Patent ID: 7532391

Claim:
An optical amplification module having a structure for constituting an optical path through which light to be amplified passes only one time, said structure comprising: a first optical amplification medium having an optical waveguide region which is doped with Yb-element as substantially only one rare earth element, said first optical amplification medium having a light entrance end on which the light to be amplified is incident and a light exit end which emits a first amplified light that has been amplified inside said first optical amplification medium; a second optical amplification medium having an optical waveguide region which is doped with Yb-element as substantially only one rare earth element in a higher concentration than the Yb-element doping concentration of said first optical amplification medium, said second optical amplification medium being connected to said first optical amplification medium, and having a light entrance end on which said first amplified light is incident and a light exit end which emits a second amplified light that has been amplified inside said second optical amplification medium; a first pumping light source for outputting a first pumping light of a predetermined wavelength; and a first optical multiplexer for multiplexing the light to be amplified and the first pumping light, said first optical multiplexer being disposed on the light entrance end side of said first optical amplification medium such that said first pumping light propagates in the order from said first optical amplification medium to said second optical amplification medium, wherein the output power of said first pumping light source and the length of said first optical amplification medium are set such that the power of the first pumping light at the light entrance end of said second optical amplification medium becomes a predetermined value that does not occur during photodarkening in said second optical amplification medium and that the population inversion of said first optical amplification medium becomes 40% or more at at least one point of said first optical amplification medium, the Yb-element doping concentration in said first optical amplification medium is not greater than half of the Yb-element doping concentration in said second optical amplification medium, and the doping concentration of the Yb-element in each of said first and second optical amplification media is 2000 wt.ppm or more.