Photonic whispering‐gallery‐mode (WGM) cavities formed by total internal reflection of light around closed paths have played a central role in modern optics. Recently, extensive efforts have been devoted to achieving topologically photonic WGM cavities that are robust against defects or obstacles. However, previous experimental studies on topological photonic WGM cavities are limited to systems with time‐reversal symmetry (TRS) and weak topological protection due to the existence of backscattering channels. Here, the study reports the experimental realization of a chiral topological WGM cavity in a gyromagnetic photonic crystal with broken TRS. Using microwave near‐field measurements, it is directly observed that the chiral topological WGM cavities are inherently nonreciprocal and exhibit superior robustness against various obstacles with strong topological protection owing to the absence of backscattering channels. More interestingly, it is demonstrated that the resonance frequencies and free spectral range (FSR) of the chiral topological WGM cavities can be tailored by adjusting the insertion length of a metallic scatterer. The work extends the research realm of topological photonic WGM cavities and may find important applications in designing arbitrary‐shaped and nonreciprocal topological photonic cavities, filters, lasers, and frequency combs.

中文翻译：

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在旋磁光子晶体中实现手性拓扑 Whispering-Gallery-Mode 腔


光子耳语画廊模式 （WGM） 腔由光围绕闭合路径的全内反射形成，在现代光学中发挥着核心作用。最近，人们投入了大量精力来实现对缺陷或障碍物具有鲁棒性的拓扑光子 WGM 腔。然而，由于背向散射通道的存在，以往对拓扑光子 WGM 腔的实验研究仅限于具有时间反转对称性 （TRS） 和较弱拓扑保护的系统。在这里，该研究报告了在具有破损 TRS 的旋磁光子晶体中手性拓扑 WGM 腔的实验实现。使用微波近场测量，可以直接观察到手性拓扑 WGM 腔本质上是非互易的，并且由于没有反向散射通道，因此对各种障碍物表现出卓越的鲁棒性，具有很强的拓扑保护。更有趣的是，结果表明，可以通过调整金属散射体的插入长度来定制手性拓扑 WGM 腔的共振频率和自由光谱范围 （FSR）。这项工作扩展了拓扑光子 WGM 腔的研究领域，并可能在设计任意形状和非互易拓扑光子腔、滤波器、激光器和频率梳中找到重要应用。