Meta-devices have significantly revitalized the study of nonlinear optical phenomena.At the nanoscale,the detrimental effects of phase mismatching between fundamental and harmonic waves can be substantially reduced.Th...Meta-devices have significantly revitalized the study of nonlinear optical phenomena.At the nanoscale,the detrimental effects of phase mismatching between fundamental and harmonic waves can be substantially reduced.This review analyzes the theoretical frameworks of how plasmonic and dielectric materials induce nonlinear optical properties.Plasmonic and dielectric nonlinear meta-devices that can excite strong resonant modes for efficiency enhancement are explored.We outline different strategies designed to shape the radiation pattern in order to increase the collection capability of nonlinear signals emitted from meta-devices.In addition,we discuss how nonlinear phase manipulation in meta-devices can integrate the benefits of efficiency enhancement and radiation shaping,not only boosting the energy density of the nonlinear signal but also facilitating a wide range of applications.Finally,potential research directions within this field are discussed.展开更多
Holography plays a crucial role in optics,yet traditional methods require complex setups and bulky devices,being unfavourable for optical integration.Although metasurface-based holograms can be ultra-compact,holograph...Holography plays a crucial role in optics,yet traditional methods require complex setups and bulky devices,being unfavourable for optical integration.Although metasurface-based holograms can be ultra-compact,holographic images generated by previously realized metadevices were mostly scalar ones,with a few vectorial holograms realized so far suffering from restrictions on efficiency,incident polarization,and resolution.We propose and experimentally demonstrate an efficient meta-platform to generate vectorial holographic images with high resolutions under arbitrary incident polarizations.Combining Gerchberg–Saxton algorithm and the wave-decomposition technique,we establish a generic strategy to retrieve the optical properties(e.g.,reflection phases and polarization-conversion capabilities)of meta-atoms required to construct a metasurface for generating a predesigned vectorial holographic image under a predesigned incident polarization.We next design a series of high-efficiency and deep-subwavelength single-structure meta-atoms exhibiting tailored reflection phases and polarization-conversion capabilities governed by both structural resonances and the Pancharatnam–Berry effect,and experimentally characterize their optical scattering properties.We finally construct a series of ultra-thin metadevices with these meta-atoms and experimentally demonstrate that they can generate pre-designed vectorial holographic images under illuminations of circularly polarized light at 1064 nm.We provide a highly efficient and ultra-thin platform to generate predesigned vectorial holographic images under illuminations of light with arbitrary given polarization,which can inspire numerous future applications in on-chip photonics.展开更多
Bound states in the continuum(BICs)can confine light with a theoretically infinite Q factor.However,in practical on-chip resonators,scattering loss caused by inevitable fabrication imperfection leads to finite Q facto...Bound states in the continuum(BICs)can confine light with a theoretically infinite Q factor.However,in practical on-chip resonators,scattering loss caused by inevitable fabrication imperfection leads to finite Q factors due to the coupling of BICs with nearby radiative states.Merging multiple BICs can improve the robustness of BICs against fabrication imperfection by improving the Q factors of nearby states over a broad wavevector range.To date,the studies of merging BICs have been limited to fundamental BICs with topological charges±1.Here we show the unique advantages of higher-order BICs(those with higher-order topological charges)in constructing merging BICs.Merging multiple BICs with a higher-order BIC can further improve the Q factors compared with those involving only fundamental BICs.In addition,higher-order BICs offer great flexibility in realizing steerable off-T merging BICs.A higher-order BIC at F can split into a few off-T fundamental BICs by reducing the system symmetry.The split BICs can then be tuned to merge with another BIC,e.g.,an accidental BIC,at an off-Γpoint.When the in-plane mirror symmetry is further broken,merging BICs become steerable in the reciprocal space.Merging BICs provide a paradigm to achieve robust ultrahigh-Q resonances,which are important in enhancing nonlinear and quantum effects and improving the performance of optoelectronic devices.展开更多
Chiral zeroth Landau levels are topologically protected bulk states.In particle physics and condensed matter physics,the chiral zeroth Landau level plays a significant role in breaking chiral symmetry and gives rise t...Chiral zeroth Landau levels are topologically protected bulk states.In particle physics and condensed matter physics,the chiral zeroth Landau level plays a significant role in breaking chiral symmetry and gives rise to the chiral anomaly.Previous experimental works on such chiral Landau levels are mainly based on three-dimensional Weyl degeneracies coupled with axial magnetic fields.Their realizations using two-dimensional Dirac point systems,being more promising for future applications,were never experimentally realized before.Here we propose an experimental scheme for realizing chiral Landau levels in a two-dimensional photonic system.By introducing an inhomogeneous effective mass through breaking local parity-inversion symmetries,a synthetic in-plane magnetic field is generated and coupled with the Dirac quasi-particles.Consequently,the zeroth-order chiral Landau levels can be induced,and the one-way propagation characteristics are experimentally observed.In addition,the robust transport of the chiral zeroth mode against defects in the system is also experimentally tested.Our system provides a new pathway for the realization of chiral Landau levels in two-dimensional Dirac cone systems,and may potentially be applied in device designs utilizing the chiral response and transport robustness.展开更多
Topological photonic insulators show promise for applications in compact integrated photonic circuits due to their ability to transport light robustly through sharp bendings.The number of topological edge states relie...Topological photonic insulators show promise for applications in compact integrated photonic circuits due to their ability to transport light robustly through sharp bendings.The number of topological edge states relies on the difference between the bulk Chern numbers across the boundary,as dictated by the bulk edge correspondence.The interference among multiple topological edge modes in topological photonics systems may allow for controllable functionalities that are particularly desirable for constructing reconfigurable photonic devices.In this work,we demonstrate magnetically controllable multimode interference based on gyromagnetic topological photonic insulators that support two unidirectional edge modes with different dispersions.We successfully achieve controllable power splitting in experiments by engineering multimode interference with the magnetic field intensity or the frequency of wave.Our work demonstrates that manipulating the interference among multiple chiral edge modes can facilitate the advancement of highly efficient and adaptable microwave devices.展开更多
基金supported by the University Grants Committee/Research Grants Council of the Hong Kong Special Administrative Region,China(AoE/P-502/20,C1015-21E,C5031-22G,CityU15303521,CityU11305223,CityU11310522,CityU11300123,and G-CityU 101/22)the City University of Hong Kong(9380131 and 7005867)the National Natural Science Foundation of China(62375232).
文摘Meta-devices have significantly revitalized the study of nonlinear optical phenomena.At the nanoscale,the detrimental effects of phase mismatching between fundamental and harmonic waves can be substantially reduced.This review analyzes the theoretical frameworks of how plasmonic and dielectric materials induce nonlinear optical properties.Plasmonic and dielectric nonlinear meta-devices that can excite strong resonant modes for efficiency enhancement are explored.We outline different strategies designed to shape the radiation pattern in order to increase the collection capability of nonlinear signals emitted from meta-devices.In addition,we discuss how nonlinear phase manipulation in meta-devices can integrate the benefits of efficiency enhancement and radiation shaping,not only boosting the energy density of the nonlinear signal but also facilitating a wide range of applications.Finally,potential research directions within this field are discussed.
基金funded by the National Key Research and Development Program of China(Grant No.2022YFA1404700)the National Natural Science Foundation of China(Grant Nos.12221004,62192771)+1 种基金the Natural Science Foundation of Shanghai(Grant No.23dz2260100)Work done in Hong Kong was supported by the Research Grants Council(RGC)of Hong Kong(Grant Nos.AoE/P-502/20 and CRS_HKUST601/23).
文摘Holography plays a crucial role in optics,yet traditional methods require complex setups and bulky devices,being unfavourable for optical integration.Although metasurface-based holograms can be ultra-compact,holographic images generated by previously realized metadevices were mostly scalar ones,with a few vectorial holograms realized so far suffering from restrictions on efficiency,incident polarization,and resolution.We propose and experimentally demonstrate an efficient meta-platform to generate vectorial holographic images with high resolutions under arbitrary incident polarizations.Combining Gerchberg–Saxton algorithm and the wave-decomposition technique,we establish a generic strategy to retrieve the optical properties(e.g.,reflection phases and polarization-conversion capabilities)of meta-atoms required to construct a metasurface for generating a predesigned vectorial holographic image under a predesigned incident polarization.We next design a series of high-efficiency and deep-subwavelength single-structure meta-atoms exhibiting tailored reflection phases and polarization-conversion capabilities governed by both structural resonances and the Pancharatnam–Berry effect,and experimentally characterize their optical scattering properties.We finally construct a series of ultra-thin metadevices with these meta-atoms and experimentally demonstrate that they can generate pre-designed vectorial holographic images under illuminations of circularly polarized light at 1064 nm.We provide a highly efficient and ultra-thin platform to generate predesigned vectorial holographic images under illuminations of light with arbitrary given polarization,which can inspire numerous future applications in on-chip photonics.
基金supported by the National Natural Science Foundation of China(Grant No.91850207,11904264 and 12134011)and the National Key R&D Program of China(Grant No.2021YFA1401104,2017YFA0303504).M.X.is also supported by the startup funding of Wuhan University.S.Z.is also supported by the Young Top-notch Talent for Ten Thousand Talent Program(2020-2023).Workdone in HongKong is supported by RGC Hong Kong(AoE/P-502/20,N_HKUST608/17)and the Croucher Foundation(CAS20SCO1).
文摘Bound states in the continuum(BICs)can confine light with a theoretically infinite Q factor.However,in practical on-chip resonators,scattering loss caused by inevitable fabrication imperfection leads to finite Q factors due to the coupling of BICs with nearby radiative states.Merging multiple BICs can improve the robustness of BICs against fabrication imperfection by improving the Q factors of nearby states over a broad wavevector range.To date,the studies of merging BICs have been limited to fundamental BICs with topological charges±1.Here we show the unique advantages of higher-order BICs(those with higher-order topological charges)in constructing merging BICs.Merging multiple BICs with a higher-order BIC can further improve the Q factors compared with those involving only fundamental BICs.In addition,higher-order BICs offer great flexibility in realizing steerable off-T merging BICs.A higher-order BIC at F can split into a few off-T fundamental BICs by reducing the system symmetry.The split BICs can then be tuned to merge with another BIC,e.g.,an accidental BIC,at an off-Γpoint.When the in-plane mirror symmetry is further broken,merging BICs become steerable in the reciprocal space.Merging BICs provide a paradigm to achieve robust ultrahigh-Q resonances,which are important in enhancing nonlinear and quantum effects and improving the performance of optoelectronic devices.
基金This work is supported by the Research Grants Council of Hong Kong through grants AoE/P-502/20,16307621,16307420,16310420 and Croucher Foundation(CAS20SCO1).
文摘Chiral zeroth Landau levels are topologically protected bulk states.In particle physics and condensed matter physics,the chiral zeroth Landau level plays a significant role in breaking chiral symmetry and gives rise to the chiral anomaly.Previous experimental works on such chiral Landau levels are mainly based on three-dimensional Weyl degeneracies coupled with axial magnetic fields.Their realizations using two-dimensional Dirac point systems,being more promising for future applications,were never experimentally realized before.Here we propose an experimental scheme for realizing chiral Landau levels in a two-dimensional photonic system.By introducing an inhomogeneous effective mass through breaking local parity-inversion symmetries,a synthetic in-plane magnetic field is generated and coupled with the Dirac quasi-particles.Consequently,the zeroth-order chiral Landau levels can be induced,and the one-way propagation characteristics are experimentally observed.In addition,the robust transport of the chiral zeroth mode against defects in the system is also experimentally tested.Our system provides a new pathway for the realization of chiral Landau levels in two-dimensional Dirac cone systems,and may potentially be applied in device designs utilizing the chiral response and transport robustness.
基金the Research Grants Council of Hong Kong(AoE/P-502/20,17309021,16303119,16310420)the Croucher Foundation(CAS20SC01)and New Cornerstone Science Foundation.
文摘Topological photonic insulators show promise for applications in compact integrated photonic circuits due to their ability to transport light robustly through sharp bendings.The number of topological edge states relies on the difference between the bulk Chern numbers across the boundary,as dictated by the bulk edge correspondence.The interference among multiple topological edge modes in topological photonics systems may allow for controllable functionalities that are particularly desirable for constructing reconfigurable photonic devices.In this work,we demonstrate magnetically controllable multimode interference based on gyromagnetic topological photonic insulators that support two unidirectional edge modes with different dispersions.We successfully achieve controllable power splitting in experiments by engineering multimode interference with the magnetic field intensity or the frequency of wave.Our work demonstrates that manipulating the interference among multiple chiral edge modes can facilitate the advancement of highly efficient and adaptable microwave devices.
