An In-Fiber Coupler for Whispering-Gallery-Mode Excitation in a Microsphere Resonator

An integrated in-fiber coupler for excitation of whispering-gallery modes (WGMs) of a microsphere resonator is proposed. The device is fabricated by embedding a microsphere into an optical fiber inner air-cavity through an open microchannel to excite various WGMs via evanescent field coupling. The asymmetric Fano resonance line shape and the symmetrical Lorentzian line shape with a slope of -13.88 dB/nm and a quality (Q)-factor of 1.81 × 10
³
are observed in the transmission spectrum of the device. Such an in-fiber WGM resonator coupling structure has the features of compactness, low-cost, robust and alignment-free.