrared band to reduce the reflection; The contact angle of micro-nano composite structure is larger than that of single micro structure or nano structure, consistent with the theoretical simulation results, which shows that the presence of micro-nanostructures can effectively improve the hydrophobicity of the silicon surface. Through theoretical simulation, experimental preparation and characterization, the anti-reflection and hydrophobic properties of sub-wavelength micro-nano composite structures are analyzed, providing new processing techniques and ideas for surface modification of micro-nano structures, and expanding the application of zone-melted silicon in the field of long-wave infrared.

In order to realize high sensitivity and high quality factor refractive index sensing characteristics, a microring resonator structure based on the slot phase-shifted Bragg grating is proposed. The structure is composed of a slotted straight waveguide embedded phase-shifted Bragg grating coupled with a single real waveguide microring. Two uniform Bragg gratings in the structure form a first-order F-P resonator. The light field oscillates in the F-P resonator through weak reflection of the gratings on both sides, forming a continuous light mode. part of the light waves are coupled into the microring and constantly surround in the microring due to evanescent field. After phase change, and part of the light is coupled back into the slot waveguide and interferes with the continuous state light mode in the F-P resonator, resulting in Fano resonance. Fano resonance has a sharp and asymmetric spectral line shape, so slight disturbance of refractive index in the external environment can cause a shift of resonant wavelength and a drastic change of transmission intensity, so as to achieve high sensitivity refractive index sensing characteristics. The light wave transfer matrix of each part of the structure is established, the light field distribution of each component in the resonator is quantified, and the light wave transmission principle of the system is analyzed. In order to further study the sensing characteristics of the structure, the physical model of SOI platform waveguide with Si as waveguide and SiO2 as substrate is established, which is compatible with CMOS technology and is very conducive to the integration of photonic devices. Classical Fano formula and the finite difference time domain method are used to fit the output spectrum and simulate the proposed device structure, respectively. The field distribution of the strip waveguide and the slot waveguide with the same size is compared in the simulation process. Compared with the single strip waveguide, the slot waveguide with high refractive index difference is more suitable for the structural design of the sensor.For the refractive index sensor, the higher the quality factor, the stronger optical signal storage ability of the device, and the higher the extinction ratio, the higher the anti-noise sensing performance can be achieved. Therefore, in order to optimizie the quality factor, extinction ratio and transmission intensity of the sensor, the influence of key physical parameters on the sensor performance is analyzed. Among them, the different values of Bragg grating period will affect the generation of Fano resonance and the amplitude of resonant peak in the structure, and the grating duty ratio directly controls the intensity of light wave reflection and the magnitude of reflection phase. At the same time, the number of grating teeth has a great influence on the performance of the sensor, and too many grating teeth will cause the effect of strong grating, resulting in the input optical signal is reflected and reduced quality factor,and the length of the F-P resonator affects the area and intensity of the interaction between the light and the object to be measured. At the same tine, the length of the F-P resonato is related to the transmission loss of the sensor system. In addition, the radius of the microring resonator is closely related to the transmission loss and bending loss of the system. By simulating the output spectrum of different sizes of Bragg grating period, grating duty ratio,grating tooth number, F-P cavity length and microring radius,the optimal structure size is set to ensure the reliable sensing performance of the proposed structure. Based on the optimized physical parameters, the simulation structure is applied to the gas refractive index sensing environment. When the refractive index of the environment to be measured increases from 1.000 to 1.01 with the step size of 0.002, the resonant peak of the output spectrum of the structure is redshifted. There is a good linear relationship between wavelength and refractive, the fitting rate is more than 98%. The proposed structure can be widely used in biological or other sensing fields.In addition, the simulation results show that the quality factor of the structure is 25 729, which is more than 3 times higher than that of the traditional microring resonator, and the extinction ratio is 18.65 dB, which is 6.46 dB higher than the traditional microring resonator. The proposed structure can realize the high noise resistance performance of the sensor characteristics, and the refractive index sensitivity can reach 122 nm/RIU. The comparison between the proposed structure and the single real waveguide microring resonator proposed in the relevant literature proves that the proposed structure has higher quality factor and refractive index sensitivity. In addition, the proposed resonator is composed of single real waveguide microring with simple and compact structure, which reduces the difficulty of the process. Therefore, the structure has certain advantages in sensing applications.