High Water-resistant and Thermal Stable Fluoride Fibers for Mid-Infrared Laser

High-power mid-infrared (MIR) fiber laser sources exhibit excellent application potential in space communications, remote sensing, material processing, spectroscopy, and medical applications. Despite recent developments in high power MIR laser sources using fluorozirconate glass fibers, the lack of fluoride fibers with good chemical and thermal stability remains the main restriction for laser power scaling at MIR. In this work，fluoroaluminate glass fiber based on the composition of AlF3-YF3-BaF2-CaF2-SrF2-MgF2 (AYF) with superior corrosion resistance, higher glass transition temperature (~425 °C) was developed and reported for the first time . The AYF fibers were fabricated by using rod-in-tube method and the loss was ~0.5 dB/m at 1.570 µm. By using Ho3+-doping single-cladding AYF fibers as the gain medium and 1150 nm laser as the pump source, a cascaded laser operating at λ~3 μm and λ~2 μm with a total unsaturated maximum output power of 11.6 W and slope efficiencies of 29%, both at 2 µm and at 3 µm were obtained. To the best of our knowledge, this is the highest output power at λ~3 μm and λ~2 μm for Ho3+-doped cascaded lasers. The results show that AYF fibers can be used as viable, high performance gain media for MIR fiber lasers.