Requirements on transmission fibre infrastructure suitable for high power amplifiers

Optical signals of long distance transmission systems accumulate amplifier noise along the transmission link. Conversely, advanced modulation formats for data rates of 100 Gbit/s and faster require higher signal-to-noise ratios than signals with lower data rates. By implementation of additional Raman amplifiers the performance of transmission systems can be improved. Raman amplification can be usefully applied to bridge distances significantly longer than 100 km of fibre between adjacent active points in order to reduce the number of active elements in a network or to bridge distances between endpoints of a transmission link with undersea cables where the installation of active elements is expensive. In case of local points of increased fibre attenuation or losses due to bending however, transmission fibres or active components can be destroyed by the high output power of pump lasers. The pump lasers' output wavelength in the range of 1383 nm may also be absorbed by the water peak of the fibres. To avoid all these hazards for fibre communication systems the fibre infrastructure used for high power pump lasers must be analysed and tested before active components are installed in order to avoid significant signal degradation or damage to active and passive components in the transmission link.