For nonlinear short-pulse propagation in long optical fibers, the conventional static approximation of the nonlinear terms in the wave equation must be extended to include the derivative of the pulse envelope. As a result, an initially symmetric pulse will develop an asymmetric self-phase modulation and a self-steepening, which ultimately lead to shock formation unless balanced by dispersion. This effect may be responsible for the pulse asymmetries observed in recent experiments.

• Received 7 September 1982

DOI:https://doi.org/10.1103/PhysRevA.27.1393