Demonstration of toroidal metasurfaces through near-field coupling of bright mode resonators

Abstract Bright mode resonances are not well-acknowledged for inducing mode hybridizations. However, we demonstrate multiple bright resonators coupled through electromagnetic fields can induce resonance mode hybridizations. Although one of the hybridized modes shows parallel magnetic moments but the other mode demonstrates anti-parallel magnetic moments leading to magnetic toroidal resonances. Normally excitation of toroidal modes demands complex structures and/or bright-dark mode interactions. However, in this work, we employ solely bright resonators to excite toroidal modes. Unlike bright-dark mode coupling, exclusive bright mode resonance coupling enables larger free space energy merging into the metasystem leading to stronger energy confinement in the metasurface array.

Download Full-text

Experimental Demonstration of Electromagnetically Induced Transparency in a Conductively Coupled Flexible Metamaterial with Cheap Aluminum Foil

Nanoscale Research Letters ◽

10.1186/s11671-019-3180-y ◽

2019 ◽

Vol 14 (1) ◽

Cited By ~ 1

Author(s):

Jie Hu ◽

Tingting Lang ◽

Weihang Xu ◽

Jianjun Liu ◽

Zhi Hong

Keyword(s):

Electromagnetically Induced Transparency ◽

Near Field ◽

Surface Current ◽

Aluminum Foil ◽

Ring Resonators ◽

Dark Mode ◽

Field Coupling ◽

New Ideas ◽

Induced Transparency ◽

Bright Mode

AbstractWe propose a conductively coupled terahertz metallic metamaterial exhibiting analog of electromagnetically induced transparency (EIT), in which the bright and dark mode antennae interact via surface currents rather than near-field coupling. Aluminum foil, which is very cheap and often used in food package, is used to fabricate our metamaterials. Thus, our metamaterials are also flexible metamaterials. In our design, aluminum bar resonators and aluminum split ring resonators (SRRs) are connected (rather than separated) in the form of a fork-shaped structure. We conduct a numerical simulation and an experiment to analyze the mechanism of the proposed metamaterial. The surface current due to LSP resonance (bright mode) flows along different paths, and a potential difference is generated at the split gaps of the SRRs. Thus, an LC resonance (dark mode) is induced, and the bright mode is suppressed, resulting in EIT. The EIT-like phenomenon exhibited by the metamaterial is induced by surface conducting currents, which may provide new ideas for the design of EIT metamaterials. Moreover, the process of fabricating microstructures on flexible substrates can provide a reference for producing flexible microstructures in the future.

Download Full-text

Asymmetric excitation of surface plasmons by dark mode coupling

Science Advances ◽

10.1126/sciadv.1501142 ◽

2016 ◽

Vol 2 (2) ◽

pp. e1501142 ◽

Cited By ~ 30

Author(s):

Xueqian Zhang ◽

Quan Xu ◽

Quan Li ◽

Yuehong Xu ◽

Jianqiang Gu ◽

...

Keyword(s):

Surface Plasmons ◽

Mode Coupling ◽

Electromagnetic Waves ◽

Electromagnetically Induced Transparency ◽

Near Field ◽

Coupling Mechanism ◽

Dark Mode ◽

Resolution Imaging ◽

Experimental Findings ◽

Induced Transparency

Control over surface plasmons (SPs) is essential in a variety of cutting-edge applications, such as highly integrated photonic signal processing systems, deep-subwavelength lasing, high-resolution imaging, and ultrasensitive biomedical detection. Recently, asymmetric excitation of SPs has attracted enormous interest. In free space, the analog of electromagnetically induced transparency (EIT) in metamaterials has been widely investigated to uniquely manipulate the electromagnetic waves. In the near field, we show that the dark mode coupling mechanism of the classical EIT effect enables an exotic and straightforward excitation of SPs in a metasurface system. This leads to not only resonant excitation of asymmetric SPs but also controllable exotic SP focusing by the use of the Huygens-Fresnel principle. Our experimental findings manifest the potential of developing plasmonic metadevices with unique functionalities.

Download Full-text

Dynamically Tunable Resonant Strength in Electromagnetically Induced Transparency (EIT) Analogue by Hybrid Metal-Graphene Metamaterials

Nanomaterials ◽

10.3390/nano9020171 ◽

2019 ◽

Vol 9 (2) ◽

pp. 171 ◽

Cited By ~ 3

Author(s):

Chaode Lao ◽

Yaoyao Liang ◽

Xianjun Wang ◽

Haihua Fan ◽

Faqiang Wang ◽

...

Keyword(s):

Optical Networks ◽

Electromagnetically Induced Transparency ◽

Near Field ◽

Monolayer Graphene ◽

Dark Mode ◽

Resonance Strength ◽

Field Coupling ◽

Terahertz Communications ◽

Unit Cells ◽

Induced Transparency

In this paper, a novel method to realize a dynamically tunable analogue of EIT for the resonance strength rather than the resonance frequency is proposed in the terahertz spectrum. The introduced method is composed of a metal EIT-like structure, in which a distinct EIT phenomenon resulting from the near field coupling between bright and dark mode resonators can be obtained, as well as an integrated monolayer graphene ribbon under the dark mode resonator that can continuously adjust the resonance strength of transparency peak by changing the Fermi level of the graphene. Comparing structures that need to be modulated individually for each unit cell of the metamaterials, the proposed modulation mechanism was convenient for achieving synchronous operations for all unit cells. This work demonstrates a new platform of modulating the EIT analogue and paves the way to design terahertz functional devices which meet the needs of optical networks and terahertz communications.

Download Full-text

Analog of multiple electromagnetically induced transparency using double-layered metasurfaces

Scientific Reports ◽

10.1038/s41598-020-65418-x ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Siyuan Liu ◽

Zhixia Xu ◽

Xiaoxing Yin ◽

Hongxin Zhao

Keyword(s):

Electromagnetically Induced Transparency ◽

Near Field ◽

Localized Surface Plasmons ◽

Dark Mode ◽

Field Coupling ◽

Double Peaks ◽

Resonant Modes ◽

Physical Essence ◽

Induced Transparency ◽

Mode A

Abstract We reported an analog of electromagnetically induced transparency (A-EIT) featured by double transparent peaks in the spectrum. The A-EIT is realized by double-layered metasurface which consists of spoof localized surface plasmons (S-LSP) and cut-wire (CW)-square rings (SR) hybrid. Electric and magnetic S-LSP are excited as bright and dark modes respectively then couple with resonant modes of CW and SR simultaneously to achieve multiple A-EIT. Two bright modes of the electric S-LSP and SR are excited by external electric field directly that produce a bright-bright mode A-EIT. Moreover, the magnetic S-LSP, which cannot be excited by external field directly, is excited through near field coupling from CW, inducing another bright-dark mode A-EIT. Theoretical analysis with corresponding experiment in microwave band are introduced for better insights into physical essence of the double-peaks A-EIT.

Download Full-text

Graphene-Modulated Terahertz Metasurfaces for Selective and Active Control of Dual-Band Electromagnetic Induced Reflection (EIR) Windows

Nanomaterials ◽

10.3390/nano11092420 ◽

2021 ◽

Vol 11 (9) ◽

pp. 2420

Author(s):

Xunjun He ◽

Chenguang Sun ◽

Yue Wang ◽

Guangjun Lu ◽

Jiuxing Jiang ◽

...

Keyword(s):

Active Control ◽

Slow Light ◽

Near Field ◽

Dual Band ◽

Destructive Interference ◽

Dark Mode ◽

Field Coupling ◽

Control Scheme ◽

Electrostatic Doping ◽

Induced Transparency

Currently, metasurfaces (MSs) integrating with different active materials have been widely explored to actively manipulate the resonance intensity of multi-band electromagnetic induced transparency (EIT) windows. Unfortunately, these hybrid MSs can only realize the global control of multi-EIT windows rather than selective control. Here, a graphene-functionalized complementary terahertz MS, composed of a dipole slot and two graphene-integrated quadrupole slots with different sizes, is proposed to execute selective and active control of dual-band electromagnetic induced reflection (EIR) windows. In this structure, dual-band EIR windows arise from the destructive interference caused by the near field coupling between the bright dipole slot and dark quadrupole slot. By embedding graphene ribbons beneath two quadrupole slots, the resonance intensity of two windows can be selectively and actively modulated by adjusting Fermi energy of the corresponding graphene ribbons via electrostatic doping. The theoretical model and field distributions demonstrate that the active tuning behavior can be ascribed to the change in the damper factor of the corresponding dark mode. In addition, the active control of the group delay is further investigated to develop compact slow light devices. Therefore, the selective and active control scheme introduced here can offer new opportunities and platforms for designing multifunctional terahertz devices.

Download Full-text

Independently tunable electromagnetically induced transparency effect and dispersion in a multi-band terahertz metamaterial

Scientific Reports ◽

10.1038/s41598-019-54414-5 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 8

Author(s):

Rakesh Sarkar ◽

Dipa Ghindani ◽

Koijam Monika Devi ◽

S. S. Prabhu ◽

Amir Ahmad ◽

...

Keyword(s):

Slow Light ◽

Electromagnetically Induced Transparency ◽

Near Field ◽

The Other ◽

Transmission Spectra ◽

Field Coupling ◽

Induced Transparency ◽

Coupled Harmonic Oscillator ◽

Bright Mode ◽

Multi Band

AbstractIn this article, we experimentally and numerically investigate a planar terahertz metamaterial (MM) geometry capable of exhibiting independently tunable multi-band electromagnetically induced transparency effect (EIT). The MM structure exhibits multi-band EIT effect due to the strong near field coupling between the bright mode of the cut-wire (CW) and dark modes of pair of asymmetric double C resonators (DCRs). The configuration allows us to independently tune the transparency windows which is challenging task in multiband EIT effect. The independent modulation is achieved by displacing one DCR with respect to the CW, while keeping the other asymmetric DCR fixed. We further examine steep dispersive behavior of the transmission spectra within the transparency windows and analyze slow light properties. A coupled harmonic oscillator based theoretical model is employed to elucidate as well as understand the experimental and numerical observations. The study can be highly significant in the development of multi-band slow light devices, buffers and modulators.

Download Full-text

Prediction of Near-Field Coupling between Misaligned Antennas

1974 IEEE Electromagnetic Compatibility Symposium Record ◽

10.1109/isemc.1974.7567128 ◽

1974 ◽

Author(s):

F. L. Cain ◽

E. E. Weaver ◽

E. F. Duffy

Keyword(s):

Near Field ◽

Field Coupling

Download Full-text

All-dielectric chiral-field-enhanced Raman optical activity

Nature Communications ◽

10.1038/s41467-021-23364-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Ting-Hui Xiao ◽

Zhenzhou Cheng ◽

Zhenyi Luo ◽

Akihiro Isozaki ◽

Kotaro Hiramatsu ◽

...

Keyword(s):

Optical Activity ◽

Metallic Nanoparticles ◽

Near Field ◽

Localized Surface Plasmon ◽

Chiral Field ◽

Resonance Spectroscopy ◽

Conformational Structure ◽

Dark Mode ◽

Spontaneous Raman Scattering ◽

Raman Optical Activity

AbstractRaman optical activity (ROA) is effective for studying the conformational structure and behavior of chiral molecules in aqueous solutions and is advantageous over X-ray crystallography and nuclear magnetic resonance spectroscopy in sample preparation and cost performance. However, ROA signals are inherently minuscule; 3–5 orders of magnitude weaker than spontaneous Raman scattering due to the weak chiral light–matter interaction. Localized surface plasmon resonance on metallic nanoparticles has been employed to enhance ROA signals, but suffers from detrimental spectral artifacts due to its photothermal heat generation and inability to efficiently transfer and enhance optical chirality from the far field to the near field. Here we demonstrate all-dielectric chiral-field-enhanced ROA by devising a silicon nanodisk array and exploiting its dark mode to overcome these limitations. Specifically, we use it with pairs of chemical and biological enantiomers to show >100x enhanced chiral light–molecule interaction with negligible artifacts for ROA measurements.

Download Full-text