Numerical simulations of watt-level 5  µm lasers based on Tb-doped and Nd-doped chalcogenide multicore fibers

We have theoretically studied watt-level mid-IR laser generation near 5 µm in Tb³⁺-doped and Nd³⁺-doped chalcogenide multicore fibers with 5×5 coupled cores pumped at 2 and 1.7 µm, respectively, taking into account different modes, whose wavelengths belong to the gain band. Comprehensive numerical simulations have been performed to determine how various factors affect the generation characteristics. We have calculated the threshold pump powers required for the development of laser generation and have found the expected laser wavelengths for different fiber intracavity lengths and output reflection coefficients. A simple feedback design, using a totally reflective mirror at one endface of the fiber and Fresnel reflection at the output fiber endface, provides higher output powers than a higher reflectivity output mirror. For this design, the maximum slope efficiencies are approximately 14.5% and 5.3% for Tb³⁺-doped and Nd³⁺-doped lasers, respectively, and the expected laser wavelengths are 5.28 µm for Tb³⁺-doped fibers and 5.68 µm for Nd³⁺-doped ones. The results reported here contribute to the understanding of the results of mid-IR lasing experiments in Tb³⁺- and Nd³⁺-doped chalcogenide fibers and may provide guidance for the development of higher performance devices.