Amplitude fluctuations and femtosecond pulse train noise in fibers

The results of numerical investigations of the femtosecond mode-locked laser radiation spectrum broadened in an optical fiber with the effect of incoming radiation noise are presented. It was found that the pulse train intensity stability, i.e., fluctuations of incoming radiation, strongly affect output spectral characteristics such as the spectral envelope and amplitudes of equidistant components in a femtosecond comb. Thus, intensity instability of about 1–10% or less can be critical for predictable and high amplitudes of spectral components; moreover, in this case, experimental measurements of spectral envelope dissemble the real femtosecond comb amplitudes.