Patent ID: 7538937
Filing Date: 2009-05-26
Classification: H01S,H04B

Abstract:
1. An optical amplifier comprising a rare-earth doped optical fiber or rare-earth doped optical waveguide serving as an amplification medium in whose core and/or clad rare-earth ions have been doped, the rare-earth ions having three or more energy levels, the rare-earth doped optical fiber or rare-earth doped optical waveguide being configured such that when the ions are excited, an ion density of at least three of the three or more energy levels cannot be approximated to zero, an excitation means for exciting the amplification medium, an optical resonator that causes laser oscillation at one or more wavelength of spontaneous emission light produced and amplified in the amplification medium, a monitoring means that monitors a power of at least one light selected from a power of at least one light with at least one prescribed wavelength band selected from the light inputted to the amplification medium and a power of at least one light selected from a power of at least one light with at least one prescribed wavelength band selected from the light outputted from the amplification medium, and a control unit that controls the excitation means based on a value from monitoring means, wherein said monitoring means is one which monitors an inputted power and an outputted power of at least one signal light, and said control unit is one which calculates a signal gain based on the value from the monitoring means, and controls an intensity of a pumping light emitted from the excitation means so that the signal gain agrees with a prescribed value or an externally decided value.