Watt-Level ~3.5 μm Er³⁺-Doped ZrF₄ Fiber Laser Using Dual-Wavelength Pumping at 655 and 1981 nm

In this letter, we propose a parallel dual-wavelength pumping (DWP) method (655 nm + 1981 nm) to realize high power output from a Er
³⁺
-doped ZrF
₄
fiber laser at ~ 3.5 μm, for the first time, to the best of our knowledge. This laser can emit a maximum power of 1.72 W, where the slope efficiency with respect to the launched 1981 nm pump is 31.5%. Further power scaling is mainly limited by the available 1981 nm pump power. Direct comparison with the common cascade DWP method (976 nm + 1981 nm) is performed. The results indicate that the parallel DWP method allows a larger output power at a certain 1981 nm pump power, thus providing another promising way for power scaling at this band.