Ultra-long Raman fibre laser transmission links

In this paper we review some recent results related to the application of ultra-long Raman fibre laser (URFL) cavities to quasi-lossless optical signal transmission. In an URFL, the transmission fibre itself is contained inside a laser cavity delimited by two fibre Bragg gratings, allowing for a more efficient distribution of the Raman gain to the transmitted signal. We explore the unique properties of these URFLs experimentally, showing the excellent agreement with numerical predictions. URFL schemes can provide reduced signal power excursion (<0.98 dB in 75 km of SMF), and improved OSNR performance compared to conventional distributed Raman and lumped amplification. We also analyze the possibility of achieving simultaneous spatio-spectral transparency in optical fibre. Thanks to their unique properties, URFLs are ideal candidates for quasi-lossless DWDM signal transmission, soliton transmission and nonlinear optical signal processing.