We design and numerically investigate an all-dielectric metasurface with a single nanodisk in a unit cell supporting quasi-bound state in the continuum (BIC) arising from the distortion of symmetry-protected BIC. We demonstrate that by breaking out-of-plane symmetry, in the direction perpendicular to a nanodisk with an inclined surface, the transformation of BIC into quasi-BIC, having Fano line-shape, can be observed with an increasing inclination angle. Such transformation is analysed in detail by calculating charge density distributions, far-field radiations and near-field distributions, demonstrating the dominant electric quadrupole component in the quasi-BIC. In addition, the quasi-BIC can be easily tailored by the intrinsic material loss and the Fermi energy of graphene. By introducing this unique degree of freedom beyond the in-plane symmetry, one can realize access to the multipolar BIC-associated leaky state in simpler metasurface, indicating potential applications in the quasi-BIC-based switching and optical modulators.

我们设计并数值研究了一个全介电超表面，在单位单元中具有单个纳米盘，支持连续体 (BIC) 中由于对称保护的 BIC 的畸变而产生的准束缚态。我们证明，通过打破平面外对称性，在垂直于具有倾斜表面的纳米盘的方向上，可以随着倾斜角的增加观察到 BIC 向具有 Fano 线形状的准 BIC 的转变。通过计算电荷密度分布、远场辐射和近场分布详细分析了这种转换，证明了准 BIC 中的主要电四极子分量。此外，准 BIC 可以通过石墨烯的固有材料损失和费米能量轻松定制。