High-repetition-rate parametric electro-optic frequency comb with flat spectrum and burst-mode operation

In this work, we demonstrate a high-repetition-rate parametric electro-optic frequency comb with tunable line spacing up to 20 GHz and an optical spectrum with approximately 15 nm bandwidth and flatness better than 5 dB. The system uses an acetylene-stabilized laser operating at 1542.384 nm as a frequency-stable seed. A first Mach–Zehnder intensity modulator generates three phase-coherent continuous-wave optical tones with nearly equalized powers, which serve as pumps for cascaded four-wave mixing in a dispersion-shifted fiber (DSF). A second low-duty-cycle intensity modulation stage gates the optical waveform prior to amplification and propagation in the DSF, producing 80 ns optical bursts repeated every 5.6 µs while preserving the 20 GHz temporal modulation, resembling the temporal hierarchy of a Q-switched mode-locked laser. Phase noise and relative intensity noise measurements indicate no significant degradation introduced by the nonlinear broadening.