Quasi-bound state in the continuum(QBIC)resonance is gradually attracting attention and being applied in Goos-Hänchen(GH)shift enhancement due to its high quality(Q)factor and superior optical confinement.Current...Quasi-bound state in the continuum(QBIC)resonance is gradually attracting attention and being applied in Goos-Hänchen(GH)shift enhancement due to its high quality(Q)factor and superior optical confinement.Currently,symmetry-protected QBIC resonance is often achieved by breaking the geometric symmetry,but few cases are achieved by breaking the material symmetry.This paper proposes a dielectric compound grating to achieve a high Q factor and high-reflection symmetry-protectede QBIC resonance based on material asymmetry.Theoretical calculations show that the symmetry-protected QBIC resonance achieved by material asymmetry can significantly increase the GH shift up to-980 times the resonance wavelength,and the maximum GH shift is located at the reflection peak with unity reflectance.This paper provides a theoretical basis for designing and fabricating high-performance GH shift tunable metasurfaces/dielectric gratings in the future.展开更多
Bound states in the continuum(BICs)have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics,biosensors,and ultrafast optical sw...Bound states in the continuum(BICs)have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics,biosensors,and ultrafast optical switches.The most common strategy to apply BICs in a metasurface is by breaking symmetry of resonators in the uniform array that leaks the otherwise uncoupled mode to free space and exhibits an inverse quadratic relationship between quality factor(Q)and asymmetry.Here,we propose a scheme to further reduce scattering losses and improve the robustness of symmetry-protected BICs by decreasing the radiation density with a hybrid BIC lattice.We observe a significant increase of radiative Q in the hybrid lattice compared to the uniform lattice with a factor larger than 14.6.In the hybrid BIC lattice,modes are transferred toГpoint inherited from high symmetric X,Y,and M points in the Brillouin zone that reveal as multiple Fano resonances in the far field and would find applications in hyperspectral sensing.This work initiates a novel and generalized path toward reducing scattering losses and improving the robustness of BICs in terms of lattice engineering that would release the rigid requirements of fabrication accuracy and benefit applications of photonics and optoelectronic devices.展开更多
Photonic waveguides are the most fundamental element for photonic integrated circuits(PICs).Waveguide properties,such as propagation loss,modal areas,nonlinear coefficients,etc.,directly determine the functionalities ...Photonic waveguides are the most fundamental element for photonic integrated circuits(PICs).Waveguide properties,such as propagation loss,modal areas,nonlinear coefficients,etc.,directly determine the functionalities and performance of PICs.Recently,the emerging waveguides with bound states in the continuum(BICs)have opened new opportunities for PICs because of their special properties in resonance and radiation.Here,we review the recent progress of PICs composed of waveguides with BICs.First,fundamentals including background physics and design rules of a BIC-based waveguide will be introduced.Next,two types of BIC-based waveguide structures,including shallowly etched dielectric and hybrid waveguides,will be presented.Lastly,the challenges and opportunities of PICs with BICs will be discussed.展开更多
The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protect...The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound in the continuum(BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.展开更多
Bound states can be supported on the surface of a periodically corrugated perfect conductor known as spoof surface plasmon polaritons with their dispersion curves reside below the light line.Here we show that bound st...Bound states can be supported on the surface of a periodically corrugated perfect conductor known as spoof surface plasmon polaritons with their dispersion curves reside below the light line.Here we show that bound states in the continuum(BICs)can also be achieved in such systems.Two types of grating structures are proposed to suppress the radiation leakage and hence generate bound states.The first one is a simple grating with broad grooves in which multiple cavity modes are accommodated.Due to the symmetry incompatibility and the destructive interaction mainly from the TM_(0)and TM_(1)modes,BICs at theΓpoint and at off-Γpoints are both realized.The second one is a dimerized grating with two grooves in each unit cell.The destructive interaction between the modes in the two grooves can suppresses the radiation and BICs at theΓpoint are observed.The Q factors of the whole bands can be further tuned by the dimerization strength effectively.This work may offer new opportunity for the applications of metallic grating in the low frequency bands.展开更多
The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room te...The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room temperature.However,the ultimate atomic-scale interaction length with light makes the SHG of Transition Metal Dichalcogenides(TM-Ds)monolayers naturally weak.Here,we propose coupling a monolayer of TMDs with a photonic grating slab that works with doubly resonant bound states in the continuum(BIC).The BIC slabs are designed to exhibit a pair of BICs,reson-ant with both the fundamental wave(FW)and the second harmonic wave(SHW).Firstly,the spatial mode matching can be fulfilled by tilting FW's incident angle.We theoretically demonstrate that this strategy leads to more than four orders of magnitude enhancement of SHG efficiency than a sole monolayer of TMDs,under a pump light intensity of 0.1 GW/cm^(2).Moreover,we demonstrate that patterning the TMDs monolayer can further enhance the spatial overlap coefficient,which leads to an extra three orders of magnitude enhancement of SHG efficiency.These results demonstrate remarkable pos-sibilities for enhancing SHG with nonlinear 2D materials,opening many opportunities for chip-based light sources,nano-lasers,imaging,and biochemical sensing.展开更多
By using the difference of the band structure for the TE and TM waves in the metal-dielectric photonic crystals beyond the light cone and the birefringence of the anisotropic crystal,a one-dimensional photonic system ...By using the difference of the band structure for the TE and TM waves in the metal-dielectric photonic crystals beyond the light cone and the birefringence of the anisotropic crystal,a one-dimensional photonic system is constructed to realize the bound states in the continuum(BICs).In addition to the BICs arising from the polarization incompatibility,the Friedrich-Wintgen BICs are also achieved when the leaking TM wave is eliminated due to the destructive interference of its ordinary and extraordinary wave components in the anisotropic crystal.A modified scheme favorable for practical application is also proposed.This scheme for BICs may help to suppress the radiation loss in the metal-dielectric photonic crystal systems.展开更多
The method of terahertz(THz)resonance with a high-quality(high-Q)factor offers a vital physical mechanism for metasurface sensors and other high-Q factor applications.However,it is challenging to excite the resonance ...The method of terahertz(THz)resonance with a high-quality(high-Q)factor offers a vital physical mechanism for metasurface sensors and other high-Q factor applications.However,it is challenging to excite the resonance with a high-Q factor in metasurfaces with proper sensitivity as well as figure of merit(FOM)values.Here,an all-dielectric metasurface composed of two asymmetrical rectangular blocks is suggested.Quartz and silicon are the materials applied for the substrate and cuboids respectively.The distinct resonance governed by bound states in the continuum(BIC)is excited by forming an asymmetric cluster by a novel hybrid method of cutting and moving the cuboids.The investigation focuses on analyzing the transmission spectra of the metasurface under different variations in structural parameters and the loss of silicon refractive index.When the proposed defective metasurface serves as a transmittance sensor,it shows a Q factor of 1.08×10^(4)and achieves an FOM up to 4.8×10^(6),which is obtained under the asymmetric parameter equalling 1μm.Simultaneously,the proposed defective metasurface is sensitive to small changes in refractive index.When the thickness of the analyte is 180μm,the sensitivity reaches a maximum value of 578 GHz/RIU.Hence,the proposed defective metasurface exhibits an extensive number of possible applications in the filters,biomedical diagnosis,security screening,and so on.展开更多
The miniaturization of nonlinear light sources is central to the integrated photonic platform,driving a quest for high-efficiency frequency generation and mixing at the nanoscale.In this quest,the high-quality(Q)reson...The miniaturization of nonlinear light sources is central to the integrated photonic platform,driving a quest for high-efficiency frequency generation and mixing at the nanoscale.In this quest,the high-quality(Q)resonant dielectric nanostructures hold great promise,as they enhance nonlinear effects through the resonantly local electromagnetic fields overlapping the chosen nonlinear materials.Here,we propose a method for the enhanced sum-frequency generation(SFG)from etcheless lithium niobate(LiNbO_(3))by utilizing the dual quasi-bound states in the continuum(quasi-BICs)in a one-dimensional resonant grating waveguide structure.Two high-Q guided mode resonances corresponding to the dual quasi-BICs are respectively excited by two near-infrared input beams,generating a strong visible SFG signal with a remarkably high conversion efficiency of 3.66×10^(-2)(five orders of magnitude higher than that of LiNbO_(3)films of the same thickness)and a small full-width at half-maximum less than 0.2 nm.The SFG efficiency can be tuned via adjusting the grating geometry parameter or choosing the input beam polarization combination.Furthermore,the generated SFG signal can be maintained at a fixed wavelength without the appreciable loss of efficiency by selectively exciting the angle-dependent quasi-BICs,even if the wavelengths of input beams are tuned within a broad spectral range.Our results provide a simple but robust paradigm of high-efficiency frequency conversion on an easy-fabricated platform,which may find applications in nonlinear light sources and quantum photonics.展开更多
Although previously reported terahertz absorbers can achieve high-sensitivity refractive index sensing,the resonant peak is too broad,which leads to a low figure of merit[FOM].Transmissive sensors based on bound state...Although previously reported terahertz absorbers can achieve high-sensitivity refractive index sensing,the resonant peak is too broad,which leads to a low figure of merit[FOM].Transmissive sensors based on bound states in the continuum[BIC]can achieve high FOM,but they have some limitations in high sensitivity.Herein,we propose a periodic triple parallel metal bars structure to obtain high quality,a strong field,and multiple hot spots by the Friedrich-Wintgen BIC.Numerical results show the sensitivity and FOM can reach 1877 GHz/RIU and 665,respectively.Compared to the previously reported transmissive sensors based on BIC,the sensitivity has been greatly improved.展开更多
Photonic bound states in the continuum(BICs)are spatially localized modes with infinitely long lifetimes,which exist within a radiation continuum at discrete energy levels.These states have been explored in various sy...Photonic bound states in the continuum(BICs)are spatially localized modes with infinitely long lifetimes,which exist within a radiation continuum at discrete energy levels.These states have been explored in various systems,including photonic and phononic crystal slabs,metasurfaces,waveguides,and integrated circuits.Robustness and availability of the BICs are important aspects for fully taming the BICs toward practical applications.Here,we propose a generic mechanism to realize BICs that exist by first principles free of fine parameter tuning based on non-Maxwellian double-net metamaterials(DNMs).An ideal warm hydrodynamic double plasma(HDP)fluid model provides a homogenized description of DNMs and explains the robustness of the BICs found herein.In the HDP model,these are standing wave formations made of electron acoustic waves(EAWs),which are pure charge oscillations with vanishing electromagnetic fields.EAW BICs have various advantages,such as(i)frequency-comb-like collection of BICs free from normal resonances;(ii)robustness to symmetry-breaking perturbations and formation of quasi-BICs with an ultrahigh Q-factor even if subject to disorder;and(iii)giving rise to subwavelength microcavity resonators hosting quasi-BIC modes with an ultrahigh Q-factor.展开更多
Bound states in the continuum(BICs)have emerged as an efficient tool for trapping light at the nanoscale,promising several exciting applications in photonics.Breaking the structural symmetry has been proposed as an ef...Bound states in the continuum(BICs)have emerged as an efficient tool for trapping light at the nanoscale,promising several exciting applications in photonics.Breaking the structural symmetry has been proposed as an effective way of exciting quasiBICs(QBICs)and generating high-Q resonances.Herein,we demonstrate that QBICs can be excited in an all-dielectric metasurface by scaling the lattice of the metasurface,causing translational symmetry breaking.The corresponding BICs arise from band folding from the band edge to the Γ point in the first Brillouin zone.Multipole analysis reveals that the toroidal dipole dominates these QBICs.Furthermore,scaling the lattice along different directions provides additional freedom for tailoring QBICs,enabling polarization-dependent or-independent QBICs.In addition,this allows the realization of two QBICs at different wavelengths using plane-wave illumination with different polarizations on the metasurface.We experimentally demonstrated the existence of these BICs by fabricating silicon metasurfaces with scaled lattices and measuring their transmission spectra.The vanished resonant linewidth identifies BICs in the transmission spectrum,and the QBICs are characterized by highQ Fano resonances with the Q-factor reaching 2000.Our results have potential applications in enhancing light-matter interaction,such as laser,nonlinear harmonic generation,and strong coupling.展开更多
The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the nanoscale optics and metamaterial-inspired nanophotonics.Because of the unique optically induced electric...The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the nanoscale optics and metamaterial-inspired nanophotonics.Because of the unique optically induced electric and magnetic Mie resonances,high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications.We study a strong coupling between modes of a single subwavelength high-index dielectric resonator and analyze the mode transformation and Fano resonances when the resonator’s aspect ratio varies.We demonstrate that strong mode coupling results in resonances with high-quality factors,which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich–Wintgen scenario of destructive interference.We explain the physics of these states in terms of multipole decomposition,and show that their appearance is accompanied by a drastic change in the far-field radiation pattern.We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra.Our theoretical findings are confirmed by microwave experiments for the scattering of high-index cylindrical resonators with a tunable aspect ratio.The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high-quality factors helps to extend substantially functionalities of all-dielectric nanophotonics,which opens horizons for active and passive nanoscale metadevices.展开更多
The scattering matrix theory has been developed to calculate the third-order nonlinear effect in sphere-grapheneslab structures. By designing structural parameters, we have demonstrated that the incident electromagnet...The scattering matrix theory has been developed to calculate the third-order nonlinear effect in sphere-grapheneslab structures. By designing structural parameters, we have demonstrated that the incident electromagnetic wave can be well confined in the graphene in these structures due to the formation of a bound state in the continuum(BIC) of radiation modes. Based on such a bound state, third-harmonic(TH) generation and four-wave mixing(FWM) have been studied. It is found that the efficiency of TH generation in monolayer graphene can be enhanced about 7 orders of magnitude. It is interesting that we can design structure parameters to make all beams(the pump beam, probe beam, and generated FWM signal) be BICs at the same time. In such a case, the efficiency of FWM in monolayer graphene can be enhanced about 9 orders of magnitude. Both the TH and FWM signals are sensitive to the wavelength, and possess high Q factors, which exhibit very good monochromaticity. By taking suitable BICs, the selective generation of TH and FWM signals for S-and P-polarized waves can also be realized,which is beneficial for the design of optical devices.展开更多
We study theoretically and experimentally the acoustic Purcell effect induced by quasi-bound states in the continuum(quasiBICs).A theoretical framework describing the acoustic Purcell effect of a resonant system is de...We study theoretically and experimentally the acoustic Purcell effect induced by quasi-bound states in the continuum(quasiBICs).A theoretical framework describing the acoustic Purcell effect of a resonant system is developed based on the system’s radiative and dissipative factors,which reveals the critical emission condition for achieving optimum Purcell factors.We show that the quasiBICs contribute to highly confined acoustic field and bring about greatly enhanced acoustic emission,leading to strong Purcell effect.Our concept is demonstrated via two coupled resonators supporting a Friedrich-Wintgen quasiBIC,and the theoretical results are validated by the experiments observing emission enhancement of the sound source by nearly two orders of magnitude.Our work bridges the gap between the acoustic Purcell effect and acoustic BICs essential for enhanced wave-matter interaction and acoustic emission,which may contribute to the research of high-intensity sound sources,high-quality-factor acoustic devices and nonlinear acoustics.展开更多
The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm (AB) interferometer are investigated theoretically by considering a local R...The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm (AB) interferometer are investigated theoretically by considering a local Rashba spin–orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations. Based on the numerical results, such a model can be applied to the design of a spin filter device.展开更多
Dielectric metasurfaces play an increasingly important role in enhancing optical nonlinear generations owing to their ability to support strong light-matter interactions based on Mie-type multipolar resonances.Compare...Dielectric metasurfaces play an increasingly important role in enhancing optical nonlinear generations owing to their ability to support strong light-matter interactions based on Mie-type multipolar resonances.Compared to metasurfaces composed of the periodic arrangement of nanoparticles,inverse,so-called,membrane metasurfaces offer unique possibilities for supporting multipolar resonances,while maintaining small unit cell size,large mode volume and high field enhancement for enhancing nonlinear frequency conversion.Here,we theoretically and experimentally investigate the formation of bound states in the continuum(BICs)from silicon dimer-hole membrane metasurfaces.We demonstrate that our BIC-formed resonance features a strong and tailorable electric near-field confinement inside the silicon membrane films.Furthermore,we show that by tuning the gap between the holes,one can open a leaky channel to transform these regular BICs into quasi-BICs,which can be excited directly under normal plane wave incidence.To prove the capabilities of such metasurfaces,we demonstrate the conversion of an infrared image to the visible range,based on the Third-harmonic generation(THG)process with the resonant membrane metasurfaces.Our results suggest a new paradigm for realising efficient nonlinear photonics metadevices and hold promise for extending the applications of nonlinear structuring surfaces to new types of all-optical near-infrared imaging technologies.展开更多
The interaction between cavity field and atoms plays an important role in exploring the abundant non-Hermitian physics and constructing powerful wave function devices.In this work,we propose theoretically and realize ...The interaction between cavity field and atoms plays an important role in exploring the abundant non-Hermitian physics and constructing powerful wave function devices.In this work,we propose theoretically and realize experimentally unidirectional perfect absorption in a non-Hermitian acoustic system with the help of the topological bound state in the continuum(BIC),which is established by the hybrid interaction between one trivial BIC and another conventional resonant state.In the 2D parameter space spanned by frequency and distance between the two resonators,the topological scattering singularities appear in pairs and are associated with topological distinguished charges.Meanwhile,we reveal the origin of topological charges and their continuous evolution with the loss factor.At a specific loss factor,two topological charges just annihilate together,and acoustic perfect absorption induced by topological BIC is realized at the left incidence,while there is no phase singularity and near-total reflection is observed at the right incidence,hence the system presents extreme asymmetry.Our work bridges the gap between scattering characteristics of non-Hermitian acoustic systems and topological scattering singularities,which may contribute to the research of novel non-Hermitian physics and the practical applications of advanced absorbers and sensors.展开更多
High-quality-factor(high-Q-factor)electromagnetic resonance plays an important role in sensor applications.Previously proposed gas refractive index sensors are often limited by the large cavity length or microscale fa...High-quality-factor(high-Q-factor)electromagnetic resonance plays an important role in sensor applications.Previously proposed gas refractive index sensors are often limited by the large cavity length or microscale fabrication process in practical applications.Recently,ultra-high Q factor resonance based on the bound state in the continuum(BIC)has provided a feasible approach to solve these problems.In this paper,we propose a metasurface structure consisting of a single size tetramer cylinder.It supports dual band toroidal dipole(TD)resonances driven by BIC.The physical mechanism of double TD resonances is clarified by the multipole decomposition of the metasurface band structure and far-field scattering power.The sensor structure based on this achieves a sensitivity of 518.3 MHz/RIU,and the maximum line width does not exceed 680kHz.The high-Q-factor electromagnetic resonance has the advantages of polarization independence and simplicity to manufacture.These findings will open up an avenue to develop the ultrasensitive sensor in the gigahertz regime.展开更多
Plasmonics could provide compact and powerful solutions for manipulating light in deep-subwavelength dimensions,which is promising for a great range of nanophotonic technologies such as plasmonic rulers and sensors.Ho...Plasmonics could provide compact and powerful solutions for manipulating light in deep-subwavelength dimensions,which is promising for a great range of nanophotonic technologies such as plasmonic rulers and sensors.However,the effective area of enhanced localized field induced by surface plasmon polaritons is typically restricted to the structural boundaries.In this work,we propose a method to generate high quality-factor extended electromagnetic fields via hybridizing the superradiant state and the quasi bound state in the continuum of graphene metasurfaces.The coupling interaction involved operates as a three-level system with multiple sharp resonances immune to the polarization,which holds great promise for developing nanodevices with high sensing capacity in two dimensions.展开更多
基金Project supported by the Zhejiang Provincial Natural Science Foundation of China(Grant No.LQ23F040001)the National Natural Science Foundation of China(Grant No.12204446)+1 种基金the Public Welfare Technology Research Project of Zhejiang Province(Grant No.LGC22E050006)the Quzhou Science and Technology Project of China(Grant No.2022K104).
文摘Quasi-bound state in the continuum(QBIC)resonance is gradually attracting attention and being applied in Goos-Hänchen(GH)shift enhancement due to its high quality(Q)factor and superior optical confinement.Currently,symmetry-protected QBIC resonance is often achieved by breaking the geometric symmetry,but few cases are achieved by breaking the material symmetry.This paper proposes a dielectric compound grating to achieve a high Q factor and high-reflection symmetry-protectede QBIC resonance based on material asymmetry.Theoretical calculations show that the symmetry-protected QBIC resonance achieved by material asymmetry can significantly increase the GH shift up to-980 times the resonance wavelength,and the maximum GH shift is located at the reflection peak with unity reflectance.This paper provides a theoretical basis for designing and fabricating high-performance GH shift tunable metasurfaces/dielectric gratings in the future.
基金This work was supported by the National Natural Science Foundation of China(Award No.62175099)Guangdong Basic and Applied Basic Research Foundation(Award No.2023A1515011085)+1 种基金Stable Support Program for Higher Education Institutions from Shenzhen Science,Technology&Innovation Commission(Award No.20220815151149004)Global recruitment program of young experts of China,and startup funding of Southern University of Science and Technology.The authors acknowledge the assistance of SUSTech Core Research Facilities and thank Yao Wang for helpful discussions on fabrication.
文摘Bound states in the continuum(BICs)have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics,biosensors,and ultrafast optical switches.The most common strategy to apply BICs in a metasurface is by breaking symmetry of resonators in the uniform array that leaks the otherwise uncoupled mode to free space and exhibits an inverse quadratic relationship between quality factor(Q)and asymmetry.Here,we propose a scheme to further reduce scattering losses and improve the robustness of symmetry-protected BICs by decreasing the radiation density with a hybrid BIC lattice.We observe a significant increase of radiative Q in the hybrid lattice compared to the uniform lattice with a factor larger than 14.6.In the hybrid BIC lattice,modes are transferred toГpoint inherited from high symmetric X,Y,and M points in the Brillouin zone that reveal as multiple Fano resonances in the far field and would find applications in hyperspectral sensing.This work initiates a novel and generalized path toward reducing scattering losses and improving the robustness of BICs in terms of lattice engineering that would release the rigid requirements of fabrication accuracy and benefit applications of photonics and optoelectronic devices.
基金Project supported by the National Key Research and Development Program of China (2021YFB2800404)National Natural Science Foundation of China (62105283)+1 种基金Zhejiang Provincial Natural Science Foundation of China (LDT23F04012F05)Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang (2021R01001)
文摘Photonic waveguides are the most fundamental element for photonic integrated circuits(PICs).Waveguide properties,such as propagation loss,modal areas,nonlinear coefficients,etc.,directly determine the functionalities and performance of PICs.Recently,the emerging waveguides with bound states in the continuum(BICs)have opened new opportunities for PICs because of their special properties in resonance and radiation.Here,we review the recent progress of PICs composed of waveguides with BICs.First,fundamentals including background physics and design rules of a BIC-based waveguide will be introduced.Next,two types of BIC-based waveguide structures,including shallowly etched dielectric and hybrid waveguides,will be presented.Lastly,the challenges and opportunities of PICs with BICs will be discussed.
基金support from the National Key Research and Development Project (Grant No. 2018YFB2200500, 2018YFB2202800)National Natural Science Foundation of China (Grant No. 61534004, 91964202, 61874081, 61851406, 91950119, and 61905196)。
文摘The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound in the continuum(BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.
基金Project supported by the National Natural Science Foundation of China(Grant No.12074049)the Fundamental Research Funds for the Central Universities,China(Grant Nos.2020CDJQY-Z006 and 2019CDXZWL002).
文摘Bound states can be supported on the surface of a periodically corrugated perfect conductor known as spoof surface plasmon polaritons with their dispersion curves reside below the light line.Here we show that bound states in the continuum(BICs)can also be achieved in such systems.Two types of grating structures are proposed to suppress the radiation leakage and hence generate bound states.The first one is a simple grating with broad grooves in which multiple cavity modes are accommodated.Due to the symmetry incompatibility and the destructive interaction mainly from the TM_(0)and TM_(1)modes,BICs at theΓpoint and at off-Γpoints are both realized.The second one is a dimerized grating with two grooves in each unit cell.The destructive interaction between the modes in the two grooves can suppresses the radiation and BICs at theΓpoint are observed.The Q factors of the whole bands can be further tuned by the dimerization strength effectively.This work may offer new opportunity for the applications of metallic grating in the low frequency bands.
基金financial supports from the National Natural Science Foundation of China(Grant No.11604150)Fundamental Research Funds for the Central Universities of China(Grant No.ZYGX2020J010)M.Rahmani.acknowledges support from the UK Research and Innovation Future Leaders Fellowship(MR/T040513/1)。
文摘The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room temperature.However,the ultimate atomic-scale interaction length with light makes the SHG of Transition Metal Dichalcogenides(TM-Ds)monolayers naturally weak.Here,we propose coupling a monolayer of TMDs with a photonic grating slab that works with doubly resonant bound states in the continuum(BIC).The BIC slabs are designed to exhibit a pair of BICs,reson-ant with both the fundamental wave(FW)and the second harmonic wave(SHW).Firstly,the spatial mode matching can be fulfilled by tilting FW's incident angle.We theoretically demonstrate that this strategy leads to more than four orders of magnitude enhancement of SHG efficiency than a sole monolayer of TMDs,under a pump light intensity of 0.1 GW/cm^(2).Moreover,we demonstrate that patterning the TMDs monolayer can further enhance the spatial overlap coefficient,which leads to an extra three orders of magnitude enhancement of SHG efficiency.These results demonstrate remarkable pos-sibilities for enhancing SHG with nonlinear 2D materials,opening many opportunities for chip-based light sources,nano-lasers,imaging,and biochemical sensing.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074049 and 12147102)。
文摘By using the difference of the band structure for the TE and TM waves in the metal-dielectric photonic crystals beyond the light cone and the birefringence of the anisotropic crystal,a one-dimensional photonic system is constructed to realize the bound states in the continuum(BICs).In addition to the BICs arising from the polarization incompatibility,the Friedrich-Wintgen BICs are also achieved when the leaking TM wave is eliminated due to the destructive interference of its ordinary and extraordinary wave components in the anisotropic crystal.A modified scheme favorable for practical application is also proposed.This scheme for BICs may help to suppress the radiation loss in the metal-dielectric photonic crystal systems.
基金the Key Research and Development Program of Ningxia Province,China(2021BEB04068)。
文摘The method of terahertz(THz)resonance with a high-quality(high-Q)factor offers a vital physical mechanism for metasurface sensors and other high-Q factor applications.However,it is challenging to excite the resonance with a high-Q factor in metasurfaces with proper sensitivity as well as figure of merit(FOM)values.Here,an all-dielectric metasurface composed of two asymmetrical rectangular blocks is suggested.Quartz and silicon are the materials applied for the substrate and cuboids respectively.The distinct resonance governed by bound states in the continuum(BIC)is excited by forming an asymmetric cluster by a novel hybrid method of cutting and moving the cuboids.The investigation focuses on analyzing the transmission spectra of the metasurface under different variations in structural parameters and the loss of silicon refractive index.When the proposed defective metasurface serves as a transmittance sensor,it shows a Q factor of 1.08×10^(4)and achieves an FOM up to 4.8×10^(6),which is obtained under the asymmetric parameter equalling 1μm.Simultaneously,the proposed defective metasurface is sensitive to small changes in refractive index.When the thickness of the analyte is 180μm,the sensitivity reaches a maximum value of 578 GHz/RIU.Hence,the proposed defective metasurface exhibits an extensive number of possible applications in the filters,biomedical diagnosis,security screening,and so on.
基金supported by the National Natural Science Foundation of China(Grant Nos.12104105,12264028,12304420,and 12364045)the Natural Science Foundation of Jiangxi Province(Grant Nos.20232BAB201040,and 20232BAB211025)+6 种基金the Chenguang Program of Shanghai Education Development FoundationShanghai Municipal Education Commission(Grant No.21CGA55)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515011024)the Science and Technology Program of Guangzhou(Grant No.202201011176)the Interdisciplinary Innovation Fund of Nanchang University(Grant No.2019-9166-27060003)the Start-up Funding of Guangdong Polytechnic Normal University(Grant No.2021SDKYA033)the China Scholarship Council(Grant No.202008420045)。
文摘The miniaturization of nonlinear light sources is central to the integrated photonic platform,driving a quest for high-efficiency frequency generation and mixing at the nanoscale.In this quest,the high-quality(Q)resonant dielectric nanostructures hold great promise,as they enhance nonlinear effects through the resonantly local electromagnetic fields overlapping the chosen nonlinear materials.Here,we propose a method for the enhanced sum-frequency generation(SFG)from etcheless lithium niobate(LiNbO_(3))by utilizing the dual quasi-bound states in the continuum(quasi-BICs)in a one-dimensional resonant grating waveguide structure.Two high-Q guided mode resonances corresponding to the dual quasi-BICs are respectively excited by two near-infrared input beams,generating a strong visible SFG signal with a remarkably high conversion efficiency of 3.66×10^(-2)(five orders of magnitude higher than that of LiNbO_(3)films of the same thickness)and a small full-width at half-maximum less than 0.2 nm.The SFG efficiency can be tuned via adjusting the grating geometry parameter or choosing the input beam polarization combination.Furthermore,the generated SFG signal can be maintained at a fixed wavelength without the appreciable loss of efficiency by selectively exciting the angle-dependent quasi-BICs,even if the wavelengths of input beams are tuned within a broad spectral range.Our results provide a simple but robust paradigm of high-efficiency frequency conversion on an easy-fabricated platform,which may find applications in nonlinear light sources and quantum photonics.
基金supported by the National Natural Science Foundation of China(Nos.U22A20258,62175178,61971300,and 61905208)the Central Guidance on Local Science and Technology Development Fund of Shanxi Province(No.YDZJSX2021A013)+2 种基金the National Key Research and Development Program of China(No.2021YFA1400601)the Program for the Top Young Talents of Shanxi Provincethe Program for the Sanjin Outstanding Talents of China。
文摘Although previously reported terahertz absorbers can achieve high-sensitivity refractive index sensing,the resonant peak is too broad,which leads to a low figure of merit[FOM].Transmissive sensors based on bound states in the continuum[BIC]can achieve high FOM,but they have some limitations in high sensitivity.Herein,we propose a periodic triple parallel metal bars structure to obtain high quality,a strong field,and multiple hot spots by the Friedrich-Wintgen BIC.Numerical results show the sensitivity and FOM can reach 1877 GHz/RIU and 665,respectively.Compared to the previously reported transmissive sensors based on BIC,the sensitivity has been greatly improved.
基金funding from the Swiss National Science Foundation (Grant No. 188647)from the Adolphe Merkle Foundation
文摘Photonic bound states in the continuum(BICs)are spatially localized modes with infinitely long lifetimes,which exist within a radiation continuum at discrete energy levels.These states have been explored in various systems,including photonic and phononic crystal slabs,metasurfaces,waveguides,and integrated circuits.Robustness and availability of the BICs are important aspects for fully taming the BICs toward practical applications.Here,we propose a generic mechanism to realize BICs that exist by first principles free of fine parameter tuning based on non-Maxwellian double-net metamaterials(DNMs).An ideal warm hydrodynamic double plasma(HDP)fluid model provides a homogenized description of DNMs and explains the robustness of the BICs found herein.In the HDP model,these are standing wave formations made of electron acoustic waves(EAWs),which are pure charge oscillations with vanishing electromagnetic fields.EAW BICs have various advantages,such as(i)frequency-comb-like collection of BICs free from normal resonances;(ii)robustness to symmetry-breaking perturbations and formation of quasi-BICs with an ultrahigh Q-factor even if subject to disorder;and(iii)giving rise to subwavelength microcavity resonators hosting quasi-BIC modes with an ultrahigh Q-factor.
基金supported by the National Natural Science Foundation of China(Grant Nos.12004084,12164008,and 62261008)the Guizhou Provincial Science and Technology Projects(Grant No.ZK[2021]030)+8 种基金the Science and Technology Innovation Team Project of Guizhou Colleges and Universities(Grant No.[2023]060)the Science and Technology Talent Support Project of the Department of Education in the Guizhou Province(Grant No.KY[2018]043)the Construction Project of Characteristic Key Laboratory in Guizhou Colleges and Universities(Grant No.Y[2021]003)the Key Laboratory of Guizhou Minzu University(Grant No.GZMUSYS[2021]03)the Australian Research Council Discovery Project(Grant No.DP200101353)the UNSW Scientia Fellowship Programand the Shanghai Pujiang Program(Grant No.22PJ1402900)support from the Royal Societythe Wolfson Foundation。
文摘Bound states in the continuum(BICs)have emerged as an efficient tool for trapping light at the nanoscale,promising several exciting applications in photonics.Breaking the structural symmetry has been proposed as an effective way of exciting quasiBICs(QBICs)and generating high-Q resonances.Herein,we demonstrate that QBICs can be excited in an all-dielectric metasurface by scaling the lattice of the metasurface,causing translational symmetry breaking.The corresponding BICs arise from band folding from the band edge to the Γ point in the first Brillouin zone.Multipole analysis reveals that the toroidal dipole dominates these QBICs.Furthermore,scaling the lattice along different directions provides additional freedom for tailoring QBICs,enabling polarization-dependent or-independent QBICs.In addition,this allows the realization of two QBICs at different wavelengths using plane-wave illumination with different polarizations on the metasurface.We experimentally demonstrated the existence of these BICs by fabricating silicon metasurfaces with scaled lattices and measuring their transmission spectra.The vanished resonant linewidth identifies BICs in the transmission spectrum,and the QBICs are characterized by highQ Fano resonances with the Q-factor reaching 2000.Our results have potential applications in enhancing light-matter interaction,such as laser,nonlinear harmonic generation,and strong coupling.
基金We acknowledge fruitful discussions with H.Atwater,I.V.Shadrivov,P.A.Belov,A.N.Poddubny,A.Polman,and A.Moroz.The numerical calculations were performed with support from the Ministry of Education and Science of the Russian Federation(Project 3.1500.2017/4.6)the Australian Research Council.The experimental study of the cylinder SCS in the microwave frequency range was supported by the Russian Science Foundation(17-79-20379)The analytical calculations with resonant-state expansion method were performed with support from the Russian Science Foundation(17-12-01581)。
文摘The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the nanoscale optics and metamaterial-inspired nanophotonics.Because of the unique optically induced electric and magnetic Mie resonances,high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications.We study a strong coupling between modes of a single subwavelength high-index dielectric resonator and analyze the mode transformation and Fano resonances when the resonator’s aspect ratio varies.We demonstrate that strong mode coupling results in resonances with high-quality factors,which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich–Wintgen scenario of destructive interference.We explain the physics of these states in terms of multipole decomposition,and show that their appearance is accompanied by a drastic change in the far-field radiation pattern.We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra.Our theoretical findings are confirmed by microwave experiments for the scattering of high-index cylindrical resonators with a tunable aspect ratio.The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high-quality factors helps to extend substantially functionalities of all-dielectric nanophotonics,which opens horizons for active and passive nanoscale metadevices.
基金National Key R&D Program of China(2017YFA0303800)National Natural Science Foundation of China(NSFC)(11574031,61421001)
文摘The scattering matrix theory has been developed to calculate the third-order nonlinear effect in sphere-grapheneslab structures. By designing structural parameters, we have demonstrated that the incident electromagnetic wave can be well confined in the graphene in these structures due to the formation of a bound state in the continuum(BIC) of radiation modes. Based on such a bound state, third-harmonic(TH) generation and four-wave mixing(FWM) have been studied. It is found that the efficiency of TH generation in monolayer graphene can be enhanced about 7 orders of magnitude. It is interesting that we can design structure parameters to make all beams(the pump beam, probe beam, and generated FWM signal) be BICs at the same time. In such a case, the efficiency of FWM in monolayer graphene can be enhanced about 9 orders of magnitude. Both the TH and FWM signals are sensitive to the wavelength, and possess high Q factors, which exhibit very good monochromaticity. By taking suitable BICs, the selective generation of TH and FWM signals for S-and P-polarized waves can also be realized,which is beneficial for the design of optical devices.
基金This work is supported by the National Key R&D Program of China(2020YFA0211400,2020YFA0211402)the National Natural Science Foundation of China(12074286,11774297)+1 种基金the Shanghai Science and Technology Committee(21JC1405600,20ZR1460900)the Research Grants Council of Hong Kong SAR(AoE/P-502/20,15205219and C6013-18G).
文摘We study theoretically and experimentally the acoustic Purcell effect induced by quasi-bound states in the continuum(quasiBICs).A theoretical framework describing the acoustic Purcell effect of a resonant system is developed based on the system’s radiative and dissipative factors,which reveals the critical emission condition for achieving optimum Purcell factors.We show that the quasiBICs contribute to highly confined acoustic field and bring about greatly enhanced acoustic emission,leading to strong Purcell effect.Our concept is demonstrated via two coupled resonators supporting a Friedrich-Wintgen quasiBIC,and the theoretical results are validated by the experiments observing emission enhancement of the sound source by nearly two orders of magnitude.Our work bridges the gap between the acoustic Purcell effect and acoustic BICs essential for enhanced wave-matter interaction and acoustic emission,which may contribute to the research of high-intensity sound sources,high-quality-factor acoustic devices and nonlinear acoustics.
基金Project supported by the Natural Science Foundation of Liaoning Province, China (Grant No. 201202085)the National Natural Science Foundation of China(Grant No. 11004138)+1 种基金the Excellent Young Scientists Fund of Liaoning Provence, China (Grant No. LJQ2011020)the Young Scientists Fund of Shenyang Ligong University (Grant No. 2011QN-04-11)
文摘The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm (AB) interferometer are investigated theoretically by considering a local Rashba spin–orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations. Based on the numerical results, such a model can be applied to the design of a spin filter device.
基金the support from the Royal Society scholarshipsupport from the UK Research and Innovation Future Leaders Fellowship (MR/T040513/1).
文摘Dielectric metasurfaces play an increasingly important role in enhancing optical nonlinear generations owing to their ability to support strong light-matter interactions based on Mie-type multipolar resonances.Compared to metasurfaces composed of the periodic arrangement of nanoparticles,inverse,so-called,membrane metasurfaces offer unique possibilities for supporting multipolar resonances,while maintaining small unit cell size,large mode volume and high field enhancement for enhancing nonlinear frequency conversion.Here,we theoretically and experimentally investigate the formation of bound states in the continuum(BICs)from silicon dimer-hole membrane metasurfaces.We demonstrate that our BIC-formed resonance features a strong and tailorable electric near-field confinement inside the silicon membrane films.Furthermore,we show that by tuning the gap between the holes,one can open a leaky channel to transform these regular BICs into quasi-BICs,which can be excited directly under normal plane wave incidence.To prove the capabilities of such metasurfaces,we demonstrate the conversion of an infrared image to the visible range,based on the Third-harmonic generation(THG)process with the resonant membrane metasurfaces.Our results suggest a new paradigm for realising efficient nonlinear photonics metadevices and hold promise for extending the applications of nonlinear structuring surfaces to new types of all-optical near-infrared imaging technologies.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFA1400602)the National Natural Science Foundation of China(Grant Nos.12074286,and 12004284)+3 种基金the Shanghai Science and Technology Committee(Grant No.21JC1405600)the Fundamental Research Funds for the Central Universities(Grant No.22120210579)the Chenguang Program of Shanghai Education Development Foundationthe Shanghai Municipal Education Commission(Grant No.21CGA22)。
文摘The interaction between cavity field and atoms plays an important role in exploring the abundant non-Hermitian physics and constructing powerful wave function devices.In this work,we propose theoretically and realize experimentally unidirectional perfect absorption in a non-Hermitian acoustic system with the help of the topological bound state in the continuum(BIC),which is established by the hybrid interaction between one trivial BIC and another conventional resonant state.In the 2D parameter space spanned by frequency and distance between the two resonators,the topological scattering singularities appear in pairs and are associated with topological distinguished charges.Meanwhile,we reveal the origin of topological charges and their continuous evolution with the loss factor.At a specific loss factor,two topological charges just annihilate together,and acoustic perfect absorption induced by topological BIC is realized at the left incidence,while there is no phase singularity and near-total reflection is observed at the right incidence,hence the system presents extreme asymmetry.Our work bridges the gap between scattering characteristics of non-Hermitian acoustic systems and topological scattering singularities,which may contribute to the research of novel non-Hermitian physics and the practical applications of advanced absorbers and sensors.
基金supported in part by the National Natural Science Foundation of China(Grant No.11811530052)Intergovernmental Scienceand Technology Regular Meeting Exchange Project of Ministry of Science and Technology of China(Grant No.CB02-20)+1 种基金Open Fund of State Key Laboratory of Applied Optics(Grant No.SKLA02020001A04)Undergraduate Research and Innovation Projects of China(Grant No.2021102Z).
文摘High-quality-factor(high-Q-factor)electromagnetic resonance plays an important role in sensor applications.Previously proposed gas refractive index sensors are often limited by the large cavity length or microscale fabrication process in practical applications.Recently,ultra-high Q factor resonance based on the bound state in the continuum(BIC)has provided a feasible approach to solve these problems.In this paper,we propose a metasurface structure consisting of a single size tetramer cylinder.It supports dual band toroidal dipole(TD)resonances driven by BIC.The physical mechanism of double TD resonances is clarified by the multipole decomposition of the metasurface band structure and far-field scattering power.The sensor structure based on this achieves a sensitivity of 518.3 MHz/RIU,and the maximum line width does not exceed 680kHz.The high-Q-factor electromagnetic resonance has the advantages of polarization independence and simplicity to manufacture.These findings will open up an avenue to develop the ultrasensitive sensor in the gigahertz regime.
基金This work was partially supported by the National Natural Science Foundation of China(Nos.12104339,62174118,1210040201,U20A20164,and 61975177)Open Fund of State Key Laboratory of Millimeter Wave,Southeast University(No.K202216)+1 种基金International Postdoctoral Exchange Fellowship Program(Talent-Introduction)China Postdoctoral Science Foundation(Nos.258023 and 2021M702403).
文摘Plasmonics could provide compact and powerful solutions for manipulating light in deep-subwavelength dimensions,which is promising for a great range of nanophotonic technologies such as plasmonic rulers and sensors.However,the effective area of enhanced localized field induced by surface plasmon polaritons is typically restricted to the structural boundaries.In this work,we propose a method to generate high quality-factor extended electromagnetic fields via hybridizing the superradiant state and the quasi bound state in the continuum of graphene metasurfaces.The coupling interaction involved operates as a three-level system with multiple sharp resonances immune to the polarization,which holds great promise for developing nanodevices with high sensing capacity in two dimensions.