Optical microresonators with low quality factor ( Q $Q$ ) can be efficiently excited by and scatter freely propagating optical waves, but those with high Q $Q$ typically cannot. Here, we present a universal model for resonators interacting with freely propagating waves and show that the stored energy of a resonator excited by a plane wave is proportional to the product of its Q $Q$ and directivity. Guided by this result, we devise a microdisk with periodic protrusions in its circumference that couples efficiently to normally incident plane waves. We experimentally demonstrate several microdisk designs, including one with a radius of 0.75 λ 0 ${\lambda }_{0}$ and Q $Q$ of 15,000. Our observation of thermally-induced bistability in this resonator at input powers as low as 0.7 mW confirms strong excitation. Their small footprints and mode volumes and the simplicity of their excitation and fabrication make wavelength-scale, free-space-coupled microdisks attractive for sensing, enhancing emission and nonlinearity, and as micro-laser cavities.

中文翻译：

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自由空间耦合波长尺度圆盘谐振器

低品质因数的光学微谐振器（ 问 $Q$ ) 可以被自由传播的光波有效地激发和散射，但那些具有高 问 $Q$ 通常不能。在这里，我们提出了谐振器与自由传播波相互作用的通用模型，并表明由平面波激发的谐振器的存储能量与它的乘积成正比。 问 $Q$ 和方向性。在这一结果的指导下，我们设计了一种在其圆周上具有周期性突起的微盘，可以有效地耦合到正常入射的平面波。我们通过实验演示了几种微盘设计，包括一种半径为 0.75 λ 0 ${\lambda }_{0}$ 和 问 $Q$ 15,000。我们在输入功率低至 0.7 mW 时对该谐振器中热致双稳态的观察证实了强激发。它们的小尺寸和模式体积以及它们的激发和制造的简单性使得波长尺度、自由空间耦合的微盘对于传感、增强发射和非线性以及作为微激光腔具有吸引力。