Optical fiber amplifier

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PROBLEM TO BE SOLVED : To decide a concrete control parameter and a control algorithm, related to gain control for an optical fiber amplifier. SOLUTION : An amplifying optical fiber 10 to which rare earth ion in which final level of amplification does not accord with basic level is added, optical multiplexers 40 and 41 that synthesize a signal light to be amplified and excitation light sources 70 and 71 connected to both ends of the amplifying optical fiber 10, an optical circulator 20, and a mirror 30 are provided. A signal light inputting end is provided with a photo-detector 80 corresponding to monitor wavelength set in an amplified band of the amplifying optical fiber 10 and a branching filter 50 that branches the signal light. A signal light outputting end is provided with a photo-detector 81 corresponding to the monitor wavelength and a light branching filter 51 that branches an output light. Based on an input/output value of the detected monitor signal light, a calculation 90 decides sum and ratio of an input excitation light power on the signal light inputting side and that on the signal light outputting side. A control unit 100 controls the excitation light sources 70 and 71 based on the decided each input excitation light power. COPYRIGHT : (C)2003, JPO