Widely-Tunable Operation of a Thulium Doped Fibre Laser Between 1654 nm and 2025 nm

Thulium (Tm) doped silica has a wide fluorescence emission band spanning the wavelength range from ~1600 nm to 2200 nm making it an attractive laser gain media with a wide range of applications. However, due to the increasingly three-level nature of the Tm transition below 1900 nm, it becomes more challenging to operate towards the shorter wavelength end of the emission band. This problem can be alleviated by combining in-band pumping with an erbium (Er) fibre laser with a core-pumped laser configuration. In previous work, Shen et al demonstrated tunability from 1723 nm to 1973 nm at >1 W power levels in a Tm-doped alumino-silicate fibre laser [1] . Wider tunability (from 1679 nm to 1992 nm) for a watt-level Tm fibre laser has only been achieved by employing Tm-doped germano-silicate fibre, which benefits from reduced signal absorption below 1800 nm and thus blue-shifted net gain [2] . Here we present a Tm-doped alumino-silicate fibre laser with a tuning range of 371 nm, from 1654 nm to 2025 nm, which represents the widest tuning range reported to date for a Tm-doped silica fibre laser.