Field calibration procedure for enhanced automatic gain control of distributed Raman amplifiers

Distributed Raman amplifiers (DRAs) have gained interest for elastic optical networking (EON) because they allow, in some configurations, to increase the amplification bandwidth, to enhance the gain flatness and to decrease the noise insertion compared to conventional erbium doped fiber amplifiers (EDFAs). However, there are operational issues in the deployment of DRAs because the transmission fiber itself serves as the gain medium. The characteristics of this fiber, that are not always perfectly known in field installations, have an influence on the Raman gain used for the signal amplification. As a consequence, the pump power of the DRAs must be adjusted to adapt to the actual fiber properties to provide accurate automatic gain control. In this paper, we present a field calibration procedure for distributed counter-propagating Raman amplifiers to enhance their automatic gain control. We demonstrate the performance of this calibration procedure in simulations for transmission fibers of different attenuation profiles.