Microbubble whispering-gallery resonators have shown great promise in fiber-optic communications because of their low confinement loss and hollow cores, which allow for facile stress-based tunability. Usually, the transmission spectrum of taper-coupled microbubbles contains closely spaced modes due to the relatively large radii and oblate geometry of microbubbles. In this letter, we develop an optical add-drop filter using a microbubble coupled to fiber taper and angle-polished fiber waveguides. Because of the extra degree of freedom in the angle of its polish surface, the angle-polished fiber can be used for the discriminatory excitation of certain radial-order modes in the optical microcavity, reducing the high modal density and enhancing add-drop selectivity. Our robust and tunable add-drop filter demonstrated a drop efficiency of 85.9% and quality factor of $2\times 10^{\mathbf {7}}$ , corresponding to a linewidth of 9.68 MHz. As a proof of concept, the drop frequency was tuned using internal aerostatic pressure at a rate of 7.3 ± 0.2 GHz/bar with no diminishing effects on the add-drop filter performance.

中文翻译：

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带角度抛光光纤耦合器的高效光学分插滤波器

微泡回音壁谐振器在光纤通信中显示出巨大的前景，因为它们的限制损耗低和空心，允许基于应力的轻松可调。通常，由于微泡相对较大的半径和扁圆的几何形状，锥形耦合微泡的透射光谱包含紧密间隔的模式。在这封信中，我们使用耦合到光纤锥度和角度抛光光纤波导的微泡开发了一种光学分插滤波器。由于其抛光表面角度的额外自由度，角度抛光的光纤可用于光学微腔中某些径向阶模式的判别激发，降低高模态密度并提高分插选择性。我们强大且可调谐的分插过滤器展示了 85 的分插效率。9% 和 $2\times 10^{\mathbf {7}}$ 的品质因数，对应于 9.68 MHz 的线宽。作为概念证明，使用内部空气静压以 7.3 ± 0.2 GHz/bar 的速率调整下降频率，对分插过滤器性能的影响没有减弱。