Wideband optical frequency comb generation using a fiber re-circulating loop cascaded with a spectrum expander including highly nonlinear fiber

A wideband optical frequency comb (OFC) generator using a fiber re-circulating loop (FRL) including a phase modulator and optical amplifier, cascaded with a spectrum expander containing a high-power erbium-doped fiber amplifier and highly nonlinear fiber (HNLF) is proposed and experimentally demonstrated, in which the FRL is used as a source to generate seed comb lines, and then generated seed comb lines are extended to a wideband optical frequency comb using cascaded four-wave mixing in the HNLF. Only using one stage spectrum expander, a stable 20-GHz optical comb with 201 comb lines within 30-dB power deviation, spanning 40-nm bandwidth, is achieved. The results show that the HNLF has unique ability to broaden output spectrum from the FRL. In addition, an optical frequency comb is dramatically broadened, which may be predicted by optimizing gain and dispersion of the FRL or configuration of the spectrum expander, or both.