Topological photonics is a new and rapidly growing field that deals with topological phases and topological insulators for light. Recently, the scope of these systems was expanded dramatically by incorporating non-spatial degrees of freedom. These synthetic dimensions can range from a discrete ladder of cavity modes or Bloch modes of an array of waveguides to a time-bin division (discrete time steps) in a pulsed system or even to parameters such as lattice constants. Combining spatial and synthetic dimensions offers the possibility to observe fundamental and exotic phenomena such as dynamics in four dimensions or higher, long-range interaction with disorder, high-dimensional nonlinear effects, and more. Here, we review the latest developments in using non-spatial dimensions as a means to enhance fundamental features of photonic topological systems, and we attempt to identify the next challenges.

中文翻译：

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合成维度中的拓扑光子学

拓扑光子学是一个快速发展的新领域，涉及光的拓扑相和拓扑绝缘体。最近，通过结合非空间自由度，这些系统的范围得到了显着扩展。这些合成维度的范围可以从空腔模式的离散阶梯或波导阵列的布洛赫模式到脉冲系统中的时间仓划分（离散时间步长），甚至是晶格常数等参数。结合空间和合成维度提供了观察基本和奇异现象的可能性，例如四维或更高维度的动力学、与无序的远程交互、高维非线性效应等。在这里，我们回顾了使用非空间维度作为增强光子拓扑系统基本特征的手段的最新进展，