Lasing action based on polarization-insensitive quasi-bound states in the continuum in dielectric metasurface

We numerically study dielectric metasurface based on silicon resonators coated with polyurethane on the silicon dioxide substrate. Such metasurface can support toroidal magnetic dipole mode and quasi-bound state in the continuum (quasi-BIC) dominated by electric quadrupole with a high Q-factor by breaking the in-plane inversion symmetry. Sharply quasi-BIC with polarization-insensitive characteristics can generate strong local field enhancement distributed in the polyurethane and be used to support lasing action. Numerical results show that the pumping power threshold can be conveniently tuned by adjusting the polarization angle and can reach up to 30.2 and 51.3 μJ/cm2 in the orthogonal direction of polarization, respectively. Our findings may provide a useful guideline to design low-threshold and high-efficient miniaturized lasers.