Fig. 1. (a) Schematic of the tapered HACF coupled microsphere resonator. (b) Cross-sectional view with the inset as the simulated mode field distribution and (c) RI profile of HACF.

Fig. 2. (a) Schematic of splicing HACF with SMF. (b) Schematic of tapering the area, with the cone-apex angle as θ and the single tapering distance as d1. (c) Micrograph of SMF-HACF transition area without tapering, with the multi-mode transition area highlighted in the blue dotted box. Micrographs of (d) SMF-HACF transition area with tapering, (e) microsphere resonator manipulated by a section of tapered fiber, and (f) microsphere resonator embedded into the coupler.

Fig. 3. (a) Simulation of the coupling efficiency as a function of cone-apex angle θ, with the inset as the energy distribution in the device. (b) Taper times versus the cone-apex angle θ by experimental and theoretical fitting results.

Fig. 4. (a) Cross section of the model. (b),(c) Model of the microsphere (b) without and (c) with being locked by the HACF. (d) Evolution of reflection spectra with t11 from 0.8 to 0.995 for the case of (b). (e) Reflection spectrum for the case of (c).

Fig. 5. (a) Experiment results and simulation results of the device with a 42.30 μm diameter microsphere in the position very close to the end face. Experiment results of the device with a 42.60 μm diameter microsphere in the position very close to the end face, shown as symmetric Lorentzian line shapes with Q-factors about (b) 1300 and 76,000, and (c) 1700 and 35,000. (d) Experiment results of the device with microsphere locked by HACF inner wall with insets corresponding to detailed views of the negative symmetrical Lorentzian, asymmetrical Fano, and positive symmetrical Lorentzian line shapes.

Fig. 6. Temperature response of the device, with inset as the reflection spectra under different temperatures.