High-quality-factor dual-band Fano resonances induced by dual bound states in the continuum using a planar nanohole slab

AbstractIn photonics, it is essential to achieve high-quality (Q)-factor resonances to improve optical devices’ performances. 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 dual bound states in the continuum (BICs). By shrinking or expanding the tetramerized holes of the superlattice of the PNS, two symmetry-protected BICs can be induced to dual-band Fano resonances and their locations 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, and they can be survived even when the geometric parameters of the PNS are significantly altered, making them more suitable for potential applications.

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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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Stability of bound states in the continuum in low-contrast photonic structures

Journal of Physics Conference Series ◽

10.1088/1742-6596/2015/1/012090 ◽

2021 ◽

Vol 2015 (1) ◽

pp. 012090

Author(s):

E. E. Maslova ◽

A.A. Bogdanov ◽

M. V. Rybin ◽

Z. F. Sadrieva

Keyword(s):

Finite Difference ◽

Finite Difference Method ◽

Scattering Theory ◽

Bound States ◽

Q Factor ◽

Low Contrast ◽

Methods Analytical ◽

Q Factors ◽

Good Agreement ◽

The Continuum

Abstract We consider quality (Q) factor of accidental bound states in the continuum in bilayer resonators consisting of low-index dielectric rods. The dependence of Q factor on the number of periods shows that Q factors increase with the increasing number of rods. We calculated the dependence of the resonator Q factor on the disorder by two methods: analytical (multiple scattering theory) and numerical (finite difference method) and showed that the results are in good agreement. Also, we investigated the dependence of the resonance frequency on disorder.

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Manipulating Optical Scattering of Quasi-BIC in Dielectric Metasurface with Off-Center Hole

Nanomaterials ◽

10.3390/nano12010054 ◽

2021 ◽

Vol 12 (1) ◽

pp. 54

Author(s):

Chaobiao Zhou ◽

Tianyao Pu ◽

Jing Huang ◽

Menghui Fan ◽

Lujun Huang

Keyword(s):

Radiation Pattern ◽

Bound States ◽

Near Field ◽

Research Work ◽

Electric Quadrupole ◽

Asymmetric Structure ◽

Far Field ◽

Q Factor ◽

Field Radiation ◽

The Continuum

Bound states in the continuum (BICs) correspond to a particular leaky mode with an infinitely large quality-factor (Q-factor) located within the continuum spectrum. To date, most of the research work reported focuses on the BIC-enhanced light matter interaction due to its extreme near-field confinement. Little attention has been paid to the scattering properties of the BIC mode. In this work, we numerically study the far-field radiation manipulation of BICs by exploring multipole interference. By simply breaking the symmetry of the silicon metasurface, an ideal BIC is converted to a quasi-BIC with a finite Q-factor, which is manifested by the Fano resonance in the transmission spectrum. We found that both the intensity and directionality of the far-field radiation pattern can not only be tuned by the asymmetric parameters but can also experience huge changes around the resonance. Even for the same structure, two quasi-BICs show a different radiation pattern evolution when the asymmetric structure parameter d increases. It can be found that far-field radiation from one BIC evolves from electric-quadrupole-dominant radiation to toroidal-dipole-dominant radiation, whereas the other one shows electric-dipole-like radiation due to the interference of the magnetic dipole and electric quadrupole with the increasing asymmetric parameters. The result may find applications in high-directionality nonlinear optical devices and semiconductor lasers by using a quasi-BIC-based metasurface.

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Analogue of Electromagnetically Induced Transparency in an All-Dielectric Double-Layer Metasurface Based on Bound States in the Continuum

Nanomaterials ◽

10.3390/nano11092343 ◽

2021 ◽

Vol 11 (9) ◽

pp. 2343

Author(s):

Fengyan He ◽

Jianjun Liu ◽

Guiming Pan ◽

Fangzhou Shu ◽

Xufeng Jing ◽

...

Keyword(s):

Double Layer ◽

Bound States ◽

Electromagnetically Induced Transparency ◽

Near Field ◽

Relative Displacement ◽

Photonic Devices ◽

Field Coupling ◽

Potential Applications ◽

Induced Transparency ◽

The Continuum

Bound states in the continuum (BICs) have attracted much attention due to their infinite Q factor. However, the realization of the analogue of electromagnetically induced transparency (EIT) by near-field coupling with a dark BIC in metasurfaces remains challenging. Here, we propose and numerically demonstrate the realization of a high-quality factor EIT by the coupling of a bright electric dipole resonance and a dark toroidal dipole BIC in an all-dielectric double-layer metasurface. Thanks to the designed unique one-dimensional (D)–two-dimensional (2D) combination of the double-layer metasurface, the sensitivity of the EIT to the relative displacement between the two layer-structures is greatly reduced. Moreover, several designs for widely tunable EIT are proposed and discussed. We believe the proposed double-layer metasurface opens a new avenue for implementing BIC-based EIT with potential applications in filtering, sensing and other photonic devices.

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Observation of miniaturized bound states in the continuum with ultra-high quality factors

10.21203/rs.3.rs-381924/v1 ◽

2021 ◽

Author(s):

Zihao Chen ◽

Xuefan Yin ◽

Jicheng Jin ◽

Zhao Zheng ◽

Zixuan Zhang ◽

...

Keyword(s):

Bound States ◽

Photonic Band Gap ◽

Light Trapping ◽

Vertical Direction ◽

Three Dimensions ◽

Quality Factors ◽

High Quality ◽

Potential Applications ◽

On Chip ◽

The Continuum

Abstract Light trapping is a constant pursuit in photonics because of its importance in science and technology. Many mechanisms have been explored, including the use of mirrors made of materials or structures that forbid outgoing waves, and bound states in the continuum that are mirror-less but based on topology. Here we report a compound method, combing mirrors and bound states in the continuum in an optimized way, to achieve a class of on-chip optical cavities that have high quality factors and small modal volumes. Specifically, light is trapped in the transverse direction by the photonic band gap of the lateral hetero-structure and confined in the vertical direction by the constellation of multiple bound states in the continuum. As a result, unlike most bound states in the continuum found in photonic crystal slabs that are de-localized Bloch modes, we achieve light-trapping in all three dimensions and experimentally demonstrate quality factors as high as Q = 1.09×106 and modal volumes as low as V = 3.56 μm3 in the telecommunication regime. We further prove the robustness of our method through the statistical study of multiple fabricated devices. Our work provides a new method of light trapping, which can find potential applications in photonic integration, nonlinear optics and quantum computing.

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Active nonlocal metasurfaces

Nanophotonics ◽

10.1515/nanoph-2020-0375 ◽

2020 ◽

Vol 10 (1) ◽

pp. 655-665

Author(s):

Stephanie C. Malek ◽

Adam C. Overvig ◽

Sajan Shrestha ◽

Nanfang Yu

Keyword(s):

Bound States ◽

Fano Resonances ◽

Spatial Control ◽

Technical Challenge ◽

Materials Engineering ◽

Narrow Bandwidth ◽

Wavefront Shaping ◽

Mechanical Stretching ◽

Proof Of Principle ◽

The Continuum

AbstractActively tunable and reconfigurable wavefront shaping by optical metasurfaces poses a significant technical challenge often requiring unconventional materials engineering and nanofabrication. Most wavefront-shaping metasurfaces can be considered “local” in that their operation depends on the responses of individual meta-units. In contrast, “nonlocal” metasurfaces function based on the modes supported by many adjacent meta-units, resulting in sharp spectral features but typically no spatial control of the outgoing wavefront. Recently, nonlocal metasurfaces based on quasi-bound states in the continuum have been shown to produce designer wavefronts only across the narrow bandwidth of the supported Fano resonance. Here, we leverage the enhanced light-matter interactions associated with sharp Fano resonances to explore the active modulation of optical spectra and wavefronts by refractive-index tuning and mechanical stretching. We experimentally demonstrate proof-of-principle thermo-optically tuned nonlocal metasurfaces made of silicon and numerically demonstrate nonlocal metasurfaces that thermo-optically switch between distinct wavefront shapes. This meta-optics platform for thermally reconfigurable wavefront shaping requires neither unusual materials and fabrication nor active control of individual meta-units.

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Near-Field Excitation of Bound States in the Continuum in All-Dielectric Metasurfaces through a Coupled Electric/Magnetic Dipole Model

Nanomaterials ◽

10.3390/nano11040998 ◽

2021 ◽

Vol 11 (4) ◽

pp. 998

Author(s):

Diego R. Abujetas ◽

José A. Sánchez-Gil

Keyword(s):

Magnetic Dipole ◽

Density Of States ◽

Bound States ◽

Local Density ◽

Near Field ◽

Field Pattern ◽

Local Density Of States ◽

Optical Modes ◽

Source Excitation ◽

The Continuum

Resonant optical modes arising in all-dielectric metasurfaces have attracted much attention in recent years, especially when so-called bound states in the continuum (BICs) with diverging lifetimes are supported. With the aim of studying theoretically the emergence of BICs, we extend a coupled electric and magnetic dipole analytical formulation to deal with the proper metasurface Green function for the infinite lattice. Thereby, we show how to excite metasurface BICs, being able to address their near-field pattern through point-source excitation and their local density of states. We apply this formulation to fully characterize symmetry-protected BICs arising in all-dielectric metasurfaces made of Si nanospheres, revealing their near-field pattern and local density of states, and, thus, the mechanisms precluding their radiation into the continuum. This formulation provides, in turn, an insightful and fast tool to characterize BICs (and any other leaky/guided mode) near fields in all-dielectric (and also plasmonic) metasurfaces, which might be especially useful for the design of planar nanophotonic devices based on such resonant modes.

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