Ultrasensitive and Broadband Optical Toroidal Modes in all‐Dielectric Nanostructures

Hsiao, Hui Hsin; Liu, Ai‐Yin

doi:10.1002/lpor.202100404

Cited by 6 publications

(5 citation statements)

References 54 publications

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“…This is the first time that the toroidal dipole was experimentally verified. Since then, much research on the dynamic toroidal dipole usually with low-loss and high field concentration has been carried out, such as electromagnetic-induced transparency [ 9 ], absorption [ 10 ], circular dichroism [ 11 ], sensing [ 12 , 13 ], optical force [ 14 ], and so on [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ].…”

Section: Introductionmentioning

confidence: 99%

Low-Loss Dual-Band Transparency Metamaterial with Toroidal Dipole

et al. 2022

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In this paper, a low-loss toroidal dipole metamaterial composed of four metal split ring resonators is proposed and verified at microwave range. Dual-band Fano resonances could be excited by normal incident electromagnetic waves at 6 GHz and 7.23 GHz. Analysis of the current distribution at the resonance frequency and the scattered power of multipoles shows that both Fano resonances derive from the predominant novel toroidal dipole. The simulation results exhibit that the sensitivity to refractive index of the analyte is 1.56 GHz/RIU and 1.8 GHz/RIU. Meanwhile, the group delay at two Fano peaks can reach to 11.38 ns and 12.85 ns, which means the presented toroidal metamaterial has significant slow light effects. The proposed dual-band toroidal dipole metamaterial may offer a new path for designing ultra-sensitive sensors, filters, modulators, slow light devices, and so on.

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Section: Introductionmentioning

confidence: 99%

Low-Loss Dual-Band Transparency Metamaterial with Toroidal Dipole

et al. 2022

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“…The complete head-to-tail configuration of the MD moments is attributed to the excitation of two out-of-phase MD dipoles pointed at z direction (MD z ) combined with two antiparallel MD moments along y direction (MD y ) within each individual nanopillar, manifesting the resonant profile of the transverse toroidal mode (see Figure S2, Supporting Information). [36] On the other hand, a strong magnetic field originated from a circular displacement current loop (white arrows) was induced for the MD mode in x--z plane (Figure 2f). Meanwhile, the corresponding electricfield distributions for both of the TD and MD modes display a strong localized field confined inside the volume of the dielectric nanoresonator (bottom panels of Figure 2e,f).…”

Section: Resultsmentioning

confidence: 97%

Third Harmonic Generation Enhanced by Generalized Kerker Condition in All‐Dielectric Metasurfaces

Liu

Hsieh

Lin

et al. 2023

Advanced Optical Materials

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The abundant multipolar resonances in all‐dielectric metasurfaces provide a new paradigm to simultaneously induce strong near‐field confinement in the interior of a nanocavity as well as to manipulate the far‐field scattering property, which is beneficial for the enhancement of nonlinear effects. Here, third‐harmonic generation (THG) of all‐dielectric silicon metasurfaces that sustain dominant electric dipole (ED), toroidal dipole (TD), and magnetic dipole (MD) moments in near‐infrared is numerically and experimentally studied. The effect of the interplay of these resonant modes on THG is investigated, and a pronounced THG enhancement is observed when these modes become spectrally overlapped, corresponding to the generalized Kerker condition. The constructive interference of the total electric dipole (refers to the summation of the ED and TD scattered fields) and MD modes results in the suppression of the backward scattering along with a strong local‐field enhancement inside the dielectric resonators. The simulation (experimental) results show a 214‐fold (17‐fold) THG enhancement in the vicinity of the generalized Kerker condition compared with the signals of the spectrally separated TD and MD resonances. The silicon‐based metasurfaces with their simple geometry are facile for large‐area fabrication and open new possibilities for the optimization of upconversion processes to achieve efficient nonlinear devices.

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“…[36] Thanks to the abundant multipolar resonant features of dielectric resonators, the diversity of the electromagnetic field distributions among different multipolar resonances enables us to tailor the field enhancement and spatial confinement of the resonant mode that alters the corresponding surface sensitivity of the quasi-BIC modes significantly. [37,38] Thus, a thorough study for the multipolar electromagnetic portrait of the quasi-BIC modes to their sensing capability is important to give guidance in optimizing dielectric sensor platform.…”

Section: Introductionmentioning

confidence: 99%

Ultrasensitive Refractive Index Sensing Based on the Quasi‐Bound States in the Continuum of All‐Dielectric Metasurfaces

Hsiao

Hsu

Liu

et al. 2022

Advanced Optical Materials

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give rise to a high-Q resonance along with its characteristic asymmetric spectral line shape. [15] Recently, a generalized concept known as bound states in the continuum (BIC) has been proposed to unify metaatoms with broken in-plane inversion symmetry, and the relationship between the structural asymmetry and the Q-factor of resonances was found to be well described by a characteristic inverse-square law. [16] Such symmetry-protected BIC originates from the forbidden coupling between the eigenmodes of resonators and the external propagating modes due to their symmetry mismatch, thus resulting in a localized state embedded in the continuum. Ideally, the BIC exhibits infinite Q-factor in a symmetry-preserved nanostructure so that it is not observable in the spectrum due to its vanishing spectral linewidth. [16] In practice, by introducing the symmetry breaking into the in-plane geometry, the quasi-BIC mode with the finite Q-factor and linewidth can be tailored by adjusting the degree of structural asymmetry, thus providing a useful platform to readily access extremely high Q-factor resonances.Recently, the quasi-BICs with ultrahigh Q-factor have been realized in various photonic systems including waveguides, [17] photonic crystals, [18] plasmonic nanostructures, [19][20][21][22] and dielectric resonators. [23] Among these demonstrations, a variety of metallic and dielectric nanostructures were used in refractive index (RI) sensing applications as the narrower resonant linewidth is beneficial for measuring small resonant shifts (Table S1, Supporting Information). [24] Generally, plasmonic sensors based on the usage of either surface plasmon polaritons or localized surface plasmons benefit from their intense optical field on the surface of metallic nanostructures [25] and thus are capable of performing significant spectral variation when external RI changes. However, the accompanied dissipative loss leads to the broadening of the resonant linewidth simultaneously. In contrary, high-index dielectric metasurfaces have emerged as a promising alternative to exhibit a much narrower resonant linewidth owing to the lack of Ohmic loss. [26,27] Thus, various asymmetric dielectric nanostructures, such as tilted elliptical nanodisk pairs, [28,29] asymmetric paired nanorods, [30][31][32] asymmetric crescent shape, [33] nanodisks with asymmetrically distributed holes, [7,34] nanobricks with symmetric or asymmetric defects, [8,35] have been demonstrated to support high-Q Symmetry-protected quasi-bound states in the continuum (BIC) controlled by metasurfaces with broken in-plane symmetry are widely exploited to achieve highly surface-sensitive and spectrally sharp resonances for nanophotonic biosensors. Through the engineering of silicon-based asymmetric nanobar pairs, a quasi-BIC mode is excited showing a dominant toroidal dipole (TD) and electric quadrupole (EQ) resonant feature in the near-infrared and performs ultrahigh sensitivity in the refractometric monitoring of local environment changes. Contrary to the typical electric ...

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Ultrasensitive and Broadband Optical Toroidal Modes in all‐Dielectric Nanostructures

Cited by 6 publications

References 54 publications

Low-Loss Dual-Band Transparency Metamaterial with Toroidal Dipole

Low-Loss Dual-Band Transparency Metamaterial with Toroidal Dipole

Third Harmonic Generation Enhanced by Generalized Kerker Condition in All‐Dielectric Metasurfaces

Ultrasensitive Refractive Index Sensing Based on the Quasi‐Bound States in the Continuum of All‐Dielectric Metasurfaces

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