Amplification characteristics of fiber Raman amplifiers are reviewed. Simultaneous Raman amplification experiments of wavelength-division multiplexed (WDM) optical signals and a Raman amplification experiment of coherent optical signals using a 1.46 μm high-power semiconductor laser pump light source and an 80km high-Raman-gain optical fiber are described. Simultaneous amplification of WDM optical signals was demonstrated using 1.2Gbt/s and 565Mbit/s, intensity-modulated optical signals in unidirectional and bidirectional configurations with optical gains of 7dB and 6dB, respectively. No significant degradation was observed in any configuration. Raman amplification of coherent optical signals was also demonstrated through a 560Mbit/s FSK optical heterodyne transmission experiment. An optical gain of 7.5dB was obtained without any degradation. The results show that fiber Raman amplifiers can be used in WDM and coherent optical telecommunication systems.
