Theoretical study and optimization of a high power mid-infrared erbium-doped ZBLAN fibre laser**Project supported by the China Postdoctoral Science Foundation (Grant No. 20090451417), the China Postdoctoral Science Special Foundation (Grant No. 201003693), the Fundamental Research Funds for the Central Universities of China (Grant No. ZYGX2009J053) and the National Natural Science Foundation of China (Grant No. 60736038).

Abstract

Based on the rate equations describing the erbium-doped fluoride glass (ZBLAN) fibre lasers with different pumping configurations being taken into account, this paper presents theoretical calculations related to the dynamic population density and the operation performance of a high power mid-infrared all-fibre erbium-doped ZBLAN fibre laser. It shows that the ground-state absorption, excited-state absorption and energy-transfer-upconversion processes co-exist and produce a population balance, causing the laser to operate stably at a continuous wave state. A good agreement between the theoretical results and recent experimental measurement is obtained. Furthermore, the laser structure parameters including fibre length, reflectance of output fibre Bragg grating and pumping configurations are quantitatively optimised to achieve the best performance. The results show, as expected, that the slope efficiency of the fibre laser can be improved significantly through optimisation, which then provides an important guide for the design of high-performance mid-infrared erbium-doped ZBLAN fibre lasers.