Distributed Raman amplification speeds communication

Distributed Raman amplification, a key technology for future long-distance high-capacity terrestrial optical communication links, can increase system performance and expand the range of operating wavelengths. In the process of stimulated Raman scattering (SRS), a pump photon gives up its energy to create a new photon at the signal wavelength, plus some residual energy that is absorbed by the fiber in the form of phonons. Distributed amplification introduces less amplified spontaneous emission noise in the communication channel, allowing for longer amplification spans and overall transmission distances. An ideal link without no apparent loss would effectively offer the best trade-off between accumulated nonlinearities and optical signal-to-noise ratio. The improved OSNR in such links could be used to increase the reach or the capacity per channel.