Fig. 1. Dispersion engineering of Si₃N₄ waveguide. (a) Cross-section of Si₃N₄ waveguide; (b) simulated group velocity dispersion (GVD) varies with waveguide width when the waveguide height is fixed at 0.7 μm; (c) simulated GVD varies with waveguide height when the waveguide width is fixed at 2.8 μm; (d) A_eff and γ of TE₀ mode in Si₃N₄ waveguide with 2.8 μm×0.7 μm cross section

Fig. 2. Generating optical frequency comb by utilizing two-stage pulse-compressed phase-locked dual-frequency laser injection into the cavity-less normal dispersion Si₃N₄ waveguide

Fig. 3. Time/frequency domain of the optical frequency comb (OFC) generated by directly pumping a normal-dispersion Si₃N₄ waveguide with a phase-locked dual-frequency laser without pulse compression. (a) Time domain; (b) frequency domain

Fig. 4. Time/frequency domain of the OFC generated by injecting the phase-locked dual-frequency laser with pulse compression into the normal dispersion Si₃N₄ waveguide at different stages of the scheme in Fig.2. (a) Position ①; (b) position ②; (c) position ③; (d) position ④; (e) position ⑤, before injecting phase-locked dual-frequency laser into Si₃N₄ waveguide; (f) output of Si₃N₄ waveguide

Fig. 5. Comparison of the OFCs generated by injecting different shapes of pulses into the Si₃N₄ waveguide. (a) Time/frequency domain of the pulses before injecting into the Si₃N₄ waveguide; (b) time/frequency domain of the OFCs output after injecting different pulses into the Si₃N₄ waveguide

Fig. 6. Time/frequency domain evolution of the OFC generated by the phase-locked dual-frequency laser with power ratio of 0.1at different stages of the scheme in Fig.2. (a) Position ①; (b) position ③; (c) position ⑤, before injecting phase-locked dual-frequency laser into Si₃N₄ waveguide; (d) OFC output by Si₃N₄ waveguide

Fig. 7. 3 dB bandwidth of the OFC generated by phase-locked dual-frequency laser with different power ratios after Gaussian shaping

Fig. 8. Time/frequency domain evolution of the OFC generated by phase-locked dual-frequency laser with frequency spacing ν_m=0.2 THz at different stages of the scheme in Fig.2. (a) Position ①; (b) OFC output by Si₃N₄ waveguide

Fig. 9. 3 dB bandwidth of the OFC generated by phase-locked dual-frequency laser with different frequency spacings after Gaussian shaping