Optical singularities are topological defects of electromagnetic fields;they include phase singularity in scalar fields,polarization singularity in vector fields,and three-dimensional(3D)singularities such as optical ...Optical singularities are topological defects of electromagnetic fields;they include phase singularity in scalar fields,polarization singularity in vector fields,and three-dimensional(3D)singularities such as optical skyrmions.The exploitation of photonic microstructures to generate and manipulate optical singularities has attracted wide research interest in recent years,with many photonic microstructures having been devised to this end.Accompanying these designs,scattered phenomenological theories have been proposed to expound the working mechanisms behind individual designs.In this work,instead of focusing on a specific type of microstructure,we concentrate on the most common geometric features of these microstructures—namely,symmetries—and revisit the process of generating optical singularities in microstructures from a symmetry viewpoint.By systematically employing the projection operator technique in group theory,we develop a widely applicable theoretical scheme to explore optical singularities in microstructures with rosette(i.e.,rotational and reflection)symmetries.Our scheme agrees well with previously reported works and further reveals that the eigenmodes of a symmetric microstructure can support multiplexed phase singularities in different components,such as out-of-plane,radial,azimuthal,and left-and right-handed circular components.Based on these phase singularities,more complicated optical singularities may be synthesized,including C points,V points,L lines,Néel-and bubble-type optical skyrmions,and optical lattices,to name a few.We demonstrate that the topological invariants associated with optical singularities are protected by the symmetries of the microstructure.Lastly,based on symmetry arguments,we formulate a so-called symmetry matching condition to clarify the excitation of a specific type of optical singularity.Our work establishes a unified theoretical framework to explore optical singularities in photonic microstructures with symmetries,shedding light on the symmetry origin of multidimensional and multiplexed optical singularities and providing a symmetry perspective for exploring many singularity-related effects in optics and photonics.展开更多
In dielectric physics,electromagnetic(EM)properties of dielectrics arise from several important polarization mechanisms that can be described by Debye,Drude or Lorentz models.Metamaterials,as well as their 2D counterp...In dielectric physics,electromagnetic(EM)properties of dielectrics arise from several important polarization mechanisms that can be described by Debye,Drude or Lorentz models.Metamaterials,as well as their 2D counterparts-metasurfaces,can exhibit bizarre EM parameters such as negative permittivity,whereas polarization mechanisms leading to such have long been discussed in dielectric physics.Drude and Lorentz's models are usually used in metamaterial design,whereas the Debye model is almost absent,though it is so important in dielectric physics.This leaves an unreconciled gap between the dielectric physics and metamaterials.In this paper,we explore Debye relaxations in metasurfaces for the sake of wideband dispersion engineering.By analyzing two fundamental resonance modes of a typical meta-atom,we first show that the reflection phase experiences 1^(st)-order Debye relaxation under the two resonances,although they are typically Lorentzian.More importantly,the two resonances can be tailored to form a 2nd-order Debye relaxation process so as to achieve smooth phase variations in between them,which lays a solid foundation for wideband dispersion engineering.As proof of concept,we propose a quad-ellipticalarc(QEA)structure as the meta-atom,whose dispersion can be customized by tailoring the 2nd-order Debye relaxation.With this meta-atom,we demonstrated two metasurface prototypes that can achieve chromatic and achromatic focusing,respectively,in the entire X band(8.0–12.0 GHz),showcasing the powerful capacity of wideband dispersion engineering.This work digs out relaxation processes in metamaterials and opens up new territories for metamaterial research,which may find wide applications in wideband devices and systems.展开更多
Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such ge...Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such geometric phases are usually spin-coupled,with the same magnitude but opposite signs for left-and right-handed circularly polarized(LCP and RCP)waves.To achieve independent control of LCP and RCP waves,it is crucial to obtain spin-decoupled geometric phases.In this paper,we propose to obtain completely spin-decoupled geometric phases by engineering the surface current paths on meta-atoms.Based on the rotational Doppler effect,the rotation manner is first analyzed,and it is found that the generation of a geometric phase lies in the rotation of the surface current paths on meta-atoms.Since the induced surface current paths under the LCP and RCP waves always start oppositely and are mirror-symmetrical with each other,it is natural that the geometric phases have the same magnitude and opposite signs when the meta-atoms are rotated.To obtain spin-decoupled geometric phases,the induced surface current under one spin should be rotated by one angle while the current under the other spin is rotated by a different angles.In this way,LCP and RCP waves can acquire different geometric phase changes.Proof-of-principle prototypes were designed,fabricated,and measured.Both the simulation and experiment results verify spin-decoupled geometric phases.This work provides a robust means to obtain a spindependent geometric phase and can be readily extended to higher frequency bands such as the terahertz,IR,and optical regimes.展开更多
The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),...The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),whose functions or operating modes can be switched or customized via on-site programming or pre-defined software.Nevertheless,most of existing PMs are wire-connected to users,manually-controlled and not real-time.Here,we propose the concept of remotely mind-controlled metasurface(RMCM)via brainwaves.Rather than DC voltage from power supply or AC voltages from signal generators,the metasurface is controlled by brainwaves collected in real time and transmitted wirelessly from the user.As an example,we demonstrated a RMCM whose scattering pattern can be altered dynamically according to the user’s brain waves via Bluetooth.The attention intensity information is extracted as the control signal and a mapping between attention intensity and scattering pattern of the metasurface is established.With such a framework,we experimentally demonstrated and verified a prototype of such metasurface system which can be remotely controlled by the user to modify its scattering pattern.This work paves a new way to intelligent metasurfaces and may find applications in health monitoring,5G/6G communications,smart sensors,etc.展开更多
Coding metasurfaces can manipulate electromagnetic wave in real time with high degree of freedom,the fascinating properties of which enrich the metasurface design with a wide range of application prospects.However,mos...Coding metasurfaces can manipulate electromagnetic wave in real time with high degree of freedom,the fascinating properties of which enrich the metasurface design with a wide range of application prospects.However,most of the coding metasurfaces are designed based on external excitation framework with the wired electrical or wireless light control devices,thus inevitably causing the interference with electromagnetic wave transmission and increasing the complexity of the metasurface design.In this work,a simplistic framework of single-pixel-programmable metasurfaces integrated with a capsuled LED array is proposed to dynamically control electromagnetic wave.The framework fully embeds the photoresistor in the meta-atom,controlling the LED array to directly illuminate the photoresistor to modulate the phase response.With this manner,the complex biasing network is transformed to the universal LED array,which means the physical control framework can be transformed to a software framework,and thus the functions of the metasurface can be freely manipulated by encoding the capsuled LED array avoiding mutual coupling of adjacent meta-atoms in real time.All the results verify that the far-field scattering pattern can be customized with this singlepixel-programmable metasurface.Encouragingly,this work provides a universal framework for coding metasurface design,which lays the foundation for metasurface intelligent perception and adaptive modulation.展开更多
基金supported by the National Natural Science Foun-dation of China(62301596 and 62288101)Shaanxi Provincial Science and Technology Innovation Team(23-CX-TD-48)+4 种基金the KU Leuven internal funds:the C1 Project(C14/19/083)the Interdisciplinary Network Project(IDN/20/014)the Small Infrastructure Grant(KA/20/019)the Research Foundation of Flanders(FWO)Project(G090017N,G088822N,and V408823N)the Danish National Research Foundation(DNRF165).
文摘Optical singularities are topological defects of electromagnetic fields;they include phase singularity in scalar fields,polarization singularity in vector fields,and three-dimensional(3D)singularities such as optical skyrmions.The exploitation of photonic microstructures to generate and manipulate optical singularities has attracted wide research interest in recent years,with many photonic microstructures having been devised to this end.Accompanying these designs,scattered phenomenological theories have been proposed to expound the working mechanisms behind individual designs.In this work,instead of focusing on a specific type of microstructure,we concentrate on the most common geometric features of these microstructures—namely,symmetries—and revisit the process of generating optical singularities in microstructures from a symmetry viewpoint.By systematically employing the projection operator technique in group theory,we develop a widely applicable theoretical scheme to explore optical singularities in microstructures with rosette(i.e.,rotational and reflection)symmetries.Our scheme agrees well with previously reported works and further reveals that the eigenmodes of a symmetric microstructure can support multiplexed phase singularities in different components,such as out-of-plane,radial,azimuthal,and left-and right-handed circular components.Based on these phase singularities,more complicated optical singularities may be synthesized,including C points,V points,L lines,Néel-and bubble-type optical skyrmions,and optical lattices,to name a few.We demonstrate that the topological invariants associated with optical singularities are protected by the symmetries of the microstructure.Lastly,based on symmetry arguments,we formulate a so-called symmetry matching condition to clarify the excitation of a specific type of optical singularity.Our work establishes a unified theoretical framework to explore optical singularities in photonic microstructures with symmetries,shedding light on the symmetry origin of multidimensional and multiplexed optical singularities and providing a symmetry perspective for exploring many singularity-related effects in optics and photonics.
基金supported by the National Natural Science Foundation of China(Nos.62401616,62101588,62301596)the National Key Research and Development Program of China(2022YFB3806200)the Young Innovation Team Project of Shaanxi province(2023-CX-TD-48).
文摘In dielectric physics,electromagnetic(EM)properties of dielectrics arise from several important polarization mechanisms that can be described by Debye,Drude or Lorentz models.Metamaterials,as well as their 2D counterparts-metasurfaces,can exhibit bizarre EM parameters such as negative permittivity,whereas polarization mechanisms leading to such have long been discussed in dielectric physics.Drude and Lorentz's models are usually used in metamaterial design,whereas the Debye model is almost absent,though it is so important in dielectric physics.This leaves an unreconciled gap between the dielectric physics and metamaterials.In this paper,we explore Debye relaxations in metasurfaces for the sake of wideband dispersion engineering.By analyzing two fundamental resonance modes of a typical meta-atom,we first show that the reflection phase experiences 1^(st)-order Debye relaxation under the two resonances,although they are typically Lorentzian.More importantly,the two resonances can be tailored to form a 2nd-order Debye relaxation process so as to achieve smooth phase variations in between them,which lays a solid foundation for wideband dispersion engineering.As proof of concept,we propose a quad-ellipticalarc(QEA)structure as the meta-atom,whose dispersion can be customized by tailoring the 2nd-order Debye relaxation.With this meta-atom,we demonstrated two metasurface prototypes that can achieve chromatic and achromatic focusing,respectively,in the entire X band(8.0–12.0 GHz),showcasing the powerful capacity of wideband dispersion engineering.This work digs out relaxation processes in metamaterials and opens up new territories for metamaterial research,which may find wide applications in wideband devices and systems.
基金Young Talent Fund of Association for Science and Technology in Shaanxi (20220102)National Natural Science Foundation of China (61971435,62101588)。
文摘Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such geometric phases are usually spin-coupled,with the same magnitude but opposite signs for left-and right-handed circularly polarized(LCP and RCP)waves.To achieve independent control of LCP and RCP waves,it is crucial to obtain spin-decoupled geometric phases.In this paper,we propose to obtain completely spin-decoupled geometric phases by engineering the surface current paths on meta-atoms.Based on the rotational Doppler effect,the rotation manner is first analyzed,and it is found that the generation of a geometric phase lies in the rotation of the surface current paths on meta-atoms.Since the induced surface current paths under the LCP and RCP waves always start oppositely and are mirror-symmetrical with each other,it is natural that the geometric phases have the same magnitude and opposite signs when the meta-atoms are rotated.To obtain spin-decoupled geometric phases,the induced surface current under one spin should be rotated by one angle while the current under the other spin is rotated by a different angles.In this way,LCP and RCP waves can acquire different geometric phase changes.Proof-of-principle prototypes were designed,fabricated,and measured.Both the simulation and experiment results verify spin-decoupled geometric phases.This work provides a robust means to obtain a spindependent geometric phase and can be readily extended to higher frequency bands such as the terahertz,IR,and optical regimes.
基金National Natural Science Foundation of China under Grant Nos.61971435,62101588,62101589National Key Research and Development Program of China(Grant No.:SQ2017YFA0700201)+1 种基金C.-W.Q.is supported by a grant(R-261-518-004-720|A-0005947-16-00)from Advanced Research and Technology Innovation Centre(ARTIC)in National University of Singapore.
文摘The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),whose functions or operating modes can be switched or customized via on-site programming or pre-defined software.Nevertheless,most of existing PMs are wire-connected to users,manually-controlled and not real-time.Here,we propose the concept of remotely mind-controlled metasurface(RMCM)via brainwaves.Rather than DC voltage from power supply or AC voltages from signal generators,the metasurface is controlled by brainwaves collected in real time and transmitted wirelessly from the user.As an example,we demonstrated a RMCM whose scattering pattern can be altered dynamically according to the user’s brain waves via Bluetooth.The attention intensity information is extracted as the control signal and a mapping between attention intensity and scattering pattern of the metasurface is established.With such a framework,we experimentally demonstrated and verified a prototype of such metasurface system which can be remotely controlled by the user to modify its scattering pattern.This work paves a new way to intelligent metasurfaces and may find applications in health monitoring,5G/6G communications,smart sensors,etc.
基金National Key Research and Development Program of China(2022YFB3806200)National Natural Science Foundation of China(12004437,61971435,62101588,62201609,62001504)Natural Science Foundation of Shaanxi Province(2022JM-352,2022JQ-630)。
文摘Coding metasurfaces can manipulate electromagnetic wave in real time with high degree of freedom,the fascinating properties of which enrich the metasurface design with a wide range of application prospects.However,most of the coding metasurfaces are designed based on external excitation framework with the wired electrical or wireless light control devices,thus inevitably causing the interference with electromagnetic wave transmission and increasing the complexity of the metasurface design.In this work,a simplistic framework of single-pixel-programmable metasurfaces integrated with a capsuled LED array is proposed to dynamically control electromagnetic wave.The framework fully embeds the photoresistor in the meta-atom,controlling the LED array to directly illuminate the photoresistor to modulate the phase response.With this manner,the complex biasing network is transformed to the universal LED array,which means the physical control framework can be transformed to a software framework,and thus the functions of the metasurface can be freely manipulated by encoding the capsuled LED array avoiding mutual coupling of adjacent meta-atoms in real time.All the results verify that the far-field scattering pattern can be customized with this singlepixel-programmable metasurface.Encouragingly,this work provides a universal framework for coding metasurface design,which lays the foundation for metasurface intelligent perception and adaptive modulation.
