Patent ID: 6952309

Claim:
An optical amplifier for amplifying, at once, multiplexed signal light belonging to a predetermined wavelength band, in which a plurality of signal light components having different wavelengths are multiplexed, comprising: one or a plurality of optical amplification sections each of which has an optical waveguide doped with a fluorescent material and amplifies the multiplexed signal light by optical pumping of the fluorescent material; optical pumping light sources for supplying predetermined optical pumping light to said optical amplification section(s); an optical filter capable of changing a gradient dL/dλ of a loss L (dB) with respect to a wavelength λ (nm) in the predetermined wavelength band in response to a change of the gain wavelength dependence in the optical amplification section(s); and control means for controlling each optical pumping light output from said optical pumping light sources so as to keep the total power of light output from said optical amplifier at predetermined level and controlling the gradient dL/dλ of said optical filter so as to flatten the wavelength dependence of light power output from said optical amplifier.