Fig. 1. Glass-forming region in AlF₃-BaF₂-CaF₂-YF₃ system^[26]

Fig. 2. Glass-forming region in AlF₃-SrF₂-MgF₂-YF₃ system^[27]

Fig. 3. Glass-forming region in AlF₃-RF₂-YF₃ system^[28]

Fig. 4. Glass-forming region in AlF₃-YF₃-PbF₂ system^[39]

Fig. 5. Optical micrographs of neck surfaces of fiber preformed rods drawn in different atmospheres^[57]. (a) In dry nitrogen; (b) in air

Fig. 6. Scanning electron micrographs of surfaces of fibers drawn in different atmospheres^[57]. (a) In air; (b) in dry nitrogen

Fig. 7. Schematic of experimental setup for ~2.868 μm fiber laser^[68]

Fig. 8. Experimental results of ~2.868 μm fiber laser^[68]. (a) Output spectrum; (b) slope efficiency

Fig. 9. Energy level diagram and energy transfer mechanism of Ho³⁺/Pr³⁺ co-doped AZF glass^[60]

Fig. 10. Schematic of experimental setup for ~2.9 μm fiber laser^[60]

Fig. 11. Experimental results of ~2.866 μm fiber laser^[60]. (a) Output spectrum; (b) slope efficiency

Fig. 12. Schematic of experimental setup for ~2.9 μm fiber laser^[62]

Fig. 13. Experimental results of ~2.9 μm fiber laser^[62]. (a) Output power versus pump power; (b) laser wavelength versus output power with laser spectrum at 969 mW output power shown in inset

Fig. 14. Experimental results of ~2.9 μm tunable fiber laser^[62]. (a) Time stability; (b) tunable spectrum

Fig. 15. Experimental results of cascade fiber lasers^[15]. (a) Output power versus pump power ; (b) output laser spectrum at highest pump power of ~20 W; (c) temporal dependence of ~3 μm laser maximum output power within 50 min

Fig. 16. Experimental setup and output power of ~2. 86 μm fiber laser^[77]. (a) Schematic of experimental setup for ~2.86 μm fiber laser; (b) output power versus pump power

Fig. 17. Experimental results of ~2.86 μm fiber laser^[77]. (a) Laser spectra under different output powers with laser spectrum shown in inset when output power is 977 mW; (b) temporal stability of output power