| 摘要 |
PURPOSE:To monitor an optical amplifier without receiving the effect of a signal component by extracting the noise part of a frequency area where the signal component included in the detection signal of a photodetector part does not exist by a filter and monitoring the state of the optical amplifier based on the noise part. CONSTITUTION:Input light is inputted in the optical amplifier 11 from an optical fiber 12 through an optical coupler 14, and amplified output light is transmitted to an optical fiber 13 through an optical coupler 15. A part of the input light and the output light branched by the couplers 14 and 15 is detected by the 1st and the 2nd photodetector parts 16 and 17, amplified by amplifier circuits 18 and 19, and inputted in the 1st and the 2nd filters 20 and 21. The filters 20 and 21 are BPFs for central frequency, which extract the frequency area where the signal component does not exist in a signal power spectrum, so that the noise component of the frequency area where the signal component included in the detection signal does not exist is extracted. Namely, the noise component included in the output light from the amplifier 11 is monitored based on the output level of the filter 21, and the beginning of the deterioration of the characteristic of the amplifier 11 is decided. |
