Towards high-power mid-infrared emission from a fibre laser

The diverse output pulsewidths, linewidths and polarization states of fibre lasers provide both high efficiency and high output power in a small, low-maintenance format that is ideal for applications throughout research, defence and industry. New directions are constantly being pursued to exploit the capabilities of this technology. One such direction involves extending the emission wavelength further into the infrared, which will benefit numerous existing and future applications. Many exciting advances have been demonstrated and many challenges remain, the most significant of which are summarized in this Review.