Due to the influences of precursors emissions,meteorology,geography and other factors,ozone formation sensitivity(OFS)is generally spatially and temporally heterogeneous.This study characterized detailed spatial and t...Due to the influences of precursors emissions,meteorology,geography and other factors,ozone formation sensitivity(OFS)is generally spatially and temporally heterogeneous.This study characterized detailed spatial and temporal variations of OFS in Guangdong-Hong Kong-Macao Greater Bay Area(GBA)from 2012 to 2016 based on OMI satellite data,and analyzed the relationships of OFS with precursors emissions,meteorology and land use types(LUTs).From 2012 to 2016,the OFS tended to be NOx-limited in GBA,with the value of FNR(HCHO/NO 2)increasing from 2.04 to 2.22.According to the total annual emission statistics of precursors,NOx emissions decreased by 33.1%and VOCs emissions increased by 35.2%from 2012 to 2016,directly resulting in OFS tending to be NO x-limited.The Grey Relation Analysis results show that total column water(TCW),surface net solar radiation(SSR),air temperature at 2 m(T2)and surface pressure(SP)are the top four meteorological factors with the greatest influences on OFS.There are significant positive correlations between FNR and T2,SSR,TCW,and significant negative correlations between FNR and SP.In GBA,the OFS tends to be NO x-limited regime in wet season(higher T2,SSR,TCW and lower SP)and VOCs-limited regime in dry season(lower T2,SSR,TCW and higher SP).The FNR displays obvious gradient variations on different LUTs,with the highest in“Rural areas”,second in“Suburban areas”and lowest in“Urban areas”.展开更多
The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that o...The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.展开更多
Nowadays,the rapid development of edge computing has driven an increasing number of deep learning applications deployed at the edge of the network,such as pedestrian and vehicle detection,to provide efficient intellig...Nowadays,the rapid development of edge computing has driven an increasing number of deep learning applications deployed at the edge of the network,such as pedestrian and vehicle detection,to provide efficient intelligent services to mobile users.However,as the accuracy requirements continue to increase,the components of deep learning models for pedestrian and vehicle detection,such as YOLOv4,become more sophisticated and the computing resources required for model training are increasing dramatically,which in turn leads to significant challenges in achieving effective deployment on resource-constrained edge devices while ensuring the high accuracy performance.For addressing this challenge,a cloud-edge collaboration-based pedestrian and vehicle detection framework is proposed in this paper,which enables sufficient training of models by utilizing the abundant computing resources in the cloud,and then deploying the well-trained models on edge devices,thus reducing the computing resource requirements for model training on edge devices.Furthermore,to reduce the size of the model deployed on edge devices,an automatic pruning method combines the convolution layer and BN layer is proposed to compress the pedestrian and vehicle detection model size.Experimental results show that the framework proposed in this paper is able to deploy the pruned model on a real edge device,Jetson TX2,with 6.72 times higher FPS.Meanwhile,the channel pruning reduces the volume and the number of parameters to 96.77%for the model,and the computing amount is reduced to 81.37%.展开更多
ZnO tetrapod-like whiskers were prepared through a hydrothermal process using zinc powder as raw material.Its microstructure and morphology were characterized by X-ray diffraction (XRD) and transmission electron micro...ZnO tetrapod-like whiskers were prepared through a hydrothermal process using zinc powder as raw material.Its microstructure and morphology were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD results showed that the crystal structure of as-obtained sample can be indexed to hexagonal wurtzite ZnO.TEM results revealed that the ZnO sample took on tetrapod-like whisker shape.The gas sensors were prepared with the traditional sintering process and their gas sensitivities were detected.The test results of gas sensitivity showed that the sensors based on ZnO tetrapod-like whiskers are very sensitive to dilute ethanol vapor and H_2S.The relatively high sensitivity and selectivity of these sensors made from ZnO tetrapod-like whiskers demonstrated the potential for developing a new class of selective ethanol sensors.展开更多
The Domain Decomposition Method(DDM) is a powerful approach to solving maily types of PDE's. DDM is especially suitable for massively Parallel computers. In the past, most research on DDM has focused on the domain...The Domain Decomposition Method(DDM) is a powerful approach to solving maily types of PDE's. DDM is especially suitable for massively Parallel computers. In the past, most research on DDM has focused on the domain splitting technique. In this paper. we focus our attention on use of a combination of techniques to solve each subproblem. The central question with DDM is that of how to doal with the pseodoboundary conditions. Here, we introduce a set of operators which act on the pseudo-boundaries in the solution process, referring to this new. procedure as the 'Generalized Domain Decomposition A.Jlethod(GDDM).' We have already obtained convergence factors for GDDM with certain classes of PDE's. These ctonvergence factors show that we can derive exact solutions of the whole problem for certain types of PDE's, and can get superior speed of convergence for other types.展开更多
Introduction:This study investigated the prevalence of metabolic dysfunction-associated steatotic liver disease(MASLD)with clinically significant fibrosis among obese patients with type 2 diabetes mellitus(T2DM).Metho...Introduction:This study investigated the prevalence of metabolic dysfunction-associated steatotic liver disease(MASLD)with clinically significant fibrosis among obese patients with type 2 diabetes mellitus(T2DM).Methods:This multicenter study enrolled T2DM patients from tertiary hospitals and primary care facilities across 21 cities in China between 2017 and 2024.Clinically significant fibrosis was defined as liver stiffness measurement(LSM)≥8 kPa assessed by vibration-controlled transient elastography(VCTE)or biopsy-confirmed fibrosis stage≥F2.Results:Of the 10,281 patients included,9,725 comprised the VCTE cohort(5,171 from clinics and 4,554 from primary care),while 556 comprised the biopsy cohort.Overall,25.6%were obese.The prevalence of MASLD with clinically significant fibrosis reached 26.7%in obese patients,significantly exceeding that in non-obese patients(8.4%).This prevalence increased progressively with rising body mass index and demonstrated a strong association with the number of cardiometabolic risk factors.Furthermore,a non-invasive model incorporating age,waist circumference,alanine aminotransferase,total bilirubin,and triglycerides exhibited reliable performance in stratifying the risk of MASLD with clinically significant fibrosis among obese patients with T2DM[Area under the receiver operating characteristic curve(AUC):0.799(95%CI:0.767-0.832)].Conclusions:MASLD with clinically significant fibrosis is highly prevalent among obese patients with T2DM,emphasizing the necessity for systematic risk stratification and integrated management of these interconnected metabolic conditions.展开更多
The commercialization of lithium niobate on insulator(LNOI) wafer has resulted in significant on-chip photonic integration application owing to its remarkable photonic,acousto-optic,electro-optic,and piezoelectric nat...The commercialization of lithium niobate on insulator(LNOI) wafer has resulted in significant on-chip photonic integration application owing to its remarkable photonic,acousto-optic,electro-optic,and piezoelectric nature.In recent years,a variety of high-performance on-chip LNOI-based photonic devices have been realized.In this study,we developed a 1-mol% erbium-doped lithium niobate crystal and its LNOI on a silicon substrate and fabricated an erbium-doped LNOI microdisk with high quality factor(~1.05×105).C-band laser emission at ~1530 and ~1560 nm(linewidth 0.12 nm) from the high-Q erbium-doped LNOI microdisk was demonstrated with 974-and 1460-nm pumping,with the latter having better thermal stability.This microlaser would play an important role in the photonic integrated circuits of the lithium niobate platform.展开更多
All-optical logic gates including AND, XOR, and NOT gates, as well as a half-adder, are realized based on twodimensional lithium niobate photonic crystal(PhC) circuits with Ph C micro-cavities.The proposed all-optical...All-optical logic gates including AND, XOR, and NOT gates, as well as a half-adder, are realized based on twodimensional lithium niobate photonic crystal(PhC) circuits with Ph C micro-cavities.The proposed all-optical devices have an extinction ratio as high as 23 dB due to the effective all-optical switch function induced by twomissing-hole micro-cavities.These proposed devices can have potential implementation of complex integrated optical functionalities including all-optical computing in a lithium niobate slab or thin film.展开更多
Future quantum information networks operated on telecom channels require qubit transfer between different wavelengths while preserving quantum coherence and entanglement. Qubit transfer is a nonlinear optical process,...Future quantum information networks operated on telecom channels require qubit transfer between different wavelengths while preserving quantum coherence and entanglement. Qubit transfer is a nonlinear optical process,but currently the types of atoms used for quantum information processing and storage are limited by the narrow bandwidth of upconversion available. Here we present the first experimental demonstration of broadband and high-efficiency quasi-phase matching second-harmonic generation(SHG) in a chip-scale periodically poled lithium niobate thin film. We achieve a large bandwidth of up to 2 THz for SHG by satisfying quasi-phase matching and group-velocity matching simultaneously. Furthermore, by changing the film thickness, the central wavelength of the quasi-phase matching SHG bandwidth can be modulated from 2.70 μm to 1.44 μm. The reconfigurable quasi-phase matching lithium niobate thin film provides a significant on-chip integrated platform for photonics and quantum optics.展开更多
In this paper,we demonstrate efficient spontaneous quasi-phase matched(SQPM)second harmonic generation(SHG)in a microracetrack resonator on X-cut thin film lithium niobate.Our approach does not involve poling,but expl...In this paper,we demonstrate efficient spontaneous quasi-phase matched(SQPM)second harmonic generation(SHG)in a microracetrack resonator on X-cut thin film lithium niobate.Our approach does not involve poling,but exploits the anisotropy of the crystals to allow the phase-matching condition to be fulfilled spontaneously as the TE-polarized light circulates in a specifically designed racetrack resonator.In experiment,normalized on-chip conversion efficiencies of 1.01×10-4/W and 0.43×10-4/W are achieved by 37th-order and 111th-order SQPM,respectively.The configurable SQPM will benefit the application of nonlinear frequency conversion and quantum source generation in chip-scale integrated photonics compatible with standard CMOS fabrication processes.展开更多
The compact and reliable ultraviolet[UV]source has attracted remarkable attention for its potential use in optical measurement systems,high-density optical storage,and biomedical applications.We demonstrate ultraviole...The compact and reliable ultraviolet[UV]source has attracted remarkable attention for its potential use in optical measurement systems,high-density optical storage,and biomedical applications.We demonstrate ultraviolet generation by frequency doubling in a lithium-tantalate-on-insulator[LTOI]microdisk via modal phase matching.The 50-μm-diameter microdisk was milled by a focused ion beam[FIB]and followed by chemo-mechanical polishing[CMP]to smooth the disk surface and edge,and the Q-factor reaches 2.74×10~5in the visible band.On-chip UV coherent light with a wavelength of384.3 nm was achieved,which shows great promise for using LTOIs in integrated ultraviolet source platforms.展开更多
The modulation bandwidth of silicon-based photonics is limited to approximately 60 GHz because of the maximum carrier mobility,which limits its development in high-capacity and high-speed information processing.Lithiu...The modulation bandwidth of silicon-based photonics is limited to approximately 60 GHz because of the maximum carrier mobility,which limits its development in high-capacity and high-speed information processing.Lithium niobate has received much attention due to its excellent electro-optic properties.展开更多
We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals. By increasing the size difference of two air holes in the same...We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals. By increasing the size difference of two air holes in the same unit cell, we find that the bandwidth of the lossless nontrivial edge state possesses a peak value of 0.0201(a/λ), which can be used to construct broadband valley photonic crystal waveguides. Mode field distributions verify that the waveguide is robust against sharp bends and exhibits chirality. When the unit cell is arranged in a bearded interface with the top and bottom components showing negative and positive valley Chern numbers, respectively, we find that the lithium niobate valley photonic crystal is more likely to exhibit a lossless edge state, which is difficult to be realized in valley waveguides with low refractive index materials. This work can provide guidance on the design of the high-performance topological waveguide.展开更多
Developing natural “free space” frequency upconversion is essential for photonic integrated circuits. In a singlecrystal lithium niobate thin film planar waveguide of less than 1 μm thickness, we achieve type I and...Developing natural “free space” frequency upconversion is essential for photonic integrated circuits. In a singlecrystal lithium niobate thin film planar waveguide of less than 1 μm thickness, we achieve type I and type II mode phase-matching conditions simultaneously for this thin film planar waveguide. Finally, by employing the mode phase matching of e t e → e with d_（33） at 1018 nm, we successfully achieve a green second-harmonic wave output with the conversion efficiency of 0.12%∕（W·cm^2）, which verifies one of our simulation results. The rich mode phase matching for three-wave mixing in a thin film planar waveguide may provide a potential application in on-chip frequency upconversions for integrated photonic and quantum devices.展开更多
Lithium niobate is a material that exhibits outstanding electro-optic,nonlinear optical,acousto-optic,piezoelectric,photorefractive,and pyroelectric properties.A thin-film lithium niobate photonic crystal can confine ...Lithium niobate is a material that exhibits outstanding electro-optic,nonlinear optical,acousto-optic,piezoelectric,photorefractive,and pyroelectric properties.A thin-film lithium niobate photonic crystal can confine light in the sub-wavelength scale,which is beneficial to the integration of the lithium niobate on-chip device.The commercialization of the lithium niobate on insulator gives birth to the emergence of high-quality lithium niobate photonic crystals.In order to provide guidance to the research of lithium niobate photonic crystal devices,recent progress about fabrication,characterization,and applications of the thin-film lithium niobate photonic crystal is reviewed.The performance parameters of the different devices are compared.展开更多
On-chip quantum information network requires qubit transfer between different wavelengths while preserving quantum coherence and entanglement,which requires the availability of broadband upconversion.Herein,we demonst...On-chip quantum information network requires qubit transfer between different wavelengths while preserving quantum coherence and entanglement,which requires the availability of broadband upconversion.Herein,we demonstrate a mode-hybridization-based broadband nonlinear frequency conversion on X-cut thin film lithium niobate.With the spontaneous quasi-phase matching and quasi-group-velocity matching being simultaneously satisfied,broadband second-harmonic generation with a 3-dB bandwidth up to 13 nm has been achieved in a micro-racetrack resonator.The same mechanism can work on the frequency conversion of the ultrashort pulse in the bent waveguide structure.This work will be beneficial to on-chip tunable frequency conversion and quantum light source generation on integrated photonic platforms and further enable on-chip large-capacity multiplexing,multichannel optical information processing,and large quantum information networks.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.41605092)and the National Key R&D Program of China(No.2017YFC0212801)We acknowledge the Tropospheric Emission Monitoring Internet Service for OMI tropospheric NO 2 column and HCHO column products.We also thank Tsinghua University,ECMWF and NASA for free access to the Multi-resolution Emission Inventory for China(MEIC)data,the reanalysis meteorological data(ERA-Interim)and the MODIS land cover type product(MCD12Q1),respectively.
文摘Due to the influences of precursors emissions,meteorology,geography and other factors,ozone formation sensitivity(OFS)is generally spatially and temporally heterogeneous.This study characterized detailed spatial and temporal variations of OFS in Guangdong-Hong Kong-Macao Greater Bay Area(GBA)from 2012 to 2016 based on OMI satellite data,and analyzed the relationships of OFS with precursors emissions,meteorology and land use types(LUTs).From 2012 to 2016,the OFS tended to be NOx-limited in GBA,with the value of FNR(HCHO/NO 2)increasing from 2.04 to 2.22.According to the total annual emission statistics of precursors,NOx emissions decreased by 33.1%and VOCs emissions increased by 35.2%from 2012 to 2016,directly resulting in OFS tending to be NO x-limited.The Grey Relation Analysis results show that total column water(TCW),surface net solar radiation(SSR),air temperature at 2 m(T2)and surface pressure(SP)are the top four meteorological factors with the greatest influences on OFS.There are significant positive correlations between FNR and T2,SSR,TCW,and significant negative correlations between FNR and SP.In GBA,the OFS tends to be NO x-limited regime in wet season(higher T2,SSR,TCW and lower SP)and VOCs-limited regime in dry season(lower T2,SSR,TCW and higher SP).The FNR displays obvious gradient variations on different LUTs,with the highest in“Rural areas”,second in“Suburban areas”and lowest in“Urban areas”.
基金The authors thank Professor Yongxiang Hu for the ns-LSP experiment on Mg-3Gd alloy and his useful discussion.The research was supported by the National Key R&D Program of China(2017YFA0303700)the National Natural Science Foundation of China(NSFC)(11574208).
基金supported by the National Natural Science Foundation of China(Grant No.52022087).
文摘The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.
基金supported by Key-Area Research and Development Program of Guangdong Province(2021B0101420002)the Major Key Project of PCL(PCL2021A09)+3 种基金National Natural Science Foundation of China(62072187)Guangdong Major Project of Basic and Applied Basic Research(2019B030302002)Guangdong Marine Economic Development Special Fund Project(GDNRC[2022]17)Guangzhou Development Zone Science and Technology(2021GH10,2020GH10).
文摘Nowadays,the rapid development of edge computing has driven an increasing number of deep learning applications deployed at the edge of the network,such as pedestrian and vehicle detection,to provide efficient intelligent services to mobile users.However,as the accuracy requirements continue to increase,the components of deep learning models for pedestrian and vehicle detection,such as YOLOv4,become more sophisticated and the computing resources required for model training are increasing dramatically,which in turn leads to significant challenges in achieving effective deployment on resource-constrained edge devices while ensuring the high accuracy performance.For addressing this challenge,a cloud-edge collaboration-based pedestrian and vehicle detection framework is proposed in this paper,which enables sufficient training of models by utilizing the abundant computing resources in the cloud,and then deploying the well-trained models on edge devices,thus reducing the computing resource requirements for model training on edge devices.Furthermore,to reduce the size of the model deployed on edge devices,an automatic pruning method combines the convolution layer and BN layer is proposed to compress the pedestrian and vehicle detection model size.Experimental results show that the framework proposed in this paper is able to deploy the pruned model on a real edge device,Jetson TX2,with 6.72 times higher FPS.Meanwhile,the channel pruning reduces the volume and the number of parameters to 96.77%for the model,and the computing amount is reduced to 81.37%.
文摘ZnO tetrapod-like whiskers were prepared through a hydrothermal process using zinc powder as raw material.Its microstructure and morphology were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD results showed that the crystal structure of as-obtained sample can be indexed to hexagonal wurtzite ZnO.TEM results revealed that the ZnO sample took on tetrapod-like whisker shape.The gas sensors were prepared with the traditional sintering process and their gas sensitivities were detected.The test results of gas sensitivity showed that the sensors based on ZnO tetrapod-like whiskers are very sensitive to dilute ethanol vapor and H_2S.The relatively high sensitivity and selectivity of these sensors made from ZnO tetrapod-like whiskers demonstrated the potential for developing a new class of selective ethanol sensors.
文摘The Domain Decomposition Method(DDM) is a powerful approach to solving maily types of PDE's. DDM is especially suitable for massively Parallel computers. In the past, most research on DDM has focused on the domain splitting technique. In this paper. we focus our attention on use of a combination of techniques to solve each subproblem. The central question with DDM is that of how to doal with the pseodoboundary conditions. Here, we introduce a set of operators which act on the pseudo-boundaries in the solution process, referring to this new. procedure as the 'Generalized Domain Decomposition A.Jlethod(GDDM).' We have already obtained convergence factors for GDDM with certain classes of PDE's. These ctonvergence factors show that we can derive exact solutions of the whole problem for certain types of PDE's, and can get superior speed of convergence for other types.
基金Supported by grants from the Key Research and Development Program of Jiangsu Province(BE2023767a)the Fundamental Research Fund of Southeast University(3290002303A2)+6 种基金the Changjiang Scholars Talent Cultivation Project of Zhongda Hospital of Southeast University(2023YJXYYRCPY03)the Research Personnel Cultivation Programme of Zhongda Hospital Southeast University(CZXM-GSP-RC125,CZXMGSP-RC119)the China Postdoctoral Science Foundation(2024M750461)the National Natural Science Foundation of China(82402413)the Natural Science Foundation of Jiangsu Province(BK20241681)the Health Research Program of Anhui(AHWJ2023A30169)the Natural Science Foundation of Anhui Province(2508085QH314).
文摘Introduction:This study investigated the prevalence of metabolic dysfunction-associated steatotic liver disease(MASLD)with clinically significant fibrosis among obese patients with type 2 diabetes mellitus(T2DM).Methods:This multicenter study enrolled T2DM patients from tertiary hospitals and primary care facilities across 21 cities in China between 2017 and 2024.Clinically significant fibrosis was defined as liver stiffness measurement(LSM)≥8 kPa assessed by vibration-controlled transient elastography(VCTE)or biopsy-confirmed fibrosis stage≥F2.Results:Of the 10,281 patients included,9,725 comprised the VCTE cohort(5,171 from clinics and 4,554 from primary care),while 556 comprised the biopsy cohort.Overall,25.6%were obese.The prevalence of MASLD with clinically significant fibrosis reached 26.7%in obese patients,significantly exceeding that in non-obese patients(8.4%).This prevalence increased progressively with rising body mass index and demonstrated a strong association with the number of cardiometabolic risk factors.Furthermore,a non-invasive model incorporating age,waist circumference,alanine aminotransferase,total bilirubin,and triglycerides exhibited reliable performance in stratifying the risk of MASLD with clinically significant fibrosis among obese patients with T2DM[Area under the receiver operating characteristic curve(AUC):0.799(95%CI:0.767-0.832)].Conclusions:MASLD with clinically significant fibrosis is highly prevalent among obese patients with T2DM,emphasizing the necessity for systematic risk stratification and integrated management of these interconnected metabolic conditions.
基金supported by the National Key R&D Program of China (Grant Nos. 2019YFB2203500, and 2017YFA0303700)the National Natural Science Foundation of China (Grant No. 91950107)the Foundation for Development of Science and Technology of Shanghai (Grant No. 17JC1400400)。
文摘The commercialization of lithium niobate on insulator(LNOI) wafer has resulted in significant on-chip photonic integration application owing to its remarkable photonic,acousto-optic,electro-optic,and piezoelectric nature.In recent years,a variety of high-performance on-chip LNOI-based photonic devices have been realized.In this study,we developed a 1-mol% erbium-doped lithium niobate crystal and its LNOI on a silicon substrate and fabricated an erbium-doped LNOI microdisk with high quality factor(~1.05×105).C-band laser emission at ~1530 and ~1560 nm(linewidth 0.12 nm) from the high-Q erbium-doped LNOI microdisk was demonstrated with 974-and 1460-nm pumping,with the latter having better thermal stability.This microlaser would play an important role in the photonic integrated circuits of the lithium niobate platform.
基金supported by the National Key R&D Program of China(No.2017YFA0303700)the National Natural Science Foundation of China(NFSC)(No.11574208)
文摘All-optical logic gates including AND, XOR, and NOT gates, as well as a half-adder, are realized based on twodimensional lithium niobate photonic crystal(PhC) circuits with Ph C micro-cavities.The proposed all-optical devices have an extinction ratio as high as 23 dB due to the effective all-optical switch function induced by twomissing-hole micro-cavities.These proposed devices can have potential implementation of complex integrated optical functionalities including all-optical computing in a lithium niobate slab or thin film.
基金National Key R&D Program of China(2017YFA0303700)National Natural Science Foundation of China(NSFC)(11574208)
文摘Future quantum information networks operated on telecom channels require qubit transfer between different wavelengths while preserving quantum coherence and entanglement. Qubit transfer is a nonlinear optical process,but currently the types of atoms used for quantum information processing and storage are limited by the narrow bandwidth of upconversion available. Here we present the first experimental demonstration of broadband and high-efficiency quasi-phase matching second-harmonic generation(SHG) in a chip-scale periodically poled lithium niobate thin film. We achieve a large bandwidth of up to 2 THz for SHG by satisfying quasi-phase matching and group-velocity matching simultaneously. Furthermore, by changing the film thickness, the central wavelength of the quasi-phase matching SHG bandwidth can be modulated from 2.70 μm to 1.44 μm. The reconfigurable quasi-phase matching lithium niobate thin film provides a significant on-chip integrated platform for photonics and quantum optics.
基金supported by the National Key R&D Program of China(Grant No.2019YFB2203501)National Natural Science Foundation of China(Grant Nos.12134009,and 91950107)+1 种基金Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01-ZX06)Shanghai Jiao Tong University(SJTU)(Grant No.21X010200828)。
文摘In this paper,we demonstrate efficient spontaneous quasi-phase matched(SQPM)second harmonic generation(SHG)in a microracetrack resonator on X-cut thin film lithium niobate.Our approach does not involve poling,but exploits the anisotropy of the crystals to allow the phase-matching condition to be fulfilled spontaneously as the TE-polarized light circulates in a specifically designed racetrack resonator.In experiment,normalized on-chip conversion efficiencies of 1.01×10-4/W and 0.43×10-4/W are achieved by 37th-order and 111th-order SQPM,respectively.The configurable SQPM will benefit the application of nonlinear frequency conversion and quantum source generation in chip-scale integrated photonics compatible with standard CMOS fabrication processes.
基金supported by the National Key R&D Program of China(No.2019YFB2203501)the National Natural Science Foundation of China(Nos.12134009 and 91950107)+1 种基金Shanghai Municipal Science and Technology Major Project(2019SHZDZX01-ZX06)SJTU(No.21X010200828)。
文摘The compact and reliable ultraviolet[UV]source has attracted remarkable attention for its potential use in optical measurement systems,high-density optical storage,and biomedical applications.We demonstrate ultraviolet generation by frequency doubling in a lithium-tantalate-on-insulator[LTOI]microdisk via modal phase matching.The 50-μm-diameter microdisk was milled by a focused ion beam[FIB]and followed by chemo-mechanical polishing[CMP]to smooth the disk surface and edge,and the Q-factor reaches 2.74×10~5in the visible band.On-chip UV coherent light with a wavelength of384.3 nm was achieved,which shows great promise for using LTOIs in integrated ultraviolet source platforms.
文摘The modulation bandwidth of silicon-based photonics is limited to approximately 60 GHz because of the maximum carrier mobility,which limits its development in high-capacity and high-speed information processing.Lithium niobate has received much attention due to its excellent electro-optic properties.
基金supported by the National Natural Science Foundation of China(No.91950107)the National Key R&D Program of China(Nos.2019YFB2203501 and 2017YFA0303701)。
文摘We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals. By increasing the size difference of two air holes in the same unit cell, we find that the bandwidth of the lossless nontrivial edge state possesses a peak value of 0.0201(a/λ), which can be used to construct broadband valley photonic crystal waveguides. Mode field distributions verify that the waveguide is robust against sharp bends and exhibits chirality. When the unit cell is arranged in a bearded interface with the top and bottom components showing negative and positive valley Chern numbers, respectively, we find that the lithium niobate valley photonic crystal is more likely to exhibit a lossless edge state, which is difficult to be realized in valley waveguides with low refractive index materials. This work can provide guidance on the design of the high-performance topological waveguide.
基金supported by the National Natural Science Foundation of China under Grant Nos.11574208 and61235009
文摘Developing natural “free space” frequency upconversion is essential for photonic integrated circuits. In a singlecrystal lithium niobate thin film planar waveguide of less than 1 μm thickness, we achieve type I and type II mode phase-matching conditions simultaneously for this thin film planar waveguide. Finally, by employing the mode phase matching of e t e → e with d_（33） at 1018 nm, we successfully achieve a green second-harmonic wave output with the conversion efficiency of 0.12%∕（W·cm^2）, which verifies one of our simulation results. The rich mode phase matching for three-wave mixing in a thin film planar waveguide may provide a potential application in on-chip frequency upconversions for integrated photonic and quantum devices.
基金supported by the National Natural Science Foundation of China(Nos.91950107,and 12134009)the National Key R&D Program of China(No.2019YFB2203501)+1 种基金the Shanghai Municipal Science and Technology Major Project(No.2019SHZDZX01-ZX06)the SJTU(No.21X010200828)。
文摘Lithium niobate is a material that exhibits outstanding electro-optic,nonlinear optical,acousto-optic,piezoelectric,photorefractive,and pyroelectric properties.A thin-film lithium niobate photonic crystal can confine light in the sub-wavelength scale,which is beneficial to the integration of the lithium niobate on-chip device.The commercialization of the lithium niobate on insulator gives birth to the emergence of high-quality lithium niobate photonic crystals.In order to provide guidance to the research of lithium niobate photonic crystal devices,recent progress about fabrication,characterization,and applications of the thin-film lithium niobate photonic crystal is reviewed.The performance parameters of the different devices are compared.
基金supported by the National Natural Science Foundation of China(Grant No.12134009)the National Key R&D Program of China(Grant No.2019YFB2203501)SJTU(Grant No.21X010200828).
文摘On-chip quantum information network requires qubit transfer between different wavelengths while preserving quantum coherence and entanglement,which requires the availability of broadband upconversion.Herein,we demonstrate a mode-hybridization-based broadband nonlinear frequency conversion on X-cut thin film lithium niobate.With the spontaneous quasi-phase matching and quasi-group-velocity matching being simultaneously satisfied,broadband second-harmonic generation with a 3-dB bandwidth up to 13 nm has been achieved in a micro-racetrack resonator.The same mechanism can work on the frequency conversion of the ultrashort pulse in the bent waveguide structure.This work will be beneficial to on-chip tunable frequency conversion and quantum light source generation on integrated photonic platforms and further enable on-chip large-capacity multiplexing,multichannel optical information processing,and large quantum information networks.
