<title>Spectroscopic multiple-vibrational modeling of Raman gain in FRA</title>

Abstract

Fiber Raman amplifiers with the theoretical limit of gain bandwidth up to 12 THz are becoming more and more essential in wavelength-division-multiplexing optical communication systems with terabit capacity. In this work, the new spectroscopic model for the Raman gain spectrum decomposition in arbitrary optical fiber using multiple vibrational modes is presented. Modeling results is given for the development of stimulated Raman gain spectrum in silica fiber. Nonlinear fitting procedure with Levenberg-Marquardt method of Raman gain profile was applied and it gives practically exact approximation of the observed Raman gain spectrum in silica fiber. The integrated intensities of model spectra are coincided with experimental spectrum within <0.3%. The optimal set of Raman gain parameters is compiled to simple analytical expressions that can be integrated and differentiated in symbolic form and are easy to evaluate numerically. Modeling results on the set of basic Raman amplifier characteristics such us: gain ripple, bandwidth, group delay, and noise performance is presented. Model is applicable to FRA design in fiber materials with known SRS spectra of any complexity.