OPTICAL FIBER AMPLIFIER AND CONTROL THEREOF

PROBLEM TO BE SOLVED: To compensate the fluctuations of a deviation of a gain due to an input signal light power, the environmental temperature of an EDF(erbium-doped optical fiber) or the like under wide operating conditions on an L-band EDFA (erbium-doped fiber amplifier). SOLUTION: This optical fiber amplifier is constituted of an EDF 1 for performing an amplifying operation in a long-wavelength band, a forward excitation light source 3 for feeding forward excitation light to this EDF 1, a backward excitation light source 4 variable an output power on the basis of a control signal, a PD 11 for detecting an input light power, a temperature detecting unit 9 for detecting the temperature of the EDF 1 and a control circuit 2 for outputting the control signal to change the output power of the light source 4 to the direction to negate a deviation of amplification of a multiple light signal on the basis of the detected input light power and temperature.