Optical amplifier, optical relay, and optical communication system

An optical amplifier amplifying and outputting signal light of a plurality of systems, the optical amplifier comprising:

• a plurality of impurity-doped optical fiber amplification units;
• a plurality of excitation light sources;
• a plurality of excitation light demultiplexing units that demultiplex excitation light from the plurality of excitation light sources;
• a plurality of excitation light multiplexing/demultiplexing units that multiplex and demultiplex excitation light from the plurality of excitation light demultiplexing units;
• and a plurality of multiplexing units each of which multiplexes one of the plurality of beams of signal light and excitation light from the plurality of excitation light multiplexing/demultiplexing units and subsequently inputs the multiplexed light to one of the plurality of impurity-doped optical fiber amplification units, wherein
• the plurality of excitation light sources include at least a first excitation light source and a second excitation light source that are driven in common by a first driving current, and a third excitation light source that is driven by a second driving current of a different system from the first driving current,
• the plurality of excitation light demultiplexing units include at least a first excitation light demultiplexing unit, a second excitation light demultiplexing unit, and a third excitation light demultiplexing unit,
• the plurality of excitation light multiplexing/demultiplexing units include at least a first excitation light multiplexing/demultiplexing unit, a second excitation light multiplexing/demultiplexing unit, and a third excitation light multiplexing/demultiplexing unit,
• excitation light from the plurality of excitation light sources goes through the plurality of excitation light demultiplexing units and the plurality of excitation light multiplexing/demultiplexing units and is input to the plurality of multiplexing units, and
• the plurality of excitation light sources, the plurality of excitation light demultiplexing units, and the plurality of excitation light multiplexing/demultiplexing units are selected in consideration of contribution of excitation light from the first excitation light source and excitation light from the second excitation light source, and contribution of excitation light from the third excitation light source, to an optical output of each impurity-doped optical fiber amplification unit among the plurality of impurity-doped optical fiber amplification units.