Fiber-optic frequency comb generation using low-seed power FWM and Brillouin-assisted power equalization

In this paper, we experimentally demonstrate an all-fiber broadband tunable optical frequency comb (OFC) operating in the C-band. The OFC is generated by broadening a power-equalized stimulated Brillouin scattering (SBS)-based seed comb (SBS-OFC) using four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). The seed SBS-OFC is obtained from a pump and Stokes power recycling cavity, which yields ≈15 comb lines with 10.8 GHz line spacing having 16 dBm average power. The seed SBS-OFC is further power-equalized by a Brillouin-assisted power equalization (BAPE) technique to minimize the high pump contribution at the recycling cavity output. The power-equalized seed SBS-OFC, which has low-power of -4.5d B m at the BAPE cavity output, is propagated down a dual-pass 200 m dispersion flattened HNLF. At the HNLF output, we obtain ≈140 comb lines within a 12 nm bandwidth having 10.8 GHz line spacing. We demonstrate wavelength tunability over a span of 35 nm by using a tunable laser source as the Brillouin pump. We also observe and measure a secondary OFC generated during the power-equalization process by placing a 10% coupler inside the BAPE cavity. Our experimental results closely match the trends obtained in the simulation.