Optical amplifier and optical communication system having the optical amplifier

An optical communication system comprising:

• an optical fiber transmission line for propagating WDM (wavelength division multiplexed) signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths;
• and
• at least one optical amplifier provided in said optical fiber transmission line, said optical amplifier comprising:
• an optical amplifying medium to which said WDM signal light is supplied;
• a pumping unit to pump said optical amplifying medium so that said optical amplifying medium gives a gain to said WDM signal light;
• a controlling unit to control said pumping unit according to an input level and an output level of said optical amplifying medium so that said gain is maintained constant;
• and
• a first detector to detect said output level of said optical amplifying medium;
• a second detector to detect the number of said plurality of optical signals;
• an optical attenuator operatively connected to said optical amplifying medium for giving a variable attenuation to said WDM signal light;
• and
• a feedback loop for controlling the attenuation of said optical attenuator to set the output of level of said optical amplifying medium in accordance with the number of said plurality of optical signals so as to maintain constant the level of each of said plurality of optical signals.

An optical amplifier comprising:

• an optical amplifying medium to which WDM (wavelength division multiplexed) signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths is supplied;
• means for pumping said optical amplifying medium so that said optical amplifying medium gives a gain to said WDM signal light;
• means for controlling said pumping means according to an input level and an output level of said optical amplifying medium so that said gain is maintained constant;
• a first detector to detect said output level of said optical amplifying medium;
• a second detector to detect the number of said plurality of optical signals;
• an optical attenuator operatively connected to said optical amplifying medium for giving a variable attenuation to said WDM signal light;
• and
• a feedback loop for controlling the attenuation of said optical attenuator to set the output of level of said optical amplifying medium in accordance with the number of said plurality of optical signals so as to maintain constant the level of each of said plurality of optical signals.