Patent ID: 8422890

Claim:
A fiber output stabilizer comprising: a rare-earth doped optical fiber in which at least one kind of a rare-earth element is added to a core; an excitation light source that supplies excitation light exciting the rare-earth element to the rare-earth doped optical fiber; a monitoring light source that emits monitoring light having a wavelength shorter than that of the excitation light source; an optical multiplexer that multiplexes the monitoring light emitted from the monitoring light source into the excitation light; a passing light detector that detects light intensity of the monitoring light passing through the rare-earth doped optical fiber; an output intensity changing unit that changes the output intensity of the excitation light source to light intensity previously determined; a monitoring light detector that detects light intensity of the monitoring light emitted from the monitoring light source; and a monitoring light intensity comparator that detects a difference between the light intensity detected by the passing light detector and the light intensity detected by the monitoring light detector, wherein the output intensity changing unit changes output intensity of the excitation light source to light intensity previously determined according to the difference detected by the monitoring light intensity comparator.