Fig. 1. Principle diagram of WGM resonance. (a) Light propagation path; (b) electric field distribution

Fig. 2. WGM spectral tuning experiment system

Fig. 3. Schematic diagram of preparation and resonance spectrum of hollow microbottle structure. (a) Chemical etching; (b) fusion splicing; (c) WGM resonance spectrum

Fig. 4. Resonant wavelength tuning characteristic of WGM. (a) Shifting process of WGM resonant wavelength; (b) resonance peak shift versus strain change

Fig. 5. Q-value tuning process. (a) Increase of strain makes resonance peak blue shift; (b) applied strain changes Q value

Fig. 6. Preparation process and microscope images of AHMB. (a) Left and right motors are simultaneously moved toward left until distance d=60 μm, to align electrode to right of microcavity; (b) tapered region formed on one side of air-microbubble after electrodes discharge and two motors move in opposite directions simultaneously; (c) microscope image of Fig. 6(a); (d) microscope image of Fig. 6(b)

Fig. 7. Tuning of WGM resonance wavelength of AHMB structure by external strain and comparison of tuning sensitivity before and after tapering. (a) Tuning of WGM resonance wavelength of AHMB structure by external strain;(b) comparison of tuning sensitivity before and after tapering