Dynamic modulation of toroidal bound states in the continuum with suppressed continuum energy

Abstract Bound states in the continuum (BICs) enable ultrahigh- Q photonic resonators critical for advanced optoelectronics, yet their dynamic reconfigurability, particularly modulation depth in single-resonance systems, remains fundamentally limited. We overcome this by synergistically coupling a toroidal dipole quasi-BIC with a Fabry–Pérot resonance in a graphene-integrated metasurface. Through overdamped mode hybridization and graphene’s gate-tunable complex conductivity, the system achieves record modulation depth of 97.7% at 1550 nm while dynamically tuning Q -factors from 240 to 2600. This dual-resonance architecture simultaneously enables spectral agility and critical coupling absorption, resolving the long-standing trade-off between ultrahigh- Q confinement and reconfigurability for intelligent photonic devices.