Microring resonators are one of the most sought-after optical components for realizing several on-chip functionalities that include sensing, data routing, new frequency generation, and quantum photonic applications. Many of these applications demand a high quality factor and large notch depth (high extinction ratio), which can be achieved by critical coupling. However, the critical coupling is very sensitive to fabrication accuracies and thermal drift. Geometrical parameters of the resonators are generally swept to attain critical coupling, where a few designs can pass the critical coupling condition criteria. In this work, we propose a methodology to circumvent this vital issue. The proposed technique is based on coupled-resonator systems where two different microrings are embedded into a larger microring, referred to as a nonconcentric nested microring resonator (NN-MRR). The NN-MRR configuration relaxes the requirement of the critical coupling condition by 20% when the strip optical waveguide has either smooth or rough sidewalls. Numerical simulations reveal that, unlike standard MRR, a high $Q$-factor (${\gt}\!{{1}}{{{0}}^5}$) and a large transmission notch depth ${\gt}\!{{10}}\;{\rm{dB}}$ can be maintained irrespective of the rings’ coupling conditions for the nested MRRs. Besides the extra degree of freedom of design provided by the inner rings, the other significant advantage of the proposed NN-MRR is its compactness. We believe that the nested MRR arrangement could be highly efficient for biosensing, nonlinear, and quantum applications within a broad ambient temperature range. We have fabricated the NN-MRRs in a silicon-on-insulator platform through electron beam lithography and experimentally demonstrated the theoretical and numerical findings.

中文翻译：

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具有高 Q 值和大制造公差的嵌套式非同心微环谐振器

微环谐振器是最受欢迎的光学元件之一，可用于实现多种片上功能，包括传感、数据路由、新频率生成和量子光子应用。许多这些应用需要高品质因数和大缺口深度（高消光比），这可以通过临界耦合来实现。然而，临界耦合对制造精度和热漂移非常敏感。通常扫描谐振器的几何参数以获得临界耦合，其中一些设计可以通过临界耦合条件标准。在这项工作中，我们提出了一种方法来规避这个重要问题。所提出的技术基于耦合谐振器系统，其中两个不同的微环嵌入到一个较大的微环中，称为非同心嵌套微环谐振器 (NN-MRR)。当带状光波导具有光滑或粗糙的侧壁时，NN-MRR 配置将临界耦合条件的要求放宽了 20%。数值模拟表明，与标准 MRR 不同，高$Q$ -factor ( ${\gt}\!{{1}}{{{0}}^5}$ ) 和大传输陷波深度${\gt}\!{{10}}\;{无论嵌套 MRR 的环耦合条件如何，都可以保持\rm{dB}}$。除了内环提供的额外设计自由度外，所提出的 NN-MRR 的另一个显着优势是其紧凑性。我们相信嵌套的 MRR 排列可以在广泛的环境温度范围内高效地用于生物传感、非线性和量子应用。我们通过电子束光刻在绝缘体上硅平台上制造了 NN-MRR，并通过实验证明了理论和数值结果。