Broadband EO-Comb Generation Based on Two-Stage Nonlinear System

Optical frequency comb (OFC) has attracted growing interest in various fields, such as frequency metrology, absorption spectroscopy, and instrumental calibrations. Electro-optic 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 two-stage nonlinear system is built to broaden a 12.5 GHz EO-comb, namely the fiber-based stage and the on-chip stage. In the fiber-based 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 Si
₃
N
₄
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.