In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of...In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of acoustic emission(AE)signals after completing the tensile tests at ambient temperature.Using in-plane tensile at 800 and 1000°C as implementing examples,supervised recognition(K-nearest neighbor(KNN))was used to identify damage mode in real time.According to the damage identification results,four main tensile damage modes of 2D C/SiC composites were identified:matrix cracking(122.6–201 kHz),interfacial debonding(201–294.4 kHz),interfacial sliding(20.6–122.6 kHz)and fiber breaking(294.4–1000 kHz).Additionally,the damage evolution mechanisms for the 2D C/SiC composites were analyzed based on the characteristics of AE energy accumulation curve during the in-plane tensile loading at ambient and elevated temperature with oxidation.Meanwhile,the energy of various damage modes was accurately calculated by harmonic wavelet packet and the damage degree of modes could be analyzed.The identification results show that compared with previous studies,using the AE analysis method,the method has higher sensitivity and accuracy.展开更多
We demonstrate visible-light all-fiber vortex lasers by incorporating the home-made mode selective couplers (MSCs). The MSC at green or red wavebands is fabricated by specially designing and fusing a single-mode fiber...We demonstrate visible-light all-fiber vortex lasers by incorporating the home-made mode selective couplers (MSCs). The MSC at green or red wavebands is fabricated by specially designing and fusing a single-mode fiber (SMF) and a few-mode fiber (FMF). The MSCs inserted into visible fiber cavities act as power splitters and mode converters from the LP01 to LP11 mode at green and red wavelengths, respectively. The red-light all-fiber vortex laser is formed by a 10-cm Pr3+/Yb3+:ZBLAN fiber, a fiber Bragg grating, a fiber end-facet mirror and the MSC at 635 nm, which generates vortex beams with OAM±1 at 634.4 nm and an output power of 13 mW. The green-light all-fiber vortex laser consists of a 12-cm Ho3+:ZBLAN fiber, two fiber pigtail mirrors, and the MSC at 550 nm, which generates vortex beams with OAM±1 at 548.9 nm and an output power of 3 mW.展开更多
Gesture recognition technology enables machines to read human gestures and has significant application prospects in the fields of human-computer interaction and sign language translation.Existing researches usually us...Gesture recognition technology enables machines to read human gestures and has significant application prospects in the fields of human-computer interaction and sign language translation.Existing researches usually use convolutional neural networks to extract features directly from raw gesture data for gesture recognition,but the networks are affected by much interference information in the input data and thus fit to some unimportant features.In this paper,we proposed a novel method for encoding spatio-temporal information,which can enhance the key features required for gesture recognition,such as shape,structure,contour,position and hand motion of gestures,thereby improving the accuracy of gesture recognition.This encoding method can encode arbitrarily multiple frames of gesture data into a single frame of the spatio-temporal feature map and use the spatio-temporal feature map as the input to the neural network.This can guide the model to fit important features while avoiding the use of complex recurrent network structures to extract temporal features.In addition,we designed two sub-networks and trained the model using a sub-network pre-training strategy that trains the sub-networks first and then the entire network,so as to avoid the subnetworks focusing too much on the information of a single category feature and being overly influenced by each other’s features.Experimental results on two public gesture datasets show that the proposed spatio-temporal information encoding method achieves advanced accuracy.展开更多
We experimentally demonstrate two kinds of all few-mode fiber(FMF) ring lasers with high-order mode(HOM)oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable ...We experimentally demonstrate two kinds of all few-mode fiber(FMF) ring lasers with high-order mode(HOM)oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable optical vortex beams(OVBs); the other is a Q-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams(CVBs). The lasers are composed of all-FMF components and few-mode erbium-doped fiber. A Sagnac interferometer made of a 3 dB FMF coupler functions as the wavelength selector, and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube-based saturable absorbers and the nonlinear polarization rotation technique are used to achieve Q-switched CVB lasers. This is the first report, to our knowledge, on the generation of switchable-wavelength and Q-switched HOM beams in all-FMF laser cavities.展开更多
An object that possesses chirality,that is,having its mirror image not overlayed on itself by rotation and translation,can provide a different optical response to a left-or right-handed circular polarized light.Chiral...An object that possesses chirality,that is,having its mirror image not overlayed on itself by rotation and translation,can provide a different optical response to a left-or right-handed circular polarized light.Chiral nanostructures may exhibit polarization-selective optical properties that can be controlled for micro-to-nano optical element engineering.An attractive way to induce such complex nanostructures in three-dimension in glass is femtosecond laser direct writing.However,the mechanism of femtosecond laser induced chirality remains to be unveiled due to complex physical and chemical processes occurring during the ultrashort light-matter interaction.Here,a phenomenological model is proposed and is built on two-layers phase shifters to account for this laser-induced optical chirality in an initially achiral material(silica glass).This model is based on the observation that femtosecond laser induced nanogratings own two principal contributions to its aggregate birefringent response:a form and a stress-related one.By refining this formalism,a multilayer approach is developed to imprint on demand optical rotation.Values up to+/-60°at 550 nm within an optimal 80μm thickness in silica glass are possible,corresponding to the highest value in a glass to date.These results provide new insights of circular-optical control in micro-nano optical manufacturing and open new opportunities for photonics applications.展开更多
A hundred-watt-level spatial mode switchable all-fiber laser is demonstrated based on a master oscillator power amplifier scheme.The performance of the amplifier with two seed lasers,i.e.,with the acoustically induced...A hundred-watt-level spatial mode switchable all-fiber laser is demonstrated based on a master oscillator power amplifier scheme.The performance of the amplifier with two seed lasers,i.e.,with the acoustically induced fiber grating (AIFG) mode converter inside and outside the seed laser cavity,is investigated.Real-time mode switching with millisecond scale switching time between the LP;and LP;modes while operating in full power (>100 W) is realized through an AIFG driven by radio frequency modulation.This work could provide a good reference for realizing high-power agile mode switchable fiber lasers for practical applications.展开更多
We experimentally demonstrated a method of generating continuously wavelength-switchable optical vortex beams （OVBs） in an all-fiber laser. A polarization-dependent microknot resonator （MKR） functions as comb filt...We experimentally demonstrated a method of generating continuously wavelength-switchable optical vortex beams （OVBs） in an all-fiber laser. A polarization-dependent microknot resonator （MKR） functions as comb filter and accounts for the narrow linewidth （0.018 nm） of multlwavelength channels. The wavelength interval corresponds to the free spectral range of the MKR. We exploit a fused SMF-FMF （single mode fiber-few mode fiber） mode coupler to obtain broadband mode conversion and successfully achieve multiwavelength switchable OVBs. As far as we know, this is the first report about identical multiwavelength vortex beams with topological charges of 4-1. It has been verified that each channel of the vortex beams preserves the same orbital angular momentum （OAM） properties through their dear spiral interferograms. Multiwavelength vortex beams with identical OAM properties are desirable for multiplexing, exchanging, and routing to further improve the capacity of optical fiber transmission.展开更多
Temporal and spatial resonant modes are always possessed in physical systems with energy oscillation.In ultrafast fiber lasers,enormous progress has been made toward controlling the interactions of many longitudinal m...Temporal and spatial resonant modes are always possessed in physical systems with energy oscillation.In ultrafast fiber lasers,enormous progress has been made toward controlling the interactions of many longitudinal modes,which results in temporally mode-locked pulses.Recently,optical vortex beams have been extensively investigated due to their quantized orbital angular momentum,spatially donut-like intensity,and spiral phase front.In this paper,we have demonstrated the first to our knowledge observation of optical vortex mode switching and their corresponding pulse evolution dynamics in a narrow-linewidth mode-locked fiber laser.The spatial mode switching is achieved by incorporating a dual-resonant acousto-optic mode converter in the vortex mode-locked fiber laser.The vortex mode-switching dynamics have four stages,including quiet-down,relaxation oscillation,quasi mode-locking,and energy recovery prior to the stable mode-locking of another vortex mode.The evolution dynamics of the wavelength shifting during the switching process are observed via the time-stretch dispersion Fourier transform method.The spatial mode competition through optical nonlinearity induces energy fluctuation on the time scale of ultrashort pulses,which plays an essential role in the mode-switching dynamic process.The results have great implications in the study of spatial mode-locking mechanisms and ultrashort laser applications.展开更多
An all-fiberized random distributed feedback Raman fiber laser(RRFL)with LP_(11) mode output at 1134 nm has been demonstrated experimentally,where an intracavity acoustically induced fiber grating is employed for moda...An all-fiberized random distributed feedback Raman fiber laser(RRFL)with LP_(11) mode output at 1134 nm has been demonstrated experimentally,where an intracavity acoustically induced fiber grating is employed for modal switching.The maximum output power of LP_(11) mode is 93.8 W with the modal purity of 82%,calculated by numerical mode decomposition technology based on stochastic parallel-gradient descent algorithm.To our best knowledge,this is the highest output power with high purity of LP_(11) mode generated from the RRFL.This work may pave a path towards advanced fiber lasers with special temporal and spatial characteristics for applications.展开更多
Cylindrical vector beams(CVBs)with special polarization distribution have been extensively investigated due to the unique ways of interacting with matter.Although several configurations have been developed to generate...Cylindrical vector beams(CVBs)with special polarization distribution have been extensively investigated due to the unique ways of interacting with matter.Although several configurations have been developed to generate CVBs,such as Q-plates and subwavelength gratings,the bandwidth of a single CVB is inherently narrow due to the phase geometry,which would limit its application for femtosecond lasers.Here,a broadband CVB mode converter based on an acoustically induced fiber grating(AIFG)and a tuning method of dispersion turning point(DTP)is demonstrated both theoretically and experimentally with the 3-dB bandwidth of 125 nm,which is more than 10 times that of conventional AIFGs.Not only can the DTP wavelength be tuned from the original 1500 nm to 1650 nm by thinning the fiber,but also the stable generation of a single broadband HE_(21)^(odd/even) mode can be controllably implemented by adjusting the polarization state of the incident light,owing to the larger beat length difference between HE21 and other CV modes.Additionally,the femtosecond CVBs and orbital angular momentum(OAM)modes are successfully generated and amplified by combining the broadband AIFG with a figure-9 mode-locked fiber laser.Meanwhile,it is verified by simulation that the choice of broadband CV mode and the tunability of DTP wavelength can be realized by designing ring-core fibers with different structures,which can furthermore improve the flexibility of generating high purity CVBs.This study provides a highly controllable technique for the generation of broadband CVBs and OAMs paving the way for high-capacity CVBs communication.展开更多
Vector vortex beams(VVBs) have attracted considerable attention due to their unique polarization distribution and helical phase wavefront. We first attempt to retrieve the modal coefficients of hybrid VVBs measured by...Vector vortex beams(VVBs) have attracted considerable attention due to their unique polarization distribution and helical phase wavefront. We first attempt to retrieve the modal coefficients of hybrid VVBs measured by their multiplex polarized intensities using the deep learning(DL)-based stochastic parallel gradient descent(SPGD) algorithm. The Xception-based DL model with multi-view images can make an accurate prediction of modal coefficients that are validated by the theoretical calculations of the waveplate angles, demonstrating a high correlation of 99.65%. The universality of the algorithm to highorder vector-eigenmodes(VMs) decomposition is proved to enable the precise reconstruction of modal patterns generated by mode-selective couplers, which promotes the accurate characteristics of VVBs in laser beam characterization and fiber mode-division multiplexing.展开更多
基金the National Natural Science Foundation of China(Grant No.12172304)the 111 Project(Grant No.BP0719007).
文摘In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of acoustic emission(AE)signals after completing the tensile tests at ambient temperature.Using in-plane tensile at 800 and 1000°C as implementing examples,supervised recognition(K-nearest neighbor(KNN))was used to identify damage mode in real time.According to the damage identification results,four main tensile damage modes of 2D C/SiC composites were identified:matrix cracking(122.6–201 kHz),interfacial debonding(201–294.4 kHz),interfacial sliding(20.6–122.6 kHz)and fiber breaking(294.4–1000 kHz).Additionally,the damage evolution mechanisms for the 2D C/SiC composites were analyzed based on the characteristics of AE energy accumulation curve during the in-plane tensile loading at ambient and elevated temperature with oxidation.Meanwhile,the energy of various damage modes was accurately calculated by harmonic wavelet packet and the damage degree of modes could be analyzed.The identification results show that compared with previous studies,using the AE analysis method,the method has higher sensitivity and accuracy.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91750115 and 91750108)the Equipment Pre-research Project of Equipment Development Department of Central Military Commission,China(Grant No.61404140112)the Science and Technology Planning Project of Xiamen City,China(Grant No.3502Z20183003).
文摘We demonstrate visible-light all-fiber vortex lasers by incorporating the home-made mode selective couplers (MSCs). The MSC at green or red wavebands is fabricated by specially designing and fusing a single-mode fiber (SMF) and a few-mode fiber (FMF). The MSCs inserted into visible fiber cavities act as power splitters and mode converters from the LP01 to LP11 mode at green and red wavelengths, respectively. The red-light all-fiber vortex laser is formed by a 10-cm Pr3+/Yb3+:ZBLAN fiber, a fiber Bragg grating, a fiber end-facet mirror and the MSC at 635 nm, which generates vortex beams with OAM±1 at 634.4 nm and an output power of 13 mW. The green-light all-fiber vortex laser consists of a 12-cm Ho3+:ZBLAN fiber, two fiber pigtail mirrors, and the MSC at 550 nm, which generates vortex beams with OAM±1 at 548.9 nm and an output power of 3 mW.
基金This work was supported,in part,by the National Nature Science Foundation of China under grant numbers 62272236in part,by the Natural Science Foundation of Jiangsu Province under grant numbers BK20201136,BK20191401in part,by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)fund.
文摘Gesture recognition technology enables machines to read human gestures and has significant application prospects in the fields of human-computer interaction and sign language translation.Existing researches usually use convolutional neural networks to extract features directly from raw gesture data for gesture recognition,but the networks are affected by much interference information in the input data and thus fit to some unimportant features.In this paper,we proposed a novel method for encoding spatio-temporal information,which can enhance the key features required for gesture recognition,such as shape,structure,contour,position and hand motion of gestures,thereby improving the accuracy of gesture recognition.This encoding method can encode arbitrarily multiple frames of gesture data into a single frame of the spatio-temporal feature map and use the spatio-temporal feature map as the input to the neural network.This can guide the model to fit important features while avoiding the use of complex recurrent network structures to extract temporal features.In addition,we designed two sub-networks and trained the model using a sub-network pre-training strategy that trains the sub-networks first and then the entire network,so as to avoid the subnetworks focusing too much on the information of a single category feature and being overly influenced by each other’s features.Experimental results on two public gesture datasets show that the proposed spatio-temporal information encoding method achieves advanced accuracy.
基金National Natural Science Foundation of China(NSFC)(61635006,91750108,61520106014)Science and Technology Commission of Shanghai Municipality(STCSM)(16520720900)
文摘We experimentally demonstrate two kinds of all few-mode fiber(FMF) ring lasers with high-order mode(HOM)oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable optical vortex beams(OVBs); the other is a Q-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams(CVBs). The lasers are composed of all-FMF components and few-mode erbium-doped fiber. A Sagnac interferometer made of a 3 dB FMF coupler functions as the wavelength selector, and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube-based saturable absorbers and the nonlinear polarization rotation technique are used to achieve Q-switched CVB lasers. This is the first report, to our knowledge, on the generation of switchable-wavelength and Q-switched HOM beams in all-FMF laser cavities.
基金Agence Nationale pour la Recherche,FLAG-IR project,grant number ANR-18-CE08-0004-01d CNRS Défi Instrumentation aux Limites,UltraBragg project,Science and Technology Commission of Shanghai Municipality(20JC1415700)+1 种基金Jiafeng Lu acknowledges the China Scholarship Council(CSC)for the funding No.202006890077We greatly acknowledge Dr.Maxime Cavillon for valuable discussions.
文摘An object that possesses chirality,that is,having its mirror image not overlayed on itself by rotation and translation,can provide a different optical response to a left-or right-handed circular polarized light.Chiral nanostructures may exhibit polarization-selective optical properties that can be controlled for micro-to-nano optical element engineering.An attractive way to induce such complex nanostructures in three-dimension in glass is femtosecond laser direct writing.However,the mechanism of femtosecond laser induced chirality remains to be unveiled due to complex physical and chemical processes occurring during the ultrashort light-matter interaction.Here,a phenomenological model is proposed and is built on two-layers phase shifters to account for this laser-induced optical chirality in an initially achiral material(silica glass).This model is based on the observation that femtosecond laser induced nanogratings own two principal contributions to its aggregate birefringent response:a form and a stress-related one.By refining this formalism,a multilayer approach is developed to imprint on demand optical rotation.Values up to+/-60°at 550 nm within an optimal 80μm thickness in silica glass are possible,corresponding to the highest value in a glass to date.These results provide new insights of circular-optical control in micro-nano optical manufacturing and open new opportunities for photonics applications.
基金This work was supported in part by National Natural Science Foundation of China(No.61805280)Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology(No.SKL2020KF03)Research Plan of National University of Defense Technology(No.ZK19-07)。
文摘A hundred-watt-level spatial mode switchable all-fiber laser is demonstrated based on a master oscillator power amplifier scheme.The performance of the amplifier with two seed lasers,i.e.,with the acoustically induced fiber grating (AIFG) mode converter inside and outside the seed laser cavity,is investigated.Real-time mode switching with millisecond scale switching time between the LP;and LP;modes while operating in full power (>100 W) is realized through an AIFG driven by radio frequency modulation.This work could provide a good reference for realizing high-power agile mode switchable fiber lasers for practical applications.
基金National Natural Science Foundation of China(NSFC)(91750108,61635006)Science and Technology Commission of Shanghai Municipality(STCSM)(16520720900)Shanghai Education Development Foundation(SHEDF)(16SG35)
文摘We experimentally demonstrated a method of generating continuously wavelength-switchable optical vortex beams （OVBs） in an all-fiber laser. A polarization-dependent microknot resonator （MKR） functions as comb filter and accounts for the narrow linewidth （0.018 nm） of multlwavelength channels. The wavelength interval corresponds to the free spectral range of the MKR. We exploit a fused SMF-FMF （single mode fiber-few mode fiber） mode coupler to obtain broadband mode conversion and successfully achieve multiwavelength switchable OVBs. As far as we know, this is the first report about identical multiwavelength vortex beams with topological charges of 4-1. It has been verified that each channel of the vortex beams preserves the same orbital angular momentum （OAM） properties through their dear spiral interferograms. Multiwavelength vortex beams with identical OAM properties are desirable for multiplexing, exchanging, and routing to further improve the capacity of optical fiber transmission.
基金National Key Research and Development Program of China(2018YFB1801800)National Natural Science Foundation of China(91750108,61635006)111 Project(D20031)。
文摘Temporal and spatial resonant modes are always possessed in physical systems with energy oscillation.In ultrafast fiber lasers,enormous progress has been made toward controlling the interactions of many longitudinal modes,which results in temporally mode-locked pulses.Recently,optical vortex beams have been extensively investigated due to their quantized orbital angular momentum,spatially donut-like intensity,and spiral phase front.In this paper,we have demonstrated the first to our knowledge observation of optical vortex mode switching and their corresponding pulse evolution dynamics in a narrow-linewidth mode-locked fiber laser.The spatial mode switching is achieved by incorporating a dual-resonant acousto-optic mode converter in the vortex mode-locked fiber laser.The vortex mode-switching dynamics have four stages,including quiet-down,relaxation oscillation,quasi mode-locking,and energy recovery prior to the stable mode-locking of another vortex mode.The evolution dynamics of the wavelength shifting during the switching process are observed via the time-stretch dispersion Fourier transform method.The spatial mode competition through optical nonlinearity induces energy fluctuation on the time scale of ultrashort pulses,which plays an essential role in the mode-switching dynamic process.The results have great implications in the study of spatial mode-locking mechanisms and ultrashort laser applications.
基金supported by the National Natural Science Foundation of China(Nos.11704409,62061136013,and 12174445)the Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology(No.SKL2020KF03)the Special Fund for Hunan Provincial Innovative Province Building(No.2019RS3017)。
文摘An all-fiberized random distributed feedback Raman fiber laser(RRFL)with LP_(11) mode output at 1134 nm has been demonstrated experimentally,where an intracavity acoustically induced fiber grating is employed for modal switching.The maximum output power of LP_(11) mode is 93.8 W with the modal purity of 82%,calculated by numerical mode decomposition technology based on stochastic parallel-gradient descent algorithm.To our best knowledge,this is the highest output power with high purity of LP_(11) mode generated from the RRFL.This work may pave a path towards advanced fiber lasers with special temporal and spatial characteristics for applications.
基金National Natural Science Foundation of China(12274281,62275148,U2241237)Open Research Fund of State Key Laboratory of Advanced Optical Communication Systems and Networks,Shanghai Jiao Tong University(2023GZKF021)+1 种基金Jiangsu Province’s Industry Outlook and Key Core Technologies-Key Projects(BE2022055-4)111 Project(D20031).
文摘Cylindrical vector beams(CVBs)with special polarization distribution have been extensively investigated due to the unique ways of interacting with matter.Although several configurations have been developed to generate CVBs,such as Q-plates and subwavelength gratings,the bandwidth of a single CVB is inherently narrow due to the phase geometry,which would limit its application for femtosecond lasers.Here,a broadband CVB mode converter based on an acoustically induced fiber grating(AIFG)and a tuning method of dispersion turning point(DTP)is demonstrated both theoretically and experimentally with the 3-dB bandwidth of 125 nm,which is more than 10 times that of conventional AIFGs.Not only can the DTP wavelength be tuned from the original 1500 nm to 1650 nm by thinning the fiber,but also the stable generation of a single broadband HE_(21)^(odd/even) mode can be controllably implemented by adjusting the polarization state of the incident light,owing to the larger beat length difference between HE21 and other CV modes.Additionally,the femtosecond CVBs and orbital angular momentum(OAM)modes are successfully generated and amplified by combining the broadband AIFG with a figure-9 mode-locked fiber laser.Meanwhile,it is verified by simulation that the choice of broadband CV mode and the tunability of DTP wavelength can be realized by designing ring-core fibers with different structures,which can furthermore improve the flexibility of generating high purity CVBs.This study provides a highly controllable technique for the generation of broadband CVBs and OAMs paving the way for high-capacity CVBs communication.
基金supported by the National Natural Science Foundation of China (Nos.12274281,U2241237,and 62275148)the Open Research Fund of State Key Laboratory of Advanced Optical Communication Systems and Networks,Shanghai Jiao Tong University (No.2023GZKF021)+1 种基金the Jiangsu Provincial Industry Outlook and Key Core Technologies Key Projects (No.BE2022055-4)111 Project (No.D20031)。
文摘Vector vortex beams(VVBs) have attracted considerable attention due to their unique polarization distribution and helical phase wavefront. We first attempt to retrieve the modal coefficients of hybrid VVBs measured by their multiplex polarized intensities using the deep learning(DL)-based stochastic parallel gradient descent(SPGD) algorithm. The Xception-based DL model with multi-view images can make an accurate prediction of modal coefficients that are validated by the theoretical calculations of the waveplate angles, demonstrating a high correlation of 99.65%. The universality of the algorithm to highorder vector-eigenmodes(VMs) decomposition is proved to enable the precise reconstruction of modal patterns generated by mode-selective couplers, which promotes the accurate characteristics of VVBs in laser beam characterization and fiber mode-division multiplexing.
