Self-amplitude modulation of optical pulses in nonlinear dispersive fibers.

We consider propagation of optical pulses in the anomalously dispersive region of single-mode fibers after including the effects of Kerr-type nonlinearity. It is found that the pulse develops an internal structure with deep amplitude modulation. We show that this self-amplitude modulation of pulses is distinct from the modulation instability of continuous-wave optical beams in nonlinear dispersive fibers. The initiation of this phenomenon does not require an external probe or spontaneous emission. Numerical results show that self-phase-modulation broadens the power spectrum enough to encompass the frequency at which self-amplitude modulation provides the maximum gain. The amplification of these side bands manifests as a breaking of the optical pulse into several subpulses. The results are presented for Gaussian, super-Gaussian, and secant hyperbolic pulses. The qualitative features of this new amplification are independent of the pulse shape.