Effects of Input Spectra on the Threshold of Modulation Instability in a Single-Mode Fiber

We investigate modulation instability (MI) in the presence of a monochromatic spectrum and on the background of a broadband amplified spontaneous emission spectrum induced by an erbium-doped fiber amplifier, respectively. For the former case, the MI threshold is ∼110 mW, which agrees well with the theoretical value. However, for the latter case, the threshold is as high as ∼170 mW, which indicates that the MI threshold depends on the shape of the input spectrum and that the broadband spectrum has a higher threshold than the monochromatic one.