Patent ID: 7920793

Claim:
An optical fiber communication system comprising: silica fiber laid throughout a city as a gain medium for Raman amplification to amplify a signal light; a pumping light source that emits a forward pumping light with a plurality of wavelengths that co-propagates through the silica fiber in the same direction as the signal light and pumps the signal light; and a multiplexer disposed between the silica fiber and the pumping light source that multiplexes the signal light and the pumping light, wherein the multiplexer is provided with a means to multiplex the signal light input thereto having a wavelength longer than the zero-dispersion wavelength of the silica fiber and the pumping light emitted from the pumping light source, the pumping light source is equipped with a means to emit forward pumping light, with the longest wavelength of the pumping light being shorter than the shortest wavelength of the signal light so as to have a frequency difference of 13.7 to 17.9 THz, the silica fiber is a dispersion-shifted fiber, and the signal light comprises a plurality of wavelengths in the L band, and the optical fiber communication system has an erbium-doped fiber amplifier having: an erbium-doped fiber gain block provided with erbium-doped fiber as a gain medium; a gain equalization optical filter disposed before or after the erbium-doped fiber gain block; a population inversion detection circuit that measures a population inversion amount in the erbium-doped fiber; and a population inversion adjustment circuit that controls the erbium-doped fiber gain block so that the population inversion amount measured by the population inversion detection circuit is a prescribed value.