| 摘要 |
PROBLEM TO BE SOLVED: To precisely execute gain fixing control by making a value, which is shown by a specific formula including a constant value corresponding to a naturally emitted light (ASE) power a light amplifier part generates at the time of operating, the detection gain of the light amplifier part. SOLUTION: An optical detector 3-1 detects an input signal optical power Pin and an optical detector 3-2 detects an output signal optical power Pout. The light amplifier 1A is provided with a rare earth added fiber 11 and an exciting light source 12 executing front excitation. A gain detecting part 4A inputs the input signal optical power Pin, the output signal optical power Pout and an ASE power PASE to make (Pout-PASE)/Pin a gain A. PASE is made a fixed constant and this value is set by an electrical circuit. An error signal extracting part 5 extracts the error signal of the gain A and a gain control part 6A varies exciting light power outputted from the light source 12 so as to make the error signal zero. |
