Simulation and design of a multistage 10W thulium-doped double clad silica fiber amplifier at 2050nm

A careful comparison of experiment and theory is important both for basic research and systematic engineering design of Thulium fiber amplifiers operating in the 2 μm region for applications such as LIDAR or spectroscopy (e.g. CO₂ atmospheric absorption at 2051.4 nm). In this paper we report the design and performance of a multistage high-power PM Tm-doped fiber amplifier, cladding pumped at 793 nm. The design is the result of a careful comparison of numerical simulation, based on a three level model including ion-ion interactions, and experiment. Our simulation model is based on precise measurements of the cross sections and other parameters for both 6 and 10 μm core diameter fibers. Good agreement for several single and multistage amplifier topologies and operating conditions will be presented. Origins of the difference between theory and experiment are discussed, with emphasis on the accuracy of the cross sections and the cross relaxation parameters. Finally based on our simulation tool, we will demonstrate a design with an output power greater than 10 W for a multistage amplifier with a single-frequency signal at 2050 nm. The power stage was constructed with a 6 μm active fiber showing a 64 % optical slope efficiency. The output power is found to be within 5 % of the simulated results and is limited only by the available launched pump power of ~24 W. No stimulated Brillouin scattering is observed at the highest output power level for an active fiber well thermalized.