Toroidal dipole excitation of quasi-BIC and EIT: decoupled control through spatial displacement

Conventional geometric symmetry breaking for exciting quasi-bound states in the continuum (BICs) often induces spectral drift. Here, we propose an all-dielectric dimer metasurface that achieves orthogonal, decoupled control of quasi-BIC and electromagnetically induced transparency (EIT) effects via spatial displacement. By utilizing horizontal and vertical offsets as independent degrees of freedom, we demonstrate that the radiation leakage of a toroidal-dipole-dominated first Brillouin zone (FBZ) induced quasi-BIC and the EIT bandwidth can be independently tuned while strictly maintaining resonant frequency stability. This spatial-coupling paradigm offers a robust platform for advanced multifunctional nanophotonics, including frequency-stable multi-channel sensing and slow-light devices.