Optical frequency comb (OFC) has attracted growing interest in various fields, such as frequency metrology, absorption spectroscopy, and instrumental calibrations. Electrooptic modulation (EOM) is one of the main comb-generating methods with the advantageous features of adjustable repetition frequency, high optical signal-to-noise ratio, and intrinsic coherence of the comb teeth. However, the spectral range of the EO-comb is limited by the modulation depth. In this paper, a twostage nonlinear system is built to broaden a 12.5 GHz EO-comb, namely the fiber-based stage and the on-chip stage. In the fiberbased stage, the pulse width of the comb is compressed to 52 fs from ~3 ps, meanwhile, the peak power is amplified to 2053 W and the comb spectrum is moderately broadened. In the on-chip stage, the comb is further broadened by an integrated Si3N4 waveguide spanning from 1200 nm up to 2000 nm. It is worth mentioning that the characteristic absorption lines of water vapor can also be observed in the broadened spectrum. These results indicate that the built system may have great application prospects in the field of parallel gas detection.

The spectral range of the optical frequency comb (OFC) generated by electro-optic modulators (EOMs) is limited by the modulation depth. In this paper, an on-chip system based on a Si3N4 waveguide is built to broaden a 12.5 GHz electrooptic comb (EO-comb). A numerical simulation is carried out to demonstrate the nonlinearities of self-phase modulation (SPM), Raman soliton self-frequency shift, and dispersive wave generation dominating the spectral broadening of the EO-comb in the waveguide.