Optically amplifying device with gain equalizing function

Abstract

An optically amplifying device with a gain equalizing function comprises: an optical fiber amplifier for receiving, as an input, a wavelength division multiplexed signal light beam which has been obtained by wavelength-division multiplexing a plurality of signal light beams having different wavelengths to output the amplified signal light beam containing the plurality of signal light beams, which is obtained by optically amplifying the wavelength division multiplexed signal light beam; and a gain equalizer for receiving, as an input, the amplified signal light beam to optically amplify the plurality of signal light beams thus amplified to equalize the optical output levels thereof, thereby outputting the equalized amplified signal light beams. The gain equalizer includes a semiconductor optical amplifier, the gain for each of the plurality of signal light beams of the semiconductor optical amplifier is set in a way that when the gain for each of the plurality of signal light beams of the semiconductor optical amplifier is superimposed on the gain for each of the plurality of signal light beams of the optical fiber amplifier, the gain difference between the signal light beam is cancelled out. The gain equalizer may be disposed either before the optical fiber amplifier or between the two optical fiber amplifiers. In the optical amplification of the wavelength division multiplexed signal light beam containing the plurality of signal light beams having different wavelengths, the optical output difference occurring between the levels of the amplified signal light beams is reduced effectively.