Ultrasensitive terahertz sensing with high-Q toroidal dipole resonance governed by bound states in the continuum in all-dielectric metasurface

Abstract Toroidal dipole (TD) with weak coupling to the electromagnetic fields offers tremendous potential for advanced design of photonic devices. However, the excitation of high quality (Q) factor TD resonances in these devices is challenging. Here, we investigate ultrahigh-Q factor TD resonances at terahertz frequencies arising from a distortion of symmetry-protected bound states in the continuum (BIC) in all-dielectric metasurface consisting of an array of high-index tetramer clusters. By elaborately arranging the cylinders forming an asymmetric cluster, two distinct TD resonances governed by BIC are excited and identified. One is distinguished as intracluster TD mode that occurs in the interior of tetramer cluster, and the other one is intercluster TD mode that arises from the two neighboring clusters. Such TD resonances can be turned into ultrahigh-Q leaky resonances by controlling the asymmetry of cluster. The low-loss TD resonances with extremely narrow linewidth are very sensitive to the change in the refractive index of the surrounding media, achieving ultrahigh sensitivity level of 489 GHz/RIU. These findings will open up an avenue to develop ultrasensitive photonic sensor in the terahertz regime.

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A Bifunctional Silicon Dielectric Metasurface Based on Quasi-Bound States in the Continuum

Nanomaterials ◽

10.3390/nano11092357 ◽

2021 ◽

Vol 11 (9) ◽

pp. 2357

Author(s):

Jianan Wang ◽

Weici Liu ◽

Zhongchao Wei ◽

Hongyun Meng ◽

Hongzhan Liu ◽

...

Keyword(s):

Bound States ◽

Polarized Light ◽

Parameter Tuning ◽

Optical Devices ◽

Low Loss ◽

High Quality ◽

Unit Structure ◽

Incident Plane ◽

Dielectric Metasurface ◽

The Continuum

Quasi-bound states in the continuum provide an effective and observable way to improve metasurface performance, usually with an ultra-high-quality factor. Dielectric metasurfaces dependent on Mie resonances have the characteristic of significantly low loss, and the polarization can be affected by the parameter tuning of the structure. Based on the theory of quasi-bound states in the continuum, we propose and simulate a bifunctional resonant metasurface, whose periodic unit structure consists of four antiparallel and symmetrical amorphous silicon columns embedded in a poly(methyl methacrylate) layer. The metasurface can exhibit an extreme Huygens’ regime in the case of an incident plane wave with linear polarization, while exhibiting chirality in the case of incident circular polarized light. Our structure provides ideas for promoting the multifunctional development of flat optical devices, as well as presenting potential in polarization-dependent fields.

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Accidental and symmetry-protected bound states in the continuum in a photonic-crystal slab: A resonant-state expansion study

Physical Review B ◽

10.1103/physrevb.103.155112 ◽

2021 ◽

Vol 103 (15) ◽

Author(s):

Sam Neale ◽

Egor A. Muljarov

Keyword(s):

Photonic Crystal ◽

Bound States ◽

Resonant State ◽

State Expansion ◽

Photonic Crystal Slab ◽

Symmetry Protected ◽

The Continuum

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Polarization-selective modulation of supercavity resonances originating from bound states in the continuum

Communications Physics ◽

10.1038/s42005-020-00453-8 ◽

2020 ◽

Vol 3 (1) ◽

Author(s):

Chan Kyaw ◽

Riad Yahiaoui ◽

Joshua A. Burrow ◽

Viet Tran ◽

Kyron Keelen ◽

...

Keyword(s):

Strong Coupling ◽

Bound States ◽

Photonic Band Gap ◽

Incidence Angle ◽

Polarization State ◽

Normal Incidence ◽

Polarization Angle ◽

Sensing Applications ◽

Symmetry Protected ◽

The Continuum

AbstractBound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Primarily, the formation of BICs in periodic photonic band gap structures are driven by symmetry incompatibility; structural manipulation or variation of incidence angle from incoming light. In this work, we report two modalities for driving the formation of BICs in terahertz metasurfaces. At normal incidence, we experimentally confirm polarization driven symmetry-protected BICs by the variation of the linear polarization state of light. In addition, we demonstrate through strong coupling of two radiative modes the formation of capacitively-driven Freidrich-Wintgen BICs, exotic modes which occur in off-Γ points not accessible by symmetry-protected BICs. The capacitance-mediated strong coupling at 0° polarization is verified to have a normalized coupling strength ratio of 4.17% obtained by the Jaynes-Cummings model. Furthermore, when the polarization angle is varied from 0° to 90° (0° ≤ ϕ < 90°), the Freidrich-Wintgen BIC is modulated until it is completely switched off at 90°.

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Low Index Asymmetric Bound States in the Continuum for Low Loss Integrated Photonics

Conference on Lasers and Electro-Optics ◽

10.1364/cleo_si.2020.sm1j.2 ◽

2020 ◽

Author(s):

Larissa Vertchenko ◽

Radu Malureanu ◽

Clayton DeVault ◽

Eric Mazur ◽

Andrei V. Lavrinenko

Keyword(s):

Bound States ◽

Integrated Photonics ◽

Low Loss ◽

The Continuum

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High Quality-Factor Dual-Band Fano Resonances Induced by Bound States in The Continuum Using A Planar Nanohole Slab

10.21203/rs.3.rs-598706/v1 ◽

2021 ◽

Author(s):

Tian Sang ◽

Qing Mi ◽

Yao Pei ◽

Chaoyu Yang ◽

Shi Li ◽

...

Keyword(s):

Bound States ◽

Near Field ◽

Dual Band ◽

Q Factor ◽

Fano Resonances ◽

High Quality ◽

Potential Applications ◽

Q Factors ◽

Symmetry Protected ◽

The Continuum

Abstract In photonics, it is essential to achieve high quality (Q)-factor resonances to enhance light-mater interactions for improving performances of optical devices. Herein, we demonstrate that high Q-factor dual-band Fano resonances can be achieved by using a planar nanohole slab (PNS) based on the excitation of bound states in the continuum (BICs). By shrinking or expanding the tetramerized holes of the superlattice of the PNS, symmetry-protected BICs can be excited and the locations of Fano resonances as well as their Q-factors can be flexibly tuned. Physical mechanisms for the dual-band Fano resonances can be interpreted as the resonant couplings between the electric-toroidal dipoles or the magnetic-toroidal dipoles based on the far-field multiple decompositions and the near-field distributions of the superlattice. The dual-band Fano resonances of the PNS possess polarization independent feature, they can be survived even the geometric parameters of the PNS are significantly altered, making them more suitable for potential applications.

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Bound states in the continuum-induced enhancement of evanescent field confinement

Journal of Physics Conference Series ◽

10.1088/1742-6596/2015/1/012083 ◽

2021 ◽

Vol 2015 (1) ◽

pp. 012083

Author(s):

S I Lepeshov ◽

A A Bogdanov

Keyword(s):

Electric Field ◽

Bound States ◽

Field Enhancement ◽

Fold Increase ◽

Evanescent Waves ◽

Electric Field Enhancement ◽

Light Line ◽

Field Localization ◽

Dielectric Metasurface ◽

The Continuum

Abstract Here, the enhancement of electromagnetic field confinement in an all-dielectric metasurface is demonstrated. The enhanced confinement is achieved when the polarization singularity, corresponding to accidental bound states in the continuum, moves to the domain of evanescent fields (under the light line). Such a hybridization of the bound states and evanescent waves results in the 70-fold increase of the electric field enhancement on the top of the metasurface and boosting of the electric field localization.

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Bound states in the continuum in periodic structures with structural disorder

Nanophotonics ◽

10.1515/nanoph-2021-0475 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Ekaterina E. Maslova ◽

Mikhail V. Rybin ◽

Andrey A. Bogdanov ◽

Zarina F. Sadrieva

Keyword(s):

Bound States ◽

Periodic Structures ◽

Structural Disorder ◽

Practical Implementation ◽

Photonic Structure ◽

Mode Localization ◽

Effective Reduction ◽

System Length ◽

Symmetry Protected ◽

The Continuum

Abstract We study the effect of structural disorder on the transition from the bound states in the continuum (BICs) to quasi-BICs by the example of the periodic photonic structure composed of two layers of parallel dielectric rods. We uncover the specificity in the robustness of the symmetry-protected and accidental BICs against various types of structural disorder. We analyze how the spatial mode localization induced by the structural disorder results in an effective reduction of the system length and limits the Q factor of quasi-BICs. Our results are essential for the practical implementation of BICs especially in natural and self-assembled photonic structures, where the structural disorder plays a crucial role.

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