Patent ID: 8064130

Claim:
An optical amplifier comprising: a plurality of optical amplification mediums each doped with a rare earth element having a center wavelength of a gain peak appearing outside a signal band; gain equalizers disposed between said optical amplification mediums, each equalizing a gain in the signal band in which the gain is tilted at a wavelength different from the wavelength having said peak value outside the signal band and each suppressing growth of an ASE light generated at a band which includes a wavelength of the gain peak and is located outside of the signal band; and a temperature control section raising or lowering a temperature of each of said optical amplification mediums so that an efficiency evaluation value becomes η 0.15 or more, the efficiency value η is represented by: η= g min /g peak where g min is a minimum value of the gain coefficient at the inside of the signal band, and g peak is a maximum value of the gain coefficient at the outside of the signal band when said optical amplification medium is pumped at an inversion ratio of 1.0.