To keep a total gain of the whole transmission line flat by compensating inter-wavelength gain deviation due to variation in input level to a rare-earth element added fiber amplification part without performing any complicated feedback control.
The optical repeating system is equipped with a Raman amplification part 18 which amplifies signal light by using Raman amplification effect and the rare-earth element added fiber amplification part 14 which amplifies the signal light by using a rare-earth element fiber as an amplifying medium and amplifies and outputs input light L1 having specific light intensity. The Raman amplification part 18 adjusts the light output intensity values of two exciting light sources 16-1 and 16-2 differing in oscillation wavelength and generates an amplification gain spectrum which has a larger gain on the short- wavelength side than on the long-wavelength side and the rare-earth element added fiber amplification part 14 generates an amplification gain spectrum which has a larger gain on the long-wavelength side than on the short- wavelength side.
SHIMIZU KATSUHIRO
SUZUKI MASAO
KOBAYASHI YUKIO
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