Energy Recycling Versus Lifetime Quenching in Erbium-Doped 3- m 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-singly-doped and Er, Pr-codoped ZBLAN fiber lasers operating at 3 m, for various Er concentrations and pump powers. Whereas both approaches resulted in similar laser performance at Er concentrations 4 mol.% and pump powers 10 W absorbed, it is theoretically shown here that the Er-singly-doped system will be advantageous for higher Er 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-doped crystal lasers. Output powers at 3 m on the order of 10 W are predicted.