Patent ID: 7295780

Claim:
An apparatus to control wavelength-division-multiplexed light, comprising: an optical amplifier to amplify wavelength-division-multiplexed light; a tunable optical filter to selectively output light of each wavelength of a portion of the wavelength-division-multiplexed light; peak detection means for detecting peaks of the light from said tunable optical filter; power detection means for detecting total power of wavelength-division-multiplexed light output from the optical amplifier; feedback means for generating a feedback signal depending on the maximum peak value, so that a maximum peak value will become a set value, or so that the detected power will become a set power, and for inputting the feedback signal to an excitation light source of the optical amplifier; and means for detecting optical gain, which is a power ratio of input light to said optical amplifier to output light from said optical amplifier; wherein, in dependence upon the maximum peak value, said feedback means inputs a feedback signal to the excitation light source of said optical amplifier (1) in such a manner that the maximum peak value will become the set value, or (2) in such a manner that the detected optical gain will become a set gain.