Slope efficiency improvement of a core-pumped thulium-doped fibre laser

Various applications in the medical, defence and industrial fields exist for thulium-doped fibre lasers (TDFL) emitting in the 2 µm spectral region. All-fibre laser architectures represent optimized designs especially for applications that require high reliability in harsh environments. These architectures can be further improved by reducing the amount of fibre components and therefore reducing the failure probability. We investigate mode field adaption techniques between an active and passive fibre by changing the refractive index profiles of both fibres. The findings of this investigation are used to optimize a core-pumped TDFL with up to 75% slope efficiency.