| 摘要 |
PROBLEM TO BE SOLVED: To sustain the optical output from an optical amplifier accurately at a constant level by extracting a part of an amplified light tram which the spontaneous emission light is removed, i.e., extracting only the part purely related to the signal light, and performing feedback control based on the level of extracted light thereby controlling the gain of an optical amplifying section. SOLUTION: The optical amplifier comprises an optical branch 22 for branching a part of output light similarly to an optical branch 21. The level of output light branched through the optical branch 22 is measured by means of a light receiver 32. A band-pass filter 42 for passing only a predetermined wavelength is interposed between the optical branch 22 and the light receiver 32. Outputs from light receivers 31, 32 are subjected to subtraction through an operational amplifier 50 which produces a monitor signal proportional only to the amplified signal light. When the gain of an optical amplifier 10 is controlled to sustain the monitor signal at a constant level, the level of amplified signal light can be controlled accurately. |
