Fig. 1. Raman comb generation. (a) The loaded Q factor of the fundamental WGM around 1561.32 nm wavelength. Inset: the scanning electron microscope (SEM) image of the fabricated microdisk, and the scale bar is 20 μm. (b) The transmission spectrum of the WGMs, where the fundamental mode family is labeled with red dots. (c) The spectrum of Raman comb when pumped at 1561.33 nm. Inset: The optical micrograph of the fundamental WGMs. (d) The spectrum of Raman comb when pumped at 1561.31 nm. (e) and (f) The enlarged spectral region labelled with the colored boxes in Fig. 1(d).

Fig. 2. Soliton comb generation from polygon modes. (a) The measured loaded-Q factor of the mode around 1542.80 nm. Inset: the optical micrograph of the polygon modes. (b) The transmission spectrum of the square mode family (labelled with red dots). (c) The spectrum of the comb lines when pumping at 1542.79 nm. (d) The RF spectrum of soliton comb, where signal and background are denoted as Sig. and BG.

Fig. 3. Dispersion design. (a) Simulated group refractive index curves. Here, the fundamental WGM TE₀ is denoted as TE₀ mode. (b) Simulated group velocity dispersion curves. (c) Simulated and its corresponding experimental integrated dispersion curves of the square modes, corresponding to the second-order dispersion D₂/(2π) of 0.8 MHz. (d) The effective cavity nonlinear volumes of WGMs and square mode as a function of cosΘ_λ,R. Inset: the calculated mode profile of the polygon mode.

Fig. 4. Comparison of geometrical features between the fundamental WGM and the square mode. (a) The WGM orbit cosΘ (Cosine) as a function of eigenvalue. (b) The mode distribution characteristics of fundamental WGM. (c) Close-up images of the WGM orbits for the relative mode numbers of −50, 0, and 50. (d) The classical orbit as a function of eigenvalue. (e) The mode distribution characteristics of the square mode. (f) Close-up images of the square orbits for the relative mode numbers of −50, 0, and 50.

Fig. 5. Evolution of the Kerr comb generation. (a-c) The spectra of the comb lines when tuning the pump wavelength from 1542.83 nm to 1542.81 nm. Inset in Fig. 5(c): the RF spectrum of chaotic comb. (d) The transmission spectrum during wavelength scanning, exhibiting a soliton step.