Optical amplifying and repeating method and optical amplifying and repeating system

An optical amplifying and repeating system for connecting between a first station and a second station with a first optical transmission line and a second optical transmission line, wherein:

• said first optical transmission line transmits an optical signal in a first direction from the first station toward the second station and includes at least one first optical amplifier on the way;
• and
• said second optical transmission line transmits an optical signal in a second direction from the second station toward the first station and includes at least one second optical amplifier on the way, said system comprising:
• a first optical circuit taking backscattering light of a first wavelength traveling in the first direction of the first optical transmission line immediately after the first optical amplifier, and coupling the same in such a manner that said backscattering light may travel in the second direction of the second optical transmission line;
• a second optical circuit taking a second wavelength traveling in the first direction of the first optical transmission line and coupling the same in such a manner that the second wavelength may travel in the first direction of the second optical transmission line;
• a third optical circuit taking backscattering light of the first wavelength traveling in the second direction of the second optical transmission line immediately after the second optical amplifier, and coupling the same in such a manner that said backscattering light may travel in the first direction of the first optical transmission line;
• and
• a fourth optical circuit taking the second wavelength traveling in the second direction of the second optical transmission line and coupling the same in such a manner that the second wavelength may travel in the second direction of the first optical transmission line.