Dynamically tunable bound states in the continuum metasurfaces with simultaneous ultrahigh-<i>Q</i> and multi-resonance tunability

The confinement of electromagnetic waves is essential for nanophotonics. Bound states in the continuum (BICs) enable perfect light confinement, while ensuring that the light remains within the continuum and does not emit radiation. In the periodic all-dielectric grating structure, six high-<i>Q</i> quasi-BIC transmission peaks approaching unity are achieved by precisely adjusting both the grating gap and incident angle. We further investigate the energy band to obtain the position of the BICs and radiative <i>Q</i>-factors of three ultrahigh-<i>Q</i> symmetry-protected (SP) BICs. As demonstrated by Cartesian multipole decomposition, the predominant influence is attributed to the electric quadrupole or toroidal dipole. The metasurface demonstrates ultrasensitive environmental perturbation detection <i>via</i> quasi-BICs, enabling ultrahigh-<i>Q</i> resonances. The sensor demonstrates gas detection capabilities with an ultrahigh figure of merit (FOM) reaching 386 000 RIU^-1 and an exceptional sensitivity of 556.2 nm RIU^-1. Symmetry breaking in the nanostructure enables perfect reflection with an ultrahigh-<i>Q</i> reaching 10⁸, with the quasi-BIC generating a giant Goos-Hänchen (GH) shift. Finally, a thin indium tin oxide (ITO) layer is deposited on the metasurface grating, and a novel methodology is employed in order to disrupt the symmetry of the system. The modulation of the four SP BICs, in conjunction with the manipulation of the <i>Q</i>-factors of the quasi-BICs and electromagnetically induced transparency (EIT), accomplished by breaking the material symmetry in the structure, is analyzed. This study advances the development of high-<i>Q</i> multi-resonance metasurfaces and provides a new approach to manipulating SP BICs, which facilitates the design of novel ultrahigh performance integrated optical devices.