Patent ID: 7209284

Claim:
An optical apparatus, comprising: an optical amplifier including an amplification medium which is doped with an active material for optical amplification and to which pump light is introduced, for amplifying an optical signal and outputting the amplified optical signal; a reflection-type variable optical attenuator including a reflecting mirror and a light receiving element; wherein the reflection-type variable optical attenuator is connected with the optical amplifier through an input fiber directly, and is input via the input fiber with the amplified optical signal, then performs attenuation control on the input light, and outputs an attenuation-controlled optical signal from an output fiber, wherein the reflecting mirror reflects the input light to generate a reflected light, and a magneto-optical crystal arranged in a position where the input light and the reflected light pass, the magneto-optical crystal being applied with a magnetic field to induce a Faraday rotation angle therein and thereby vary an amount of attenuation of the amplified optical signal, and part of light transmitted through the reflecting mirror being converted, as input monitor light, into an electrical signal, wherein the light receiving element converts the part of the light transmitted through the reflecting mirror, as the input monitor light, into the electrical signal, and wherein the light receiving element is displaced from an optical axis of feedback light which is returned from a reflecting point succeeding the reflection-type variable optical attenuator after being emitted from an output fiber, so as not to detect the feedback light which includes noise, when the light receiving element is arranged behind the reflecting mirror, and no optical isolator is used between the reflecting mirror and the light receiving element; and a controller to monitor the electrical signal and, in accordance with the monitoring result, controls the pump light power.