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Fiber Fabry-Perot Interferometer-Based Fano Resonance Coupler for Whispering-Gallery-Mode Resonators

In this letter, we present an optical fiber coupler for Fano resonance excitation of whispering gallery modes in microsphere resonators. The coupler can be fabricated conveniently by fusion-splicing an endface-etched fiber with a tapered fiber. Owing to the effective reflections from the fusion splicing-induced in-fiber bubble and the fiber taper tip, Fabry-Perot interference can be observed in the reflective spectrum of the fiber coupler. Since the coupler itself is a Fabry-Perot interferometer, asymmetric Fano resonance can be also excited. The fiber tip-based Fano resonance coupler is simple, compact, and can be used as a probe in the reflection mode, allowing for simple interrogation in biomedical sensing and optical switching applications.