All-fiber Er:ZBLAN ring cavity laser in the 2.8 μm band

We demonstrate the first, to our knowledge, all-fiber ring cavity laser with light emission in the mid-infrared. For this purpose, a low-loss single-mode ZBLAN optical fiber coupler, a tapered pump combiner, and an inline polarization controller are specifically developed. These components are combined for the first time to our knowledge, along with an Er:ZBLAN fiber, to realize the ring cavity. The output power reaches 36 mW of continuous wave emission in the wavelength band of 2.8 μm. Two different pump wavelengths, 0.976 and 0.785 µm, are used to characterize the laser output. The investigation of polarization state impact on laser output reveals that polarization control suppresses mode competition, leading to improved output stability.