Tunable Quasi Bound States in the Continuum with High Q factor using Magneto-Optical Metasurface

The electromagnetic field enhancement caused by high Q factor resonance can greatly contribute to the magneto-optical Kerr effect of nanophotonic devices. Here we propose a magneto-optical metasurface supporting quasi bound states in the continuum (quasi-BIC) and theoretically investigate the evolution process from BIC to quasi-BIC. By applying external magnetic field, the BIC in our proposed metasurface can transform into quasi-BIC with finite Q factor up to 33620. Meanwhile, the polarization singularity of the quasi-BIC can be tuned by different magnetization directions, based on different time-reversal symmetry breaking phenomena in magneto-optical material under alternating magnetic field. The quasi-BIC in our magneto-optical metasurface keeps Fano reflection peak in parameter sweep, maintaining 99.99% reflection and almost zero absorption. Our results enrich the light control mechanisms of magneto-optical metasurface, and provide a unique opportunity for promising future applications requiring tunability and high Q factors, such as sensing, laser source and filtering.