| 摘要 |
PROBLEM TO BE SOLVED: To allow for building of a network inexpensively while continuing the service, when the input signal of an optical amplifier is reduced from a normal operation range, although it is not interrupted completely, due to abnormality of an optical transmission line or failure of a host device.SOLUTION: An optical amplifier includes an OFA 11 for amplifying input light, an AGC circuit 17 for controlling the gain depending on the output light level Pfrom the OFA 11, a fixed amplification circuit 18 for fixing the gain, and a control selection unit 19 for operating the fixed amplification circuit 18 when the input optical level Pis less than a first threshold P1, otherwise operating the AGC circuit 17. |
