Multispectral tunable symmetry-protected bound states in the continuum in all-dielectric split-ring resonator metasurfaces

Abstract

Symmetry incompatible bound states in the continuum (BICs) are the non-radiating states that remain decoupled from the radiation continuum due to the symmetry mismatch. However, it has always been challenging to observe multiple symmetry-protected BICs in single resonator dielectric metasurfaces. This work reports multiple symmetry-protected BICs for both linear polarizations in all-dielectric metasurfaces made up of split-ring resonators (SRRs). Intensive numerical simulations predict that SRR can support a high-quality factor (Q) of 106 for standalone and with substrate in presence of asymmetry. However, for a realistic and practical scenario, a Q-factor of ∼ 8000 for standalone structures is achieved, which reduces by a factor of 1.25 in the presence of silica substrate. Even if the out-of-plane asymmetry is introduced either in the geometry or variation in the angle of incidence, BICs are transformed into quasi-BICs possessing Fano resonance. Eigenmode and multipole decomposition analysis confirm multiple BIC resonances; notable dominant contributions are from magnetic dipole, toroidal dipole, and electric and magnetic quadrupole. Integrating monolayer graphene adds tunability to the metasurface, where distinct quasi-BIC modes can be employed to facilitate an excellent switching.

Enhancing the Goos–Hänchen shift based on quasi-bound states in the continuum through material asymmetric dielectric compound gratings

“…BIC is a ubiquitous physical phenomenon that was originally proposed in hypothetical quantum structures by Neumann and Wigner. [8] BIC is a local state that coexists with the continuum spectrum, is found in many physical structures, such as gratings or metasurfaces, [9][10][11][12] and has been used to realize interesting physical phenomena such as high Q near perfect absorption resonance with unpolarized focused light [13] and Goos-Hänchen (GH) shift enhancement. [14,15] However, BIC is a dark mode with an invisible scattering spectrum, [16] which makes it impossible to detect in practice.…”

Large Rabi splitting energy in resonant quasi-BIC WSe2 metasurfaces

“…By adjusting the perturbation parameters, the Q-factor of QBIC can be effectively adjusted, it provides a new platform for strong light trapping, and can be widely used in space light modulators, nonlinear effect and other fields [24][25][26][27]. Therefore, by employing by the QBIC with high Q-factor also become an important platform for raising the Rabi split value [28][29][30][31][32][33][34][35][36]. Currently, many researchers have integrated single-layer TMDCs into QBIC-enabled micro-nano devices, obtaining relatively large values of Rabi splitting.…”

The impact of light polarization and the nature of modes in the formation of quasi-bound states in the continuum at near-normal incidence

“…Thus, an all-dielectricbased metasurface with high index scatterers is proposed as an alternative to plasmonic metasurfaces. Dielectric structures like split ring resonators [18,19], nanorods, and inverse structures [20] have been reported to support structure-induced optical resonances by exciting various multipolar moments.…”