Patent ID: 7215464

Claim:
An optical amplifier having a variable optical attenuator and an external attenuating medium connected in series, the optical amplifier comprising: an attenuation amount detection means for detecting an attenuation amount of signal light, caused by the variable optical attenuator and the external attenuating medium, by means of a front optical detection means of a front optical amplification block provided before the variable optical attenuator and the external attenuating medium and a back optical detection means of a back optical amplification block provided after the variable optical attenuator and the external attenuating medium; an attenuation amount control means for controlling the variable optical attenuator such that the attenuation amount of signal light is kept constant; and a connection detection means for detecting a connection or disconnection of the external attenuating medium, depending on the attenuation amount of signal light detected while the variable optical attenuator provides a minimum amount of attenuation.