光学奇点是电磁场的拓扑缺陷，包括标量场中的相位奇点、矢量场中的偏振奇点以及光学斯格明子等三维奇点。近年来，利用光子微结构来产生和操纵光学奇点引起了广泛的研究兴趣，并为此设计了许多光子微结构。伴随着这些设计，人们提出了一系列基于现象的理论来阐释诸多设计背后的工作机制。在这项工作中，我们不关注特定类型的微结构，而集中研究微结构最常见的几何特征--即对称性，并从对称性的角度出发重新审视了微结构中光学奇点的产生过程。通过系统地运用群表示论中的投影算符，我们开发出了一种广泛适用的理论方案，用于探索具有旋转和反射对称性的微结构中的光学奇点。我们的方案与之前报道的工作一致，并进一步揭示了对称微结构的特征模的不同分量，如平面外分量、径向分量、切向分量和左右手圆分量，可以支持（复用）相位奇点。基于这些相位奇点，我们可以合成更复杂的光学奇点，包括 C 点、V 点、L 线、奈尔型和气泡型光学斯格明子以及光学晶格等。我们证明，与光学奇点相关的拓扑不变性受到微结构对称性的保护。最后，基于对称性论证，我们提出了所谓的对称性匹配条件，以阐明特定类型光学奇点的激发。我们的工作建立了一个统一的理论框架来探索具有对称性的光子微结构中的光学奇点，揭示了多维和复用光学奇点的对称性起源，并为探索光学、光子学中许多与奇点相关的效应提供了一个对称性视角。

Optical singularities are topological defects of electromagnetic fields; they include phase singularity in scalar fields, polarization singularity in vector fields, and three-dimensional (3D) singularities such as optical skyrmions. The exploitation of photonic microstructures to generate and manipulate optical singularities has attracted wide research interest in recent years, with many photonic microstructures having been devised to this end. Accompanying these designs, scattered phenomenological theories have been proposed to expound the working mechanisms behind individual designs. In this work, instead of focusing on a specific type of microstructure, we concentrate on the most common geometric features of these microstructures—namely, symmetries—and revisit the process of generating optical singularities in microstructures from a symmetry viewpoint. By systematically employing the projection operator technique in group theory, we develop a widely applicable theoretical scheme to explore optical singularities in microstructures with rosette (i.e., rotational and reflection) symmetries. Our scheme agrees well with previously reported works and further reveals that the eigenmodes of a symmetric microstructure can support multiplexed phase singularities in different components, such as out-of-plane, radial, azimuthal, and left- and right-handed circular components. Based on these phase singularities, more complicated optical singularities may be synthesized, including C points, V points, L lines, Néel- and bubble-type optical skyrmions, and optical lattices, to name a few. We demonstrate that the topological invariants associated with optical singularities are protected by the symmetries of the microstructure. Lastly, based on symmetry arguments, we formulate a so-called symmetry matching condition to clarify the excitation of a specific type of optical singularity. Our work establishes a unified theoretical framework to explore optical singularities in photonic microstructures with symmetries, shedding light on the symmetry origin of multidimensional and multiplexed optical singularities and providing a symmetry perspective for exploring many singularity-related effects in optics and photonics.