Tutorial: applications of Raman gain in optical transmission systems

The nonlinear stimulated Raman scattering process leads to broadband amplification when high power 14 xx nm pump photons scatter off vibrations of the glass matrix (acoustic phonons), down-shift in frequency and coherently add to signal photons. While erbium-doped fiber amplifiers spent the 1990´s becoming the preferred commercially viable amplification technology, there has been renewed interest in Raman amplification. The prime reason is it´s ability to provide distributed amplification along transmission fiber, hence acting as a low-noise pre-amplifier enabling ultra-long 10Gbps as well as 40 Gbps transmission. Additionally, bandwidth flexibility-particularly it´s location, magnitude and flatness-has increased excitement of all-Raman systems. This tutorial will cover the fundamentals of Raman amplification, compare it to erbium amplifiers, discuss distributed and discrete applications and review recent Raman-based transmission experiments.