Extreme light confinement observed in periodic photonic structures, such as the vortex singularities in momentum (k) space, has been associated with their topological nature. Consequently, by exploiting and tuning their topological properties, optical metasurfaces have been demonstrated as an attractive platform for active photonics. However, given the fact that most active media under external excitations can only provide limited refractive index change, the potential advancements offered by the topological character of active metasurfaces have remained mostly unexplored. Zinc oxide (ZnO), which has recently exhibited optically-induced extraordinarily large permittivity modulations at visible and near-infrared frequencies, is an excellent active material for dynamic metasurfaces exhibiting strong tuning. This work demonstrates that a hybrid metasurface consisting of an array of ZnO nanodisks on a silver backplane displays broadly tunable topological properties. In particular, by performing k-space scattering simulations using measured pump-fluence-dependent material properties of ZnO, we study in detail the light reflection from the hybrid metasurface. Our results validate that the large k-space topology tuning of the metasurface can result in enormously strong polarization manipulation of near-infrared light in the vicinity of the topological features. The observed polarization switching effect is highly sensitive to the polarization and wavelength of an incident wave, owing to the symmetry and dispersion characteristics of the proposed system. Our study indicates that leveraging a combination of the extraordinary material properties and the k-space topology, hybrid metasurfaces based on ZnO may open new avenues for creating all-optical switchable metadevices.

中文翻译：

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具有广泛可调拓扑特性的氧化锌 (ZnO) 杂化超表面

在周期性光子结构中观察到极端光限制，例如动量中的涡旋奇点（ķ) 空间，与它们的拓扑性质有关。因此，通过利用和调整它们的拓扑特性，光学超表面已被证明是有源光子学的一个有吸引力的平台。然而，鉴于大多数在外部激发下的活性介质只能提供有限的折射率变化，因此活性超表面的拓扑特征所提供的潜在进步大多仍未得到探索。氧化锌 (ZnO) 最近在可见光和近红外频率下表现出光诱导的非常大的介电常数调制，是一种用于表现出强调谐的动态超表面的优异活性材料。这项工作表明，由银背板上的 ZnO 纳米盘阵列组成的混合超表面显示出广泛可调的拓扑特性。特别是，通过执行ķ- 使用测量的 ZnO 的泵浦注量相关材料特性进行空间散射模拟，我们详细研究了混合超表面的光反射。我们的结果验证了大ķ- 超表面的空间拓扑调整可以导致拓扑特征附近的近红外光的极强偏振操纵。由于所提出系统的对称性和色散特性，观察到的偏振切换效应对入射波的偏振和波长高度敏感。我们的研究表明，利用非凡的材料特性和ķ-空间拓扑，基于 ZnO 的混合超表面可能为创建全光可切换超器件开辟新途径。