Patent ID: 6903324

Claim:
An optical amplifier, which has an optical amplification medium and an optical attenuator, used in an optical communications system transmitting wavelength multiplexed light with a plurality of optical amplifiers, comprising: a gain controlling circuit holding a gain of the optical amplification medium to be a constant value; and a level controlling circuit controlling a loss in the optical attenuator so that an output level of the optical amplifier is held to be a value corresponding to a control signal notified to the plurality of optical amplifiers within the optical communications system, wherein a time constant of said level controlling circuit, which is a time period from when the output level of the optical amplifier changes until when the loss in the optical attenuator is adjusted to make the output level of the optical amplifier revert to a designated level, is longer than a time period required for transmitting the control signal from a supervisory controlling unit which generates the control signal via the optical communications system to the plurality of the optical amplifiers within the optical communications system.