Strong Purcell effect of magnetic quasi-BICs in the dielectric metasurface

Abstract The ultra-strong light field trapping in micro- and nanostructures, derived from optical bound states in the continuum (BICs), provides a new platform for the facilitation of light-matter interactions. In this work, we numerically study the spontaneous emission enhancement of dipole quantum emitters with the use of magnetic quasi-BICs metasurfaces. It is found that an ultrahigh Purcell factor (>10⁵) can be easily achieved when the asymmetry parameter is decreased. In theory, an infinite Purcell factor may be emerged due to the infinite Q-factor at the BICs state. In addition, the Purcell factor exhibits a strong dependence on the polarization direction of dipole emitter and the local field distribution in the metasurface. Finally, the photoluminescence enhancement for different perturbation parameters is calculated to confirm the strong Purcell effect in the quasi-BICs metasurface. These results show that the magnetic dipole BICs mode holds an enormous potential in manipulating spontaneous emission.