We propose a split ring metasurface supporting simultaneously symmetry-protected dual bound states in the continuum (BIC) under normal excitation. Such two BICs can be classified as symmetry protected toroidal dipole (TD) BIC and magnetic dipole (MD) BIC, and the asymmetrically distributed holes can convert these two BICs into TD quasi-BIC and MD quasi-BIC with ultrahigh Q-factors, respectively. Two eigenmodes reveal the existence of symmetry protected BICs with an infinite lifetime and exhibit the intrinsic TD and MD characters by multipole analysis. In addition, it is shown that the two quasi-BICs can be switched on and off at orthogonal incident polarization orientations simultaneously. Further, such two quasi-BICs can be efficiently modulated by varying the Fermi energy of the graphene covered on the dielectric metasurface, indicating that the TD and MD quasi-BICs in the proposed metasurface have potential applications in designing novel quasi-BIC-based optical modulator and switching.

我们提出了在正常激发下在连续谱（BIC）中同时支持对称保护双键态的裂环超表面。这两个BIC可以分为对称保护的环形偶极（TD）BIC和磁偶极（MD）BIC，并且不对称分布的空穴可以将这两个BIC分别转换为具有超高Q因子的TD准BIC和MD准BIC。 。两种本征模式揭示了存在无限寿命的对称保护BIC，并通过多极点分析显示了固有的TD和MD特性。另外，示出了可以在正交入射偏振方向上同时打开和关闭两个准BIC。此外，通过改变覆盖在介电超表面上的石墨烯的费米能，可以有效地调制这两个准BIC，