Tunable quasi-bound states in the continuum in magneto-optical metasurfaces

Abstract

The enhancement of electromagnetic field with high Q factor in metasurface has attracted extension attention. Magneto-optical metasurface (MOMS) provides approaches with controllable magnetic field to modulate optical response, which contribute to the magneto-optical Kerr effect in nanophotonic devices. However, it is a challenge for MOMS to obtain narrow spectra peak with high Q factor. Here we propose a MOMS 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 quasi-BIC shows magnetization-related circular dichroism with a vortex point in polarization graph, based on time-reversal symmetry breaking in magneto-optical material under condition of external magnetic field. The quasi-BIC also keeps nearly unity reflection and almost zero absorption, which shows promising future in sensing. Our results enrich the light control mechanisms of MOMS, and provide a unique opportunity for applications requiring flexible tunability and high Q factors, such as sensor, laser source, filter and chiral-related elements.