Comparison between theory and experiment of nonlinear propagation for a few-cycle and an ultraband optical pulses in a fiber-beyond the slowly-varying envelope approximation

Summary form only given.To describe the propagation of short-duration and broadband optical pulses in a fiber, the conventional slowly-varying envelope approximation (SVEA), has the following two limitations: (1) the approximation of the slowness of the envelope compared with the optical cycle time becomes invalid for an ultrashort pulse, (2) its treatment of linear dispersion of the fiber, i.e., including ordinary up to 3rd-order terms around the center frequency of the pulse, becomes incorrect when the bandwidth of the pulse spectrum becomes extremely large. To solve the first problem, we have derived a nonlinear fiber propagation equation by the method similar to the slowly-evolving-wave approximation. To solve the second problem, we have developed a novel method to include all orders of terms for the linear material and waveguide dispersion in the numerical calculations. In summary, a nonlinear pulse propagation equation that can be used to describe ultrabroadband and small-cycle optical pulses in a fiber is derived and the calculated spectra obtained from it for self phase modulation agrees well with the experimental spectra.