The atomic fountain clock is one cold atom applied apparatus possessing important applications. Compact laser system design is one of the key techniques for a portable cold atomic fountain clock. This paper introduces a gridded optical platform built with the general aluminum profiles, and based on it, we construct a compact optical path for the 85Rb fountain clock. Through simulation, it is proved that the profile gridded platform has better mechanical properties in two-dimensional direction. On this platform, we design and build the modules of such as four-pass frequency shift, injection locked amplifier, cooling optical path, repumping and probing paths to satisfy all requirements of an atomic fountain clock. The platform covers an area of 50 cm×50 cm and has a height of 2.5-3 cm. The optical path has been running continuously for more than 8 months with a power fluctuation less than 5%. Based on the compact optical system, we have completed the subsequent physical and microwave experiments of 85Rb fountain clocks.

We investigate the device properties of In0.53Ga0.47As/InP avalanche photodiodes (APDs) with different multiplication layer thicknesses of 1.5, 1.0 and 0.8 μm by the Zinc diffusion method. The punch-through voltage and the breakdown voltage increase with the increase of the multiplication layer thickness. On the basis of the simulation by the Silvaco software, the influences of the multiplication layer thickness on the electric field, current-voltage characteristics, breakdown voltages and punch-through voltages are studied. As the multiplication layer thickness increases, the electric field intensity decreases, in contrast, both of the punch-through and breakdown voltages increase,which are consistent with the experimental results. A further study shows that when the multiplication layer thickness is smaller than 0.8 μm and as the multiplication layer thickness increases, the breakdown voltage first decreases and then increases, while the punch-through voltage monotonically increases.

In this study, a novel immunosensor based on graphene-oxide (GO)-encapsulated Au-nanoshell (EGO-AuNS)-coated long-period fiber grating (LPFG) is presented for avian influenza virus (AIV) detection. The EGO-AuNS composites were obtained by coating GO on the surface of AuNS via electrostatic bonding, and immobilized on the surface of LPFG via covalent bonding using a silane coupling agent. Then, AIV monoclonal antibodies (AIV-MAbs), which serve as specific biomolecule recognition units, were fixed on the grating surface to realize the EGO-AuNS-LPFG immunosensor. The experimental results indicate that the refractive index (RI) sensitivity of the EGO-AuNS-LPFG immunosensor is -66.60 nm/RIU when RI is from 1.333 to 1.411, which is six times greater than that of the LPFG-based sensor. Based on the detection of AIV antigen solutions with different concentrations, the limit of detection of the immunosensor is observed to be approximately 8 ng/mL. Further, the immunosensor becomes saturated at approximately 50 μg/mL and exhibits a linearity sensitivity of approximately 2946.25 pm/(μg·mL -1), which is 7.3 times greater than that of the GO-coated cladding-etched LPFG immunosensor. Based on the detection results of several allantoic fluids, the proposed immunosensor exhibits good specificity and clinical effectiveness. Furthermore, it exhibits considerable promise for application in the biomedical field.

A novel strain sensor based on a weakly coupled fiber structure with three tapered cores is proposed. This structure comprises two thin-core fibers and a tapered three-core fiber, in which the tapered three-core fiber is sandwiched between two thin-core fibers. The strain and temperature characteristics of the sensor were studied using various lengths of the tapered three-core fiber. The results show that the interference spectrum of the sensor is blue-shifted with increasing strain in the range of 0--1600 με. With a three-core fiber length of 7.4 cm and a cone diameter of 41.20 μm, the maximum strain sensitivity is -3.47 pm/με, and the linearity is 0.9876. At the same time, we also investigated the temperature sensing characteristics. In the temperature range of 25--60 ℃, the temperature sensitivity of the sensor is 34.52 pm/℃, and the linearity is 0.9979. The cross-sensitivity is 9.95 με/℃. The proposed sensor has the advantages of low cost, simple structure, and wide measurement range, and has potential applications in fields such as industrial production and construction monitoring.

In this paper, a low-complexity, sparsity adaptive compressed sensing algorithm is proposed based on fingerprint localization of visible light communication. First, the localization problem is transformed into a sparse matrix reconstruction problem based on the sparsity of location fingerprints. Second, the nearest neighbor value is adaptively calculated based on the reconstructed residual value. Finally, the impact of fingerprint sampling interval, signal-to-noise ratio, modulation bandwidth, and transmission power on positioning errors are analyzed in detail. Moreover, the time complexity, distribution of the optimal nearest neighbor values, number of the light-emitting diodes, and maximum number of nearest neighbor fingerprints of the proposed positioning algorithm on positioning errors are also analyzed. The simulation results show that the proposed positioning algorithm has comparatively low average calculation time and small positioning error. When the signal-to-noise ratio and the distance between the fingerprints are 10 dB and 40 cm, respectively, the average positioning error of the proposed positioning algorithm is 1.56 cm, which is significantly lower than those of existing algorithms.

In this article, we study the visible light communication system based on light-emitting diode(LED)indicator. In the transmitter, we employ the hard drive indicator of an embedded personal computer to build a hardware experimental platform. We statistically collect and analyze data to obtain the parameters of the signal model. In the receiver, we employ the single-photon avalanche diode (SPAD) as the receiver to improve the sensitivity of the receiver and extend the communication distance of the system. To solve the problem of clock drift, we propose a pulse width long-short keying (PWLSK) modulation scheme to replace the traditional on-off keying (OOK) scheme; we verify the scheme by hardware experiments. The experimental results show that under the experimental conditions, the bit error rate (BER) of the OOK modulation scheme can not be reduced to below 10 -4, which is difficult to meet the communication requirements. Additionally, simulation experiments show that the OOK modulation is more sensitive to ambient light intensity, and can be reduced to 10 -5 only when the ambient light intensity is less than 1 lx, while PWLSK modulation scheme can reduce its BER in complex environments with higher ambient light intensity. Based on the above analysis, the proposed scheme can realize the transmission of instant message, file, or voice signal.

In 5G networks, user data will assemble larger packets through ultra-dense base stations. When these packets are amplified by erbium-doped fiber amplifier (EDFA) in the dense wavelength division multiplexing (DWDM) system using an asynchronous switching system, interchannel crosstalk will occur and the bit error rate (BER) of the data packets will be deteriorated. Based on the measurement of gain recovery time of EDFA, the BER deterioration is studied in depth. The calculation formula of BER caused by crosstalk is derived, and the factors that influence BER are discussed. An experimental device of large data packet crosstalk is set up. Both theoretical and experimental results show that the greater the packet length and optical power of the data packet in one channel, the greater the effect on the BER of the data packet in another channel. When the packet length is less than 5 μs, the effect of crosstalk on the BER is negligible.

We propose an implementation scheme for generating orthogonal frequency division multiplexing (OFDM) vector millimeter-wave (mm-wave) based on two parallel phase modulators (PMs). Compared with previous schemes, the proposed scheme only needs two PMs without complex circuits to control the direct current bias of the modulator and precoding technology, which greatly reduces the complexity of the transmitter and the system cost. The OFDM vector signal and radio frequency (RF) signal are generated by digital signal processing (DSP) module to ensure the flexible adjustment of RF signal frequency. In the DSP module, one up-converted OFDM vector signal and the unmodulated radio frequency signal are transformed by Hilbert transform to obtain the dual single sideband (SSB) signals, respectively, which drive phase modulators. An optical interleaver is used to filter out optical carriers, and a high-speed photodetector is used to obtain the OFDM vector mm-wave signal through beat frequency. Based on the proposed scheme, we demonstrate the generation of a 50-GHz quadrature phase-shift keying (QPSK)-modulated OFDM vector mm-wave signal by simulation with the MATLAB and the optical communication commercial software. The measured results versus received optical power and phase deviation drift are analyzed. The results show that the bit error rate of the transmission system is less than the hard decision forward error correction threshold of 3.8×10 -3, which shows that the scheme of OFDM vector mm-wave signal generation is feasible.

Based on the comparison test platform of the dual-axis tracking trough solar system, the effect of the dust accumulation on the photothermal performance of the trough solar energy system is studied through theoretical analysis and experimental tests. The dust reflection factor and correction coefficient of the acquisition factor are introduced to quantify the effect of dust accumulation on the photothermal performance of the system. The results show that the dust on the condenser has a significant effect on the concentrating characteristic of the focal plane. The uneven distribution of the dust causes more serious scattered radiation. As the amount of dust increases, the energy obtained by the focal plane within a certain size decreases. The energy flux density at the center of the focal plane is reduced, and the receiver with small aperture is more sensitive to the change of energy that can be collected on the focal plane. To ensure the correction coefficient of the acquisition factor of the trough concentrator is greater than 0.90, the dust reflection factor should be less than 4.3%. A prediction model of the effect of dust accumulation on the heat collection performance of the trough solar system is established and verified by the experimental test. The relative error between the predicted value of the model and the experimental value is less than 5.07%, and the good agreement between them is obtained. This prediction method has good universality and can provide theoretical guidance for practical engineering applications.

In this paper, we propose a cascade multi-scale information fusion generative adversarial network (CMIF-GAN) for infrared image simulation, which can estimate the infrared map from a visible image. Inspired by the connections and differences between visible and infrared features, CMIF-GAN adopts a cascaded structure composed of two levels of adversarial networks. With a large overall receptive field, the first-level adversarial network focuses on reconstructing structural information of the infrared image, and adds a semantic segmentation image task as auxiliary information. To enrich detailed texture information of the infrared image, the second-level adversarial network uses the grayscale inverted visible (GIV) images as auxiliary information and adopts a small overall receptive field network. Otherwise, the second-level adversarial network can integrate the multiple receptive information by a multi-scale fusion module (MFM) to improve algorithm accuracy. Experiments on public dataset demonstrate that CMIF-GAN can efficiently translate visible images to corresponding infrared images, and outperform previous methods in objective metrics and subjective vision.

Intensity saturation zone in the fringe pattern will appear when fringe projection profilometry is used to measure objects with high dynamic range reflectivity, which will affect the phase reconstruction of the tested object. In this paper, we proposed a fringe pattern inpainting method based on convolutional neural network (CNN) denoising regularization. Two fringe patterns under normal and short exposure time are respectively captured to quickly build a fringe with good quality using following steps. Otsu threshold method is used to determine highlight region by treating the modulation information of short exposure fringe pattern. Set an initial value for iteration by fusing the normal exposure fringe pattern with gray-adjusted short exposure fringe pattern. Realize fast fringe pattern inpainting using CNN denoising regularization and finally obtain a fringe to realize the high dynamic range phase reconstruction. Compared with other methods, the proposed method has advantage in effect and time of fringe inpainting.

The process of training a deep learning model requires many annotation samples, even though annotation data is difficult to obtain in the medical field. A self-supervised learning algorithm combined with partial annotation data is proposed as a solution to this problem, in order to improve classification performance of 3D pulmonary nodules. Based on the traditional self-supervised training network structure, a multitask learning network structure is designed to address a large amount of unannotated data and a small amount of annotated data obtained from medical image processing tasks. First, the proposed algorithm trains the unannotated data, and then explores the annotation data to continuously train the model. Thus, this algorithm manages to share partial network structures and parameters between the annotated and unannotated data. Compared to traditional self-supervised learning methods, the proposed algorithm can learn to recognize the discriminant features of pulmonary nodules to ensure the model's capacity to generalize, therefore, model transfer learning can also perform better when applied to the classification of pulmonary nodules. The classification accuracy of the proposed algorithm on LIDC-IDRI dataset is 0.886, and the area under the curve (AUC) is 0.929. The results of the investigation indicate that the proposed algorithm can effectively improve classification performance of pulmonary nodules.

The iteration progress of coherent modulation imaging (CMI) is equivalent to gradient search algorithm, and a CMI convergence model is established. From the perspective of solving equations, the basic conditions to ensure the uniqueness of reconstruction results are put forward, i.e., the number of non-zero points of the diffraction pattern with a modulation plate is twice as much as that without the modulation plate, or the ratio of the spectrum cut-off width after enlarging λL (λ is the wavelength and L is the diffraction distance) times with the modulation plate to the spectrum cut-off width without the modulation plate is at least 0.414. It is verified by simulation. This study provides a theoretical basis for further optimization of CMI.

In order to clarify the working mechanism of the image field modulated Fourier transform imaging spectrometer, we establish the theoretical model of an image field modulated interference imaging spectrometer by analyzing the phase modulation characteristics of the imaging field induced by a multi-micro-mirror. The numerical calculation shows that the panoramic image of the target scene can be reconstructed by image shearing and image splicing on the obtained interference image data cube. In addition, the spectral information of each target point in the scene can be recovered by fringe splicing and spectral demodulation on the sheared interference image unit. In order to verify the working principle of this instrument, we conduct the interference imaging scanning experiment of the target scene with the developed prototype and obtain the interference image data cube of the scene target. Through the edge detection and feature registration on each frame interference image, we realize the shearing of the interference image unit and the splicing of the panoramic image. Meanwhile, by means of fringe splicing, baseline correction, addressing apodization, and discrete Fourier transform, we recover the spectrum of the feature object. Finally, the recovered spectrum is optimized by means of non-uniform sampling correction and empirical mode decomposition, and the spectral performance is effectively improved.

To solve the problem that a methane telemetry device can not be dynamically adjusted when it is used in different detection environments due to its fixed optical collimation, an electronically controlled zoom lens is introduced into the optical path collimation design to achieve automatic optical path collimation. Test results show that for different detection distances and auxiliary targets, the fast zoom can be achieved by changing the driving current of the electronically controlled zoom lens. The receiving optical power of the telemetry device can be maximized while dynamically adjusting the laser beam divergence effect. Compared with the non-zoom lens, the receiving optical power can be increased by more than 1.7 times, and the signal-to-noise ratio of the detection system is improved. In view of the new problems of the zoom lens in telemetry applications, such as beam deflection caused by the gravity effect, a deformation model is proposed, and theoretical calculation and simulation analysis are carried out. A methane gas bag is used to conduct a leak simulation test. Through the Allan variance analysis, we obtain that when the integration time is 18 s, the limit standard deviation is 1.51×10 -6. The field measurement for the device is conducted, the test distance is 52.2 m, and the methane gas with the concentration (volume fraction) of 4.95×10 -6 is detected in the corridor air. The research demonstrates the feasibility and the application value of using an electronically controlled variable focus lens to realize automatic collimation and optimization of the optical path in a gas leakage telemetry device.

A color-camera-based shearography system using dual-wavelength lasers was developed for simultaneously measuring the in-plane and out-of-plane displacement derivatives of a deformed object. Lasers of dual wavelengths are arranged to symmetrically and simultaneously illuminate on the object with identical angles of incidence. A set of phase-shifter and a modified Michelson interferometer are used to build a temporal-phase-shift dual-wavelength shearography. The interferograms formed by the two wavelength are recorded by one 3-chip color camera with green and blue channels. The phases related to the in-plane and out-of-plane components are extracted from the shearograms by using Carré algorithm. Experiment on a cantilevered aluminum beam deformation was performed to verify the feasibility and the capability of the testing system.

Point cloud segmentation is a key step in point cloud processing, and its segmentation quality determines the accuracy of target measurement, pose estimation, and other tasks. This paper proposes a method of depth image (RGB-D) point cloud segmentation using spatial projection. Based on the camera model, RGB-D data characteristics, and the relationship between the image threshold and the target point cloud, a target coordinate system and point cloud regions are established. Further, based on the target coordinate system and the image threshold, the point cloud is transformed to the target coordinate system to highlight the target region and weaken the background region. Also, the projected pixel values are processed by image morphology and the corresponding point cloud region is obtained by segmenting the image. Finally, three test scenarios are established to acquire three different groups of point cloud data, and four methods are adopted to segment and compare point clouds. The spatial projection based method can obtain better point cloud segmentation quality. The relationship among the expansion element, numerical value, and segmentation quality is tested and analyzed. The results show that the spatial projection method is effective and feasible for RGB-D point cloud segmentation.

Traditional off-axis reflecting optical antennas have the disadvantage of short exit pupil distance, leading to the fact that a relay optics is required to re-image the exit pupil on the fast steering mirror and thus the following optical paths and structures are complicate. Moreover, the backward scattering light in the relay optical system has a severe influence on the laser communication terminals. To overcome the above defects, we design an off-axis four-mirror optical antenna, in which the exit pupil of optical antenna is directly designed on the fast steering mirror and thus the relay optical system can be removed. First, the aberration formulas and the initial structural equation are deduced based on the theory of coaxial three-mirror aberration. Then, the initial structural parameters of the off-axis four-mirror optical antenna are calculated according to the aberration theory and the requirement of the exit pupil position. In addition, the ray tracing and the performance optimization of the initial structure are implemented using the Zemax software. Finally, the tolerance analysis of the off-axis four-mirror optical antenna is conducted. The results illustrate that the designed system has the advantages of excellent performance, compact structure, and reasonable manufacture and alignment tolerance. The performance of the designed system can meet the requirements of laser communication terminals.

The traditional plant lighting design only optimizes the uniformity of a certain reference surface, which leads to the unevenness of the light environment in the plant growth space. In order to solve this problem, we conduct the research based on the spatial illunimation uniformity evaluation system. First, three potential design schemes are proposed for the stereo plant light sources with high spatial illumination uniformity, and the effect of structural parameters on illumination is studied with the help of the TracePro commercial simulation software. Further, the Taguchi method is used to optimize the experimental process and the optimal structural parameters are obtained with the ANOVA analysis. Then, the illumination effect during plant growth is tested based on the obtained optimal solution. Finally, the technical advantages of the stereo light source system compared with the traditional array LED light source are introduced. The experimental results show that the optimal structure can provide a uniform illumination space with illumination uniformity of horizontal planes and illumination uniformity of vertical planes of 92.00% and 83.12%, respectively, and with the red and blue color-mixed uniformity of two spatial reference planes of 94.19% and 90.70%, respectively. The plant light source system can meet the need of a uniform spatial illumination environment during plant growth.

To cool a mechanical resonator to its ground-state is the key to realize the quantum manipulation of this mechanical resonator. We propose a cooling method based on electromagnetically-induced-transparency (EIT) and investigate the ground-state cooling of a mechanical resonator in a three-Laguerre-Gaussian-cavity optomechanical system, where two auxiliary cavities are coupled to the original one in the standard optomechanical system, respectively. When the optimal parameters are chosen, the optical fluctuation spectrum changes from Lorentzian shape to EIT-like one in a three-level atomic system. The asymmetry between cooling and heating rates makes it possible to realize the ground-state cooling of a mechanical resonator. The research results here provide a theoretical guidance for the cooling of mechanical resonators in three-Laguerre-Gaussian-cavity systems.

FY-3B medium resolution imaging spectrometer (MERIS) cannot achieve the absolute calibration for the visible and near-infrared bands. To improve the MERIS absolute calibration accuracy, the six widely used north African desert pseudo-invariant targets are adopted herein, taking the advantage of the high-quality SeaWiFS data to construct the bidirectional reflectance distribution function(BRDF) model and then using the MODTRAN radiative transfer model and ERA-Interim absorption gas reanalysis data to construct the spectral band adjustment factor (SBAF). Lastly, five years of FY-3B MERIS data are used for the cross-calibration. The constructed BRDF model in this study can accurately express the top of atmosphere (TOA) reflectance (ρTOA) over the pseudo-invariant targets, and the prediction error is basically within 3%. The TOA reflectance of MERIS can be effectively predicted through the parameterized SBAF which considers the observation geometry and absorbed gas content. Cross-calibration results show that the time series are extremely stable and have no obvious trends, which are consistent with the characters of TOA reflectance over pseudo-invariant targets. Compared with the operational calibration results of MERIS L1, the cross-calibration results of bands 8--12 are lower and the bias is less than zero, whereas for bands 13--16, the results are higher and the bias is greater than zero. Except for band 8, the biases of the other eight bands are within -5%--5%. The monthly mean deviation of bands with a wavelength less than 600 nm are larger, particularly the three blue bands (bands 8--10). The monthly mean relative deviations of bands 13--16 are relatively stable, and they are basically within -5%--5%.

Geosynchronous orbit (GEO) space is an ideal place for the synthetic aperture ladar (SAL) technology because there is no atmospheric interference and no attenuation and wavefront distortion during beam transmission in it. A space-borne SAL can provide the optical image of a GEO target with ultra-diffraction-limited resolution. To realize this aim, we establish the theoretical model of space-borne SAL imaging based on optical heterodyne detection and investigate the imaging data processing methods related to the orbital parameters, using the three-dimensional coordinate relationship between the space-borne SAL and the GEO target moving along different circular orbits around the earth's core under the effect of universal gravitation. The research results show that the space-borne SAL can produce super-diffraction-limit imaging of a GEO target using the gravitational orbital motion. Besides, the changes of orbit radius, orbital plane angle and imaging position show certain influence on the processing of imagining data, reduce imaging resolution and result in the geometric deformation of the focused image. Moreover, the position near the intersection points is the best position for space-borne SAL imaging, where the distance between the space-borne SAL and the GEO target is small, and thus the geometric deformation of focused images is small and the imaging resolution is high.

Tasks such as global mapping and overseas target positioning have the higher and higher requirements for space remote sensing geometric calibration and positioning accuracy. The current measurement error of the image pixel coordinates does not match the accuracy of the ground control points (GCP), which limits the reliability of the calibration results of the space sensors. The point source target has a good geometry in the aerospace image and can provide precise pixel coordinates for the geometric calibration task. In this paper, the pixel coordinates of the simulated point source images are solved, and the errors the pixel coordinates are below 0.04 pixel and the root mean square error is only 0.01 pixel, superior to those by the current measurement software and the manual selection. In addition, the effect of pixel measurement error on the calibration and positioning results is examined. The results show that the use of point source target as GCP can make the calibration parameter and positioning accuracy better than those using the traditional GCPs. In the absence of GCPs, adding two point source targets can reduce the positioning error to the decimeter level. The point source target can effectively improve the accuracy of geometric calibration and positioning results and has the potential to develop into a new generation of geometric calibration tools.

In this study, the Pd/BiF3 thin films are successfully prepared by the facile in-situ electrochemical-photoreduction method from the Bi plates, and the photocatalytic performances of the BiF3 thin films with different mass fractions of Pd are investigated for comparison. The Pd/BiF3 thin films are characterized by the XRD, SEM, XPS and UV-Vis DRS methods. The photocatalytic performance of Pd/BiF3 thin films is investigated with rhodamine B (RhB) as the photocatalytic degradation object. Our characterization results indicate that when the noble metal Pd is loaded uniformly on the surface of BiF3 thin films and the mass fraction of Pd is 2.0%, the Pd/BiF3 thin films exhibit the optimal photocatalytic activity and stability for the degradation of RhB. In addition, there exist an obvious redshift of optical absorption bands and a decrease of bandgap from 3.70 eV to 3.03 eV. The capture experiment of active species confirms that when the mass fraction of Pd is 2.0%, the roles of the ·OH, · O2- and h + are from large to small during the photocatalytic degradation of RhB by Pd/BiF3 films. Finally, an enhancement mechanism of photocatalytic performance of Pd/BiF3 thin films is proposed.

Variable energy X-ray imaging technology is an important method to realize the internal information detection of large thickness ratio targets. This method can use the gradually changing tube voltage to obtain the trans-illumination sub-graphs of different thickness regions in the workpiece, and then the high dynamic range digital image, which can completely represent the structural information of the workpiece, is realized by fusion. However, due to the limited dynamic range of the display device, the details in the fused high dynamic range X-ray image cannot be displayed effectively. In view of the above problem, we use the characteristic that one X-ray image mainly shows the information of a mutation structure and propose the algorithm based on nonlinear enhancement of image gradients. This algorithm uses the gray-scale change information in the enhanced image to achieve image enhancement and meanwhile is combined with the multi-resolution characteristics of the image to realize the enhancement and fusion of gradient images with different resolution levels, and thus the retention and enhancement of structural information with different degrees of change are realized. Finally, the experiment is designed to image a large thickness ratio target by variable energy X-ray and to enhance the fused high dynamic range image. The results show that this method can be used to effectively enhance the structural information of a high dynamic range image.