Linearly polarized polarization-maintaining Er3+-doped fluoride fiber laser in the mid-infrared

We demonstrated the ∼2.8-μm and ∼3.5-μm linearly polarized continuous wave (CW) laser outputs from a polarization-maintaining (PM) Er³⁺-doped fluoride fiber laser. By introducing a film polarizer into the cavity to select the laser polarization orientation, the ∼2.8-μm linearly polarized CW laser with a high polarization extinction ratio (PER) of ∼23 ​dB and maximum output power of 2.37 ​W was achieved under double-end pumping at 976 ​nm. By adding another 1981-nm pump source simultaneously, the ∼3.5-μm linearly polarized CW laser was also obtained, giving higher PER of ∼27 ​dB and maximum output power of 307 ​mW which is only limited by the available power of 1981-nm pump. To the best of our knowledge, this is the first report on a mid-infrared linearly polarized CW PM fiber laser in the >2.5-μm mid-infrared region. This work not only opens up opportunities for some new mid-infrared applications, but also provides a promising platform for developing high-stability and versatile mid-infrared laser sources.