| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical fiber amplifier which can be prevented from deteriorating in noise characteristics, signal light maximum output, and signal transfer quality. SOLUTION: Signal light inputted into a rare earth element-doped fiber 4c through a signal light terminal 1 through the intermediary of an isolator 5a and an optical multiplexer/branching filter 3a is branched off by a branching device 8b. Output light from the output terminal 82b of the branching device 8b is outputted through a signal light output terminal 6 passing through an isolator 5b, so that the rare earth element-doped fiber 4c is not affected by a reflected light. Output light outputted through the output terminal 84b of the optical branching device 8b is separated by an optical wavelength filter 11 into a signal light wavelength component and the residual component, and the signal light wavelength component and the residual component are each inputted into photodetectors 9b and 9c. An input level of signal light inputted to the rare earth element-doped fiber 4c is obtained by the a signal light output level and an ASE light (spontaneous emission light) level outputted from the photodetectors 9b and 9c. |
