Fig. 1. (a) Optical image of the LNOI microring resonator; inset, zoom-in of the coupling region; (b) cross-sectional schematic of the LN waveguide, with W (width) of 1.6 µm, E (etch depth) of 0.32 µm, and T (thickness) of 0.62 µm; (c) simulated LN waveguide integrated dispersion D_int/(2π) (blue); inset, local zoom-in within the black dashed box with the experimentally extracted data points (orange circles).

Fig. 2. (a) Schematic of experimental testing setups, including CW (continuous wave) source, EDFA (erbium-doped fiber amplifier), PC (polarization controller), PD (photodetector), OSC (oscilloscope), OSA (optical spectrum analyzer), ESA (electrical spectrum analyzer), GF (grating filter), and OPM (optical power meter); (b) MRR transmission spectrum in a slightly undercoupled state; (c) laser cavity detuning of the pump resonance mode (blue dot) with fitting Lorentz curve (red); (d) resonator transmission at a high-power pump when the laser frequency decreased.

Fig. 3. Characterization of frequency combs generated on LN microresonator (radius 100 µm). The frequency comb spectra in different states are characterized, including (a) chaos comb, (c) single-soliton comb, and (e), (g) two-soliton combs with different relative angles between solitons. The mode-locked single-soliton comb was featured with a sech² fitting curve [(c), red dotted line]. Furthermore, the intensity noise of the all frequency combs was characterized and shown in the right panel corresponding to each graph [(b), (d), (f), (h)]. The stable generation of the single soliton for the long term is realized by photorefractive and thermo-optical effects [(i) and (j)].

Fig. 4. Spectral characteristics of the LN microresonator (radius 60 µm) as well as simulation; the black dashed line marks the position of the dispersive wave in experimental results. (a) Simulated D_int curves; (b) normalized optical spectrum of the wideband Kerr comb.