We report the observation of polarization singularities in momentum space of 2D photonic quasicrystal slabs. Supercell approximation and band-unfolding approach are applied to obtain approximate photonic dispersions and the far-field polarization states defined on them. We discuss the relations between the topological charges of the polarization vortex singularities at $\mathrm{\Gamma }$ points and the symmetries of photonic quasicrystal slabs. With a perspective of multipolar expansions for the supercell, we confirm that the singularities are protected by the point-group symmetry of the photonic quasicrystal slab. We further uncover that the polarization singularities of photonic quasicrystal slab correspond to quasibound states in the continuum with exceptionally high-quality factors. Polarization singularities of different topological charges are also experimentally verified. Our Letter introduces core concepts of optical singularities into quasiperiodic systems, providing new platforms for explorations merging topological and singular optics.

中文翻译：

---

动量空间中光子准晶体的偏振奇异性

我们报告了对二维光子准晶板动量空间中偏振奇点的观察。应用超胞近似和带展开方法来获得近似的光子色散和定义在它们上的远场偏振态。我们讨论了极化涡旋奇点的拓扑电荷之间的关系$\mathrm{\Gamma }$点和光子准晶板的对称性。从超胞多极膨胀的角度来看，我们确认奇点受到光子准晶板的点群对称性的保护。我们进一步发现，光子准晶体板的偏振奇异点对应于连续介质中的准束缚态，具有非常高的品质因子。还通过实验验证了不同拓扑电荷的极化奇点。我们的信函将光学奇点的核心概念引入准周期系统，为探索拓扑光学和奇异光学的融合提供了新的平台。