Patent ID: 7119950

Claim:
An optical amplification method which: separates a wavelength division multiplexed signal light including a plurality of signal channels of different wavelengths into signal lights of at least two wavelength bandwidths by a demultiplexer; amplifies each of the separated signal lights of each wavelength bandwidth by optical amplifier sections corresponding to each wavelength bandwidth; controls the total power of the signal lights output from each of the amplifier sections to be constant at a preset level, and multiplexes the constant output controlled signal lights of each wavelength bandwidth by a multiplexer, comprising; designing the bandwidth of the signal light output from each output port of said demultiplexer to have a different value in accordance with the gain wavelength characteristics of each of said optical amplifier sections, so that inter-wavelength deviation in optical output levels that occur in each of said optical amplifier sections falls within a preset range, and individually adjusting the gain of each of the optical amplifier sections in relation to fluctuations in the power level without channel number changes of the wavelength division multiplexed signal light input to said demultiplexer, so that the signal level of each wavelength of the wavelength division multiplexed signal light that is multiplexed by said multiplexer is within a preset range.