Mid-IR fluoride fibers: materials, fabrication, and fiber laser applications

The mid-infrared (mid-IR) spectral region (2-25 μm) holds immense promise for applications in molecular spectroscopy, environmental sensing, biomedical diagnostics, and defense technologies.Among various enabling platforms, fluoride glass fibers stand out due to their broad transmission window, low phonon energy, and excellent rare-earth ion solubility, making them ideal candidates for high-efficiency mid-IR photonic systems.This review comprehensively examines the materials science, fabrication strategies, and laser applications of mid-IR fluoride fibers.We critically examine the structural and optical properties of leading glass systems-fluozirconate, fluoroaluminate, and fluoroindate-highlighting their roles in fiber design and mid-IR luminescence.State-of-the-art fabrication methods, including built-in casting, rod-in-tube, extrusion, and crucible-based fiber drawing, are analyzed in detail alongside the latest commercial fiber developments.Particular emphasis is placed on rare-earth-doped fluoride fiber lasers and supercontinuum sources, covering their physical mechanisms, system architectures, and emerging application scenarios.Finally, the current challenges in glass stability, fabrication scalability, and moisture resistance are discussed, and future research directions are proposed to advance fluoride fibers toward practical mid-IR photonic integration.This review aims to provide insights into the multidisciplinary progress driving the next generation of mid-IR fiber technologies.