METHODS AND ARRANGEMENTS IN A PUMPED FIBER AMPLIFIER

An arrangement and method provide an optical thulium doped fiber amplifier utilizing a dual wavelength pumping scheme for amplifying an optical signal. The method includes the steps of: a first deposition (a) of energy into the fiber amplifier by pumping with radiation of a first wavelength; and a second deposition (b) of energy into the fiber amplifier by pumping with radiation of a second wavelength. The radiation of the first wavelength is arranged to induce, by single photon absorption, a population to the 3H4 level of the thulium dopant, and the radiation of the second wavelength primarily depopulates the 3F4 level, by excited absorption of a single photon, preferably by strong excited state absorption to the 3F2 level. The steps gives a population inversion between the 3H4 and the 3F4 levels and facilitate a power efficient high gain amplification.