High-powered 1639-1853nm tunable fiber laser with cascaded thulium- and bismuth-doped fiber

We demonstrate a continuous-wave, widely tunable fiber laser using a cascade of bismuth-doped fiber (BDF) and thulium-doped fiber (TDF). We use a diffraction grating in a Littman configuration for wavelength tuning and obtain a tuning range of 214 nm from 1639-1853nm. We achieve a maximum output power of 780 mW at 1720 nm when pumped at 1570 nm, with a power conversion efficiency of 15%. We show that utilizing cascaded BDF-TDF enables significantly broader tunability and higher output power compared to using BDF or TDF alone.