Raman response function of silica-core fibers

Abstract

Nonlinear propagation of short high-intensity optical pulses in single-mode optical fibers is best treated in the time domain using the nonlinear Schrodinger equation. Here we show how Raman gain is included in such a time domain analysis as a response function. The essential feature of the approach is the recognition that all the nonlinear index is not instantaneous. Introducing such a noninstantaneous component of the nonlinear index produces in the frequency domain real and imaginary parts of the third-order susceptibility, which can be identified with a Raman contribution. The noninstantaneous component of the nonlinear index is the response function. We develop the response function for silica-core fibers from measurements of the Raman spectrum. The response function has a strong peak at 40 fs corresponding to the 430-cm −1 maximum in the gain spectrum.