Patent ID: 6972895

Claim:
An optical fiber amplifier for amplifying an input optical signal in a long wavelength band, comprising: a first pumping light source for generating and outputting a first pumping light of a predetermined wavelength; a photo detector for detecting an intensity of the input optical signal; an erbium-doped optical fiber that is brought to a first-pumped state by the first pumping light output from the first pumping light source, which generates an amplified spontaneous emission in a short wavelength band, and that is brought to a second-pumped state by the amplified spontaneous emission, which causes an induced emission light in the long wavelength band to be output; a second pumping light source for outputting a second pumping light in the same wavelength band as the amplified spontaneous emission, while controlling an intensity of the second pumping light by an output control signal, so as to control an intensity of the second-pumped state of the erbium-doped optical fiber; and, a controller for calculating an amount of optical intensity loss and a number of channels of the input optical signal, based on an optical intensity of the input optical signal detected by the photo detector, and transmitting the output control signal to the second pumping light source in order to compensate the amount of optical intensity loss of the input optical signal.