OPTICAL AMPLIFIER, METHOD OF CONTROLLING SAME, COMPUTER PROGRAM USED FOR CONTROL, AND RECORDING M

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PROBLEM TO BE SOLVED : To easily avoid noise generation in an optical amplifier with a reduced cost. SOLUTION : The optical amplifier comprises an input port 1 to which an input light is inputted, an LD 20 that supplies a pumping light, a multiplexer 12 that multiplexes the input light and the pumping light, a rare-earth-element doped fiber 13 to which the multiplexed wave of the input light and the pumping light is input and from which the amplified input light is output, and an output port 2 that outputs the output light. The amplifier further comprises a demultiplexer 14 that branches the output light from the rare-earth-element doped fiber 13 for taking out, a PD 16 that measures the intensity of the output light from the demultiplexer 14, and a control computer 15 that controls the intensity of the pumping light on the basis of the output light intensity measured by the PD 16. The control computer 15 estimates the input light intensity from the output light intensity on the basis of the preset relation between the input light intensity and the output light intensity. When the estimated input light intensity is lower than a predetermined value, the supply of the pumping light from the LD 20 is stopped.