Optical transmission system, optical repeater, and optical transmission method

An optical transmission system comprising:

• a first optical repeater comprising excitation means for exciting at least light in a short wavelength band included in wavelength-multiplexed light so that said light in the short wavelength band is distributively amplified at a first transmission line, and
• an amplifier for amplifying at least said short wavelength band and a long wavelength band relative to said short wavelength band by an output of said first transmission line;
• a second transmission line for transmitting an output of said first optical repeater;
• and
• a second optical repeater for performing backward excitation on a short wavelength band of wavelength-multiplexed light propagating through said third transmission line, and performing distributive amplification within said third transmission line.

An optical repeater comprising:

• first coupling means for wavelength-multiplexing both first excitation light, which distributively amplifies at least a specific wavelength band included in light propagating through a first transmission line, and said light propagating through said first transmission line;
• and
• second coupling means for wavelength-multiplexing both second excitation light, which distributively amplifies at least a specific wavelength band included in light propagating through a second transmission line, and said light propagating through said second transmission line;
• said first coupling means and said second coupling means being provided between end offices and optical repeaters, between said optical repeaters, or between said first transmission line and said second transmission line disposed between said end offices.