A 62-fs All-fiber Wideband Flat-top Spectrum Electro-optic Comb via Time-frequency Domain Shaping

The utilization of wideband flat-top spectrum electro-optical (EO) combs with enhanced robustness and coherence enables their application as multicarrier sources in wavelength-division multiplexing, thereby facilitating the development of novel techniques for optical communication. This study presents a new approach for achieving an all-fiber flat broadband spectrum EO comb through time-frequency domain shaping. We developed a hybrid pulse shaping technique utilizing the nonlinear optical loop mirror and the effect of nonlinear polarization rotation. This mechanism effectively compresses the pulse width and eliminates the pulse pedestals of the EO comb. Spectrum shaping through gain-narrowing during the power amplification is demonstrated, effectively removing the nonlinear chirp component of the spectrum. In the experiment, we obtained a 62-fs pulse train coherent 10 GHz EO comb with a 4 dB spectrum bandwidth of 120 nm, which fits well with the simulation. In addition, a broad spectrum covering the optical communication band above 500 nm was also acquired by fine-tuning the dispersion and polarization states.