System Margin Enhancement with Raman Gain in Multi-Span WDM Transmission

The capacity of dense wavelength division multiplexed optical fiber communications systems is increasing at a very fast pace to cope with the exponentially growing data traffic and the internet. To upgrade the capacity of the existing fiber plant it is necessary to evolve solutions for high speed signal transport without incurring impairments due to non-linear effects in the fiber at high channel power. In addition to the high capacity, in terrestrial networks it is desirable to reduce the number of amplifier sites in the transmission path to reduce the overall cost of the transmission system. Raman amplification has been successfully used to demonstrate long reach repeaterless transmission systems. Raman amplification by itself has been shown to have significant power budget improvement in a single span. In this paper, we report, for the first time, the improvement in the system power margin of 4 dB in a multi-span L-band WDM transmission system by the use of distributed Raman gain. The improvement in power budget permits error free transmission of 40 WDM channels at 10 Gb/s over 600 km of dispersion-shifted fiber (DSF).