We report for the first time, to our knowledge, a technique that has the capability to measure both the Raman gain coefficient and the nonlinear refractive index of an optical fiber, using the same experimental setup. This measurement utilizes the induced-grating autocorrelation (IGA) technique, which is based upon time-delayed four-beam coupling in a photorefractive crystal. The standard IGA trace, which is based upon two-beam coupling, fits a simple model based on pure self-phase modulation (SPM). We demonstrate that, in the negligible-dispersion regime of an optical fiber, the addition of stimulated Raman scattering (SRS) leads to a measurable distortion of the standard (pure SPM) IGA trace. We have developed a new IGA model from the analytical solution of the coupled-amplitude nonlinear Schrodinger equation. This new model successfully accounts for the effect of SRS on the IGA trace in the negligible-dispersive regime of the fiber and allows the direct determination of the Raman gain coefficient and the nonlinear refractive index from the fit of the SRS distorted IGA trace. The measured nonlinear refractive index and the Raman gain coefficient are in good agreement with published results.
© 2005 Optical Society of America
Ferdinand A. Oguama, Hernando Garcia, and Anthony M. Johnson, "Simultaneous measurement of the Raman gain coefficient and the nonlinear refractive index of optical fibers: theory and experiment," J. Opt. Soc. Am. B 22, 426-436 (2005)