Fig. 1. (a) Schematic representation of different resonances in the cavity. The equally spaced comb lines are shown by black dashed lines, with a spacing of D12π. (b) By inducing different amounts of mode splitting for different resonances, it is possible to overlap each of the equidistant comb lines with one of the cavity resonances. (c) Scanning electron microscope (SEM) images of a SiN resonator with partially modulated inner edge at different scales.

Fig. 2. (a) Schematic representations of partially and fully modulated resonators, showing resonator designs (top) and their corresponding mode splitting profiles (bottom). The top left illustrates the resonator with its key parameters: modulation period (Pmod), modulation amplitude (Amod), number of modulations (nmod), and angle of modulation (θmod). The bottom right shows a fully modulated resonator, inducing mode splitting in only one mode, while the bottom left illustrates how a partially modulated resonator can induce mode splitting in multiple modes depending on the design. (b) Variation of maximum mode splitting as a function of Amod for small modulation amplitudes (Sample01) and large modulation amplitudes (Sample02). Pmod and nmod are 475 nm and 100, respectively. Inset: mode splitting profile variation for large modulation amplitudes (Sample02). (c) Change in the splitting profile with nmod. Amod and Pmod are 250 nm and 475 nm, respectively. (d) Mode splitting profile variation in relation to Pmod, while nmod and Amod are fixed to 100 and 125 nm, respectively.

Fig. 3. (a)–(c) Schematic representation of three different configurations of the reflectors’ relative angular distance. (d) Variation of the mode splitting for the three different configurations illustrated in (a)–(c).

Fig. 4. (a) Variation of the measured mode splitting, divided by two, for the modulated resonator with four reflectors specified in Table 1. A fourth-order polynomial is fitted to the data. The inset provides a schematic of the resonator, showing four reflectors positioned at angular locations of 150°, 220°, 290°, and 20°. (b) Variation of the intrinsic quality factor (Qint) for the unmodulated and modulated resonators. (c) The fourth-order polynomial fit in (a) is incorporated into the simulated Dint/2π for an unmodulated 600-nm-thick resonator (blue), providing a flatter dispersion (orange). The green dots show the measured dispersion of an unmodulated 400-nm-thick resonator. (d) Dark comb generation is compared between modulated and unmodulated 600-nm-thick resonators in (c) by running simulations with the Lugiato-Lefever equation (LLE). The optimized dispersion results in a substantial bandwidth increase in the generated comb, with certain comb lines exhibiting more than 30 dB enhancement.