Patent ID: 7113328

Claim:
A method of amplifying an optical signal in a thulium doped fiber amplifier comprising the steps of: a first deposition of energy into the fiber amplifier by pumping with radiation of a first wavelength; a second deposition of energy into the fiber amplifier by pumping with radiation of a second wavelength; wherein the radiation of the first wavelength by single photon absorption populates the 3 H 4 level of the thulium dopant, and the radiation of the second wavelength depopulates the 3 F 4 level by strong excited state absorption of a single photon to the 3 F 2 level; and wherein the radiation of the second wavelength simultaneously populates the 3 H 4 level through the 3 F 2 level, whereby achieving a population inversion between the 3 H 4 and the 3 F 4 levels.