Active dual quasi-BICs in a dielectric metasurface with VO2 for slow light and optical modulation

We investigate the temperature tunable dual quasi-bound states in the continuum (qBICs) in a silicon/vanadium dioxide (Si/VO 2 ) hybrid metasurface with Q -factor being as large as 9.3 × 10 6 and 2.8 × 10 7 by breaking the in-plane C 2 symmetry. The far-field scattering of multipoles and near-field distributions confirm that the toroidal dipole and magnetic quadrupole dominate the dual qBICs resonance. The high performance of slow light with ultralarge group index exceeding 5.6 × 10 5 and the inverse quadratic law between the group index and asymmetric parameter are achieved. By temperature tuning of the VO 2 thin film at the sub-10 K scale, a modulation depth of 90% and the ON/OFF ratio exceeding 12.8 dB are obtained. The proposed temperature tunable dual qBICs have potential applications in the fields of tunable slow light, temperature switches, and sensors.