Data transmission rates in optical communication systems are approaching the limits of conventional multiplexing methods.Orbital angular momentum(OAM)in optical vortex beams offers a new degree of freedom and the pote...Data transmission rates in optical communication systems are approaching the limits of conventional multiplexing methods.Orbital angular momentum(OAM)in optical vortex beams offers a new degree of freedom and the potential to increase the capacity of free-space optical communication systems,with OAM beams acting as information carriers for OAM division multiplexing(OAM-DM).We demonstrate independent collinear OAM channel generation,transmission and simultaneous detection using Dammann optical vortex gratings(DOVGs).We achieve 80/160 Tbit s^(-1) capacity with uniform power distributions along all channels,with 1600 individually modulated quadrature phase-shift keying(QPSK)/16-QAM data channels multiplexed by 10 OAM states,80 wavelengths and two polarizations.DOVG-enabled OAM multiplexing technology removes the bottleneck of massive OAM state parallel detection and offers an opportunity to raise optical communication systems capacity to Pbit s^(-1) level.展开更多
Light beams with a helical phase-front possess orbital angular momentum along their direction of propagation in addition to the spin angular momentum that describes their polarisation.Until recently,it was thought tha...Light beams with a helical phase-front possess orbital angular momentum along their direction of propagation in addition to the spin angular momentum that describes their polarisation.Until recently,it was thought that these two‘rotational’motions of light were largely independent and could not be coupled during light–matter interactions.However,it is now known that interactions with carefully designed complex media can result in spin-to-orbit coupling,where a change of the spin angular momentum will modify the orbital angular momentum and vice versa.In this work,we propose and demonstrate that the birefringence of plasmonic nanostructures can be wielded to transform circularly polarised light into light carrying orbital angular momentum.A device operating at visible wavelengths is designed from a space-variant array of subwavelength plasmonic nano-antennas.Experiment confirms that circularly polarised light transmitted through the device is imbued with orbital angular momentum of 62"(with conversion efficiency of at least 1%).This technology paves the way towards ultrathin orbital angular momentum generators that could be integrated into applications for spectroscopy,nanoscale sensing and classical or quantum communications using integrated photonic devices.展开更多
The back propagation (BP)-based artificial neural nets (ANN) can identify complicated relationships among dissolved gas contents in transformer oil and corresponding fault types, using the highly nonlinear mapping nat...The back propagation (BP)-based artificial neural nets (ANN) can identify complicated relationships among dissolved gas contents in transformer oil and corresponding fault types, using the highly nonlinear mapping nature of the neural nets. An efficient BP-ALM (BP with Adaptive Learning Rate and Momentum coefficient) algorithm is proposed to reduce the training time and avoid being trapped into local minima, where the learning rate and the momentum coefficient are altered at iterations. We developed a system of transformer fault diagnosis based on Dissolved Gases Analysis (DGA) with a BP-ALM algorithm. Training patterns were selected from the results of a Refined Three-Ratio method (RTR). Test results show that the system has a better ability of quick learning and global convergence than other methods and a superior performance in fault diagnosis compared to convectional BP-based neural networks and RTR.展开更多
PETREL, a winged hybrid-driven underwater glider is a novel and practical marine survey platform which combines the features of legacy underwater glider and conventional AUV （autonomous underwater vehicle）. It can b...PETREL, a winged hybrid-driven underwater glider is a novel and practical marine survey platform which combines the features of legacy underwater glider and conventional AUV （autonomous underwater vehicle）. It can be treated as a multi-rigid-body system with a floating base and a particular hydrodynamic profile. In this paper, theorems on linear and angular momentum are used to establish the dynamic equations of motion of each rigid body and the effect of translational and rotational motion of internal masses on the attitude control are taken into consideration. In addition, due to the unique external shape with fixed wings and deflectable rudders and the dual-drive operation in thrust and glide modes, the approaches of building dynamic model of conventional AUV and hydrodynamic model of submarine are introduced, and the tailored dynamic equations of the hybrid glider are formulated. Moreover, the behaviors of motion in glide and thrust operation are analyzed based on the simulation and the feasibility of the dynamic model is validated by data from lake field trials.展开更多
Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer.In the case of 3D trapping with a single beam,this is termed optical tweezers.Optical tweezers ...Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer.In the case of 3D trapping with a single beam,this is termed optical tweezers.Optical tweezers are a powerful and noninvasive tool for manipulating small objects,and have become indispensable in many fields,including physics,biology,soft condensed matter,among others.In the early days,optical trapping was typically accomplished with a single Gaussian beam.In recent years,we have witnessed rapid progress in the use of structured light beams with customized phase,amplitude,and polarization in optical trapping.Unusual beam properties,such as phase singularities on-axis and propagation invariant nature,have opened up novel capabilities to the study of micromanipulation in liquid,air,and vacuum.We summarize the recent advances in the field of optical trapping using structured light beams.展开更多
With inherent orthogonality,both the spin angular momentum(SAM)and orbital angular momentum(OAM)of photons have been utilized to expand the dimensions of quantum information,optical communications,and information proc...With inherent orthogonality,both the spin angular momentum(SAM)and orbital angular momentum(OAM)of photons have been utilized to expand the dimensions of quantum information,optical communications,and information processing,wherein simultaneous detection of SAMs and OAMs with a single element and a single-shot measurement is highly anticipated.Here,a single azimuthal-quadratic phase metasurface-based photonic momentum transformation(PMT)is illustrated and utilized for vortex recognition.Since different vortices are converted into focusing patterns with distinct azimuthal coordinates on a transverse plane through PMT,OAMs within a large mode space can be determined through a single-shot measurement.Moreover,spin-controlled dual-functional PMTs are proposed for simultaneous SAM and OAM sorting,which is implemented by a single spin-decoupled metasurface that merges both the geometric phase and dynamic phase.Interestingly,our proposed method can detect vectorial vortices with both phase and polarization singularities,as well as superimposed vortices with a certain interval step.Experimental results obtained at several wavelengths in the visible band exhibit good agreement with the numerical modeling.With the merits of ultracompact device size,simple optical configuration,and prominent vortex recognition ability,our approach may underpin the development of integrated and high-dimensional optical and quantum systems.展开更多
基金This work was partially supported by the National Natural Science Foundation of China under Grant numbers 61036013,61138003,61427819,61001101 and 61435006XY acknowledges support from the Ministry of Science and Technology of China under National Basic Research Program of China(973)grant no.2015CB352004.
文摘Data transmission rates in optical communication systems are approaching the limits of conventional multiplexing methods.Orbital angular momentum(OAM)in optical vortex beams offers a new degree of freedom and the potential to increase the capacity of free-space optical communication systems,with OAM beams acting as information carriers for OAM division multiplexing(OAM-DM).We demonstrate independent collinear OAM channel generation,transmission and simultaneous detection using Dammann optical vortex gratings(DOVGs).We achieve 80/160 Tbit s^(-1) capacity with uniform power distributions along all channels,with 1600 individually modulated quadrature phase-shift keying(QPSK)/16-QAM data channels multiplexed by 10 OAM states,80 wavelengths and two polarizations.DOVG-enabled OAM multiplexing technology removes the bottleneck of massive OAM state parallel detection and offers an opportunity to raise optical communication systems capacity to Pbit s^(-1) level.
文摘Light beams with a helical phase-front possess orbital angular momentum along their direction of propagation in addition to the spin angular momentum that describes their polarisation.Until recently,it was thought that these two‘rotational’motions of light were largely independent and could not be coupled during light–matter interactions.However,it is now known that interactions with carefully designed complex media can result in spin-to-orbit coupling,where a change of the spin angular momentum will modify the orbital angular momentum and vice versa.In this work,we propose and demonstrate that the birefringence of plasmonic nanostructures can be wielded to transform circularly polarised light into light carrying orbital angular momentum.A device operating at visible wavelengths is designed from a space-variant array of subwavelength plasmonic nano-antennas.Experiment confirms that circularly polarised light transmitted through the device is imbued with orbital angular momentum of 62"(with conversion efficiency of at least 1%).This technology paves the way towards ultrathin orbital angular momentum generators that could be integrated into applications for spectroscopy,nanoscale sensing and classical or quantum communications using integrated photonic devices.
文摘The back propagation (BP)-based artificial neural nets (ANN) can identify complicated relationships among dissolved gas contents in transformer oil and corresponding fault types, using the highly nonlinear mapping nature of the neural nets. An efficient BP-ALM (BP with Adaptive Learning Rate and Momentum coefficient) algorithm is proposed to reduce the training time and avoid being trapped into local minima, where the learning rate and the momentum coefficient are altered at iterations. We developed a system of transformer fault diagnosis based on Dissolved Gases Analysis (DGA) with a BP-ALM algorithm. Training patterns were selected from the results of a Refined Three-Ratio method (RTR). Test results show that the system has a better ability of quick learning and global convergence than other methods and a superior performance in fault diagnosis compared to convectional BP-based neural networks and RTR.
基金supported by the National Natural Science Foundation of China(Grant Nos. 50835006 and 51005161)the Science & Technology Support Planning Foundation of Tianjin(Grant No. 09ZCKFGX03000)the Natural Science Foundation of Tianjin(Grant No. 09JCZDJC23400)
文摘PETREL, a winged hybrid-driven underwater glider is a novel and practical marine survey platform which combines the features of legacy underwater glider and conventional AUV （autonomous underwater vehicle）. It can be treated as a multi-rigid-body system with a floating base and a particular hydrodynamic profile. In this paper, theorems on linear and angular momentum are used to establish the dynamic equations of motion of each rigid body and the effect of translational and rotational motion of internal masses on the attitude control are taken into consideration. In addition, due to the unique external shape with fixed wings and deflectable rudders and the dual-drive operation in thrust and glide modes, the approaches of building dynamic model of conventional AUV and hydrodynamic model of submarine are introduced, and the tailored dynamic equations of the hybrid glider are formulated. Moreover, the behaviors of motion in glide and thrust operation are analyzed based on the simulation and the feasibility of the dynamic model is validated by data from lake field trials.
基金We thank Professor Kishan Dholakia for his instructive advice and help on the preparation of the manuscript.Y.Y thanks Dr.Leiming Zhou for the helpful discussion.This work was supported by the National Natural Science Foundation of China(11874102 and 61975047)the Sichuan Province Science and Technology Support Program(2020JDRC0006)the Fundamental Research Funds for the Central Universities(ZYGX2019J102).M.C.and Y.A.thank the UK Engineering and Physical Sciences Research Council for funding.
文摘Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer.In the case of 3D trapping with a single beam,this is termed optical tweezers.Optical tweezers are a powerful and noninvasive tool for manipulating small objects,and have become indispensable in many fields,including physics,biology,soft condensed matter,among others.In the early days,optical trapping was typically accomplished with a single Gaussian beam.In recent years,we have witnessed rapid progress in the use of structured light beams with customized phase,amplitude,and polarization in optical trapping.Unusual beam properties,such as phase singularities on-axis and propagation invariant nature,have opened up novel capabilities to the study of micromanipulation in liquid,air,and vacuum.We summarize the recent advances in the field of optical trapping using structured light beams.
基金the National Natural Science Funds of China under Grant Nos.61875253 and 61975210 and the Chinese Academy of Sciences Youth Innovation Promotion Association under Grant No.2019371.
文摘With inherent orthogonality,both the spin angular momentum(SAM)and orbital angular momentum(OAM)of photons have been utilized to expand the dimensions of quantum information,optical communications,and information processing,wherein simultaneous detection of SAMs and OAMs with a single element and a single-shot measurement is highly anticipated.Here,a single azimuthal-quadratic phase metasurface-based photonic momentum transformation(PMT)is illustrated and utilized for vortex recognition.Since different vortices are converted into focusing patterns with distinct azimuthal coordinates on a transverse plane through PMT,OAMs within a large mode space can be determined through a single-shot measurement.Moreover,spin-controlled dual-functional PMTs are proposed for simultaneous SAM and OAM sorting,which is implemented by a single spin-decoupled metasurface that merges both the geometric phase and dynamic phase.Interestingly,our proposed method can detect vectorial vortices with both phase and polarization singularities,as well as superimposed vortices with a certain interval step.Experimental results obtained at several wavelengths in the visible band exhibit good agreement with the numerical modeling.With the merits of ultracompact device size,simple optical configuration,and prominent vortex recognition ability,our approach may underpin the development of integrated and high-dimensional optical and quantum systems.
