Patent ID: 7643206

Claim:
An optical amplifier for amplifying a wavelength division multiplexed light containing a plurality of signal lights of different wavelengths, comprising; an input port and an output port; first and second optical amplifying sections connected in series to each other between said input port and said output port; a first variable optical attenuator arranged between said input port and said first optical amplifying section; a second variable optical attenuator arranged between said first optical amplifying section and said second optical amplifying section; an optical amplification control section that monitors the power of the wavelength division multiplexed light input to said input port and the power of the wavelength division multiplexed light output from said output port, and controls said first and second optical amplifying sections so that a gain calculated based on monitoring results is held constant; and an optical attenuation control section that decides a value of the sum of attenuation amounts of said first and second variable optical attenuators according to the signal light input power per one wavelength of the wavelength division multiplexed light input to said input port, and also, monitors the signal light power of the wavelength division multiplexed light output from each of said first and second variable optical attenuators, and controls the attenuation amounts of said first and second variable optical attenuators, so that monitor values of the output powers from said first and second variable optical attenuators approximate the same value, while holding the decided value of the sum of the attenuation amounts constant.