Patent ID: 7075709

Claim:
An optical transmission system amplifying wavelength division multiplexed light which includes lights in a first specific wavelength band and a second specific wavelength band wavelength multiplexed together, the optical transmission system comprising: a first set of amplifiers Raman amplifying the lights in the first specific wavelength band as the wavelength division multiplexed light travels through a transmission line, the amplifiers of the first set being spaced apart from each other by a first interval; and a second set of amplifiers Raman amplifying the lights in the first specific wavelength band and the lights in the second specific wavelength band as the wavelength division multiplexed light travels through the transmission line, the amplifiers of the second set being spaced apart from each other by a second interval, wherein the first interval is shorter than the second interval, and the first and second intervals together with amplification provided by the first and second sets of amplifiers causing light intensities of the lights in the first specific wavelength band and lights in the second specific wavelength band to become the same at an end of the transmission line.