When the vortex beams propagate in the atmosphere, the turbulence effect causes the crosstalk of its orbital angular momentum, which reduces the transmission quality. In order to effectively reduce the influence of turbulence on the propagation of light waves in the atmosphere and explore the measures to slow down the turbulence effect, the influences of anisotropic non-Kolmogorov atmospheric turbulence and beam parameters on the spiral spectrum broadening and receiving power of focused Bessel beams are studied by using the spiral spectrum analysis theory. The results show that the wavelength, topological charge, waist radius, width parameters, turbulence intensity, anisotropy, and internal and external scales all affect the received power. In addition, the spiral spectrum distribution of focused and collimated Bessel beams is comparably studied by using multi-layer phase screen simulation method. It is concluded that the focused Bessel beam has higher receiving power and lower crosstalk power.

This paper presents an estimate of surface layer optical turbulence in Northwest China using an artificial neural network. We optimize the configuration of the multilayer perceptron (MLP), including 10 features in the input layer and 40 neurons in the hidden layer. The performance of the constructed MLP is investigated. The results show that when the training set and testing set are from the same site, the mean relative error of the model is 1.34%. The goodness of fit between measured and estimated refractive index structure constants is 0.94. We propose that when the training set and testing set come from different sites, the generalization ability of the MLP should be enhanced.

An approximation model of multiple-scattering among horizontally adjacent fields is proposed as a means of improving the three-dimensional (3D) radiative transfer calculation for clouds in remote-sensing applications. Horizontal radiative-exchange equations are established after analyzing the mechanism of radiation flux density variation among horizontally adjacent cloud units. By introducing the solar-compensation function, the influence of the solar incidence angle upon radiative transfer is corrected. The experiment is conducted using I3RC Phase Ⅱ cumulus (Cu), stratocumulus (Sc) and altocumulus (Ac) data generated by the multi-scale superposition fractal algorithm based on actual observation and correction. The experimental results show that compared with the independent pixel approximation (IPA) and combined strict single-scattering and Eddington multiple-scattering (SSEddMS) models, the mean relative error of the upwelling source function (USF) calculated using the proposed model is better than 13% when the solar zenith angle is in the range of 0°-60°. The accuracy of the proposed model is improved by even more than 15% under low solar zenith angles. The accuracy of the pixel-level-radiance calculation of the proposed model falls within 5% under different observational conditions. Furthermore, it can be applied to 3D clouds with different optical thicknesses and horizontal non-uniformities. This has obvious advantages for stability, applicability, and accuracy.

In this paper, by virtue of a finite element method, we studied the mode field characteristics, evanescent field characteristics, and bending loss of a weakly-coupled eccentric-core few-mode fiber in higher-order modes. Furthermore, we investigated the influence of fiber parameters on the minimum effective refractive index difference between adjacent modes, and optimized the fiber to support 10 linearly polarized modes and satisfy the weak coupling condition. In addition, we analyzed the power distribution and bending loss of the 10 modes at the wavelength of 1550 nm. The research results indicate that the minimum effective refractive index difference between adjacent modes is larger than 10 -4 over the whole C-band. Besides, the fiber shows higher evanescent field intensity, higher sensing sensitivity and larger bending loss in higher-order modes and can distinguish a specific bending direction. In conclusion, these results have potential application value for improving the sensitivity of sensors.

A fiber-optic Michelson interferometer based on a photonic crystal fiber (PCF) is proposed, constructed by fusing a piece of PCF and a single-mode fiber (SMF). The taper between the SMF and the PCF works as a coupler. It excites the high-order cladding modes and couples the fundamental mode of the core and high-order cladding mode after being reflected by the end face of the PCF to form an intermodal interference. Since all the air holes in the PCF are exposed to the environment, the moisture and the fiber are fully affected, effectively improving the sensor's humidity sensitivity. The experimental results show that the humidity sensitivity of the designed sensor is -0.095 dB/% with a linearity of 0.998 in a 30%-90% relative humidity range. The temperature sensitivity is 0.008 nm/℃ with a linearity of 0.997 from 20 ℃-100 ℃, and error in the humidity measurement, caused by temperature, is 0.01%/℃. The stability experiment indicates a humidity standard deviation of 0.25%, and the human breathing test shows a sensor response time of 190 ms. Importantly, the designed sensor has a simple structure, high sensitivity, good stability, fast response time, and is easy to fabricate, indicating excellent potential in humidity detection applications.

Faster-than-Nyquist (FTN) transmission technology can effectively improve the transmission rate of free space optical communications. Unfortunately, the inter-symbol interference (ISI) introduced by FTN greatly affects the system reliability. To this issue, a point-by-point elimination adaptive pre-equalized algorithm is proposed. The theoretical bit error rate and computational complexity under 4 order pulse amplitude modulation are derived. The simulation results show that this algorithm can eliminate the ISI brought by FTN pulse shaping filter, and its performance is almost equal to that of orthogonal transmission system. In addition, the system computational complexity is inversely proportional to the acceleration constant. When the acceleration constant is less than 0.4, the computational complexity increases rapidly.

Super-resolution microscopy techniques invented at the beginning of the 21 st century provide unprecedented access to life science researches owing to its impressive ability of studying subcellular structures at the micrometer and nanometer scales. However, these techniques often require high cost of time and money. Recently, many researchers work on super-resolution image reconstruction algorithms based on deep learning. Herein, we obtained the super-resolution images of cell microtubule cytoskeletons by the self-built stochastic optical reconstruction microscopy (STORM), and then the bilinear interpolation down-sampling method was used to obtain the low-resolution input atlas. The traditional cubic spline interpolation method and the enhanced depth super-resolution neural network were used for learning and training to realize the super-resolution reconstruction of the low-resolution image. Results show that the effects of all kinds of down-sampling images reconstructed by deep learning are better than those obtained by traditional interpolation method; the super-resolution images of microtubule skeletons obtained by double down-sampling and experiments are comparable in subjective and objective evaluation indexes. Based on the enhanced depth super-resolution neural network, the super-resolution reconstruction of cytoskeleton images is expected to provide a simple, effective, and cost-effective imaging method, which can be applied to the rapid prediction of cytoskeleton super-microstructures.

Here, we present a method for identifying benign and malignant pulmonary nodules that combines convolutional neural network(CNN)learning features and conventional hand-crafted features. First, the pulmonary nodules area is segmented from computed tomography (CT) images, and traditional machine learning methods are used to extract the image features of the nodule area. Then, the CNN features of network learning are extracted, using the intercepted pulmonary nodules to train the 3D-Inception-ResNet model, and the 2 kinds of features are combined, the random forest (RF) model is used for feature selection. Finally, support vector machine (SVM) and RF classifier are used to identify benign and malignant pulmonary nodules. The 1036 pulmonary nodules in the LIDC-IDRI database are used for experimental verification. Classification accuracy, sensitivity, specificity, and area under the receiver operating characteristic (ROC) curve (AUC) of the proposed method can reach 94.98%, 90.02%, 97.03%, and 97.43%, respectively. The proposed method can accurately distinguish benign and malignant lung nodules, more effectively than most existing mainstream methods, as shown by the experimental results.

The separation of coal gangue from coal is of great significance for environmental protection and resource-saving. Therefore, this article proposes an intelligent separation method for coal gangue based on multi-spectral imaging technology and object detection. First, a multi-spectral data acquisition system for coal and coal gangue is set up in the laboratory, and 850 groups of multispectral data are collected. Second, by studying the coal gangue recognition rate and the correlation of each band of multi-spectral data, three bands from 25 bands are selected to form a pseudo-RGB (Red, Green, and Blue) image. Finally, the improved object detection model YOLO v4.1 is used to detect coal gangue. Experimental results show that the the mean average precision of YOLO v4.1 for coal and coal gangue detection on the test set is 98.26%, and the detection time is about 4.18 s. The method can not only precisely identify coal and coal gangue, but also obtain their relative position and size, which is important for the seperation operation of coal gangue.

Based on the model of algae fluorescence yield and with the fluorescence saturation parameter Eσ as the judgment standard of saturated excitation light intensity, we proposed a self-adaptive method of excitation light intensity to accurately acquire the photosynthetic fluorescence parameters of different species of algae. The results show that with the self-adaptive method, the saturated excitation light intensity could be quickly and stably obtained in the seven species of algae, and the relative standard deviations (RSDs) of the adjustment results were all smaller than 2.5%. Furthermore, the effective light absorption cross-sections σPSII of the seven species of algae were measured by the tunable pulse laser induced fluorescence (TPLIF) technique based on the self-adaptive method, and the difference in the σPSII of different species of algae was analyzed. Finally, we measured the Chlorella samples at different growth stages through the TPLIF technique and recorded their fluorescence parameter Fv/Fm and relevant variation trend. It turns out that the recorded results are consistent with the measurement results of the photosynthetic activity analyzer Fast-Ocean, with the correlation coefficient being 0.9939. In conclusion, this study provides an effective way of saturation excitation for accurately measuring the photosynthetic fluorescence parameters of different species of algae at different growth stages (with obvious differences in growth status).

The wavefront errors (WFE) of optical freeform surfaces are complex, diverse and asymmetric. When the peak valley values of WFE meet the requirements, the corresponding optical modulation transfer function may not meet the requirements. Therefore, it is necessary to obtain the main optical performance parameters for evaluation. However, there is no special software to realize the mutual conversion between optical performance parameters. Based on the theory of Fourier optics and phase retrieval, the basic index evaluation system of optical performance is established in this work. The multi parameter evaluation of optical performance is realized by measuring a single optical performance parameter. The measurement cost is reduced and the measurement efficiency is improved. The correctness of the system is verified by simulation and experiment. The research results can provide theoretical guidance for surface error compensation and optical quality controllable manufacturing of free-form imaging surface imaging optical system.

An ultracompact refractive index sensor based on an integrated optical waveguide trench coupler is proposed herein. The structure includes incident, reflection, and transmission waveguides as well as a submicron-wide trench which is located at the intersection of the incident and the reflection waveguides. The guided wave in the incident waveguide occurs, and the frustrated total internal reflection at the sidewall of the trench makes it so that the light can be partly converted into a transmission wave through evanescent field coupling, while the other partial light will be reflected into the reflection waveguide. The intensity of the transmission light depends on the coupling efficiency of evanescent field, and the reflection light intensity depends on the refractive index of the trench, implying that this integrated optical waveguide trench coupler can be used as a micro/nanosensor for the real-time detection of liquid refractive index or solution concentration. Herein, the new refractive index sensor based on the aluminum nitride rib waveguide is designed and verified via simulation. After the structural optimization, the refractive index sensor has a sensitivity of 207.05%/RIU.

In order to make the refractive index sensor has high quality factor and high sensitivity, a one-dimensional photonic crystal microring resonator based on a grooved optical waveguide is proposed. In this structure, the light modes of two different states interfere with each other in different optical paths to produce in Fano resonance. This asymmetric linear structure can obtain higher extinction ratio and quality factor, and it also has better sensitivity in refractive index sensing. The structure is analyzed and simulated by using finite-difference time domain method. The simulation results show that the quality factor of the proposed structure reaches 30950, which is more than 4 times higher than the traditional microring resonator, and the extinction ratio is 29.08 dB, which is 16.89 dB higher than that of the traditional microring resonator. In the analysis of refractive index sensing characteristics, the sensitivity of the proposed structure reaches 344 nm/RIU, which is 3 times higher than of traditional microring resonators, and the lower limit of sensitivity detection is 1.4×10 -4 RIU.

To design and fabricate a high-speed swept source, we built a short ring cavity based on a fiber Fabry-Perot tunable filter and a semiconductor optical amplifier. First, by on-off control on the semiconductor optical amplifier, a swept laser beam with a duty cycle of 50% was obtained. Then, the beam was subject to staggered superposition after it was divided into two beams by an interleaver, and thus we attained a swept laser beam with a duty cycle of 100% and a swept frequency twice the vibration frequency of the tunable filter. Finally, after re-amplification via a secondary semiconductor optical amplifier, the beam achieved higher power. Specifically, the swept laser beam obtained in this study featured a swept frequency of 245 kHz, a center wavelength of about 1544 nm, a sweep range of 73 nm, an effective coherence length of 12 mm, and average output power of more than 20 mW. In conclusion, the design scheme adopted in this study has important practical significance for the fabrication of a high-speed swept source with high performances and low costs.

The uniformity of irradiance intensity is an important parameter of a solar simulator. There are some problems, such as designing complexity and high cost, in the process of using an optical integrator to obtain uniformity light. The microsphere surface reflective lens is pressed by the ultra-efficient mirror with the moulds prepared by three-dimensional printing technology. A new type of uniform light device is composed of two microsphere surface reflective lenses and a cylindrical light pipes. The non-uniformity of irradiance intensity of a light spot with a 150 mm diameter is 1.12% obtained by the principle of diffuse reflection of light. The result reaches the A level of IEC 60904-9. The new type of uniform light device has some characters such as simple structure, high utilization rate of light source, and low cost.

The wxAMPS software is used to simulate the GaN/Si single heterojunction solar cells, and the effects of doping concentration, thickness, and temperature of each layer on the battery open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (F) and conversion efficiency are investigated. The simulation results show that as the acceptor concentration in the Si layer increases, JSC decreases, but all of VOC, F, and conversion efficiency increase. When the doping concentration of GaN is 5×10 18 cm -3 and the doping concentration of Si is 5×10 19 cm -3, the conversion efficiency of the ultra-thin cell with a Si layer of 16 μm thickness can reach 16.91%. As the thickness of the Si layer increases, all of VOC, JSC, F, and conversion efficiency increase. When the thickness of the GaN layer is 0.005 μm and the thickness of the Si layer is 100 μm, the efficiency can reach 24.58%. The simulation results show that when the thickness of the GaN/Si single heterojunction solar cell is 60% of the thickness of the current most efficient silicon-based solar cell, the efficiency of the former can reach 92% that of the latter. The research results are helpful to fabricate high-efficiency GaN/Si single heterojunction solar cells.

In this paper, we established a double-layered spherical model of tissues with an inserted optical fiber, considering that a finite-diameter photon beam was emitted from the optical fiber embedded in the tissue during the laser-induced interstitial thermotherapy (LITT). Firstly, based on the Monte Carlo method, we obtained the absorption of an infinitely narrow beam in the tissue. Then, we attained the light transmission equation of a finite-diameter photon beam through the convolution between the incident light intensity and the Green's function. Finally, taking a Gaussian beam and a flat-topped beam as examples, we compared the changes in the absorption of the finite-diameter photon beam with or without considering the inserted optical fiber. The results show that the absorption of tissues for the flat-topped beam is smaller than that for the Gaussian beam. Besides, the influence of the inserted optical fiber on the absorption of the flat-topped beam is smaller, whereas its influence on the absorption of the Gaussian beam near the photon emission center is larger. Therefore, the influence of the inserted optical fiber on the absorption of light energy of tissues should be considered in LITT using the Gaussian beams. The proposed model follows the actual situation of LITT, which is of great significance for accurately predicting the thermal damage range of LITT.

In order to solve the problems of thick lens thickness and uneven illumination in conventional irradiance illumination systems, a double freeform-surface lens with a distance to height ratio (DHR) of 3 is designed. According to the energy mapping theory, the light source and the target surface are meshed, the edge-ray theory and Snell's law are used to construct the double freeform-surface lens, and the actual light source is used for simulation. Compared with the single freeform-surface lens, the thickness of the double freeform-surface lens is reduced by 2.95% and the transverse size of the lens is reduced by 10.50%. The complementary feedback correction method is used to optimize the lens. The optimized single and double freeform-surface lens have 80.48% and 87.05% illumination uniformity, respectively, and the energy utilization rate is 88.61% and 91.23%, respectively. Compared with the single freeform-surface surface lighting system, the optical performance of the double freeform-surface lens is improved. For the lighting system with high DHR and small lens size, higher illuminance uniformity and energy utilization can be achieved.

In the existing studies, the Markov process model without memory effects is usually used to describe the random degradation of optoelectronic equipment, ignoring the long-term correlation of states in the degradation process. In view of this, we firstly proposed a random degradation model with memory effects based on nonlinear fractional Brownian motion to describe the degradation process of optoelectronic equipment under the influence of measurement errors and random effects. On this basis, we employed the weak convergence theory to derive the approximate analytical formula of the remaining useful life of equipment in the sense of the first hitting time. Secondly, we adopted the maximum likelihood estimation algorithm and Bayesian inference to complete the offline estimation and real-time update of the model parameters, thus realizing the adaptive prediction of the remaining useful life. Finally, the proposed method was applied to the performance monitoring data of GaAs lasers. The experimental results show that the proposed method can effectively improve the prediction accuracy of the remaining useful life of optoelectronic equipment.

There is much difference between the measurement results of polycrystalline powder pellets and single crystals. The infrared transmission spectra of single crystals can't be obtained from the powder pellets and there is an abnormal transmission peak in the infrared cut-off band on the spectra of polycrystalline powder pellets. The above phenomena are analyzed in principle. In this work, by simplifying the theoretical model of infrared dielectric properties of crystals, a method for measuring infrared dielectric properties of crystals based on transmission spectra of polycrystalline powder pellets is proposed. The infrared dielectric properties of AgGaS2 and ZnGeP2 crystals, such as infrared cut-off wavelength and long optical phonon transverse mode frequency, have been measured by this method. The results are in good agreement with those of single crystals. This study is of great value for screening high-quality materials in the exploration of new infrared functional crystals.

In its practical applications, quantum key distribution is affected by the finite detector dead time. When the signal pulse transmission rate is too large, the probability of detector's measurement failure increases and the security key generation rate decreases. In this paper, the finite detector dead time problem is analyzed for measurement-device-independent quantum key distribution under the heralded pair coherent state photon source. The relationship between the security key generation rate and the signal transmission rate is studied and simulated. Considering the detector's dead time, the secure key generation rate of the measurement-device-independent quantum key distribution protocol based on the heralded pair coherent state photon source is higher than that of the measurement-device-independent quantum key distribution protocol based on the weak coherent state photon source. In addition, the security key generation rates are analyzed with the respective finite detector's dead time τ of 50, 100, and 150 ns. The results show that the higher the detector's dead time is, the lower the limit value of the security key generation rate is. The relation between the limit value of the security key generation rate and the finite detector's dead time is 8.1×10 3/τ.

In this paper, a TiO2 film/tin-diffused glass composite optical waveguide (OWG) component is prepared by the dip-coating method, and a zinc phthalocyanine (ZnPc) sensitive layer is fixed on the surface by the spin coating method to prepare a highly-sensitive hydrogen sulfide (H2S) gas sensor based on a composite OWG. The preparation conditions of sensors is optimized. When the dip-coating speed of the dip coater is 80 mm·min -1, the rotating speed of the spin coater is 1600 r·min -1, and the mass fraction of the ZnPc solution is 0.05%, the sensor has the best selective response to H2S gas and can detect the H2S gas with a volume fraction of 1×10 -9. In addition, the sensor shows good stability within one month.

The fusion of a vision sensor and LiDAR can achieve a simultaneous localization and mapping (SLAM) system superior to a single sensor. However, the existing vision and LiDAR fusion algorithms still have such problems as high computational complexity and the system accuracy and stability susceptible to wrong depth matching. In order to combine vision and LiDAR information more efficiently and robustly, we made full use of ground plane information in the images and LiDAR point clouds, and proposed an efficient SLAM algorithm of vision-assisted LiDAR. Firstly, the ground point cloud was segmented from the laser point cloud to extract the ground ORB feature points in the images, and feature matching was verified by the cross-ratio invariance in the homography transformation. In this way, the absolute scale motion estimation of camera was realized efficiently and robustly via the homography matrix decomposition. Then, the obtained motion estimate of the camera was interpolated in the form of Lie group SE(3) to correct the point cloud distortion generated by the LiDAR during its own motion. Finally, the motion estimate of the monocular camera was taken as the initial value for the position optimization of LiDAR odometry. The test results of KITTI, a public data set, and the actual environment show that the proposed algorithm can effectively employ the motion estimate of the camera to correct the point cloud distortion of LiDAR and achieve odometry and mapping in real time and accurately.

In order to explore the scattering hygroscopic growth characteristics of haze particles caused by hygroscopicity, based on the humidity growth model of haze particles, we used the Mie scattering theory and multi-sphere T-matrix calculation method to study the scattering hygroscopic growth characteristics of five typical kinds of haze particles and their clusters when the incident wavelength was 532 nm and the relative humidity range was 60%-95%. The results demonstrate that for a single kind of haze particle, secondary water-soluble inorganic particles and clusters, such as sulfuric acid, ammonium sulfate, and ammonium nitrate, show prominent scattering hygroscopic growth. In comparison, the scattering hygroscopic growth is gentle for dust and inhibitory for carbonaceous aerosols. Meanwhile, the scattering hygroscopic growth of small particles is exponential, while that of large particles fluctuates with a negative growth trend. For the clusters of haze particles, the curve of scattering hygroscopic growth factor exhibits a declined overall increment. The volume fraction of the particle clusters has an obvious effect on the scattering hygroscopicity. Moreover, with an increase of the volume fraction, the curve of scattering hygroscopic growth factor has a higher fluctuation frequency and a smaller amplitude. However, the overall hygroscopic growth is determined by the size range and composition of cluster particles, and the size range of clusters has a greater impact. In conclusion, this study provides theoretical support for the research on the scattering hygroscopic growth characteristics and air pollution of haze particles.

Methane (CH4) is the main component of mine gas and one of greenhouse gases, and the measurement of CH4 concentration is of great significance for industrial production safety and human health security. In this paper, an on-beam quartz tuning fork enhanced photoacoustic spectroscopic system for CH4 detection was proposed, and a quartz tuning fork with a high quality factor was used to overcome the shortcomings of the traditional photoacoustic spectroscopy where microphones were susceptible to environmental noise. Furthermore, a miniaturized gas chamber with a volume of only 3 cm×2 cm×1 cm was developed, which simplified the structure of the detection system. Combining the wavelength modulation technology, we analyzed the relationship between the amplitude of second harmonic (2f) signal and the modulation depth. The experimental results demonstrate that the amplitude of optimal modulation signal was 0.175 V and the corresponding modulation depth was 0.169 cm -1. In addition, the CH4 volume fraction in the range of 5×10 -4-5×10 -3 and the 2f signal amplitude were fitted and their linearity was found to be 0.99791. Besides, the stability of the system was analyzed based on Allan variance. When the average time was 5 s, the 1σ lower detection limit of the system was 4.337×10 -5. In summary, the photoacoustic spectroscopic gas sensor based on a small-volume photoacoustic gas cell has the advantages of small size, light weight and low cost, which is more suitable for portable sensing applications.

Considering the urgent demand for the characterization of chemical composition in the micro-zone of samples with complex morphology, we developed a confocal laser-induced breakdown spectroscopy (LIBS) microscope in this study. First, the microscope used the continuous laser reflected from a sample to construct a laser confocal system with high spatial resolution, ensuring accurate focusing and three-dimensional (3D) morphological measurement of the sample. Then, the LIBS signals were excited by common-path pulsed laser to achieve full-elemental detection of the sample, thereby realizing 3D elemental imaging with high spatial resolution and anti-drift properties. The experimental results show that the lateral resolution of multi-elemental maps can reach 10 μm, and the combined uncertainty of the system's spectral detection is 2.24%. Furthermore, 3D elemental maps were constructed after combining with the in-situ morphological information and LIBS information in the system. In conclusion, the system provides new perspectives for the chemical analysis of samples with complex morphology such as biological tissue and micro-nano materials.

ITO film, as typical antireflection film in crystalline silicon heterogeneous solar cells, has low UV transmittance and high near-infrared optical loss, which restricts the efficiency improvement of the solar cells. Therefore, triple-layer antireflection film was designed in this paper. Firstly, we simulated and analyzed the optical performance of the triple-layer antireflection film and the electrical characteristics of the corresponding solar cell by using optical film design software TFCalc, light ray tracing program (OPAL 2), and solar cell simulation software PC1D. Then, the refractive-index dispersion effect, the surface morphology of crystalline silicon substrate, and the thickness tolerance of the films were discussed. The results show that the triple-layer antireflection film considering the refractive-index dispersion effect presented smaller parasitic absorption and larger antireflection bandwidth than ITO film. Besides, the weighted average optical loss of the triple-layer antireflection film on textured silicon was 2.43 percentage points lower than that on planar silicon, and the short-circuit current density and conversion efficiency of the corresponding solar cells were increased by 0.82 mA/cm 2 and 0.34 percentage points, respectively. In addition, the SiOx films with low refractive index had a larger thickness tolerance range.