| 摘要 |
PROBLEM TO BE SOLVED: To provide a light amplifier of a structure, wherein monitoring light is taken out from a 4-port coupler in a low loss to detect the monitoring light and a pumping signal from a pumping light source can be controlled. SOLUTION: An input optical fiber is connected with a first port of a 4-port coupler, a pump 125 is connected with a second port of the coupler, an erbium- doped optical fiber for amplifying a light signal is connected with a third port of the coupler, and a detector 115 is connected with a fourth port of the coupler. An input signal from the first port is coupled with a pumping signal for the second port to output the coupled signals from the third port, and the coupled signals are made to pass through the erbium-doped optical fiber. One part of the pumping signal is taken out from the fourth port to detect the one part, the pumping signal from the pump 125 is controlled by a feedback control circuit 127 according to a detection signal, and a light amplifier is made a circuit operation perform so that an output amplified from the amplifier becomes constant. |
