Sideband instability induced by periodic power variation in long-distance fiber links.

Periodically spaced amplifiers along a transoceanic cable provide the phase-matching condition for a four-wave mixing process owing to Kerr nonlinearity. A new kind of sideband instability, shows up in both positive and negative dispersion regimes that is similar to modulation instability. A comparison with the sideband instability that was recently discovered for solitons is carried out.