Patent ID: 8279518

Claim:
An optical amplifier apparatus for amplifying a wavelength division multiplexed signal light, the optical amplifier comprising: a detector configured to detect a wavelength division multiplexed signal light; a dispersion compensator configured to compensate for a dispersion of the wavelength division multiplexed signal light after being detected by the detector; an optical amplifier configured to amplify the wavelength division multiplexed signal light after the wavelength division multiplexed light is compensated for dispersion by the dispersion compensator, the optical amplifier amplifying the wavelength division multiplexed signal light by providing pump light to an optical gain medium including a rare-earth element so that the pump light travels through the optical gain medium as the wavelength division multiplexed light travels through the optical gain medium; a propagation delay detector configured to detect a propagation delay time of the wavelength division multiplexed signal light between the detector and the optical amplifier, and to subtract a relaxation time from the detected propagation delay time to thereby provided an adjusted propagation delay time, the relaxation time being a period of time in which electrons of the rare-earth element fall to an energy level causing stimulated emission with the pump light in the optical gain medium; and a controller configured to control a gain of the optical amplifier, based on the adjusted propagation delay time such that a change of the gain of the optical amplifier is adjusted by the adjusted propagation delay time.