Theoretical-based ocean wave retrieval algorithms are applied by inverting a synthetic aperture radar(SAR)intensity spectrum into a wave spectrum, that has been developed based on a SAR wave mapping mechanism. In our ...Theoretical-based ocean wave retrieval algorithms are applied by inverting a synthetic aperture radar(SAR)intensity spectrum into a wave spectrum, that has been developed based on a SAR wave mapping mechanism. In our previous studies, it was shown that the wave retrieval algorithm, named the parameterized first-guess spectrum method(PFSM), works for C-band and X-band SAR at low to moderate sea states. In this work, we investigate the performance of the PFSM algorithm when it is applied for dual-polarization c-band sentinel-1(S-1) SAR acquired in extra wide-swath(EW) and interferometric wide-swath(IW) mode under cyclonic conditions.Strong winds are retrieved from six vertical-horizontal(VH) polarization S-1 SAR images using the c-band crosspolarization coupled-parameters ocean(C-3 PO) model and then wave parameters are obtained from the image at the vertical-vertical(VV) polarization channel. significant wave height(SWH) and mean wave period(MWP) are compared with simulations from the WAVEWATCH-III(WW3) model. The validation shows a 0.69 m root mean square error(RMSE) of SWH with a –0.01 m bias and a 0.62 s RMSE of MWP with a –0.17 s bias. Although the PFSM algorithm relies on a good quality SAR spectrum, this study confirms the applicability for wave retrieval from an S-1 SAR image. Moreover, it is found that the retrieved results have less accuracy on the right sector of cyclone eyes where swell directly affects strong wind-sea, while the PFSM algorithm works well on the left and rear sectors of cyclone eyes where the interaction of wind-sea and swell is relatively poor.展开更多
The purpose is to study the accuracy of ocean wave parameters retrieved from C-band VV-polarization Sentinel-1Synthetic Aperture Radar（SAR） images, including both significant wave height（SWH） and mean wave period...The purpose is to study the accuracy of ocean wave parameters retrieved from C-band VV-polarization Sentinel-1Synthetic Aperture Radar（SAR） images, including both significant wave height（SWH） and mean wave period（MWP）, which are both calculated from a SAR-derived wave spectrum. The wind direction from in situ buoys is used and then the wind speed is retrieved by using a new C-band geophysical model function（GMF） model,denoted as C-SARMOD. Continuously, an algorithm parameterized first-guess spectra method（PFSM） is employed to retrieve the SWH and the MWP by using the SAR-derived wind speed. Forty-five VV-polarization Sentinel-1 SAR images are collected, which cover the in situ buoys around US coastal waters. A total of 52 subscenes are selected from those images. The retrieval results are compared with the measurements from in situ buoys. The comparison performs good for a wind retrieval, showing a 1.6 m/s standard deviation（STD） of the wind speed, while a 0.54 m STD of the SWH and a 2.14 s STD of the MWP are exhibited with an acceptable error.Additional 50 images taken in China＇s seas were also implemented by using the algorithm PFSM, showing a 0.67 m STD of the SWH and a 2.21 s STD of the MWP compared with European Centre for Medium-range Weather Forecasts（ECMWF） reanalysis grids wave data. The results indicate that the algorithm PFSM works for the wave retrieval from VV-polarization Sentinel-1 SAR image through SAR-derived wind speed by using the new GMF C-SARMOD.展开更多
We prove that under the condition of closed boundary to mass flux, pure advection is not a valid mechanism to make a practical thermal diode. Among the various designs of thermal diodes, many of them involve circulati...We prove that under the condition of closed boundary to mass flux, pure advection is not a valid mechanism to make a practical thermal diode. Among the various designs of thermal diodes, many of them involve circulating fluid flow, such as in thermosyphons. However, those designs often employ natural convection, which is basically a nonlinear process. It thus remains unclear how the pure advection of temperature field induced by a decoupled velocity field influences the symmetry of heat transfer. Here we study three typical models with pure advection:one with open boundary, one with closed boundary at unsteady state, and one with closed boundary at steady state. It is shown that only the last model is practical, while it cannot become a thermal diode. Finally, a general proof is given for our claim by analyzing the diffusive reciprocity.展开更多
Pursuing higher data rate with limited spectral resources is a longstanding topic that has triggered the fast growth of modern wireless communication techniques.However,the massive deployment of active nodes to compen...Pursuing higher data rate with limited spectral resources is a longstanding topic that has triggered the fast growth of modern wireless communication techniques.However,the massive deployment of active nodes to compensate for propagation loss necessitates high hardware expenditure,energy consumption,and maintenance cost,as well as complicated network interference issues.Intelligent metasurfaces,composed of a number of subwavelength passive or active meta-atoms,have recently found to be a new paradigm to actively reshape wireless communication environment in a green way,distinct from conventional works that passively adapt to the surrounding.In this review,we offer a unified perspective on how intelligent metasurfaces can facilitate wireless communication in three manners:signal relay,signal transmitter,and signal processor.We start by the basic modeling of wireless channel and the evolution of metasurfaces from passive,active to intelligent metasurfaces.Integrated with various deep learning algorithms,intelligent metasurfaces adapt to cater for the ever-changing environments without human intervention.Then,we overview specific experimental advancements using intelligent metasurfaces.We conclude by identifying key issues in the practical implementations of intelligent metasurfaces,and surveying new directions,such as gain metasurfaces and knowledge migration.展开更多
Being invisible at will has been a long-standing dream for centuries, epitomized by numerous legends;humans have never stopped their exploration steps to realize this dream. Recent years have witnessed a breakthrough ...Being invisible at will has been a long-standing dream for centuries, epitomized by numerous legends;humans have never stopped their exploration steps to realize this dream. Recent years have witnessed a breakthrough in this search due to the advent of transformation optics, metamaterials, and metasurfaces. However, the previous metasurface cloaks typically work in a reflection manner that relies on a high-reflection background, thus limiting the applications. Here, we propose an easy yet viable approach to realize the transmitted metasurface cloak, just composed of two planar metasurfaces to hide an object inside, such as a cat. To tackle the hard-to-converge issue caused by the nonuniqueness phenomenon, we deploy a tandem neural network(T-NN) to efficiently streamline the inverse design. Once pretrained, the T-NN can work for a customer-desired electromagnetic response in one single forward computation, saving a great amount of time. Our work opens a new avenue to realize a transparent invisibility cloak, and the tandem-NN can also inspire the inverse design of other metamaterials and photonics.展开更多
Recent breakthroughs in deep learning have ushered in an essential tool for optics and photonics,recurring in various applications of material design,system optimization,and automation control.Deep learning-enabled on...Recent breakthroughs in deep learning have ushered in an essential tool for optics and photonics,recurring in various applications of material design,system optimization,and automation control.Deep learning-enabled on-demand metasurface design has been the subject of extensive expansion,as it can alleviate the time-consuming,low-efficiency,and experience-orientated shortcomings in conventional numerical simulations and physics-based methods.However,collecting samples and training neural networks are fundamentally confined to predefined individual metamaterials and tend to fail for large problem sizes.Inspired by object-oriented C++programming,we propose a knowledge-inherited paradigm for multi-object and shape-unbound metasurface inverse design.Each inherited neural network carries knowledge from the"parent"metasurface and then is freely assembled to construct the"offspring"metasurface;such a process is as simple as building a container-type house.We benchmark the paradigm by the free design of aperiodic and periodic metasurfaces,with accuracies that reach 86.7%.Furthermore,we present an intelligent origami metasurface to facilitate compatible and lightweight satellite communication facilities.Our work opens up a new avenue for automatic metasurface design and leverages the assemblability to broaden the adaptability of intelligent metadevices.展开更多
Chromatic aberration-free meta-devices(e.g.,achromatic meta-devices and abnormal chromatic meta-devices)play an essential role in modern science and technology.However,current efforts suffer the issues of low efficien...Chromatic aberration-free meta-devices(e.g.,achromatic meta-devices and abnormal chromatic meta-devices)play an essential role in modern science and technology.However,current efforts suffer the issues of low efficiency,narrow operating band,and limited wavefront manipulation capability.We propose a general strategy to design chromatic aberration-free meta-devices with high-efficiency and ultrabroadband properties,which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval.The phase dispersion is tuned successfully based on a multiresonant Lorentz model,and high reflection is guaranteed by the presence of the metallic ground.As proof of the concept,two microwave meta-devices are designed,fabricated,and experimentally characterized.An achromatic meta-mirror is proposed within 8 to 12 GHz,and another abnormal chromatic meta-mirror can tune the reflection angle as a linear function.Both meta-mirrors exhibit very high efficiencies(85%to 94%in the frequency band).Our findings open a door to realize chromatic aberration-free meta-devices with high efficiency and wideband properties and stimulate the realizations of chromatic aberration-free metadevices with other functionalities or working at higher frequency.展开更多
The Bloch band theory and Brillouin zone(BZ)that characterize wave-like behaviors in periodic mediums are two cornerstones of contemporary physics,ranging from condensed matter to topological physics.Recent theoretica...The Bloch band theory and Brillouin zone(BZ)that characterize wave-like behaviors in periodic mediums are two cornerstones of contemporary physics,ranging from condensed matter to topological physics.Recent theoretical breakthrough revealed that,under the projective symmetry algebra enforced by artificial gauge fields,the usual two-dimensional(2D)BZ(orientable Brillouin two-torus)can be fundamentally modified to a non-orientable Brillouin Klein bottle with radically distinct manifold topology.However,the physical consequence of artificial gauge fields on the more general three-dimensional(3D)BZ(orientable Brillouin three-torus)was so far missing.Here,we theoretically discovered and experimentally observed that the fundamental domain and topology of the usual 3D BZ can be reduced to a non-orientable Brillouin Klein space or an orientable Brillouin half-turn space in a 3D acoustic crystal with artificial gauge fields.We experimentally identify peculiar 3D momentum-space non-symmorphic screw rotation and glide reflection symmetries in the measured band structures.Moreover,we experimentally demonstrate a novel stacked weak Klein bottle insulator featuring a nonzero Z2 topological invariant and self-collimated topological surface states at two opposite surfaces related by a nonlocal twist,radically distinct from all previous 3D topological insulators.Our discovery not only fundamentally modifies the fundamental domain and topology of 3D BZ,but also opens the door towards a wealth of previously overlooked momentum-space multidimensional manifold topologies and novel gaugesymmetry-enriched topological physics and robust acoustic wave manipulations beyond the existing paradigms.展开更多
Controlling electromagnetic(EM)waves at will is fundamentally important for diverse applications,ranging from optical microcavities,super-resolution imaging,to quantum information processing.Decades ago,the forays int...Controlling electromagnetic(EM)waves at will is fundamentally important for diverse applications,ranging from optical microcavities,super-resolution imaging,to quantum information processing.Decades ago,the forays into metamaterials and transformation optics have ignited unprecedented interest to create an invisibility cloak—a closed space with any object inside invisible.However,all features of the scattering waves become stochastic and uncontrollable when EM waves interact with an open and disordered environment,making an open invisible space almost impossible.Counterintuitively,here we for the first time present an open,cluttered,and dynamic but invisible space,wherein any freely-moving object maintains invisible.To adapt to the disordered environment,we randomly organize a swarm of reconfigurable metasurfaces,and master them by MetaSeeker,a population-based reinforcement learning(RL).MetaSeeker constructs a narcissistic internal world to mirror the stochastic physical world,capable of autonomous preferment,evolution,and adaptation.In the perception-decision-execution experiment,multiple RL agents automatically interact with the ever-changing environments and integrate a post-hoc explainability to visualize the decision-making process.The hidden objects,such as vehicle cluster and experimenter,can freely scale,race,and track in the invisible space,with the environmental similarity of 99.5%.Our results constitute a monumental stride to reshape the evolutionary landscape of metasurfaces from individual to swarm intelligence and usher in the remote management of entire EM space.展开更多
Metasurface modeling,designs,and applications using computational approaches are by now well established as an essential pillar in photonics,physics,and materials science.The past years have witnessed tremendous advan...Metasurface modeling,designs,and applications using computational approaches are by now well established as an essential pillar in photonics,physics,and materials science.The past years have witnessed tremendous advances in methodologies and technologies to unearth the intricate light–matter interaction and promote adaptive metadevices.They have pushed the studies of metasurfaces from early passive,reconfigurable modalities to the next generation of intelligent metasurfaces.In this review,we elaborate general architecture for intelligent metasurfaces,constructed by the algorithm layer,tunable metasurface layer,and application layer.We first discuss a variety of deep learning models,ranging from the fundamental neural networks inspired by computer science to sophisticated algorithms embedded with physical specialty,highlighting their potential in the forward prediction,inverse design,and spectral correlation of metasurfaces.We then discuss adaptive metadevices in the main applications of invisibility cloaks,smart vision,intelligent sensing,and wireless communication.Finally,we pinpoint current challenges and future perspectives to embrace the coming era of intelligent metasurfaces.展开更多
Optical logic operations lie at the heart of optical computing,and they enable many applications such as ultrahighspeed information processing.However,the reported optical logic gates rely heavily on the precise contr...Optical logic operations lie at the heart of optical computing,and they enable many applications such as ultrahighspeed information processing.However,the reported optical logic gates rely heavily on the precise control of input light signals,including their phase difference,polarization,and intensity and the size of the incident beams.Due to the complexity and difficulty in these precise controls,the two output optical logic states may suffer from an inherent instability and a low contrast ratio of intensity.Moreover,the miniaturization of optical logic gates becomes difficult if the extra bulky apparatus for these controls is considered.As such,it is desirable to get rid of these complicated controls and to achieve full logic functionality in a compact photonic system.Such a goal remains challenging.Here,we introduce a simple yet universal design strategy,capable of using plane waves as the incident signal,to perform optical logic operations via a diffractive neural network.Physically,the incident plane wave is first spatially encoded by a specific logic operation at the input layer and further decoded through the hidden layers,namely,a compound Huygens’metasurface.That is,the judiciously designed metasurface scatters the encoded light into one of two small designated areas at the output layer,which provides the information of output logic states.Importantly,after training of the diffractive neural network,all seven basic types of optical logic operations can be realized by the same metasurface.As a conceptual illustration,three logic operations(NOT,OR,and AND)are experimentally demonstrated at microwave frequencies.展开更多
Recent advances in non-radiative wireless power transfer(WPT)technique essentially relying on magnetic resonance and near-field coupling have successfully enabled a wide range of applications.However,WPT systems based...Recent advances in non-radiative wireless power transfer(WPT)technique essentially relying on magnetic resonance and near-field coupling have successfully enabled a wide range of applications.However,WPT systems based on double resonators are severely limited to short-or mid-range distance,due to the deteriorating efficiency and power with long transfer distance.WPT systems based on multi-relay resonators can overcome this problem,which,however,suffer from sensitivity to perturbations and fabrication imperfections.Here,we experimentally demonstrate a concept of topological wireless power transfer(TWPT),where energy is transferred efficiently via the near-field coupling between two topological edge states localized at the ends of a one-dimensional radiowave topological insulator.Such a TWPT system can be modelled as a parity-time-symmetric Su-Schrieffer-Heeger(SSH)chain with complex boundary potentials.Besides,the coil configurations are judiciously designed,which significantly suppress the unwanted cross-couplings between nonadjacent coils that could break the chiral symmetry of the SSH chain.By tuning the inter-and intra-cell coupling strengths,we theoretically and experimentally demonstrate high energy transfer efficiency near the exceptional point of the topological edge states,even in the presence of disorder.The combination of topological metamaterials,non-Hermitian physics,and WPT techniques could promise a variety of robust,efficient WPT applications over long distances in electronics,transportation,and industry.展开更多
Being invisible ad libitum has long captivated the popular imagination,particularly in terms of safeguarding modern high-end instruments from potential threats.Decades ago,the advent of metamaterials and transformatio...Being invisible ad libitum has long captivated the popular imagination,particularly in terms of safeguarding modern high-end instruments from potential threats.Decades ago,the advent of metamaterials and transformation optics sparked considerable interest in invisibility cloaks,which have been mainly demonstrated in ground and waveguide modalities.However,an omnidirectional flying cloak has not been achieved,primarily due to the challenges associated with dynamic synthesis of metasurface dispersion.We demonstrate an autonomous aeroamphibious invisibility cloak that incorporates a suite of perception,decision,and execution modules,capable of maintaining invisibility amidst kaleidoscopic backgrounds and neutralizing external stimuli.The physical breakthrough lies in the spatiotemporal modulation imparted on tunable metasurfaces to sculpt the scattering field in both space and frequency domains.To intelligently control the spatiotemporal metasurfaces,we introduce a stochastic-evolution learning that automatically aligns with the optimal solution through maximum probabilistic inference.In a fully self-driving experiment,we implement this concept on an unmanned drone and showcase adaptive invisibility in three canonical landscapes-sea,land,and air-with a similarity rate of up to 95%.Our work extends the family of invisibility cloaks to flying modality and inspires other research on material discoveries and homeostatic meta-devices.展开更多
All-optical modulators with ultrahigh speed are in high demand due to the rapid development of optical interconnection and computation. However, due to weak photon–photon interaction, the advancement of all-optical m...All-optical modulators with ultrahigh speed are in high demand due to the rapid development of optical interconnection and computation. However, due to weak photon–photon interaction, the advancement of all-optical modulators is consequently hampered by the large footprint and high power consumption. In this work, the enhanced sensitivity around an exceptional point(EP) from parity-time(PT) symmetry theory is initiatively introduced into a nonlinear all-optical modulator design. Further, a non-Hermitian all-optical modulator based on PT symmetry is proposed, which utilizes the large Kerr nonlinearity from indium tin oxide(ITO) in its epsilon-near-zero(ENZ) region. The whole system is expected to operate around EP, giving rise to the advantages of nanoscale integration and large modulation depth. This presented modulator with high efficiency and high-speed all-optical control can be commendably extended to the design methodology of various nanostructures and further prompt the development of all-optical signal processing.展开更多
Recent advances in engineered material technologies(e.g.,photonic crystals,metamaterials,plasmonics,etc.)provide valuable tools to control Cherenkov radiation.In all these approaches,however,the particle velocity is a...Recent advances in engineered material technologies(e.g.,photonic crystals,metamaterials,plasmonics,etc.)provide valuable tools to control Cherenkov radiation.In all these approaches,however,the particle velocity is a key parameter to affect Cherenkov radiation in the designed material,while the influence of the particle trajectory is generally negligible.Here,we report on surface Dyakonov-Cherenkov radiation,i.e.the emission of directional Dyakonov surface waves from a swift charged particle moving atop a birefringent crystal.This new type of Cherenkov radiation is highly susceptible to both the particle velocity and trajectory,e.g.we observe a sharp radiation enhancement when the particle trajectory falls in the vicinity of a particular direction.Moreover,close to the Cherenkov threshold,such a radiation enhancement can be orders of magnitude higher than that obtained in traditional Cherenkov detectors.These distinct properties allow us to determine simultaneously the magnitude and direction of particle velocities on a compact platform.The surface Dyakonov-Cherenkov radiation studied in this work not only adds a new degree of freedom for particle identification,but also provides an all-dielectric route to construct compact Cherenkov detectors with enhanced sensitivity.展开更多
基金The National Key Research and Development Program of China under contract No.2017YFA0604901the National Natural Science Foundation of China under contract Nos 41806005 and 41776183the Public Welfare Technical Applied Research Project of Zhejiang Province of China under contract No.LGF19D060003
文摘Theoretical-based ocean wave retrieval algorithms are applied by inverting a synthetic aperture radar(SAR)intensity spectrum into a wave spectrum, that has been developed based on a SAR wave mapping mechanism. In our previous studies, it was shown that the wave retrieval algorithm, named the parameterized first-guess spectrum method(PFSM), works for C-band and X-band SAR at low to moderate sea states. In this work, we investigate the performance of the PFSM algorithm when it is applied for dual-polarization c-band sentinel-1(S-1) SAR acquired in extra wide-swath(EW) and interferometric wide-swath(IW) mode under cyclonic conditions.Strong winds are retrieved from six vertical-horizontal(VH) polarization S-1 SAR images using the c-band crosspolarization coupled-parameters ocean(C-3 PO) model and then wave parameters are obtained from the image at the vertical-vertical(VV) polarization channel. significant wave height(SWH) and mean wave period(MWP) are compared with simulations from the WAVEWATCH-III(WW3) model. The validation shows a 0.69 m root mean square error(RMSE) of SWH with a –0.01 m bias and a 0.62 s RMSE of MWP with a –0.17 s bias. Although the PFSM algorithm relies on a good quality SAR spectrum, this study confirms the applicability for wave retrieval from an S-1 SAR image. Moreover, it is found that the retrieved results have less accuracy on the right sector of cyclone eyes where swell directly affects strong wind-sea, while the PFSM algorithm works well on the left and rear sectors of cyclone eyes where the interaction of wind-sea and swell is relatively poor.
基金The Public Welfare Technical Applied Research Project of Zhejiang Province of China under contract No.2015C31021the National Key Research and Development Program of China under contract No.2016YFC1401605the Scientific Foundation of Zhejiang Ocean University of China
文摘The purpose is to study the accuracy of ocean wave parameters retrieved from C-band VV-polarization Sentinel-1Synthetic Aperture Radar（SAR） images, including both significant wave height（SWH） and mean wave period（MWP）, which are both calculated from a SAR-derived wave spectrum. The wind direction from in situ buoys is used and then the wind speed is retrieved by using a new C-band geophysical model function（GMF） model,denoted as C-SARMOD. Continuously, an algorithm parameterized first-guess spectra method（PFSM） is employed to retrieve the SWH and the MWP by using the SAR-derived wind speed. Forty-five VV-polarization Sentinel-1 SAR images are collected, which cover the in situ buoys around US coastal waters. A total of 52 subscenes are selected from those images. The retrieval results are compared with the measurements from in situ buoys. The comparison performs good for a wind retrieval, showing a 1.6 m/s standard deviation（STD） of the wind speed, while a 0.54 m STD of the SWH and a 2.14 s STD of the MWP are exhibited with an acceptable error.Additional 50 images taken in China＇s seas were also implemented by using the algorithm PFSM, showing a 0.67 m STD of the SWH and a 2.21 s STD of the MWP compared with European Centre for Medium-range Weather Forecasts（ECMWF） reanalysis grids wave data. The results indicate that the algorithm PFSM works for the wave retrieval from VV-polarization Sentinel-1 SAR image through SAR-derived wind speed by using the new GMF C-SARMOD.
文摘We prove that under the condition of closed boundary to mass flux, pure advection is not a valid mechanism to make a practical thermal diode. Among the various designs of thermal diodes, many of them involve circulating fluid flow, such as in thermosyphons. However, those designs often employ natural convection, which is basically a nonlinear process. It thus remains unclear how the pure advection of temperature field induced by a decoupled velocity field influences the symmetry of heat transfer. Here we study three typical models with pure advection:one with open boundary, one with closed boundary at unsteady state, and one with closed boundary at steady state. It is shown that only the last model is practical, while it cannot become a thermal diode. Finally, a general proof is given for our claim by analyzing the diffusive reciprocity.
基金sponsored by the Key Research and Development Program of the Ministry of Science and Technology under Grant Nos.2022YFA1404704,2022YFA1405200,and 2022YFA1404902the National Natural Science Foundation of China(NNSFC)under Grant Nos.62422514,62471432,62101485 and 61975176+1 种基金the Key Research and Development Program of Zhejiang Province under Grant No.2022C01036the Fundamental Research Funds for the Central Universities.
文摘Pursuing higher data rate with limited spectral resources is a longstanding topic that has triggered the fast growth of modern wireless communication techniques.However,the massive deployment of active nodes to compensate for propagation loss necessitates high hardware expenditure,energy consumption,and maintenance cost,as well as complicated network interference issues.Intelligent metasurfaces,composed of a number of subwavelength passive or active meta-atoms,have recently found to be a new paradigm to actively reshape wireless communication environment in a green way,distinct from conventional works that passively adapt to the surrounding.In this review,we offer a unified perspective on how intelligent metasurfaces can facilitate wireless communication in three manners:signal relay,signal transmitter,and signal processor.We start by the basic modeling of wireless channel and the evolution of metasurfaces from passive,active to intelligent metasurfaces.Integrated with various deep learning algorithms,intelligent metasurfaces adapt to cater for the ever-changing environments without human intervention.Then,we overview specific experimental advancements using intelligent metasurfaces.We conclude by identifying key issues in the practical implementations of intelligent metasurfaces,and surveying new directions,such as gain metasurfaces and knowledge migration.
基金National Natural Science Foundation of China(11961141010,61625502,61975176,61975182,62071424)Top-Notch Young Talents Program of ChinaFundamental Research Funds for the Central Universities。
文摘Being invisible at will has been a long-standing dream for centuries, epitomized by numerous legends;humans have never stopped their exploration steps to realize this dream. Recent years have witnessed a breakthrough in this search due to the advent of transformation optics, metamaterials, and metasurfaces. However, the previous metasurface cloaks typically work in a reflection manner that relies on a high-reflection background, thus limiting the applications. Here, we propose an easy yet viable approach to realize the transmitted metasurface cloak, just composed of two planar metasurfaces to hide an object inside, such as a cat. To tackle the hard-to-converge issue caused by the nonuniqueness phenomenon, we deploy a tandem neural network(T-NN) to efficiently streamline the inverse design. Once pretrained, the T-NN can work for a customer-desired electromagnetic response in one single forward computation, saving a great amount of time. Our work opens a new avenue to realize a transparent invisibility cloak, and the tandem-NN can also inspire the inverse design of other metamaterials and photonics.
基金sponsored by the Key Research and Development Program of the Ministry of Science and Technology under Grants No.2022YFA1404704,2022YFA1404902,2022YFA1405200the National Natural Science Foundation of China(NNSFC)under Grants No.11961141010,No.61975176,the Top-Notch Young Talents Program of China and the Fundamental Research Funds for the Central Universities.
文摘Recent breakthroughs in deep learning have ushered in an essential tool for optics and photonics,recurring in various applications of material design,system optimization,and automation control.Deep learning-enabled on-demand metasurface design has been the subject of extensive expansion,as it can alleviate the time-consuming,low-efficiency,and experience-orientated shortcomings in conventional numerical simulations and physics-based methods.However,collecting samples and training neural networks are fundamentally confined to predefined individual metamaterials and tend to fail for large problem sizes.Inspired by object-oriented C++programming,we propose a knowledge-inherited paradigm for multi-object and shape-unbound metasurface inverse design.Each inherited neural network carries knowledge from the"parent"metasurface and then is freely assembled to construct the"offspring"metasurface;such a process is as simple as building a container-type house.We benchmark the paradigm by the free design of aperiodic and periodic metasurfaces,with accuracies that reach 86.7%.Furthermore,we present an intelligent origami metasurface to facilitate compatible and lightweight satellite communication facilities.Our work opens up a new avenue for automatic metasurface design and leverages the assemblability to broaden the adaptability of intelligent metadevices.
基金This work was supported by the National Natural Science Foundation of China under Grant Nos.61871394,61901512,11604167,61625502,11961141010,61975176, 62071423Postdoctoral Innovation Talents Support Program of China under Grant No.BX20190293, Natural Science Foundation of Shaanxi Province under Grant No.2019JQ-013.
文摘Chromatic aberration-free meta-devices(e.g.,achromatic meta-devices and abnormal chromatic meta-devices)play an essential role in modern science and technology.However,current efforts suffer the issues of low efficiency,narrow operating band,and limited wavefront manipulation capability.We propose a general strategy to design chromatic aberration-free meta-devices with high-efficiency and ultrabroadband properties,which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval.The phase dispersion is tuned successfully based on a multiresonant Lorentz model,and high reflection is guaranteed by the presence of the metallic ground.As proof of the concept,two microwave meta-devices are designed,fabricated,and experimentally characterized.An achromatic meta-mirror is proposed within 8 to 12 GHz,and another abnormal chromatic meta-mirror can tune the reflection angle as a linear function.Both meta-mirrors exhibit very high efficiencies(85%to 94%in the frequency band).Our findings open a door to realize chromatic aberration-free meta-devices with high efficiency and wideband properties and stimulate the realizations of chromatic aberration-free metadevices with other functionalities or working at higher frequency.
基金funding from the National Natural Science Foundation of China(62375118,6231101016,and 12104211)Shenzhen Science and Technology Innovation Commission(20220815111105001)+8 种基金SUSTech(Y01236148 and Y01236248)Zhengyou Liu acknowledges funding from the National Key R&D Program of China(2022YFA1404900 and 2018YFA0305800)the National Natural Science Foundation of China(11890701)the National Natural Science Foundation of China(12304484)Basic and Applied Basic Research Foundation of Guangdong Province(2414050002552)Shenzhen Science and Technology Innovation Commission(202308073000209)Perry Ping Shum acknowledges the National Natural Science Foundation of China(62220106006)Shenzhen Science and Technology Program(SGDX20211123114001001)Kexin Xiang acknowledges the Special Funds for the Cultivation of Guangdong College Students’Scientific and Technological Innovation(pdjh2023c21002).
文摘The Bloch band theory and Brillouin zone(BZ)that characterize wave-like behaviors in periodic mediums are two cornerstones of contemporary physics,ranging from condensed matter to topological physics.Recent theoretical breakthrough revealed that,under the projective symmetry algebra enforced by artificial gauge fields,the usual two-dimensional(2D)BZ(orientable Brillouin two-torus)can be fundamentally modified to a non-orientable Brillouin Klein bottle with radically distinct manifold topology.However,the physical consequence of artificial gauge fields on the more general three-dimensional(3D)BZ(orientable Brillouin three-torus)was so far missing.Here,we theoretically discovered and experimentally observed that the fundamental domain and topology of the usual 3D BZ can be reduced to a non-orientable Brillouin Klein space or an orientable Brillouin half-turn space in a 3D acoustic crystal with artificial gauge fields.We experimentally identify peculiar 3D momentum-space non-symmorphic screw rotation and glide reflection symmetries in the measured band structures.Moreover,we experimentally demonstrate a novel stacked weak Klein bottle insulator featuring a nonzero Z2 topological invariant and self-collimated topological surface states at two opposite surfaces related by a nonlocal twist,radically distinct from all previous 3D topological insulators.Our discovery not only fundamentally modifies the fundamental domain and topology of 3D BZ,but also opens the door towards a wealth of previously overlooked momentum-space multidimensional manifold topologies and novel gaugesymmetry-enriched topological physics and robust acoustic wave manipulations beyond the existing paradigms.
基金sponsored by the Key Research and Development Program of the Ministry of Science and Technology under Grant Nos.2022YFA1404704,2022YFA1405200,and 2022YFA1404902the National Natural Science Foundation of China(NNSFC)under Grant Nos.62422514,62471432,and 62101485+1 种基金the Key Research and Development Program of Zhejiang Province under Grant No.2022C01036the Fundamental Research Funds for the Central Universities.
文摘Controlling electromagnetic(EM)waves at will is fundamentally important for diverse applications,ranging from optical microcavities,super-resolution imaging,to quantum information processing.Decades ago,the forays into metamaterials and transformation optics have ignited unprecedented interest to create an invisibility cloak—a closed space with any object inside invisible.However,all features of the scattering waves become stochastic and uncontrollable when EM waves interact with an open and disordered environment,making an open invisible space almost impossible.Counterintuitively,here we for the first time present an open,cluttered,and dynamic but invisible space,wherein any freely-moving object maintains invisible.To adapt to the disordered environment,we randomly organize a swarm of reconfigurable metasurfaces,and master them by MetaSeeker,a population-based reinforcement learning(RL).MetaSeeker constructs a narcissistic internal world to mirror the stochastic physical world,capable of autonomous preferment,evolution,and adaptation.In the perception-decision-execution experiment,multiple RL agents automatically interact with the ever-changing environments and integrate a post-hoc explainability to visualize the decision-making process.The hidden objects,such as vehicle cluster and experimenter,can freely scale,race,and track in the invisible space,with the environmental similarity of 99.5%.Our results constitute a monumental stride to reshape the evolutionary landscape of metasurfaces from individual to swarm intelligence and usher in the remote management of entire EM space.
基金sponsored by the National Key Research and Development Program(Ministry of Science and Technology,Grant Nos.2022YFA1404704,2022YFA1405200,and 2022YFA1404902)the National Natural Science Foundation of China(NNSFC)(Grant Nos.61975176,62422514,62471432,and 62101485)+1 种基金the Key Research and Development Program of Zhejiang Province(Grant No.2022C01036)the Fundamental Research Funds for the Central Universities.
文摘Metasurface modeling,designs,and applications using computational approaches are by now well established as an essential pillar in photonics,physics,and materials science.The past years have witnessed tremendous advances in methodologies and technologies to unearth the intricate light–matter interaction and promote adaptive metadevices.They have pushed the studies of metasurfaces from early passive,reconfigurable modalities to the next generation of intelligent metasurfaces.In this review,we elaborate general architecture for intelligent metasurfaces,constructed by the algorithm layer,tunable metasurface layer,and application layer.We first discuss a variety of deep learning models,ranging from the fundamental neural networks inspired by computer science to sophisticated algorithms embedded with physical specialty,highlighting their potential in the forward prediction,inverse design,and spectral correlation of metasurfaces.We then discuss adaptive metadevices in the main applications of invisibility cloaks,smart vision,intelligent sensing,and wireless communication.Finally,we pinpoint current challenges and future perspectives to embrace the coming era of intelligent metasurfaces.
基金sponsored by the National Natural Science Foundation of China(NNSFC)under Grants Nos.61625502,11961141010,and 61975176the Top-Notch Young Talents Programme of China+4 种基金the Fundamental Research Funds for the Central UniversitiesNanyang Technological University for NAP Start-Up Grantthe Singapore Ministry of Education(Grant Nos.MOE2018-T2-1-022(S),MOE2016-T3-1-006 and Tier 1 RG174/16(S))supported by the Chinese Scholarship Council(CSC No.201906320294)Zhejiang University Academic Award for Outstanding Doctoral Candidates.
文摘Optical logic operations lie at the heart of optical computing,and they enable many applications such as ultrahighspeed information processing.However,the reported optical logic gates rely heavily on the precise control of input light signals,including their phase difference,polarization,and intensity and the size of the incident beams.Due to the complexity and difficulty in these precise controls,the two output optical logic states may suffer from an inherent instability and a low contrast ratio of intensity.Moreover,the miniaturization of optical logic gates becomes difficult if the extra bulky apparatus for these controls is considered.As such,it is desirable to get rid of these complicated controls and to achieve full logic functionality in a compact photonic system.Such a goal remains challenging.Here,we introduce a simple yet universal design strategy,capable of using plane waves as the incident signal,to perform optical logic operations via a diffractive neural network.Physically,the incident plane wave is first spatially encoded by a specific logic operation at the input layer and further decoded through the hidden layers,namely,a compound Huygens’metasurface.That is,the judiciously designed metasurface scatters the encoded light into one of two small designated areas at the output layer,which provides the information of output logic states.Importantly,after training of the diffractive neural network,all seven basic types of optical logic operations can be realized by the same metasurface.As a conceptual illustration,three logic operations(NOT,OR,and AND)are experimentally demonstrated at microwave frequencies.
基金sponsored by the National Natural Science Foundation of China (61625502, 11961141010, 61975176, and U19A2054)the Top-Notch Young Talents Program of China+1 种基金the Fundamental Research Funds for the Central Universitiessponsored by Singapore Ministry of Education under Grant Nos. MOE2018-T2-1-022 (S), MOE2015-T2-1-070, MOE2016-T3-1-006, and Tier 1 RG174/16 (S)
文摘Recent advances in non-radiative wireless power transfer(WPT)technique essentially relying on magnetic resonance and near-field coupling have successfully enabled a wide range of applications.However,WPT systems based on double resonators are severely limited to short-or mid-range distance,due to the deteriorating efficiency and power with long transfer distance.WPT systems based on multi-relay resonators can overcome this problem,which,however,suffer from sensitivity to perturbations and fabrication imperfections.Here,we experimentally demonstrate a concept of topological wireless power transfer(TWPT),where energy is transferred efficiently via the near-field coupling between two topological edge states localized at the ends of a one-dimensional radiowave topological insulator.Such a TWPT system can be modelled as a parity-time-symmetric Su-Schrieffer-Heeger(SSH)chain with complex boundary potentials.Besides,the coil configurations are judiciously designed,which significantly suppress the unwanted cross-couplings between nonadjacent coils that could break the chiral symmetry of the SSH chain.By tuning the inter-and intra-cell coupling strengths,we theoretically and experimentally demonstrate high energy transfer efficiency near the exceptional point of the topological edge states,even in the presence of disorder.The combination of topological metamaterials,non-Hermitian physics,and WPT techniques could promise a variety of robust,efficient WPT applications over long distances in electronics,transportation,and industry.
基金sponsored by the National Natural Science Foundation of China(Grant Nos.61625502,11961141010,61975176,62071424,and 62101485)the Young Elite Scientists Sponsorship Program by CAST(Grant No.2022QNRC001)+1 种基金the Top-Notch Young Talents Program of Chinathe Fundamental Research Funds for the Central Universities
文摘Being invisible ad libitum has long captivated the popular imagination,particularly in terms of safeguarding modern high-end instruments from potential threats.Decades ago,the advent of metamaterials and transformation optics sparked considerable interest in invisibility cloaks,which have been mainly demonstrated in ground and waveguide modalities.However,an omnidirectional flying cloak has not been achieved,primarily due to the challenges associated with dynamic synthesis of metasurface dispersion.We demonstrate an autonomous aeroamphibious invisibility cloak that incorporates a suite of perception,decision,and execution modules,capable of maintaining invisibility amidst kaleidoscopic backgrounds and neutralizing external stimuli.The physical breakthrough lies in the spatiotemporal modulation imparted on tunable metasurfaces to sculpt the scattering field in both space and frequency domains.To intelligently control the spatiotemporal metasurfaces,we introduce a stochastic-evolution learning that automatically aligns with the optimal solution through maximum probabilistic inference.In a fully self-driving experiment,we implement this concept on an unmanned drone and showcase adaptive invisibility in three canonical landscapes-sea,land,and air-with a similarity rate of up to 95%.Our work extends the family of invisibility cloaks to flying modality and inspires other research on material discoveries and homeostatic meta-devices.
基金National Natural Science Foundation of China(62005237)National Key Research and Development Program of China(2021YFB2801801).
文摘All-optical modulators with ultrahigh speed are in high demand due to the rapid development of optical interconnection and computation. However, due to weak photon–photon interaction, the advancement of all-optical modulators is consequently hampered by the large footprint and high power consumption. In this work, the enhanced sensitivity around an exceptional point(EP) from parity-time(PT) symmetry theory is initiatively introduced into a nonlinear all-optical modulator design. Further, a non-Hermitian all-optical modulator based on PT symmetry is proposed, which utilizes the large Kerr nonlinearity from indium tin oxide(ITO) in its epsilon-near-zero(ENZ) region. The whole system is expected to operate around EP, giving rise to the advantages of nanoscale integration and large modulation depth. This presented modulator with high efficiency and high-speed all-optical control can be commendably extended to the design methodology of various nanostructures and further prompt the development of all-optical signal processing.
基金Y.L.was sponsored in part by Singapore Ministry of Education(No.MOE2018-T2-2-189(S)),MOE2017-T1-001-239(RG91/17(S)),A*Star AME Programmatic Funds(No.A18A7b0058)and National Research Foundation Singapore Competitive Research Program(No.NRF-CRP18-2017-02)B.Z.was sponsored in part by Singapore Ministry of Education(No.MOE2018‐T2‐1‐022(S),MOE2016‐T3‐1‐006 and Tier 1 RG174/16(S))+3 种基金L.J.W.was sponsored in part by the Advanced Manufacturing and Engineering Young Individual Research Grant(No.A1984c0043)from the Science and Engineering Research Council of the Agency for Science,Technology and Research,SingaporeX.L.was sponsored in part by the National Natural Science Foundation of China(NSFC)(No.62175212)Fundamental Research Funds for the Central Universities(No.2021FZZX001-19)Zhejiang University Global Partnership Fund.
文摘Recent advances in engineered material technologies(e.g.,photonic crystals,metamaterials,plasmonics,etc.)provide valuable tools to control Cherenkov radiation.In all these approaches,however,the particle velocity is a key parameter to affect Cherenkov radiation in the designed material,while the influence of the particle trajectory is generally negligible.Here,we report on surface Dyakonov-Cherenkov radiation,i.e.the emission of directional Dyakonov surface waves from a swift charged particle moving atop a birefringent crystal.This new type of Cherenkov radiation is highly susceptible to both the particle velocity and trajectory,e.g.we observe a sharp radiation enhancement when the particle trajectory falls in the vicinity of a particular direction.Moreover,close to the Cherenkov threshold,such a radiation enhancement can be orders of magnitude higher than that obtained in traditional Cherenkov detectors.These distinct properties allow us to determine simultaneously the magnitude and direction of particle velocities on a compact platform.The surface Dyakonov-Cherenkov radiation studied in this work not only adds a new degree of freedom for particle identification,but also provides an all-dielectric route to construct compact Cherenkov detectors with enhanced sensitivity.
