Energy recycling versus lifetime quenching in erbium-doped 3-μm fiber lasers

Based on recently published spectroscopic measurements of the relevant energy-transfer parameters, we performed a detailed analysis of the population mechanisms and the characteristics of the output from Er/sup 3+/-singly-doped and Er/sup 3+/, Pr/sup 3+/-codoped ZBLAN fiber lasers operating at 3 /spl mu/m, for various Er/sup 3+/ concentrations and pump powers. Whereas both approaches resulted in similar laser performance at Er/sup 3+/ concentrations <4 mol.% and pump powers <10 W absorbed, it is theoretically shown here that the Er/sup 3+/-singly-doped system will be advantageous for higher Er/sup 3+/ concentrations and pump powers. In this case, energy recycling by energy-transfer upconversion from the lower to the upper laser level can increase the slope efficiency to values greater than the Stokes efficiency, as is associated with a number of Er/sup 3+/-doped crystal lasers. Output powers at 3 /spl mu/m on the order of 10 W are predicted.