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Liu W, Liu Q, Ni X, Jia Y, Ziegler K, Alù A, Chen F. Floquet parity-time symmetry in integrated photonics. Nat Commun 2024; 15:946. [PMID: 38297005 PMCID: PMC10830577 DOI: 10.1038/s41467-024-45226-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Accepted: 01/16/2024] [Indexed: 02/02/2024] Open
Abstract
Parity-time (PT) symmetry has been unveiling new photonic regimes in non-Hermitian systems, with opportunities for lasing, sensing and enhanced light-matter interactions. The most exotic responses emerge at the exceptional point (EP) and in the broken PT-symmetry phase, yet in conventional PT-symmetric systems these regimes require large levels of gain and loss, posing remarkable challenges in practical settings. Floquet PT-symmetry, which may be realized by periodically flipping the effective gain/loss distribution in time, can relax these requirements and tailor the EP and PT-symmetry phases through the modulation period. Here, we explore Floquet PT-symmetry in an integrated photonic waveguide platform, in which the role of time is replaced by the propagation direction. We experimentally demonstrate spontaneous PT-symmetry breaking at small gain/loss levels and efficient control of amplification and suppression through the excitation ports. Our work introduces the advantages of Floquet PT-symmetry in a practical integrated photonic setting, enabling a powerful platform to observe PT-symmetric phenomena and leverage their extreme features, with applications in nanophotonics, coherent control of nanoscale light amplification and routing.
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Affiliation(s)
- Weijie Liu
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, 250100, Jinan, China
| | - Quancheng Liu
- Department of Physics, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 52900, Israel
| | - Xiang Ni
- School of Physics, Central South University, 410083, Changsha, Hunan, China
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA
| | - Yuechen Jia
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, 250100, Jinan, China
| | - Klaus Ziegler
- Institut für Physik, Universität Augsburg, 86135, Augsburg, Germany
| | - Andrea Alù
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA.
- Physics Program, Graduate Center, City University of New York, New York, NY, 10016, USA.
| | - Feng Chen
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, 250100, Jinan, China.
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2
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Wang T, Niu Y. Defect modes in defective one dimensional parity-time symmetric photonic crystal. Sci Rep 2023; 13:21338. [PMID: 38049510 PMCID: PMC10696044 DOI: 10.1038/s41598-023-48737-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 11/29/2023] [Indexed: 12/06/2023] Open
Abstract
The introduction of defect layers into one-dimensional parity-time (PT) symmetric photonic crystals gives rise to resonances within the photonic bandgaps. These resonances can be effectively explained by our generalized temporal coupled mode theory. The scattering properties and dispersion relation of defect modes exhibit distinct characteristics compared to conventional one-dimensional Hermitian photonic crystals with defect layers. By tuning the non-Hermiticity or other model parameters, the modulus of the generalized decay rate can be reduced, consequently, the electric field concentrated within the defect layer strengthens. This arises due to the unique band structure of one-dimensional PT-symmetric photonic crystals, which differs significantly from that of traditional one-dimensional Hermitian photonic crystals. Furthermore, the interaction between multiple resonances is investigated through the introduction of multiple defect layers. Our study not only provides insights into resonance phenomena in defective non-Hermitian systems but also contributes to the design of relevant optical resonance devices.
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Affiliation(s)
- Tiecheng Wang
- College of Physics and Electronic Engineering, Shanxi University, 030006, Taiyuan, China.
| | - Yong Niu
- Institute of Theoretical Physics, Shanxi University, Taiyuan, 030006, China
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3
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Zhou L, Zhang DJ. Non-Hermitian Floquet Topological Matter-A Review. ENTROPY (BASEL, SWITZERLAND) 2023; 25:1401. [PMID: 37895522 PMCID: PMC10606436 DOI: 10.3390/e25101401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 09/19/2023] [Accepted: 09/27/2023] [Indexed: 10/29/2023]
Abstract
The past few years have witnessed a surge of interest in non-Hermitian Floquet topological matter due to its exotic properties resulting from the interplay between driving fields and non-Hermiticity. The present review sums up our studies on non-Hermitian Floquet topological matter in one and two spatial dimensions. We first give a bird's-eye view of the literature for clarifying the physical significance of non-Hermitian Floquet systems. We then introduce, in a pedagogical manner, a number of useful tools tailored for the study of non-Hermitian Floquet systems and their topological properties. With the aid of these tools, we present typical examples of non-Hermitian Floquet topological insulators, superconductors, and quasicrystals, with a focus on their topological invariants, bulk-edge correspondences, non-Hermitian skin effects, dynamical properties, and localization transitions. We conclude this review by summarizing our main findings and presenting our vision of future directions.
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Affiliation(s)
- Longwen Zhou
- College of Physics and Optoelectronic Engineering, Ocean University of China, Qingdao 266100, China
- Key Laboratory of Optics and Optoelectronics, Qingdao 266100, China
- Engineering Research Center of Advanced Marine Physical Instruments and Equipment of MOE, Qingdao 266100, China
| | - Da-Jian Zhang
- Department of Physics, Shandong University, Jinan 250100, China
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Li Z, Li C, Xu G, Chen W, Xiong Z, Jing H, Ho JS, Qiu CW. Synergetic positivity of loss and noise in nonlinear non-Hermitian resonators. SCIENCE ADVANCES 2023; 9:eadi0562. [PMID: 37406112 DOI: 10.1126/sciadv.adi0562] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 06/01/2023] [Indexed: 07/07/2023]
Abstract
Loss and noise are usually undesirable in electronics and optics, which are generally mitigated by separate ways in the cost of bulkiness and complexity. Recent studies of non-Hermitian systems have shown a positive role of loss in various loss-induced counterintuitive phenomena, while noise still remains a fundamental challenge in non-Hermitian systems particularly for sensing and lasing. Here, we simultaneously reverse the detrimental loss and noise and reveal their coordinated positive role in nonlinear non-Hermitian resonators. This synergetic effect leads to the amplified spectrum intensity with suppressed spectrum fluctuations after adding both loss and noise. We reveal the underlying mechanism of nonlinearity-induced bistability engineered by loss in the non-Hermitian resonators and noise-loss enhanced coherence of eigenfrequency hopping driven by temporal modulation of detuning. Our findings enrich counterintuitive non-Hermitian physics and lead to a general recipe to overcome loss and noise from electronics to photonics with applications from sensing to communication.
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Affiliation(s)
- Zhipeng Li
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Chenhui Li
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Guoqiang Xu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Weijin Chen
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Ze Xiong
- Wireless and Smart Bioelectronics Lab, School of Biomedical Engineering, ShanghaiTech University, Shanghai 201210, China
| | - Hui Jing
- Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education, Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications, Hunan Normal University, Changsha 410081, China
| | - John S Ho
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Cheng-Wei Qiu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
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5
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Analysis of Symmetric Electromagnetic Components Using Magnetic Group Theory. Symmetry (Basel) 2023. [DOI: 10.3390/sym15020415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023] Open
Abstract
We discuss a method of analysis of symmetric electromagnetic components with magnetic media based on magnetic group theory. In this description, some of the irreducible corepresentations assume complex values exp(iθ) with the real parameter θ. A possible physical interpretation of this parameter is given. We demonstrate the application of the symmetry-adapted linear combination method combined with the corepresentation theory to the problem of current modes in an array of magnetized graphene elements where Faraday and Kerr effects can exist. The elements are described by the magnetic symmetry C4 or C4v(C4). The scattering matrix of the array and its eigensolutions are defined and analyzed and some numerical simulations are presented as well. An example of a waveguide described by symmetry C4v(C2v) with a specific type of degeneracy is also discussed.
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Xu C, Ahmed WW, Wu Y. Broad-angle coherent perfect absorption-lasing and super-collimation in two-dimensional non-Hermitian photonic crystals. OPTICS EXPRESS 2023; 31:2112-2119. [PMID: 36785232 DOI: 10.1364/oe.481141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Accepted: 12/26/2022] [Indexed: 06/18/2023]
Abstract
Coherent perfect absorption-lasing (CPAL) and collimation have been intensively studied for normal and small angle wave incidence. Here, we report a two-dimensional non-Hermitian photonic crystal for broad-angle CPAL and super-collimation. The synergy of a nonsymmorphic glide symmetry of the lattice, gain-loss modulation and an optimization of unit cell induces a parity-time phase transition in the band structure along the Brillouin zone boundary. The transition points, i.e., the exceptional points, form a slab-like contour, with nearly zero dispersion in both real and imaginary parts of the band structure. Such dispersionless band structure significantly enhances the range of incident angle for CPAL and collimation.
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Yang S, Zhang X, Sun H. Exceptional point protected robust on-chip optical logic gates. EXPLORATION (BEIJING, CHINA) 2022; 2:20210243. [PMID: 37323707 PMCID: PMC10191016 DOI: 10.1002/exp.20210243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 02/25/2022] [Indexed: 06/17/2023]
Abstract
Optical logic gates are crucial components for information processing and communication using photons. Current optical logic gates typically rely on the light interference principle which requires an accurate manipulation of the dynamical phase of light, making the device quite sensitive to system disturbances such as fabrication errors. Here we introduce non-Hermitian principles into the design of optical logic gates that work in the signal transmission process. We propose an exclusive-or gate for silicon-on-insulator platform by employing the physics in the exceptional point (EP) encirclement process. The EP induced mode switching behavior is applied to manipulate the phase of light which is topologically protected by the energy surface around the EP. As a result, the performance of the device is found to be extremely robust to structural parameter disturbances. The proposed non-Hermitian principle is expected to find applications for other on-chip photonic devices toward high robust performance.
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Affiliation(s)
- Song‐Rui Yang
- State Key Laboratory of Integrated OptoelectronicsCollege of Electronic Science and EngineeringJilin UniversityChangchunChina
- College of PhysicsJilin UniversityChangchunChina
| | - Xu‐Lin Zhang
- State Key Laboratory of Integrated OptoelectronicsCollege of Electronic Science and EngineeringJilin UniversityChangchunChina
| | - Hong‐Bo Sun
- State Key Laboratory of Integrated OptoelectronicsCollege of Electronic Science and EngineeringJilin UniversityChangchunChina
- State Key Laboratory of Precision Measurement Technology and InstrumentsDepartment of Precision InstrumentTsinghua UniversityHaidianBeijingChina
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Non-Hermitian Sensing in Photonics and Electronics: A Review. SENSORS 2022; 22:s22113977. [PMID: 35684602 PMCID: PMC9182944 DOI: 10.3390/s22113977] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/22/2022] [Revised: 05/13/2022] [Accepted: 05/16/2022] [Indexed: 12/04/2022]
Abstract
Recently, non-Hermitian Hamiltonians have gained a lot of interest, especially in optics and electronics. In particular, the existence of real eigenvalues of non-Hermitian systems has opened a wide set of possibilities, especially, but not only, for sensing applications, exploiting the physics of exceptional points. In particular, the square root dependence of the eigenvalue splitting on different design parameters, exhibited by 2 × 2 non-Hermitian Hamiltonian matrices at the exceptional point, paved the way to the integration of high-performance sensors. The square root dependence of the eigenfrequencies on the design parameters is the reason for a theoretically infinite sensitivity in the proximity of the exceptional point. Recently, higher-order exceptional points have demonstrated the possibility of achieving the nth root dependence of the eigenfrequency splitting on perturbations. However, the exceptional sensitivity to external parameters is, at the same time, the major drawback of non-Hermitian configurations, leading to the high influence of noise. In this review, the basic principles of PT-symmetric and anti-PT-symmetric Hamiltonians will be shown, both in photonics and in electronics. The influence of noise on non-Hermitian configurations will be investigated and the newest solutions to overcome these problems will be illustrated. Finally, an overview of the newest outstanding results in sensing applications of non-Hermitian photonics and electronics will be provided.
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9
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Liu T, An S, Gu Z, Liang S, Gao H, Ma G, Zhu J. Chirality-switchable acoustic vortex emission via non-Hermitian selective excitation at an exceptional point. Sci Bull (Beijing) 2022; 67:1131-1136. [DOI: 10.1016/j.scib.2022.04.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2022] [Revised: 02/27/2022] [Accepted: 04/06/2022] [Indexed: 10/18/2022]
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10
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Wen H, Ren L, Shi L, Zhang X. Parity-time symmetry in monolithically integrated graphene-assisted microresonators. OPTICS EXPRESS 2022; 30:2112-2121. [PMID: 35209358 DOI: 10.1364/oe.448371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Accepted: 12/24/2021] [Indexed: 06/14/2023]
Abstract
Recently, optical systems with parity-time (PT) symmetry have attracted considerable attention due to its remarkable properties and promising applications. However, these systems usually require separate photonic devices or active semiconductor materials. Here, we investigate PT symmetry and exceptional points (EPs) in monolithically integrated graphene-assisted coupled microresonators. Raman effect and graphene cladding are utilized to introduce the balanced gain and loss. We show that PT-symmetry breaking and EPs can be achieved by changing the pump power and the chemical potential. In addition, the intracavity field intensities experience suppression and revival as the graphene-induced loss increases. Due to the unique distribution of optical field, tunable nonreciprocal light transmission is theoretically demonstrated when introducing the gain saturation nonlinearity. The maximum isolation ratio can reach 26 dB through optimizing the relevant parameters. Our proposed scheme is monolithically integrated, CMOS compatible, and exhibits remarkable properties for microscale light field manipulation. These superior features make our scheme has promising applications in optical communication, computing and sensing.
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11
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Chen Z, Peng Y, Li H, Liu J, Ding Y, Liang B, Zhu XF, Lu Y, Cheng J, Alù A. Efficient nonreciprocal mode transitions in spatiotemporally modulated acoustic metamaterials. SCIENCE ADVANCES 2021; 7:eabj1198. [PMID: 34731003 PMCID: PMC8565901 DOI: 10.1126/sciadv.abj1198] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Accepted: 09/15/2021] [Indexed: 05/31/2023]
Abstract
In linear, lossless, time-invariant, and nonbiased acoustic systems, mode transitions are time reversible, consistent with Lorentz reciprocity and implying a strict symmetry in space-time for sound manipulation. Here, we overcome this fundamental limitation by implementing spatiotemporally modulated acoustic metamaterials that support nonreciprocal sound steering. Our mechanism relies on the coupling between an ultrathin membrane and external biasing electromagnetic fields, realizing programmable dynamic control of the acoustic impedance over a motionless and noiseless platform. The fast and flexible impedance modulation of our metamaterial imparts an effective unidirectional momentum in space-time to realize nonreciprocal transitions in k-ω space between different diffraction modes. On the basis of these principles, we demonstrate efficient nonreciprocal sound steering, showcasing unidirectional evanescent wave conversion and nonreciprocal upconversion focusing. More generally, our metamaterial platform offers opportunities for generation of nonreciprocal Bloch waves and extension to other domains, such as non-Hermitian topological and parity-time symmetric acoustics.
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Affiliation(s)
- Zhaoxian Chen
- Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
- College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Yugui Peng
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY 10031, USA
| | - Haoxiang Li
- Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Jingjing Liu
- Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Yujiang Ding
- Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Bin Liang
- Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Xue-Feng Zhu
- School of Physics and Innovation Institute, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People’s Republic of China
| | - Yanqing Lu
- College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Jianchun Cheng
- Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
| | - Andrea Alù
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY 10031, USA
- Physics Program, Graduate Center, City University of New York, New York, NY 10016, USA
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Han P, Li W, Zhou Y, Jiang S, Chang X, Huang A, Zhang H, Xiao Z. Giant and tunable Goos-Hänchen shift with a high reflectance induced by PT-symmetry in atomic vapor. OPTICS EXPRESS 2021; 29:30436-30448. [PMID: 34614773 DOI: 10.1364/oe.432082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 08/26/2021] [Indexed: 06/13/2023]
Abstract
The Goos-Hänchen (GH) shifts of light beams reflected from conventional passive optical systems could be enhanced using the Brewster angle effect or resonance effect, but the maximum GH shift is located at the reflectance minima, which is difficult for experimental detection. In this paper, we present an efficient and flexible scheme to realize complex parity-time (PT)-symmetric periodic optical potentials (complex crystals) in helium atomic vapor. The GH shifts of probe light reflected from the complex crystal are theoretically investigated and large GH shifts could be obtained inside the high-reflection band. When the complex crystal is operated near the coherent perfect absorption-laser point, the maximum GH shift of probe light is exactly located at the reflectance peak. Moreover, the GH shifts could be easily controlled by adjusting the intensity of control light.
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Yang SR, Zhang XL, Sun HB. Design of a non-Hermitian on-chip mode converter using phase change materials. OPTICS LETTERS 2020; 45:4630-4633. [PMID: 32797027 DOI: 10.1364/ol.400251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Accepted: 07/14/2020] [Indexed: 06/11/2023]
Abstract
The introduction of non-Hermiticity into photonics has enabled new design principles for photonic devices. Here we propose the design of a tunable non-Hermitian on-chip mode converter working at telecommunication wavelengths. The key component of the converter is a phase change material, and switching its working state can enable a topological change in the energy surface of the system. The conversion functionality can be realized by dynamically encircling an exceptional point in the parameter space of the device. The device based on this non-Hermitian principle is robust to perturbations of structural parameters and works in broadband. The non-Hermitian principle can be applied for the design of more complex on-chip photonic devices.
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Li S, Zhang X, Xu Q, Liu M, Kang M, Han J, Zhang W. Exceptional point in a metal-graphene hybrid metasurface with tunable asymmetric loss. OPTICS EXPRESS 2020; 28:20083-20094. [PMID: 32680076 DOI: 10.1364/oe.391917] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 06/10/2020] [Indexed: 06/11/2023]
Abstract
Observation of exceptional points (EPs) in non-Hermitian parity-time (PT) symmetric systems has led to various nontrivial physics and exotic phenomena. Here, a metal-graphene hybrid non-Hermitian metasurface is proposed in the terahertz regime, whose unit cell is composed of two orthogonally oriented split-ring resonators (SRRs) with identical dimensions but only one SRR containing a graphene patch at the gap. An EP in polarization space is theoretically observed at a certain Fermi level of the graphene patch, where the induced asymmetric loss and the coupling strength between the two SRRs match a certain relation predicted by a coupled mode theory. The numerical fittings using the coupled mode theory agree well with the simulations. Besides, an abrupt phase flip around the EP frequency is observed in the transmission in circular polarization basis, which can be very promising in ultra-sensitive sensing applications.
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Lan J, Zhang X, Wang L, Lai Y, Liu X. Bidirectional acoustic negative refraction based on a pair of metasurfaces with both local and global PT-symmetries. Sci Rep 2020; 10:10794. [PMID: 32612196 PMCID: PMC7330048 DOI: 10.1038/s41598-020-67793-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 06/15/2020] [Indexed: 11/09/2022] Open
Abstract
Negative refraction plays an important role in acoustic wave manipulation and imaging. However, conventional systems based on acoustic metamaterials suffer from the limits induced by loss-related and resolution issues. In this work, a parity-time (PT)-symmetric system is introduced to realize loss-free bidirectional acoustic negative refraction. The system is composed of a pair of locally PT-symmetric multi-layer metasurfaces sandwiching a region of free space, which also forms a global PT symmetry. The property of bidirectional negative refraction, which is rare for general PT-symmetric structures, is related to the coexistence of amplification and absorption in the locally PT-symmetric metasurfaces at their PT-broken phases. Such metasurfaces can freely switch their states between coherent perfect absorber (CPA) and amplifier depending on the direction of incidence. Our results provide a physical mechanism for realizing bidirectional functions in acoustic PT-symmetric systems.
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Affiliation(s)
- Jun Lan
- Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, People's Republic of China
| | - Xiaowei Zhang
- Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, People's Republic of China
| | - Liwei Wang
- Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, People's Republic of China
| | - Yun Lai
- Key Laboratory of Modern Acoustics, National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, People's Republic of China.
| | - Xiaozhou Liu
- Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, People's Republic of China.
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16
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Zhang XL, Jiang T, Chan CT. Dynamically encircling an exceptional point in anti-parity-time symmetric systems: asymmetric mode switching for symmetry-broken modes. LIGHT, SCIENCE & APPLICATIONS 2019; 8:88. [PMID: 31645932 PMCID: PMC6804564 DOI: 10.1038/s41377-019-0200-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 09/03/2019] [Accepted: 09/09/2019] [Indexed: 05/25/2023]
Abstract
Dynamically encircling an exceptional point (EP) in parity-time (PT) symmetric waveguide systems exhibits interesting chiral dynamics that can be applied to asymmetric mode switching for symmetric and anti-symmetric modes. The counterpart symmetry-broken modes (i.e., each eigenmode is localized in one waveguide only), which are more useful for applications such as on-chip optical signal processing, exhibit only non-chiral dynamics and therefore cannot be used for asymmetric mode switching. Here, we solve this problem by resorting to anti-parity-time (anti-PT) symmetric systems and utilizing their unique topological structure, which is very different from that of PT-symmetric systems. We find that the dynamical encircling of an EP in anti-PT-symmetric systems with the starting point in the PT-broken phase results in chiral dynamics. As a result, symmetry-broken modes can be used for asymmetric mode switching, which is a phenomenon and application unique to anti-PT-symmetric systems. We perform experiments to demonstrate the new wave-manipulation scheme, which may pave the way towards designing on-chip optical systems with novel functionalities.
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Affiliation(s)
- Xu-Lin Zhang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun, China
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Tianshu Jiang
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - C. T. Chan
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
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Yim J, Zhao H, Midya B, Feng L. Non-Hermitian heterostructure for two-parameter sensing. OPTICS LETTERS 2019; 44:1626-1629. [PMID: 30933107 DOI: 10.1364/ol.44.001626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Accepted: 02/25/2019] [Indexed: 06/09/2023]
Abstract
Non-Hermitian systems at exceptional point (EP) degeneracy are demonstrated to be highly sensitive to environmental perturbation. Here, we propose and theoretically investigate a novel multilayered heterostructure favoring double EPs for a unique set of material parameters at which forward- and backward-reflection coefficients vanish, respectively. Such an EP heterostructure is shown to scatter off light when system parameters are perturbed away from the degeneracies due to the effect of ambient temperature and mechanical stress fluctuations. The proposed structure is conducive to manipulating optical responses for two mutually independent parameters sensing.
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