| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that the inversion distribution state caused by backward stimulation is worse at a signal light incidence end with anticipated degradation of noise index since an EDF is long when an input power is small. SOLUTION: A control circuit 25 controls a directional coupler optical switch 29 so that the stimulation light from a stimulation LD light source 28 is inputted into an EDF30 mainly through a WDM coupler 24a for enhanced forward stimulation. Then, the drive current of light source 28 is controlled to output the signal light of a desired value. If the signal light power of the desired value is not provided even when the drive current of light source 28 reaches the upper limit, the control circuit 25 gradually increases the percentage of stimulation light inputted in the EDF30 through a WDM coupler 24b while controlling the drive current of the light source 28, to output the signal light of the desired value. |
