  Side-pumping fibre combiners offer several advantages in fibre laser design,
including distributed pump absorption, reduced heat load, and improved
flexibility and reliability. These benefits are particularly important for
all-fibre lasers and amplifiers operating in the mid-IR wavelength range and
based on soft-glass optical fibres. However, conventional fabrication methods
face limitations due to significant differences in the thermal properties of
pump-delivering silica fibres and signal-guiding fluoride-based fibres. To
address these challenges, this work introduces a design for a fuse-less
side-polished (D-shaped) fibre-based pump combiner comprising multimode silica
and double-clad fluoride-based fibres. The results demonstrate stable coupling
efficiency exceeding 80% at a 980-nm wavelength over 8 hours of continuous
operation under active thermal control. The developed pump combiner has also
been successfully integrated into a linear Er-doped fibre laser cavity, showing
continuous-wave generation at 2731 or 2781-nm central wavelength with an output
power of 0.87 W. Overall, this innovative approach presents a simple,
repeatable, and reproducible pump combiner design that opens up new
possibilities for leveraging fibre-based component technology in soft glass
matrices and other emerging fibres with unique compositions.
