Method for transmitting WDM optical signal to be amplified by optical amplification repeaters and systems used in same

摘要

It is the object of the invention to eliminate a limitation on the transmission distance of a WDM optical transmission system caused by wavelength dependencies of gains of optical amplification repeaters. The transmission characteristic of optical signal of the transmission system against the signal wavelength can be flatted by using plural kinds of the optical amplification repeaters with different gain peak wavelengths, and the longer transmission distance can be obtained.