Low propagation loss in high confinement waveguides is critical for chip‐based nonlinear photonics applications. Sophisticated fabrication processes which yield sub‐nm roughness are generally needed to reduce scattering points at the waveguide interfaces to achieve ultralow propagation loss. Here, ultralow propagation loss is shown by shaping the mode using a highly multimode structure to reduce its overlap with the waveguide interfaces, thus relaxing the fabrication processing requirements. Microresonators with intrinsic quality factors (Q) of 31.8 ± 4.4 million are experimentally demonstrated. Although the microresonators support ten transverse modes only the fundamental mode is excited and no higher order modes are observed when using nonlinear adiabatic bends. A record‐low threshold pump power of 73 µW for parametric oscillation is measured and a broadband, almost octave spanning single‐soliton frequency comb without any signatures of higher order modes in the spectrum spanning from 1097 to 2040 nm (126 THz) is generated in the multimode microresonator. This work provides a design method that can be applied to different material platforms to achieve and use ultrahigh‐Q multimode microresonators.

中文翻译：

---

为宽带频率梳开发超低损耗多模波导

高约束波导中的低传播损耗对于基于芯片的非线性光子学应用至关重要。通常需要产生亚纳米粗糙度的精密制造工艺来减少波导界面处的散射点，以实现超低传播损耗。在此，通过使用高度多模的结构对模进行整形以减少其与波导界面的重叠来显示超低传播损耗，从而放宽了制造工艺要求。具有固有品质因数的微谐振器（Q实验证明了31.8±440万）。尽管微谐振器支持十种横向模式，但在使用非线性绝热弯曲时，仅基本模式被激发，并且未观察到更高阶的模式。测量了创纪录的73 µW的阈值泵浦功率，用于参数振荡，并产生了宽带，几乎倍频程的单孤子频率梳，在1097至2040 nm（126 THz）的频谱中没有高阶模的任何信号。多模微谐振器。这项工作提供了一种可应用于不同材料平台的设计方法，以实现和使用超高Q多模微谐振器。