Multiple Fano resonances excitation on all-dielectric nanohole arrays metasurfaces

Abstract

Both toroidal dipoles, electric dipoles and magnetic dipoles belong to one type of electromagnetic excitation. In this paper, we present an all-dielectric metasurface composed of an array of square nanoholes. It can simultaneously generate four resonance responses excited by TD, EQ and MD in the continuous near-infrared band. By introducing the in-plane symmetry breaking of the unit cell, asymmetric dielectric nanohole arrays are used to achieve two quasi-BIC resonance modes with high Q-factors excited by EQ and MD. The paper theoretically analyzes and demonstrates the relationship between structural asymmetry and the radiative Q-factor of two Fano resonances, that are governed by symmetry-protected BICs. And multipole decomposition and near-field analysis are performed to demonstrate the dominant role of various electromagnetic excitations in the four modes. The spectra response is also calculated for different incident polarization angles and medium refractive indices. The proposed metasurface is more feasible and practical compared to other complex nanostructures, which may open avenues for the development of applications such as biochemical sensing, optical switches and optical modulators, and provide a reference for the design of devices with polarization-independent properties.

Dual‐Band Chiral Nonlinear Metasurface Supported by Quasibound States in the Continuum

“…For the x ‐polarized incident light, three Fano‐type dips are observed at 1020.1, 1074.9, and 1277.9 nm, called modes F1, M1, and M2, respectively. According to a previous study, [ 18 ] modes M1 and M2 are both considered quasi‐BICs, which are attributed to the introduction of perturbation (α). By changing the long‐side size of the left nanohole, the inversion symmetry can be broken, and an ideal BICs mode radiating channel to free space is provided, showing sharp Fano dips.…”

“…This indicates that the mechanisms of the two Fano dips are also consistent with the quasi‐BIC modes of the undistorted structure mentioned above. To further verify the resonance responses at M1 and M2, we fit the transmittance spectra of modes M1 and M2 by using the typical Fano formula, as follows: [ 18 ] $$\begin{equation} T_{Fano}(\omega )={\left|a_{1}+ja_{2}+\frac{b}{\omega -\omega _{0}+j\gamma }\right|}^{2} \end{equation}$$where ω 0 is the resonant central frequency, γ is the overall damping loss of the resonance, $$a_{1}, a_{2}$$ and b are constant real numbers, and the radiative Q‐factor is determined by the equation: $$\mathrm{Q} = \omega _{0}/2\gamma$$. The Fano fitting results for M1 and M2 are shown in Figure 4b,c.…”

“…Dielectric metasurfaces exhibit a stronger CD, lower optical loss, and higher light damage threshold, demonstrating better DOI: 10.1002/andp.202200263 application prospects. [4,6] In addition, dielectric metasurfaces can also support many kinds of resonances, such as Mie resonance, [17] Fano resonances, [18] bound states in the continuum (BICs), [19][20][21] and anapole modes, [22] which suggests that dielectric metasurfaces can more effectively control the light field as well as enhance CD responses and nonlinearity.…”

Efficient Excitation and Tuning of Multi-Fano Resonances with High Q-Factor in All-Dielectric Metasurfaces

“…When the inner square hole moves horizontally to the right, the symmetry of the SHND nanostructures is broken; there are two obvious transmission dips near λ = 1294.9 nm and λ = 1389.5 nm, which show obvious Fano characteristics. This means that the BIC state becomes unstable with Q-factor is defined by Q = ω 0 /2γ [45,46], where ω 0 is the resonance frequency and γ is the damping loss. Figure 3 shows the variation in the Q-factor of F3 with different asymmetric parameters.…”

Electromagnetically induced transparency based on magnetic toroidal mode of dielectric reverse-symmetric spiral metasurfaces

“…Hence, MTD and ETD exhibit a high electromagnetic field confinement, small radiation loss, and weak coupling in free space [31], which is conducive to the formation of resonance with a high Q-factor [32]. Some reports have been published on ETD Fano [33][34][35] and EIT resonance [17]. However, so far, there are only a few studies on the realization of MTD EIT resonance.…”