Patent ID: 7068422

Claim:
An optical fiber amplification method by which a multi-wavelength multiplexed input signal is amplified using pump light, the optical fiber amplification method comprising: (a) setting initial values including target gains of first and second amplifications for an optical amplifier amplifying the input light signal, the target gain for the first amplification is obtained by comparing power of a first input signal with measured power of a first output signal, the target gain for the second amplification is obtained by comparing power of the first input signal with measured power of a second output signal; (b) indirectly measuring power of the input light signal and estimating number of channels of the input light signal based on power of the input light signal to control power of first and second backward pump lights proceeding in the opposite direction to the input light signal; (c) firstly amplifying the input light signal and calculating a first amplification gain of the amplified light signal; (d) controlling power of a first forward pump light proceeding in the same direction as the input light signal so that the first amplification gain can be substantially equal to the target gain of the first amplification; (e) secondly amplifying the firstly amplified light signal and calculating a second amplification gain with respect to the input light signal; and (f) controlling the power of a second forward pump light proceeding in the same direction as the input light signal so that the second amplification gain can be substantially equal to the target gain of the second amplification.