We demonstrate a 20 GHz optical frequency comb generated using a resonant electro-optic modulator and an acetylene-stabilized continuous-wave laser at 1542.384 nm. The comb spans the S, C, and L optical communications bands, and its coherence was investigated in both the optical and radio frequency domains. Phase-noise analysis shows that the comb noise closely follows the phase noise of the radio-frequency synthesizer, while relative intensity noise is dominated by the seed continuous-wave laser. Propagation through highly nonlinear fibers with normal and anomalous dispersion for supercontinuum generation results in only minimal degradation of coherence. Heterodyne beat measurements reveal a slight linewidth broadening of the comb teeth, yet the overall performance remains compatible with high precision optical metrology. Furthermore, both experimental and numerical simulation results demonstrate spectral control through highly nonlinear fiber-based broadening while preserving coherence across the supercontinuum. Second-harmonic generation of the broadband comb has also been demonstrated. This work provides a comprehensive view of the noise budget of frequency combs based on resonant electro-optic modulators and highlights their robustness for applications in astronomical spectrograph calibration, optical communications, fast dual-comb spectroscopy, and frequency metrology.
Correia et al. (Mon,) studied this question.