A method to predict the Raman gain spectra of germanosilicate fibers with arbitrary index profiles

In this letter, we present a technique for calculating the Raman gain spectra of germanosilicate fibers from their index profiles. The gain spectra depend on radial profiles of the guided optical modes and the glass composition, in particular the distribution of Si-O-Si and Ge-O-Si bridging bonds. We have obtained spectral coefficients, which represent the contributions from these bonds using Raman gain measurements made on a set of calibration fibers with well-characterized index profiles. We describe how these spectral coefficients can be used in the design of Raman gain fibers, and we demonstrate the accuracy of our technique over a broad range of fiber types.