Monolithic, narrow linewidth, polarization maintaining, thulium fiber laser using femtosecond laser written fiber Bragg gratings

We have demonstrated an all-fiber thulium laser system that, without any intracavity polarizing elements or free-space components, yielded a stable polarization extinction ratio (PER) of similar to 18 dB. The system is based on single-mode polarization-maintaining silica fiber and its cavity is formed from each a high and low reflectivity femtosecond laser written fiber Bragg grating resonant at 2054 nm. The output of the fiber is not only highly polarized, but maintains a narrow linewidth of 78 pm at its maximum output power of 5.24 W. The high PER without any polarizing elements in the cavity is of great interest and makes the systems useful for spectral beam combining and other applications which require polarization dependent optical elements.