Fig. 1. Fabrication of microcavity. (a) Schematic diagram of SiO₂ micro-cavity preparation; (b) Picture of SiO₂ crystalline resonator

Fig. 2. Morphology of microcavity. (a) 3D surface profile of the microcavity; (b) Surface roughness diagram of microcavity; (c)-(d) Characterization of microcavity roundness

Fig. 3. Measurement of resonant peak of SiO₂ microcavity. (a) Schematic diagram of microcavity coupling test; (b) Power transmission spectrum of microcavity; (c) Lorentz fitting spectral line; (d) Ringdown fitting

Fig. 4. Coupling characteristics of microcavity

Fig. 5. Decay curve of microcavity Q value with time

Fig. 6. Optical frequency comb generation. (a) Transmission lines of microcavity at high pump power；(b) Partially amplified transmission line of Fig.(a); (c)-(e) Evolution process of optical frequency comb corresponds to three different positions of microcavity transmission line in Fig.(a)

Fig. 7. Simulated optical frequency comb evolution based on LLE. (a) Figures I, II，III and IV show the evolution process of optical frequency comb; (b) Corresponding to the time-domain spectra in different comb states in Fig.(a)