Stability of symmetry-protected BICs in dielectric metasurfaces

Optical metasurfaces with high Q -factors have attracted much attention due to their sharp spectral features and significant field enhancement. The excitation of symmetry-protected bound states in the continuum (SP-BICs) is an efficient way to achieve a high Q -factor resonator. The experimental Q -factors of resonant quasi-SP-BIC metasurfaces are currently not high. In this work, we numerically demonstrate the stability of SP-BICs in silicon metasurfaces. The two SP-BICs are transformed into quasi-SP-BICs by breaking the in-plane symmetry of the structure, and their resonance properties are discussed by far-field radiation and near-field distribution. Moreover, the effects of different periods, sizes, substrate refractive indices, and shape factors on the SP-BICs are explored, and the Q -factors of quasi-SP-BICs always exhibit the same inverse quadratic dependence on asymmetry parameters, which demonstrates the stability of the SP-BIC. Our results may provide theoretical support for the experimental realization of ultrahigh Q -factor quasi-SP-BICs.