Optical amplifier

An optical amplifier for amplifying light, comprising:

• a light source means for emitting pump light in accordance with current amount;
• a rear earth element doped optical fiber doped rear earth element, the rear earth element doped optical fiber pumped by the pump light from the light source;
• a detector means for detecting upconversion light leaked from the rear earth element doped optical fiber;
• a memory means for storing correspondence relationship data of the current amount for the light source and an intensity of the upconversion light in normal state of the light source;
• a difference calculator means for calculating a difference between the intensity of the upconversion light being detected by the detector and a converted amount being converted the current amount for the light source by the use of the correspondence relationship data;
• and
• a discriminator means for discriminating whether the difference calculated at the difference calculator exceeds a predetermined value.

A method for detecting degradation of a light source for pumping a rear earth element doped optical fiber for amplifying light, the method comprising:

• detecting upconversion light leaked from the rear earth element doped optical fiber;
• storing correspondence relationship data of the current amount for the light source and an intensity of the upconversion light in normal state of the light source;
• calculating a difference between the intensity of the upconversion light being detected by the detector and a converted amount being converted the current amount for the light source by the use of the correspondence relationship data;
• and
• discriminating whether the difference calculated at the difference calculator exceeds a predetermined value.