An integrated in-fiber coupling configuration for simultaneously exciting whispering gallery mode (WGM) and Fabry-Perot (FP) resonances in one cavity is proposed and demonstrated experimentally. The WGMs traveling circularly in both clockwise and counter-clockwise directions are simultaneously excited by perpendicularly injecting the light from the single-mode-fiber (SMF) core into a polymeric microsphere embedded in the femtosecond laser micromachined coupling structure. While the standing wave between the two axial interfaces of the microsphere and its external media results in a spherical FP resonator, meaning that the WGM and the FP resonances coexist in the same spherical cavity. The superposition of WGM and FP resonances results in asymmetric Fano-like lineshape, which is of high importance for optical fiber sensors, filters, and switches due to its sharp slope around the resonant wavelength. Experimental results show that asymmetric spectral lineshape can be achieved even as the spatial coupling gap is larger than the wavelength, indicating that the proposed coupler has higher fabrication tolerance than the evanescent field-based coupling configuration. Such an integrated coupling configuration provides an effective method for the coupling between the optical fiber and WGM cavities made of any functional material by liberating them from the phase-matching condition and enriching the functionality by importing other resonance into the same cavity.

中文翻译：

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具有回音壁模式和法布里-珀罗共振的光纤内对接耦合球形微腔


提出并通过实验证明了一种集成光纤内耦合配置，用于在一个腔中同时激发回音壁模式（WGM）和法布里-珀罗（FP）谐振。通过将来自单模光纤 (SMF) 纤芯的光垂直注入嵌入飞秒激光微加工耦合结构中的聚合物微球，同时激发沿顺时针和逆时针方向循环运行的 WGM。而微球与其外部介质的两个轴向界面之间的驻波形成球形FP谐振器，这意味着WGM和FP谐振共存于同一球形腔中。 WGM 和 FP 谐振的叠加会产生不对称的类 Fano 线形，由于其在谐振波长周围的陡峭斜率，这对于光纤传感器、滤波器和开关非常重要。实验结果表明，即使空间耦合间隙大于波长，也可以实现不对称的谱线形状，这表明所提出的耦合器比基于倏逝场的耦合配置具有更高的制造公差。这种集成耦合配置为光纤和由任何功能材料制成的WGM腔之间的耦合提供了一种有效的方法，将它们从相位匹配条件中解放出来，并通过将其他谐振引入同一腔来丰富功能。