Optical amplifier

An optical amplifier comprising:

• an input terminal configured to input an optical communication signal;
• a first excitation light coupler configured to synthesize the optical communication signal and an excitation light;
• a first optical amplification medium provided downstream of the first excitation light coupler and configured to amplify the optical communication signal by the excitation light;
• a first optical switch provided downstream of the first optical amplification medium and configured to output the optical communication signal output from the first optical amplification medium to either a first branch path or a second branch path;
• a second optical switch configured to select either the first branch path or the second branch path and transmit the optical communication signal transmitted through the selected branch path to downstream;
• and
• an output terminal provided downstream of the second optical switch and configured to output the optical communication signal,
• the first branch path including:
• a second optical amplification medium configured to amplify the optical communication signal by the excitation light;
• a second excitation light coupler provided downstream of the second optical amplification medium and configured to synthesize the optical communication signal and the excitation light directed towards the second optical amplification medium;
• and
• a first gain equalizer provided downstream of the second excitation light coupler and configured to correct gain wavelength characteristics, the second branch path including:
• a third excitation light coupler configured to synthesize the optical communication signal and the excitation light directed towards the first optical switch;
• and
• a second gain equalizer provided downstream of the third excitation light coupler and configured to correct gain wavelength characteristics.