THz absorbers with an ultrahigh Q-factor empowered by the quasi-bound states in the continuum for sensing application

Abstract

The exceptional resonances excited by symmetry-protected quasi-bound states in the continuum (QBICs) have provided significant potential in high-sensitive sensing applications. Herein, we have proposed a type of metal-insulator-metal (MIM) absorbers supported by QBIC-induced resonances, and the ideal Q-factors of QBIC-induced resonances can be enhanced up to 105 in the THz regime. The coupled mode theory and the multipole scattering theory are employed to thoroughly interpret the QBIC-induced absorption mechanism. Furthermore, the refractive index sensing capacities of the as-presented absorbers have been investigated, where the maximum values of the sensing sensitivity and figure of merit (FOM) can reach up to 187 GHz per refractive index unit and 286, respectively. Therefore, it is believed that the proposed absorbers enabled by QBIC-induced resonances hold promising potential in a broad range of highly demanding sensing applications.

Photonic spin-selective perfect absorptance on planar metasurfaces driven by chiral quasi-bound states in the continuum

“…When the intrinsic Q-BIC is excited by the LCP light under the oblique incidence of Φ = 0°, the dynamic equations for the single-port system are described by 74 …”

“…The γ = δ suggests that the energy is coupled into the system at the same rate as that of the dissipation, and thus is defined as the critical coupling. 74 Besides the critical coupling, the γ < δ is defined as the under coupling, whereas the γ > δ is defined as the over coupling. At the under coupling of γ < δ , the reflection coefficient at the resonant frequency ω 0 is expressed as…”

“…The further increase in the θ, however, leads to the decrease of absorptance intensity. The proposed single-port system permits the use of the versatile CMT [73][74][75] to reveal the unusual behavior in the absorptance intensity induced by the change in θ.…”

Coupling-Based Multiple Bound States in the Continuum and Grating-Assisted Permittivity Retrieval in the Terahertz Metasurface

“…To reveal the differences in the coupling of different arrangements, we employ temporal coupled mode theory (TCMT) to fit the transmission results. The dynamical equation of the coupled system can be described as 42,43 = +…”

“…To reveal the differences in the coupling of different arrangements, we employ temporal coupled mode theory (TCMT) to fit the transmission results. The dynamical equation of the coupled system can be described as , d a i d t = j true[ .25ex2ex lefttrue ω 1 k k ω 2 true] a i − [ γ 1 γ 12 γ 21 γ 2 ] a i + true[ .25ex2ex lefttrue k 11 k 12 k 21 k 22 true] s i + where the first term on the right side of the equal sign is the Hamiltonian of the system, ω i is the resonance frequencies of the intrinsic modes, a i is the positive frequency amplitude, and k is the coupling coefficient between two modes. The second term represents the loss (γ i and γ i j = γ i γ j ), and the third term ( k ij ) is the coupling coefficient between the ports and the modes.…”