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topological photonics in metamaterials

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photonics Insights 2022年第1期1卷 30-47页

作者： Shaojie Ma Biao Yang Shuang Zhang Department of Physics University of Hong KongHong KongChina College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangshaChina Department of Electrical&Electronic Engineering University of Hong KongHong KongChina

Originally a pure mathematical concept,topology has been vigorously developed in various physical systems in recent years,and underlies many interesting phenomena such as the quantum Hall effect and quantum spin Hall effect.Its widespread influence in physics led the award of the 2016 Nobel Prize in Physics to this field.topological photonics further expands the research field of topology to classical wave systems and holds promise for novel devices and applications,e.g.,topological quantum computation and topological lasers.Here,we review recent developments in topological photonics but focus mainly on their realizations based on metamaterials.Through artificially designed resonant units,metamaterials provide vast degrees of freedom for realizing various topological states,e.g.,the Weyl point,nodal line,Dirac point,topological insulator,and even the Yang monopole and Weyl surface in higher-dimensional synthetic spaces,wherein each specific topological nontrivial state endows novel metamaterial responses that originate from the feature of some high-energy physics.

关键词： topological photonics metamaterial constitutive relation semimetal.

Second Chern crystals with inherently non-trivial topology

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National Science Review 2023年第8期10卷 148-155页

作者： Xiao-Dong Chen Fu-Long Shi Jian-Wei Liu Ke Shen Xin-Tao He C.T. Chan Wen-Jie Chen Jian-Wen Dong School of Physics and State Key Laboratory of Optoelectronic Materials and Technologies Sun Yat-sen University Department of Physics The Hong Kong University of Science and Technology

Chern insulators have been generalized to many classical wave systems and thereby lead to many potential applications such as robust waveguides, quantum computation and high-performance lasers. However, the band structure of a material can be either topologically trivial or non-trivial, depending on how the crystal structure is designed. Here, we propose a second Chern crystal in a four-dimensional parameter space by introducing two extra synthetic translation dimensions. Since the topology of the bulk bands in the synthetic translation space is intrinsically non-trivial, our proposed four-dimensional crystal is guaranteed to be topologically non-trivial regardless of the crystal’s detailed configuration. We derive the topologically protected modes on the lower dimensional boundaries of such a crystal via dimension reduction.Remarkably, we observe the one-dimensional gapless dislocation modes and confirm their robustness in experiments. Our findings provide novel perspectives on topologically non-trivial crystals and may inspire designs of classical wave devices.

关键词： topological photonics synthetic dimension photonic crystals dislocation mode

A scheme for realizing nonreciprocal interlayer coupling in bilayer topological systems

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Frontiers of Optoelectronics 2023年第4期16卷 71-80页

作者： Xiaoxiao Wang Ruizhe Gu Yandong Li Huixin Qi Xiaoyong Hu Xingyuan Wang Qihuang Gong State Key Laboratory for Mesoscopic Physics and Department of Physics Collaborative Innovation Center of Quantum Matter&Frontiers Science Center for Nano-OptoelectronicsBeijing Academy of Quantum Information SciencesPeking UniversityBeijing 100871China Peking University Yangtze Delta Institute of Optoelectronics Nantong 226010China Collaborative Innovation Center of Extreme Optics Shanxi UniversityTaiyuan 030006China Hefei National Laboratory Hefei 230088China College of Mathematics and Physics Beijing University of Chemical TechnologyBeijing 100029China

Nonreciprocal interlayer coupling is difcult to practically implement in bilayer non-Hermitian topological photonic systems.In this work,we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss.The similarity transformation is widely applicable,and we show its application in one-and two-dimensional bilayer topological systems as examples.The bilayer non-Hermitian system with nonreciprocal interlayer coupling,whose topological number can be defned using the gauge-smoothed Wilson loop,is topologically equivalent to the bilayer system with on-site gain/loss.We also show that the topological number of bilayer non-Hermitian C6v-typed domaininduced topological interface states can be defned in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model.Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems.This scheme is useful for observation of non-Hermitian skin efect in three-dimensional systems.

关键词： Nonreciprocal Bilayer Interlayer coupling topological photonics

Dual-polarization two-dimensional valley photonic crystals

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Science China(Physics,Mechanics & Astronomy) 2022年第8期65卷 102-109页

作者： Xin-Tao He Jian-Wei Liu Fu-Long Shi Ke Shen Wen-Jie Chen Xiao-Dong Chen Jian-Wen Dong School of Physics State Key Laboratory of Optoelectronic Materials and TechnologiesSun Yat-sen UniversityGuangzhou510275China

The recent realization of valley physics in photonic systems has enriched the topological phases of light with protected edge modes and shown applications in designing high-performance photonic devices. However, the widely reported valley Hall effect of light in two-dimensional systems is limited to one single polarization. Here, we present dual-polarization two-dimensional valley photonic crystals by simultaneously opening two frequency accidental degenerate Dirac cones. Two band gaps with different polarizations are characterized by opposite-valley Chern numbers, which are confirmed by the opposite-phase vortex distributions of bulk modes and opposite Berry curvatures. This situation results in the polarization-dependent refraction of bulk and edge modes, which locate in opposite valleys. The polarization-independent topological valley transport is also demonstrated. Our work shows the flexible control of light in topological photonic systems with a polarization degree of freedom and has applications in polarization multiplexing photonic devices.

关键词： topological photonics valley photonic crystals polarization

Unidirectional electromagnetic windmill scattering in a magnetized gyromagnetic cylinder

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Chinese Optics Letters 2022年第5期20卷 58-64页

作者：陈剑锋潘剑波郑义栋梁文耀李志远 School of Physics and Optoelectronics South China University of TechnologyGuangzhou 510640China State Key Laboratory of Luminescent Materials and Devices South China University of TechnologyGuangzhou 510640China

We present a discovery of an unusual unidirectionally rotating windmill scattering of electromagnetic waves by a magnetized gyromagnetic cylinder via an analytical theory for rigorous solution to fields and charges and an understanding of the underlying mathematical and physical mechanisms. Mathematically, the generation of nonzero off-diagonal components can break the symmetry of forward and backward scattering coefficients, producing unidirectional windmill scattering. Physically, this windmill scattering originates from the nonreciprocal unidirectional rotation of polarized magnetic charges on the surface of a magnetized gyromagnetic cylinder, which drives the scattering field to radiate outward in the radial direction and unidirectionally emit in the tangential direction. Interestingly, the unidirectional electromagnetic windmill scattering is insensitive to the excitation direction. Moreover, we also discuss the size dependence of unidirectional windmill scattering by calculating the scattering spectra of the gyromagnetic cylinder. These results are helpful for exploring and understanding novel interactions between electromagnetic waves and gyromagnetic materials or structures and offer deep insights for comprehending topological photonic states in gyromagnetic systems from the aspect of fundamental classical electrodynamics and electromagnetics.

关键词： unidirectional electromagnetic windmill scattering magnetized gyromagnetic cylinder topological photonics

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极高品质因子微缩化连续区束缚态观测

Science Bulletin 2022年第4期67卷 359-366,M0003页

作者：陈子豪尹雪帆金纪诚郑昭张子璇王非凡何力甄博彭超 State Key Laboratory of Advanced Optical Communication Systems and Networks Department of Electronics&Frontiers Science Center for Nano-optoelectronicsPeking UniversityBeijing 100871China Department of Physics and Astronomy University of PennsylvaniaPhiladelphiaPA 19104USA Peng Cheng Laboratory Shenzhen 518055China

光束缚在科学和技术上的重要价值使之成为了一个学界不断探索的研究领域.光束缚可利用材料或者结构反射镜实现,也可利用拓扑保护连续区束缚态构成的无反射镜结构实现.将面内反射边界与连续区束缚态结合,即可实现一类具有极高品质因子、... 详细信息

光束缚在科学和技术上的重要价值使之成为了一个学界不断探索的研究领域.光束缚可利用材料或者结构反射镜实现,也可利用拓扑保护连续区束缚态构成的无反射镜结构实现.将面内反射边界与连续区束缚态结合,即可实现一类具有极高品质因子、极小模式体积的新型片上光学微腔.具体来说,利用光子晶体异质结构引入的光子禁带在水平方向将光约束在有限区域内,同时调控动量空间中连续区束缚态构成的拓扑星座实现垂直方向上的光约束,最终可实现全三维空间中的光束缚.本文在实验中观测到了高达1.09×10^(6)的品质因子,其模式体积仅为17.74(λ_(0)/n)^(3).多个样品表征结果的统计分析表明,该设计具有优秀的工艺鲁棒性.本研究为在微小尺度上实现光束缚提供了一种新的设计范式,在光子集成、非线性光学以及量子计算等领域具有可期的应用前景.

关键词： Bound state in the continuum Photonic crystal High-Q cavity topological photonics

Type-I Weyl points induced by negative coupling in photonic crystal

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Science China(Physics,Mechanics & Astronomy) 2021年第6期64卷 66-73页

作者： ZhaoXian Su BingYi Liu LingLing Huang YongTian Wang Beijing Engineering Research Center of Mixed Reality and Advanced Display School of Oprics and PhotonicsBeijing Instirute of TechnologyBeijing 100081China

Weyl points,which are the degenerate points in three-dimensional momentum space,have been widely studied in the photonic system,and show some intriguing phenomena such as topologically protected surface states and chiral anomalies.Type-I Weyl systems possess a complete bandgap,and topologically protected surface states can be excited without disturbing the bulk states.In this work,we investigate the influence of the sign of coupling coefficient on the topological property of the system and find that type-I Weyl points can be realized by introducing a negative coupling between the stacking layers of the designed photonic crystal.We propose a new strategy to construct a type-I Weyl system by stacking the hexagonal photonic lattice.Different from the topological nontrivial photonic system with a positive coefficient,the negative couplings in the photonic system are realized by adding another resonating site between stacking layers.We theoretically demonstrate that the effective coupling between the resonating sites in adjacent layers sign-flips through the judicious design of the nearest coupling strength and eigenfrequency of the additional sites.The surface states at opposite boundaries of the proposed system have opposite group velocities,which is the feature of type-I Weyl points.Our study provides a new method of exploring topologically protected photonic systems and developing possible topological devices.

关键词： topological photonics Weyl semimetal photonic crystal

Experimental verification of ill-defined topologies and energy sinks in electromagnetic continua

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Advanced photonics 2022年第3期4卷 97-104页

作者： David E.Fernandes Ricardo A.M.Pereira Sylvain Lannebère Tiago A.Morgado Mário G.Silveirinha University of Coimbra Instituto de Telecomunicações and Department of Electrical EngineeringCoimbraPortugal University of Aveiro Instituto de TelecomunicaçõesDepartment of ElectronicsTelecommunications and InformaticsAveiroPortugal University of Lisbon Instituto Superior Técnico and Instituto de TelecomunicaçõesDepartment of Electrical EngineeringLisboaPortugal

.It is experimentally verified that nonreciprocal photonic systems with continuous translation symmetry may have an ill-defined topology.The topological classification of such systems is only feasible when the material response is regularized with a spatial-frequency cutoff.We experimentally demonstrate that adjoining a small air layer to the relevant material interface may effectively imitate an idealized spatial cutoff that suppresses the nonreciprocal response for short wavelengths and regularizes the topology.Furthermore,it is experimentally verified that nonreciprocal systems with an ill-defined topology may be used to abruptly halt the energy flow in a unidirectional waveguide due to the violation of the bulk-edge correspondence.In particular,we report the formation of an energy sink that absorbs the incoming electromagnetic waves with a large field enhancement at the singularity.

关键词： topological photonics nonreciprocity topological singularities bulk edge correspondence.

High-performance chiral all-optical OR logic gate based on topological edge states of valley photonic crystal

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Chinese Physics B 2023年第7期32卷 392-398页

作者：王晓蓉费宏明林瀚武敏康丽娟张明达刘欣杨毅彪肖连团 College of Physics Taiyuan University of TechnologyTaiyuan 030024China Key Laboratory of Advanced Transducers and Intelligent Control System Ministry of EducationTaiyuan University of TechnologyTaiyuan 030024China School of Science RMIT UniversityMelbourneVictoria 3000Australia

For all-optical communication and information processing,it is necessary to develop all-optical logic gates based on photonic structures that can directly perform logic operations.All-optical logic gates have been demonstrated based on conventional waveguides and interferometry,as well as photonic crystal structures.Nonetheless,any defects in those structures will introduce high scattering loss,which compromises the fidelity and contrast ratio of the information process.Based on the spin-valley locking effect that can achieve defect-immune unidirectional transmission of topological edge states in valley photonic crystals(VPCs),we propose a high-performance all-optical logic OR gate based on a VPC structure.By tuning the working bandwidth of the two input channels,we prevent interference between the two channels to achieve a stable and high-fidelity output.The transmittance of both channels is higher than 0.8,and a high contrast ratio of 28.8 dB is achieved.Moreover,the chirality of the logic gate originated from the spin-valley locking effect allows using different circularly polarized light as inputs,representing“1”or“0”,which is highly desired in quantum computing.The device’s footprint is 18μm×12μm,allowing high-density on-chip integration.In addition,this design can be experimentally fabricated using current nanofabrication techniques and will have potential applications in optical communication,information processing,and quantum computing.

关键词： topological photonics topological edge state valley photonic crystal all-optical logic gate