Effects of erbium-doped fiber amplifier induced pump noise on soliton Kerr frequency combs for 64-quadrature amplitude modulation transmission.

We experimentally investigate the effects of erbium-doped fiber amplifier induced pump noise on soliton Kerr frequency combs for 64-quadrature amplitude modulation (QAM) transmission. We find that the optical carrier-to-noise ratios (OCNRs) of the comb lines across the C-band almost linearly depend on the pump OCNR and are similar for a constant input pump power and noise. For a specific three-soliton state, despite higher comb line power, there is no noticeable OCNR improvement compared to the single-soliton comb. When the ASE noise on the pump is varied by 10 dB in the stable single-soliton state, the comb linewidths remain relatively unchanged and similar to the pump linewidth. Furthermore, four lines of the single-soliton Kerr comb produced by a pump light at an OCNR larger than 52 dB are used as coherent light sources to transmit 20-Gbaud 64-QAM signals over a 25-km fiber with bit error rate below the forward-error correction threshold.