Quantum technology establishes a foundation for secure communication via quantum key distribution （QKD）. In the last two decades, the rapid development of QKD makes a global quantum communication network feasible. I...Quantum technology establishes a foundation for secure communication via quantum key distribution （QKD）. In the last two decades, the rapid development of QKD makes a global quantum communication network feasible. In order to construct this network, it is economical to consider small-sized and low-cost QKD payloads, which can be assembled on satellites with different sizes, such as space stations. Here we report an experimental demonstration of space-to-ground QKD using a small-sized payload, from Tiangong-2 space lab to Nanshan ground station. The 57.9-kg payload integrates a tracking system, a QKD transmitter along with modules for synchronization, and a laser communication transmitter. In the space lab, a 50MHz vacuum＋weak decoy-state optical source is sent through a reflective telescope with an aperture of 200mm. On the ground station, a telescope with an aperture of 1200mm collects the signal photons. A stable and high-transmittance communication channel is set up with a high-precision bidirectional tracking system, a polarization compensation module, and a synchronization system. When the quantum link is successfully established, we obtain a key rate over 100bps with a communication distance up to 719km. Together with our recent development of QKD in daylight, the present demonstration paves the way towards a practical satellite-constellation-based global quantum secure network with small-sized QKD payloads.展开更多
The gravitational wave spacecraft is a complex multi-input multi-output dynamic system.The gravitational wave detection mission requires the spacecraft to achieve single spacecraft with two laser links and high-precis...The gravitational wave spacecraft is a complex multi-input multi-output dynamic system.The gravitational wave detection mission requires the spacecraft to achieve single spacecraft with two laser links and high-precision control.Establishing one spacecraftwith two laser links,compared to one spacecraft with a single laser link,requires an upgraded decoupling algorithmfor the link establishment.The decoupling algorithmwe designed reassigns the degrees of freedomand forces in the control loop to ensure sufficient degrees of freedomfor optical axis control.In addressing the distinct dynamic characteristics of different degrees of freedom,a transfer function compensation method is used in the decoupling process to further minimize motion coupling.The open-loop frequency response of the systemis obtained through simulation.The upgraded decoupling algorithms effectively reduce the open-loop frequency response by 30 dB.The transfer function compensation method efficiently suppresses the coupling of low-frequency noise.展开更多
The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave...The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave infrared wavelengths as beacon light can reduce atmospheric absorption and signal attenuation.However,there are strong non-uniformity and blind pixels in the short-wave infrared image,which makes the image distorted and leads to the decrease of spot centroid positioning accuracy.Therefore,the high-precision localization of the spot centroid of the short-wave infrared images is of great research significance.A high-precision spot centroid positioning model for short-wave infrared is proposed to correct for non-uniformity and blind pixels in short-wave infrared images and quantify the localization errors caused by the two,further model-based localization error simulations are performed,and a novel spot centroid positioning payload for satellite laser communications has been designed using the latest 640×512 planar array InGaAs shortwave infrared detector.The experimental results show that the non-uniformity of the corrected image is reduced from 7%to 0.6%,the blind pixels rejection rate reaches 100%,the frame rate can be up to 2000 Hz,and the spot centroid localization accuracy is as high as 0.1 pixel point,which realizes high-precision spot centroid localization of high-frame-frequency short-wave infrared images.展开更多
For the first time, this article introduces a LiDAR Point Clouds Dataset of Ships composed of both collected and simulated data to address the scarcity of LiDAR data in maritime applications. The collected data are ac...For the first time, this article introduces a LiDAR Point Clouds Dataset of Ships composed of both collected and simulated data to address the scarcity of LiDAR data in maritime applications. The collected data are acquired using specialized maritime LiDAR sensors in both inland waterways and wide-open ocean environments. The simulated data is generated by placing a ship in the LiDAR coordinate system and scanning it with a redeveloped Blensor that emulates the operation of a LiDAR sensor equipped with various laser beams. Furthermore,we also render point clouds for foggy and rainy weather conditions. To describe a realistic shipping environment, a dynamic tail wave is modeled by iterating the wave elevation of each point in a time series. Finally, networks serving small objects are migrated to ship applications by feeding our dataset. The positive effect of simulated data is described in object detection experiments, and the negative impact of tail waves as noise is verified in single-object tracking experiments. The Dataset is available at https://github.com/zqy411470859/ship_dataset.展开更多
The encoding aperture snapshot spectral imaging system,based on the compressive sensing theory,can be regarded as an encoder,which can efficiently obtain compressed two-dimensional spectral data and then decode it int...The encoding aperture snapshot spectral imaging system,based on the compressive sensing theory,can be regarded as an encoder,which can efficiently obtain compressed two-dimensional spectral data and then decode it into three-dimensional spectral data through deep neural networks.However,training the deep neural net⁃works requires a large amount of clean data that is difficult to obtain.To address the problem of insufficient training data for deep neural networks,a self-supervised hyperspectral denoising neural network based on neighbor⁃hood sampling is proposed.This network is integrated into a deep plug-and-play framework to achieve self-supervised spectral reconstruction.The study also examines the impact of different noise degradation models on the fi⁃nal reconstruction quality.Experimental results demonstrate that the self-supervised learning method enhances the average peak signal-to-noise ratio by 1.18 dB and improves the structural similarity by 0.009 compared with the supervised learning method.Additionally,it achieves better visual reconstruction results.展开更多
The Visible and Near-Infrared Imaging Spectrometer （VNIS）, using two acousto-optic tunable filters as dispersive components, consists of a VIS/NIR imag- ing spectrometer （0.45-0.95 μm）, a shortwave IR spectromet...The Visible and Near-Infrared Imaging Spectrometer （VNIS）, using two acousto-optic tunable filters as dispersive components, consists of a VIS/NIR imag- ing spectrometer （0.45-0.95 μm）, a shortwave IR spectrometer （0.9-2.4 p.m） and a calibration unit with dust-proofing functionality. The VNIS was utilized to detect the spectrum of the lunar surface and achieve in-orbit calibration, which satisfied the re- quirements for scientific detection. Mounted at the front of the Yutu rover, lunar ob- jects that are detected with the VNIS with a 45° visual angle to obtain spectra and ge- ometrical data in order to analyze the mineral composition of the lunar surface. After landing successfully on the Moon, the VNIS performed several explorations and cal- ibrations, and obtained several spectral images and spectral reflectance curves of the lunar soil in the region of Mare Imbrium. This paper describes the working principle and detection characteristics of the VNIS and provides a reference for data processing and scientific applications.展开更多
We demonstrate a compact periodically poled MgO-doped lithium niobate（MgO：PPLN）-based optical parametric oscillator（OPO） quasi-synchronously pumped by a fiber laser system with burst-mode operation.The pump sourc...We demonstrate a compact periodically poled MgO-doped lithium niobate（MgO：PPLN）-based optical parametric oscillator（OPO） quasi-synchronously pumped by a fiber laser system with burst-mode operation.The pump source is a peak-power-selectable pulse-multiplied picosecond Yb fiber laser.The chirped pulses from a figure of eight-cavity modelocked fiber laser seed are narrowed to a duration of less than 50 ps using an FBG reflector and a circulator.The narrowed pulses are directed to pass through a pulse multiplier and to form pulse bunches,each of which is composed of 13 subpulses.The obtained pulse bunches are amplified by two-stage fiber pre-amplifiers：one-stage is core-pumped and the other is cladding-pumped.A fiberized acousto-optic modulator is inserted to control the pulse repetition rate（PRR） of the pulse bunches before they are power-amplified in the final amplifier stage with a large mode area（LMA） PM Yb-doped fiber.The maximum average powers from the final amplifier are 85 W,60 W,and 45 W,respectively,corresponding to the PRR of2.72 MHz,1.36 MHz,and 0.68 MHz.The amplified pulses are directed to pump an MgO：PPLN-based optical parametric oscillator（OPO）.A maximum peak power at 3.45 μm is obtained approximately to be 8.4 kW.Detailed performance characteristics are presented.展开更多
The Chang＇e-3 Visible and Near-infrared Imaging Spectrometer （VNIS） is one of the four payloads on the Yutu rover. After traversing the landing site during the first two lunar days, four different areas are detecte...The Chang＇e-3 Visible and Near-infrared Imaging Spectrometer （VNIS） is one of the four payloads on the Yutu rover. After traversing the landing site during the first two lunar days, four different areas are detected, and Level 2A and 2B ra- diance data have been released to the scientific community. The released data have been processed by dark current subtraction, correction for the effect of temperature, radiometric calibration and geometric calibration. We emphasize approaches for re- flectance analysis and mineral identification for in-situ analysis with VNIS. Then the preliminary spectral and mineralogical results from the landing site are derived. After comparing spectral data from VNIS with data collected by the Ma instrument and samples of mare that were returned from the Apollo program, all the reflectance data have been found to have similar absorption features near 1000 nm except lunar sample 71061. In addition, there is also a weak absorption feature between 1750-2400nm on VNIS, but the slopes of VNIS and Ma reflectance at longer wavelengths are lower than data taken from samples of lunar mare. Spectral parameters such as Band Centers and Integrated Band Depth Ratios are used to analyze mineralogical features. The results show that detection points E and N205 are mixtures of high-Ca pyroxene and olivine, and the composition of olivineat point N205 is higher than that at point E, but the compositions of detection points S3 and N203 are mainly olivine-rich. Since there are no obvious absorption features near 1250 nm, plagioclase is not directly identified at the landing site.展开更多
Yutu is the first lunar rover after the Apollo program and Luna missions. One of the payloads on the Yutu rover, the Visible and Near-infrared Imaging Spectrometer （VNIS）, has acquired four VIS/NIR images and SWIR s...Yutu is the first lunar rover after the Apollo program and Luna missions. One of the payloads on the Yutu rover, the Visible and Near-infrared Imaging Spectrometer （VNIS）, has acquired four VIS/NIR images and SWIR spectra near its landing site in Mare Imbrium. The radiance images were reduced through repairing bad lines and bad points, and applying flat field correction, and then were converted into reflectance values based on the solar irradiance and angles of incidence. A significant shadow effect was observed in the VIS/NIR image. The shadowed regions show lower reflectance with a darkening trend compared with illuminated regions. The re- flectance increased by up to 24% for entire images and 17% for the VIS/NIR-SWlR overlapping regions after shadow correction. The correction for the shadow effect will remarkably decrease the estimate of FeO content, by up to 4.9 wt.% in this study. The derived FeO contents of CD-005-008 after shadow correction are around 18.0 wt.%.展开更多
The influence of the single photon laser altimeter range-gate width on the detection probability and ranging accuracy is discussed and analyzed,according to the LiDAR equation,single photon detection equation and the ...The influence of the single photon laser altimeter range-gate width on the detection probability and ranging accuracy is discussed and analyzed,according to the LiDAR equation,single photon detection equation and the Monte Carlo method to simulate the experiment.The simulated results show that the probability of detection is not affected by the range gate,while the probability of false alarm is relative to the gate width.When the gate width is 100 ns,the ranging accuracy can accord with the requirements of satellite laser altimeter.But when the range gate width exceeds 400 ns,ranging accuracy will decline sharply.The noise ratio will be more as long as the range gate to get larger,so the refined filtering algorithm during the data processing is important to extract the useful photons effectively.In order to ensure repeated observation of the same point for 25 times,we deduce the quantitative relation between the footprint size,footprint,and frequency repetition according to the parameters of ICESat-2.The related conclusions can provide some references for the design and the development of the domestic single photon laser altimetry satellite.展开更多
The laser altimeter loaded on the GaoFen-7(GF-7)satellite is designed to record the full waveform data and footprint image,which can obtain high-precision elevation control points for stereo image.The footprint camera...The laser altimeter loaded on the GaoFen-7(GF-7)satellite is designed to record the full waveform data and footprint image,which can obtain high-precision elevation control points for stereo image.The footprint camera equipped on the GF-7 laser altimetry system can capture the energy distribution at the time of laser emission and the image of the ground object where the laser falls,which can be used to judge whether the laser is affected by the cloud.At the same time,the centroid of laser spot on the footprint image can be extracted to monitor the change of laser pointing stability.In this manuscript,a data quality analysis scheme of laser altimetry based on footprint image is presented.Firstly,the cloud detection of footprint image is realized based on deep learning.The fusion result of the model is about 5%better than that of the traditional cloud detection algorithm,which can quickly and accurately determine whether the laser spot is affected by cloud.Secondly,according to the characteristics of footprint image,a threshold constrained ellipse fitting method for extracting the centroid of laser spot is proposed to monitor the pointing stability of long-period lasers.Based on the above method,the change of laser spot centroid since GF-7 satellite was put into operation is analyzed,and the conclusions obtained have certain reference significance for the quality control of satellite laser altimetry data and the analysis of pointing angle stability.展开更多
We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators （OPO） in different wavelength tuning ...We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators （OPO） in different wavelength tuning ranges, where the primary signals from the OPO process are recycled to enhance the pump-to-idler conversion efficiencies via the simultaneous dif- ference frequency generation （DFG） process by monolithic aperiodically poled, magnesium oxide doped lithium niobate （APMgLN） crystals. The APMgLN crystals are designed with different chirp parameters for the DFG process to broaden their thermal acceptance bandwidths to different extents. The idler wavelength tuning of the cascaded OPO is realized by changing the temperature of the designed APMgLN crystal and the cascaded oscillation is achieved in a single pump pass singly resonant linear cavity. The pump-to-idler conversion efficiencies with respect to the pump pulse duration and ratio of OPO coefficient to DFG coefficient are calculated by numerically solving the coupled wave equations. The optimal work- ing conditions of the tunable cascaded OPOs pumped by pulses with energies of 350 p_J and 700 ~J are compared to obtain the general rules of optimization. It is concluded that the optimization becomes the interplay between the ratio of OPO coefficient to DFG coefficient and the pump pulse duration when the idler wavelength tuning range and the pump pulse energy are fixed. Besides, higher pump pulse energy is beneficial for reaching higher optimal pump-to-idler conversion efficiency as long as the APMgLN crystal is optimized according to this pump condition. To the best of our knowledge, this is the first numerical analysis of idler wavelength tunable cascaded OPOs based on chirp-assisted APMgLN crystals.展开更多
Terahertz wave is between microwave and infrared bands in the electromagnetic spectrum with the frequency range from 0.1 THz to 10 THz. Controlling and processing of the polarization state in terahertz wave are the fo...Terahertz wave is between microwave and infrared bands in the electromagnetic spectrum with the frequency range from 0.1 THz to 10 THz. Controlling and processing of the polarization state in terahertz wave are the focus due to its great influence on the characteristics. In this paper, a transmissive metasurface terahertz polarization converter is designed in 3D structure with an upper surface of ruler-like rectangular, an intermediate dielectric layer and a lower surface of metal grid wires. Numerical simulations of the converter show that the polarization conversion ratio(PCR) is above 99.9% at 0.288 THz–1.6 THz, the polarization rotation angle(PRA) is close to 90° at 0.06 THz–1.4 THz, and the ellipticity angle(EA) is close to 0° at 0.531 THz–1.49 THz. The origin of the efficient polarization conversion is explained by analyzing the electric field intensity, magnetic field intensity, surface current, electric field energy density, and magnetic field energy density distributions of the converter at 1.19 THz and 0.87 THz, which are consistent with the energy transmittance and transmittance coefficient. In addition, the effects of different thickness and material of intermediate layer, thickness of upper surface material, polarized wave incidence angle, and metasurface materials on the performance of the polarization converter are discussed, and how they affect the conversion performance of the polarization converter are also explained.Our results provide a strong theoretical basis and technical support to develop high performance transmission-type terahertz polarization converters, and play an important role to promote the development of terahertz science and technology.展开更多
Aiming at the problems in a linear frequency modulation continuous wave(LFMCW)ranging lidar system,such as low signal-to-noise in echo beat frequency and difficult extraction of the signal frequency,a method with high...Aiming at the problems in a linear frequency modulation continuous wave(LFMCW)ranging lidar system,such as low signal-to-noise in echo beat frequency and difficult extraction of the signal frequency,a method with high-speed and high accuracy based on field programmable gate array(FPGA)is proposed.Firstly,the laser echo beat signal is sampled by high-speed analog to digital converter(ADC)and then processed in FPGA for data preprocessing.After the signal is processed by the 8192-point FPGA will obtain the frequency spectrum and then apply the frequency spectrum to data processing and adaptive noise signal peak detection.These two steps realize the real-time and accurate extraction process of the target echo beat signal frequency.Finally,the spectrum data is transmitted to the host computer and processed through the external data acquisition board for real-time spectrum display.Experimental results show that data preprocessing and spectrum data processing can effectively suppress DC bias and system modulation noise.Adaptive noise peak detection can accurately divide the threshold contour according to the dynamic noise of the system and realize the detection of target signal peak.When the sampling clock of the system is 100 MHz,the time needed for each calculation of the spectrum is 81.92μs,and the refresh rate of the spectrum reaches 12.2 kHz,which meets the real-time requirements of the system.展开更多
A hertz-linewidth ultra-stable laser(USL), which will be used to detect the clock transition line, in a strontium optical clock will be launched into the China Space Station(CSS) in late 2022. As the core of the USL, ...A hertz-linewidth ultra-stable laser(USL), which will be used to detect the clock transition line, in a strontium optical clock will be launched into the China Space Station(CSS) in late 2022. As the core of the USL, an interference-filter-based externalcavity diode laser(IF-ECDL) was developed. The IF-ECDL has a compact, stable, and environmentally insensitive design.Performances of the IF-ECDL are presented. The developed IF-ECDL can pass the aerospace environmental tests, indicating that the IF-ECDL can be suitable for space missions in the CSS.展开更多
Infrared signatures of aircraft are the basis for detection and monitoring. In past years, most of the studies focused on the aircraft＇s infrared signature in the mid-wave spectral region and long-wave spectral regio...Infrared signatures of aircraft are the basis for detection and monitoring. In past years, most of the studies focused on the aircraft＇s infrared signature in the mid-wave spectral region and long-wave spectral region for missile guidance or aircraft survivability studies. For the security of civil aviation, methods and instruments that can detect and monitor aircrafts from space are expected to be developed in the coming years. A short-wave infrared hyperspectral imager aboard the Tiangong-1 spacecraft acquired some civil aircraft＇s spectral data. The differences between the aircraft and the background in their spectral signatures are analyzed and discussed. Less absorption in the vapor absorption bands and a reflection spike is discovered at the 1.84 μm spectral band. The result shows that 1.84 μm and other vapor absorption bands can make contributions to aircraft detection in the daytime.展开更多
Future optical clock networks will require high-precision optical time-frequency transfer between satellites and ground stations.However,due to atmospheric turbulence,satellite motion and time delay between the satell...Future optical clock networks will require high-precision optical time-frequency transfer between satellites and ground stations.However,due to atmospheric turbulence,satellite motion and time delay between the satellite–ground transmission links will cause spatial and temporal variations,respectively,resulting in the breakdown of the time-of-flight reciprocity on which optical two-way time-frequency transfer is based.Here,we experimentally simulate the atmospheric effects by two-way spatio-temporally separated links between two stationary terminals located 113 km apart and measure the effects for optical two-way time-frequency transfer.Our experiment shows that the effect on the link instability is less than 2.3×10^(−19) at 10,000 s.This indicates that when the link instability of satellite-ground optical time-frequency transfer is on the order of 10^(−19),it is not necessary to consider the atmospheric non-reciprocity effects.展开更多
Water has been detected in lunar regolith,with multiple sources identified through the analysis of individual grains.However,the primary origin of water in the bulk lunar regolith remains uncertain.This study presents...Water has been detected in lunar regolith,with multiple sources identified through the analysis of individual grains.However,the primary origin of water in the bulk lunar regolith remains uncertain.This study presents spectroscopic analyses of water content in sealed Chang’e-5 samples.These samples were sieved into various size fractions(bulk,<45μm,and 45–355μm)inside a glovebox filled with high-purity nitrogen.Results indicate a higher water content in the fine fractions(~87±11.9 ppm)than in bulk soil(~37±4.8 ppm)and coarse fractions(~11±1.5 ppm).This suggests that water is predominantly concentrated in the outermost rims of the regolith grains,and thus exhibits dependence on the surface volume ratio(also known as surface correlation),indicating solar wind is a primary source of lunar surface water.Laboratory,in-situ,and orbital results bridge sample analysis and remote sensing,offering a cohesive understanding of lunar surface water characteristics as represented by Chang’e-5.The discovery provides statistical evidence for the origin of water in lunar soil and can be considered representative of the lunar surface conditions.The water enrichment of the finest fraction suggests the feasibility of employing size sorting of lunar soils as a potential technological approach for water resource extraction in future lunar research stations.展开更多
Deep learning is widely used for lesion segmentation in medical images due to its breakthrough performance.Loss functions are critical in a deep learning pipeline,and they play important roles in segmenting performanc...Deep learning is widely used for lesion segmentation in medical images due to its breakthrough performance.Loss functions are critical in a deep learning pipeline,and they play important roles in segmenting performance.Dice loss is the most commonly used loss function in medical image segmentation,but it also has some disadvantages.In this paper,we discuss the advantages and disadvantages of the Dice loss function,and group the extensions of the Dice loss according to its improved purpose.The performances of some extensions are compared according to core references.Because different loss functions have different performances in different tasks,automatic loss function selection will be the potential direction in the future.展开更多
Millimeter and terahertz wave photodetectors have a wide range of applications. However, the state-of-the-art techniques lag far behind the urgent demand due to the structure and performance limitations. Here, we repo...Millimeter and terahertz wave photodetectors have a wide range of applications. However, the state-of-the-art techniques lag far behind the urgent demand due to the structure and performance limitations. Here, we report sensitive and direct millimeter and terahertz wave photodetection in compact InGaAs-based subwavelength ohmic metal–semiconductor–metal structures. The photoresponse originates from unidirectional transportation of nonequilibrium electrons induced by surface plasmon polaritons under irradiation. The detected quantum energies of electromagnetic waves are far below the bandgap of InGaAs, offering, to the best of our knowledge, a novel direct photoelectric conversion pathway for InGaAs beyond its bandgap limit. The achieved room temperature rise time and noise equivalent power of the detector are 45 μs and 20 pW · Hz^(-1∕2), respectively,at the 0.0375 THz(8 mm) wave. The detected wavelength is tunable by mounting different coupling antennas.Room temperature terahertz imaging of macroscopic samples at around 0.166 THz is also demonstrated. This work opens an avenue for sensitive and large-area uncooled millimeter and terahertz focal planar arrays.展开更多
基金Supported by China Manned Space Program,Technology and Engineering Center for Space Utilization Chinese Academy of Sciences,Chinese Academy of Sciencesthe National Natural Science Foundation of China
文摘Quantum technology establishes a foundation for secure communication via quantum key distribution （QKD）. In the last two decades, the rapid development of QKD makes a global quantum communication network feasible. In order to construct this network, it is economical to consider small-sized and low-cost QKD payloads, which can be assembled on satellites with different sizes, such as space stations. Here we report an experimental demonstration of space-to-ground QKD using a small-sized payload, from Tiangong-2 space lab to Nanshan ground station. The 57.9-kg payload integrates a tracking system, a QKD transmitter along with modules for synchronization, and a laser communication transmitter. In the space lab, a 50MHz vacuum＋weak decoy-state optical source is sent through a reflective telescope with an aperture of 200mm. On the ground station, a telescope with an aperture of 1200mm collects the signal photons. A stable and high-transmittance communication channel is set up with a high-precision bidirectional tracking system, a polarization compensation module, and a synchronization system. When the quantum link is successfully established, we obtain a key rate over 100bps with a communication distance up to 719km. Together with our recent development of QKD in daylight, the present demonstration paves the way towards a practical satellite-constellation-based global quantum secure network with small-sized QKD payloads.
基金supported by the National Key Research and Development Program of China(2022YFC2203700).
文摘The gravitational wave spacecraft is a complex multi-input multi-output dynamic system.The gravitational wave detection mission requires the spacecraft to achieve single spacecraft with two laser links and high-precision control.Establishing one spacecraftwith two laser links,compared to one spacecraft with a single laser link,requires an upgraded decoupling algorithmfor the link establishment.The decoupling algorithmwe designed reassigns the degrees of freedomand forces in the control loop to ensure sufficient degrees of freedomfor optical axis control.In addressing the distinct dynamic characteristics of different degrees of freedom,a transfer function compensation method is used in the decoupling process to further minimize motion coupling.The open-loop frequency response of the systemis obtained through simulation.The upgraded decoupling algorithms effectively reduce the open-loop frequency response by 30 dB.The transfer function compensation method efficiently suppresses the coupling of low-frequency noise.
基金Supported by the Short-wave Infrared Camera Systems(B025F40622024)。
文摘The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave infrared wavelengths as beacon light can reduce atmospheric absorption and signal attenuation.However,there are strong non-uniformity and blind pixels in the short-wave infrared image,which makes the image distorted and leads to the decrease of spot centroid positioning accuracy.Therefore,the high-precision localization of the spot centroid of the short-wave infrared images is of great research significance.A high-precision spot centroid positioning model for short-wave infrared is proposed to correct for non-uniformity and blind pixels in short-wave infrared images and quantify the localization errors caused by the two,further model-based localization error simulations are performed,and a novel spot centroid positioning payload for satellite laser communications has been designed using the latest 640×512 planar array InGaAs shortwave infrared detector.The experimental results show that the non-uniformity of the corrected image is reduced from 7%to 0.6%,the blind pixels rejection rate reaches 100%,the frame rate can be up to 2000 Hz,and the spot centroid localization accuracy is as high as 0.1 pixel point,which realizes high-precision spot centroid localization of high-frame-frequency short-wave infrared images.
基金supported by the National Natural Science Foundation of China (62173103)the Fundamental Research Funds for the Central Universities of China (3072022JC0402,3072022JC0403)。
文摘For the first time, this article introduces a LiDAR Point Clouds Dataset of Ships composed of both collected and simulated data to address the scarcity of LiDAR data in maritime applications. The collected data are acquired using specialized maritime LiDAR sensors in both inland waterways and wide-open ocean environments. The simulated data is generated by placing a ship in the LiDAR coordinate system and scanning it with a redeveloped Blensor that emulates the operation of a LiDAR sensor equipped with various laser beams. Furthermore,we also render point clouds for foggy and rainy weather conditions. To describe a realistic shipping environment, a dynamic tail wave is modeled by iterating the wave elevation of each point in a time series. Finally, networks serving small objects are migrated to ship applications by feeding our dataset. The positive effect of simulated data is described in object detection experiments, and the negative impact of tail waves as noise is verified in single-object tracking experiments. The Dataset is available at https://github.com/zqy411470859/ship_dataset.
基金Supported by the Zhejiang Provincial"Jianbing"and"Lingyan"R&D Programs(2023C03012,2024C01126)。
文摘The encoding aperture snapshot spectral imaging system,based on the compressive sensing theory,can be regarded as an encoder,which can efficiently obtain compressed two-dimensional spectral data and then decode it into three-dimensional spectral data through deep neural networks.However,training the deep neural net⁃works requires a large amount of clean data that is difficult to obtain.To address the problem of insufficient training data for deep neural networks,a self-supervised hyperspectral denoising neural network based on neighbor⁃hood sampling is proposed.This network is integrated into a deep plug-and-play framework to achieve self-supervised spectral reconstruction.The study also examines the impact of different noise degradation models on the fi⁃nal reconstruction quality.Experimental results demonstrate that the self-supervised learning method enhances the average peak signal-to-noise ratio by 1.18 dB and improves the structural similarity by 0.009 compared with the supervised learning method.Additionally,it achieves better visual reconstruction results.
基金Supported by the National Natural Science Foundation of China
文摘The Visible and Near-Infrared Imaging Spectrometer （VNIS）, using two acousto-optic tunable filters as dispersive components, consists of a VIS/NIR imag- ing spectrometer （0.45-0.95 μm）, a shortwave IR spectrometer （0.9-2.4 p.m） and a calibration unit with dust-proofing functionality. The VNIS was utilized to detect the spectrum of the lunar surface and achieve in-orbit calibration, which satisfied the re- quirements for scientific detection. Mounted at the front of the Yutu rover, lunar ob- jects that are detected with the VNIS with a 45° visual angle to obtain spectra and ge- ometrical data in order to analyze the mineral composition of the lunar surface. After landing successfully on the Moon, the VNIS performed several explorations and cal- ibrations, and obtained several spectral images and spectral reflectance curves of the lunar soil in the region of Mare Imbrium. This paper describes the working principle and detection characteristics of the VNIS and provides a reference for data processing and scientific applications.
基金supported by the National Natural Science Foundation of China(Grant No.61078015)the National Basic Research Program of China(Grant No.2011CB311803)
文摘We demonstrate a compact periodically poled MgO-doped lithium niobate（MgO：PPLN）-based optical parametric oscillator（OPO） quasi-synchronously pumped by a fiber laser system with burst-mode operation.The pump source is a peak-power-selectable pulse-multiplied picosecond Yb fiber laser.The chirped pulses from a figure of eight-cavity modelocked fiber laser seed are narrowed to a duration of less than 50 ps using an FBG reflector and a circulator.The narrowed pulses are directed to pass through a pulse multiplier and to form pulse bunches,each of which is composed of 13 subpulses.The obtained pulse bunches are amplified by two-stage fiber pre-amplifiers：one-stage is core-pumped and the other is cladding-pumped.A fiberized acousto-optic modulator is inserted to control the pulse repetition rate（PRR） of the pulse bunches before they are power-amplified in the final amplifier stage with a large mode area（LMA） PM Yb-doped fiber.The maximum average powers from the final amplifier are 85 W,60 W,and 45 W,respectively,corresponding to the PRR of2.72 MHz,1.36 MHz,and 0.68 MHz.The amplified pulses are directed to pump an MgO：PPLN-based optical parametric oscillator（OPO）.A maximum peak power at 3.45 μm is obtained approximately to be 8.4 kW.Detailed performance characteristics are presented.
基金Supported by the National Natural Science Foundation of China
文摘The Chang＇e-3 Visible and Near-infrared Imaging Spectrometer （VNIS） is one of the four payloads on the Yutu rover. After traversing the landing site during the first two lunar days, four different areas are detected, and Level 2A and 2B ra- diance data have been released to the scientific community. The released data have been processed by dark current subtraction, correction for the effect of temperature, radiometric calibration and geometric calibration. We emphasize approaches for re- flectance analysis and mineral identification for in-situ analysis with VNIS. Then the preliminary spectral and mineralogical results from the landing site are derived. After comparing spectral data from VNIS with data collected by the Ma instrument and samples of mare that were returned from the Apollo program, all the reflectance data have been found to have similar absorption features near 1000 nm except lunar sample 71061. In addition, there is also a weak absorption feature between 1750-2400nm on VNIS, but the slopes of VNIS and Ma reflectance at longer wavelengths are lower than data taken from samples of lunar mare. Spectral parameters such as Band Centers and Integrated Band Depth Ratios are used to analyze mineralogical features. The results show that detection points E and N205 are mixtures of high-Ca pyroxene and olivine, and the composition of olivineat point N205 is higher than that at point E, but the compositions of detection points S3 and N203 are mainly olivine-rich. Since there are no obvious absorption features near 1250 nm, plagioclase is not directly identified at the landing site.
基金supported by the Chinese Academy of Sciences (KGZD-EW-603)the National Natural Science Foundation of China (Grant No. 41103031)
文摘Yutu is the first lunar rover after the Apollo program and Luna missions. One of the payloads on the Yutu rover, the Visible and Near-infrared Imaging Spectrometer （VNIS）, has acquired four VIS/NIR images and SWIR spectra near its landing site in Mare Imbrium. The radiance images were reduced through repairing bad lines and bad points, and applying flat field correction, and then were converted into reflectance values based on the solar irradiance and angles of incidence. A significant shadow effect was observed in the VIS/NIR image. The shadowed regions show lower reflectance with a darkening trend compared with illuminated regions. The re- flectance increased by up to 24% for entire images and 17% for the VIS/NIR-SWlR overlapping regions after shadow correction. The correction for the shadow effect will remarkably decrease the estimate of FeO content, by up to 4.9 wt.% in this study. The derived FeO contents of CD-005-008 after shadow correction are around 18.0 wt.%.
基金National Natural Science Foundation of China(No.41871382)Open Foundation of the Key Laboratory of Space Active Opto-electronics Technologyand Chinese Academy of Sciences(No.2018-ZDKF-1)。
文摘The influence of the single photon laser altimeter range-gate width on the detection probability and ranging accuracy is discussed and analyzed,according to the LiDAR equation,single photon detection equation and the Monte Carlo method to simulate the experiment.The simulated results show that the probability of detection is not affected by the range gate,while the probability of false alarm is relative to the gate width.When the gate width is 100 ns,the ranging accuracy can accord with the requirements of satellite laser altimeter.But when the range gate width exceeds 400 ns,ranging accuracy will decline sharply.The noise ratio will be more as long as the range gate to get larger,so the refined filtering algorithm during the data processing is important to extract the useful photons effectively.In order to ensure repeated observation of the same point for 25 times,we deduce the quantitative relation between the footprint size,footprint,and frequency repetition according to the parameters of ICESat-2.The related conclusions can provide some references for the design and the development of the domestic single photon laser altimetry satellite.
基金National Nature Science Foundation(Nos.41971425,41601505)Special Fund for High Resolution Images Surveying and Mapping Application System(No.42-Y30B04-9001-19/21)。
文摘The laser altimeter loaded on the GaoFen-7(GF-7)satellite is designed to record the full waveform data and footprint image,which can obtain high-precision elevation control points for stereo image.The footprint camera equipped on the GF-7 laser altimetry system can capture the energy distribution at the time of laser emission and the image of the ground object where the laser falls,which can be used to judge whether the laser is affected by the cloud.At the same time,the centroid of laser spot on the footprint image can be extracted to monitor the change of laser pointing stability.In this manuscript,a data quality analysis scheme of laser altimetry based on footprint image is presented.Firstly,the cloud detection of footprint image is realized based on deep learning.The fusion result of the model is about 5%better than that of the traditional cloud detection algorithm,which can quickly and accurately determine whether the laser spot is affected by cloud.Secondly,according to the characteristics of footprint image,a threshold constrained ellipse fitting method for extracting the centroid of laser spot is proposed to monitor the pointing stability of long-period lasers.Based on the above method,the change of laser spot centroid since GF-7 satellite was put into operation is analyzed,and the conclusions obtained have certain reference significance for the quality control of satellite laser altimetry data and the analysis of pointing angle stability.
基金supported by the National Natural Science Foundation of China(Grant No.61505236)the Innovation Program of Shanghai Institute of Technical Physics,China(Grant No.CX-2)the Program of Shanghai Subject Chief Scientist,China(Grant No.14XD1404000)
文摘We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators （OPO） in different wavelength tuning ranges, where the primary signals from the OPO process are recycled to enhance the pump-to-idler conversion efficiencies via the simultaneous dif- ference frequency generation （DFG） process by monolithic aperiodically poled, magnesium oxide doped lithium niobate （APMgLN） crystals. The APMgLN crystals are designed with different chirp parameters for the DFG process to broaden their thermal acceptance bandwidths to different extents. The idler wavelength tuning of the cascaded OPO is realized by changing the temperature of the designed APMgLN crystal and the cascaded oscillation is achieved in a single pump pass singly resonant linear cavity. The pump-to-idler conversion efficiencies with respect to the pump pulse duration and ratio of OPO coefficient to DFG coefficient are calculated by numerically solving the coupled wave equations. The optimal work- ing conditions of the tunable cascaded OPOs pumped by pulses with energies of 350 p_J and 700 ~J are compared to obtain the general rules of optimization. It is concluded that the optimization becomes the interplay between the ratio of OPO coefficient to DFG coefficient and the pump pulse duration when the idler wavelength tuning range and the pump pulse energy are fixed. Besides, higher pump pulse energy is beneficial for reaching higher optimal pump-to-idler conversion efficiency as long as the APMgLN crystal is optimized according to this pump condition. To the best of our knowledge, this is the first numerical analysis of idler wavelength tunable cascaded OPOs based on chirp-assisted APMgLN crystals.
基金supported by the National Natural Science Fundation (Grant Nos. 12134016 and 61625505)Chinese Academy of Sciences (Grant No. ZDBS-LY-JSC025)+1 种基金Sino– Russia International Joint Laboratory of Terahertz Materials and Devices (Grant No. 18590750500)Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX01)。
文摘Terahertz wave is between microwave and infrared bands in the electromagnetic spectrum with the frequency range from 0.1 THz to 10 THz. Controlling and processing of the polarization state in terahertz wave are the focus due to its great influence on the characteristics. In this paper, a transmissive metasurface terahertz polarization converter is designed in 3D structure with an upper surface of ruler-like rectangular, an intermediate dielectric layer and a lower surface of metal grid wires. Numerical simulations of the converter show that the polarization conversion ratio(PCR) is above 99.9% at 0.288 THz–1.6 THz, the polarization rotation angle(PRA) is close to 90° at 0.06 THz–1.4 THz, and the ellipticity angle(EA) is close to 0° at 0.531 THz–1.49 THz. The origin of the efficient polarization conversion is explained by analyzing the electric field intensity, magnetic field intensity, surface current, electric field energy density, and magnetic field energy density distributions of the converter at 1.19 THz and 0.87 THz, which are consistent with the energy transmittance and transmittance coefficient. In addition, the effects of different thickness and material of intermediate layer, thickness of upper surface material, polarized wave incidence angle, and metasurface materials on the performance of the polarization converter are discussed, and how they affect the conversion performance of the polarization converter are also explained.Our results provide a strong theoretical basis and technical support to develop high performance transmission-type terahertz polarization converters, and play an important role to promote the development of terahertz science and technology.
基金Supported by Joint Astronomical Fund of National Natural Science Foundation of China(U1831133)Key Laboratory of Space Active Opto-electronics Technology of Chinese Academy of Sciences(20212DKF4)Shanghai Natural Science Foundation(17ZR1443500)
文摘Aiming at the problems in a linear frequency modulation continuous wave(LFMCW)ranging lidar system,such as low signal-to-noise in echo beat frequency and difficult extraction of the signal frequency,a method with high-speed and high accuracy based on field programmable gate array(FPGA)is proposed.Firstly,the laser echo beat signal is sampled by high-speed analog to digital converter(ADC)and then processed in FPGA for data preprocessing.After the signal is processed by the 8192-point FPGA will obtain the frequency spectrum and then apply the frequency spectrum to data processing and adaptive noise signal peak detection.These two steps realize the real-time and accurate extraction process of the target echo beat signal frequency.Finally,the spectrum data is transmitted to the host computer and processed through the external data acquisition board for real-time spectrum display.Experimental results show that data preprocessing and spectrum data processing can effectively suppress DC bias and system modulation noise.Adaptive noise peak detection can accurately divide the threshold contour according to the dynamic noise of the system and realize the detection of target signal peak.When the sampling clock of the system is 100 MHz,the time needed for each calculation of the spectrum is 81.92μs,and the refresh rate of the spectrum reaches 12.2 kHz,which meets the real-time requirements of the system.
基金This work was supported by the National Key R&D Program of China(No.2020YFC2201300)the National Natural Science Foundation of China(No.11903041)。
文摘A hertz-linewidth ultra-stable laser(USL), which will be used to detect the clock transition line, in a strontium optical clock will be launched into the China Space Station(CSS) in late 2022. As the core of the USL, an interference-filter-based externalcavity diode laser(IF-ECDL) was developed. The IF-ECDL has a compact, stable, and environmentally insensitive design.Performances of the IF-ECDL are presented. The developed IF-ECDL can pass the aerospace environmental tests, indicating that the IF-ECDL can be suitable for space missions in the CSS.
基金supported by the Innovation Funds from Chinese Academy of SciencesChinese Manned Space Engineering, who funded the R&D of the high-resolution hyperspectral imager
文摘Infrared signatures of aircraft are the basis for detection and monitoring. In past years, most of the studies focused on the aircraft＇s infrared signature in the mid-wave spectral region and long-wave spectral region for missile guidance or aircraft survivability studies. For the security of civil aviation, methods and instruments that can detect and monitor aircrafts from space are expected to be developed in the coming years. A short-wave infrared hyperspectral imager aboard the Tiangong-1 spacecraft acquired some civil aircraft＇s spectral data. The differences between the aircraft and the background in their spectral signatures are analyzed and discussed. Less absorption in the vapor absorption bands and a reflection spike is discovered at the 1.84 μm spectral band. The result shows that 1.84 μm and other vapor absorption bands can make contributions to aircraft detection in the daytime.
基金National Key Research and Development Program of China(2020YFA0309800,2020YFC2200103)Strategic Priority Research Programme of Chinese Academy of Sciences(XDA15020400,XDB35030000)+5 种基金National Natural Science Foundation of China(12274398,61825505,T2125010)Anhui Initiative in Quantum Information Technologies(AHY010100)Key RD Plan of Shandong Province(2020CXGC010105,2021ZDPT01)Shanghai Municipal Science and Technology Major Project(2019SHZDZX01)Innovation Programme for Quantum Science and Technology(2021ZD0300100)Youth Innovation Promotion Association of the Chinese Academy of Sciences(2018492,2021457).
文摘Future optical clock networks will require high-precision optical time-frequency transfer between satellites and ground stations.However,due to atmospheric turbulence,satellite motion and time delay between the satellite–ground transmission links will cause spatial and temporal variations,respectively,resulting in the breakdown of the time-of-flight reciprocity on which optical two-way time-frequency transfer is based.Here,we experimentally simulate the atmospheric effects by two-way spatio-temporally separated links between two stationary terminals located 113 km apart and measure the effects for optical two-way time-frequency transfer.Our experiment shows that the effect on the link instability is less than 2.3×10^(−19) at 10,000 s.This indicates that when the link instability of satellite-ground optical time-frequency transfer is on the order of 10^(−19),it is not necessary to consider the atmospheric non-reciprocity effects.
基金supported by the National Natural Science Foundation of China(42241106,42230206)the Key Research Program of the Institute of Geology and Geophysics+2 种基金Chinese Academy of Sciences(IGGCAS-202101)the Young Elite Scientists Sponsorship Program by China Association for Science and Technology(2021QNRC001)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2023071)。
文摘Water has been detected in lunar regolith,with multiple sources identified through the analysis of individual grains.However,the primary origin of water in the bulk lunar regolith remains uncertain.This study presents spectroscopic analyses of water content in sealed Chang’e-5 samples.These samples were sieved into various size fractions(bulk,<45μm,and 45–355μm)inside a glovebox filled with high-purity nitrogen.Results indicate a higher water content in the fine fractions(~87±11.9 ppm)than in bulk soil(~37±4.8 ppm)and coarse fractions(~11±1.5 ppm).This suggests that water is predominantly concentrated in the outermost rims of the regolith grains,and thus exhibits dependence on the surface volume ratio(also known as surface correlation),indicating solar wind is a primary source of lunar surface water.Laboratory,in-situ,and orbital results bridge sample analysis and remote sensing,offering a cohesive understanding of lunar surface water characteristics as represented by Chang’e-5.The discovery provides statistical evidence for the origin of water in lunar soil and can be considered representative of the lunar surface conditions.The water enrichment of the finest fraction suggests the feasibility of employing size sorting of lunar soils as a potential technological approach for water resource extraction in future lunar research stations.
文摘Deep learning is widely used for lesion segmentation in medical images due to its breakthrough performance.Loss functions are critical in a deep learning pipeline,and they play important roles in segmenting performance.Dice loss is the most commonly used loss function in medical image segmentation,but it also has some disadvantages.In this paper,we discuss the advantages and disadvantages of the Dice loss function,and group the extensions of the Dice loss according to its improved purpose.The performances of some extensions are compared according to core references.Because different loss functions have different performances in different tasks,automatic loss function selection will be the potential direction in the future.
基金Ministry of Education-Singapore(MOE)(RG177/17)Economic Development Board-Singapore(EDB)(NRF2013SAS-SRP001-019)+2 种基金Agency for Science,Technology and Research(A*STAR)(1720700038)China National Funds for Distinguished Young Scientists(61625505)Science and Technology Commission of Shanghai Municipality(STCSM)(16JC1403400)
文摘Millimeter and terahertz wave photodetectors have a wide range of applications. However, the state-of-the-art techniques lag far behind the urgent demand due to the structure and performance limitations. Here, we report sensitive and direct millimeter and terahertz wave photodetection in compact InGaAs-based subwavelength ohmic metal–semiconductor–metal structures. The photoresponse originates from unidirectional transportation of nonequilibrium electrons induced by surface plasmon polaritons under irradiation. The detected quantum energies of electromagnetic waves are far below the bandgap of InGaAs, offering, to the best of our knowledge, a novel direct photoelectric conversion pathway for InGaAs beyond its bandgap limit. The achieved room temperature rise time and noise equivalent power of the detector are 45 μs and 20 pW · Hz^(-1∕2), respectively,at the 0.0375 THz(8 mm) wave. The detected wavelength is tunable by mounting different coupling antennas.Room temperature terahertz imaging of macroscopic samples at around 0.166 THz is also demonstrated. This work opens an avenue for sensitive and large-area uncooled millimeter and terahertz focal planar arrays.
