Optical gain equalizer and optical gain equalizing method

An optical gain equalizer that controls the gain wavelength characteristic of wavelength division multiplexed light, comprising:

• an optical fiber amplification medium that amplifies wavelength division multiplexed light;
• an optical directional coupler that branches amplified wavelength division multiplexed light;
• a filter that selects first light and second light out of branched light;
• and
• a control circuit that controls the optical fiber amplification medium based upon difference in a level between the first and second lights, wherein:
• said control circuit comprises:
• an optical receiver that respectively converts the first and second lights to electric information;
• a comparator that compares these electric information;
• and
• a pumping light source that sends pumping light to said optical fiber amplification medium based upon the output of the comparator.

An optical gain equalizer that controls the gain wavelength characteristic of wavelength division multiplexed light, comprising:

• an optical fiber amplification medium that amplifies wavelength division multiplexed light;
• an optical directional coupler that branches amplified wavelength division multiplexed light;
• a control circuit that controls the optical fiber amplification medium based upon branched light;
• a variable optical attenuator that attenuates wavelength division multiplexed light;
• a filter that selects first and second lights out of branched light;
• and
• control means that controls the variable optical attenuator based upon difference in a level between the first and second lights.

A method of equalizing the gain of wavelength division multiplexed light, comprising:

• a step for selecting two lights having wavelengths mutually different out of wavelength division multiplexed light;
• a step for comparing the two lights;
• and
• a step for controlling pumping light to an optical fiber amplification medium that amplifies the wavelength division multiplexed light based upon the result of the comparison and controlling the inclination of the gain of the wavelength division multiplexed light.

A method of equalizing the gain of wavelength division multiplexed light, comprising:

• a step for selecting two lights having wavelengths mutually different out of wavelength division multiplexed light;
• a step for comparing the two lights;
• a step for attenuating wavelength division multiplexed light based upon the result of the comparison;
• and
• a step for controlling pumping light to an optical fiber amplification medium based upon the attenuated wavelength division multiplexed light and controlling the inclination of the gain of wavelength division multiplexed light.