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 Er3+-singly-doped and Er3+, Pr3+-codoped ZBLAN fiber lasers operating at 3 mum, for various Er3+ concentrations and pump powers. Whereas both approaches resulted in similar laser performance at Er3+ concentrations <4 mol.% and pump powers <10 W absorbed, it is theoretically shown here that the Er3+-singly-doped system will be advantageous for higher Er3+ 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 Er3+-doped crystal lasers. Output powers at 3 mum on the order of 10 W are predicted.