Standing-wave supermode microresonators that are created through the strong coupling between counter-propagating modes have emerged as versatile platforms for sensing and nonlinear optics. For example, these microresonators have shown potential in nanoparticle sizing and counting, as well as enhancing the single-photon optomechanical coupling rate of stimulated Brillouin scattering. However, it has been observed that the relation between the mode linewidth and on-resonance transmission of the split supermodes differs obviously from that of the non-split modes. This behavior is typically quantified by the coupling ideality (I), which remains inadequately explored for the standing-wave supermodes. In this study, we theoretically and experimentally investigate the coupling ideality of standing-wave supermodes in a commonly employed configuration involving a SiO2 microresonator side-coupled to a tapered fiber. Our findings demonstrate that, even with a single-mode tapered fiber, the coupling ideality of the standing-wave supermodes is limited to 0.5, due to the strong backscattering-induced energy loss into the counter-propagating direction, resulting in an additional equivalent parasitic loss. While achieving a coupling ideality of 0.5 presents challenges for reaching over-coupled regimes, it offers a convenient approach for adjusting the total linewidth of the modes while maintaining critically-coupled conditions.

中文翻译：

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驻波超模微谐振器的耦合理想性


通过反向传播模式之间的强耦合创建的驻波超模微谐振器已成为传感和非线性光学的多功能平台。例如，这些微谐振器在纳米粒子尺寸测定和计数以及增强受激布里渊散射的单光子光机械耦合率方面显示出潜力。然而，已经观察到，分裂超模的模式线宽和谐振传输之间的关系与非分裂超模明显不同。这种行为通常通过耦合理想性来量化（我），对于驻波超模的探索仍然不够充分。在这项研究中，我们从理论上和实验上研究了常用配置中驻波超模的耦合理想性，其中涉及二氧化硅2微谐振器侧面耦合到锥形光纤。我们的研究结果表明，即使使用单模锥形光纤，驻波超模的耦合理想度也仅限于 0.5，这是由于反向传播方向上强烈的反向散射引起的能量损失，导致额外的等效寄生损失。虽然实现 0.5 的耦合理想度对达到过耦合状态提出了挑战，但它提供了一种在保持临界耦合条件的同时调整模式总线宽的便捷方法。