A tapered hollow annular core fiber (HACF) coupler for excitation of whispering-gallery modes (WGMs) of anembedded microsphere resonator is proposed and demonstrated. Using HACF as the coupling medium can avoid thecomplicated fabrication process such as chemical corrosion and improve the robustness and stability of the device. Thecoupling efficiency from the SMF to HACF is enhanced after tapering the joint section to excite various WGMs. In boththeory and experiment, we observe symmetrical Lorentzian and asymmetric Fano line shapes by varying the microsphereresonator size and location. Finally, the temperature sensing sensitivity and stability of the device are tested. Thesensitivity of the device reaches 10.8 pm/°C. This novel tapered HACF based microsphere resonator is expected topromote the environmental adaptability in the practical application.
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