Patent ID: 8174758

Claim:
An optical amplifier for amplifying light, comprising: a light source for emitting pump light in accordance with current amount; a rare earth element doped optical fiber doped with rare earth element, the rare earth element doped optical fiber pumped by the pump light from the light source; a detector for detecting upconversion light leaked from the rare earth element doped optical fiber; a memory for storing correspondence relationship data between an inputted current amount for the light source and a reference intensity of the upconversion light leaked from the rare earth element doped optical fiber pumped by a normal pump light, the normal pump light being emitted by the light source in normal state in accordance with the inputted current amount; a difference calculator for calculating a difference between an intensity of the upconversion light detected by the detector and the reference intensity of the upconversion light obtained from the memory on the basis of the current amount inputted to the light source by use of the correspondence relationship data; and a discriminator for discriminating whether the difference calculated at the difference calculator exceeds a predetermined value.