Optical amplifier and abnormality detection method for the same

The optical amplifier for amplifying wavelength-division multiplexed light, comprising a first optical amplification unit which amplifies input light, a variable optical attenuation unit which attenuates an output of said first optical amplification unit, a second optical amplification unit which amplifies an output of said variable optical attenuation unit, and a loss amount control unit which controls an amount of loss to be introduced by said variable optical attenuation unit, wherein an external attenuating optical medium is inserted between said variable optical attenuation unit and said second optical amplification unit, and said loss amount control unit compensates for variations in optical loss of said external attenuating optical medium by controlling the amount of loss to be introduced by said variable optical attenuation unit, said optical amplifier further comprising:

• an abnormal loss detecting unit which detects an excessive loss in said external attenuating optical medium based on a difference between light levels detected before and after said external attenuating optical medium;
• and
• an abnormal loss detection invalidating unit which invalidates any abnormality detected by said abnormal loss detecting unit when the light level detected between said variable optical attenuation unit and said external attenuating optical medium is lower than a predetermined threshold level, wherein
• said predetermined threshold level represents the light level that said variable optical attenuation unit is to output when the number of multiplexed wavelengths input to said optical amplifier is 1 and when the amount of loss introduced by said variable optical attenuation unit is equal to a predetermined amount of loss, and
• said predetermined amount of loss is the amount of loss necessary to compensate for a predetermined minimum amount of loss permitted in said optical amplifier as the amount of loss due to the insertion of said external attenuating optical medium.

An abnormality detection method used in an optical amplifier for amplifying wavelength-division multiplexed light, wherein said optical amplifier comprises a first optical amplification unit which amplifies input light, a variable optical attenuation unit which attenuates an output of said first optical amplification unit, a second optical amplification unit which amplifies an output of said variable optical attenuation unit, and a loss amount control unit which controls an amount of loss to be introduced by said variable optical attenuation unit, wherein an external attenuating optical medium is inserted between said variable optical attenuation unit and said second optical amplification unit, and said loss amount control unit compensates for variations in optical loss of said external attenuating optical medium by controlling the amount of loss to be introduced by said variable optical attenuation unit, and wherein said abnormality detection method detects abnormality in optical loss between said first and second optical amplification units, comprising:

• detecting abnormality in optical loss between said first and second optical amplification units based on a light level detected between said external attenuating optical medium and said second optical amplification unit;
• and
• disabling detection of said abnormality when a light level detected between said variable optical attenuation unit and said external attenuating optical medium is lower than a predetermined threshold level.

An abnormality detection method used in an optical amplifier for amplifying wavelength-division multiplexed light, wherein said optical amplifier comprises a first optical amplification unit which amplifies input light, a variable optical attenuation unit which attenuates an output of said first optical amplification unit, a second optical amplification unit which amplifies an output of said variable optical attenuation unit, and a loss amount control unit which controls an amount of loss to be introduced by said variable optical attenuation unit, wherein an external attenuating optical medium is inserted between said variable optical attenuation unit and said second optical amplification unit, and said loss amount control unit compensates for variations in optical loss of said external attenuating optical medium by controlling the amount of loss to be introduced by said variable optical attenuation unit, wherein said abnormality detection method detects abnormality in optical loss between said first and second optical amplification units, comprising:

• detecting an excessive loss in said external attenuating optical medium based on a difference between light levels detected before and after said external attenuating optical medium;
• and
• disabling detection of said abnormality when the light level detected between said variable optical attenuation unit and said external attenuating optical medium is lower than a predetermined threshold level, wherein
• said predetermined threshold level represents the light level that said variable optical attenuation unit is to output when the number of multiplexed wavelengths input to said optical amplifier is 1 and when the amount of loss introduced by said variable optical attenuation unit is equal to a predetermined amount of loss, and
• said predetermined amount of loss is the amount of loss necessary to compensate for a predetermined minimum amount of loss permitted in said optical amplifier as the amount of loss due to the insertion of said external attenuating optical medium.