Fig. 1. Requirements for mandrels in high brightness Yb-doped LMA-PCF

Fig. 2. MCVD process flowchart[26]

Fig. 3. Preparation of preform by DND process[35]

Fig. 4. Powder sintering process[37]

Fig. 5. Process of phase separation to prepare porous[43]

Fig. 6. Fabrication of rare earth doped optical fibers by phase separation method[45]

Fig. 7. Fabrication of large mode ytterbium doped fiber process by sol-gel process

Fig. 8. (a) Glass forming region of Yb/Al/P doped silica glass; (b) magnified view of glass forming region in area with high content of SiO224

Fig. 9. Performances of Yb3+ in YAP series samples[29]. (a) Absorption spectrum; (b) emission spectrum

Fig. 10. Raman spectra of Yb3+/Al3+/P5+ doped silica glass[26]

Fig. 11. Structure of Yb3+/Al3+/P5+ co-doped quartz glass[26]

Fig. 12. Effects of Yb2O3, Al2O3, P/Al ratio, and AlPO4 on refractive index of silica glass[26,29,31]

Fig. 13. Photographs of Yb-doped quartz glass mandrels

Fig. 14. Photographs of photonic crystal fibers and composition distribution of fiber cores. (a) PCF cross-sectional photographs; (b) EPMA line scan maps of Yb, Al, P, and F elements in fiber core

Fig. 15. Laser amplification system and output laser characteristics. (a) Main oscillator power amplifier system; (b) average pulse amplification power versus pump power. Insets are beam qualities at 120 W and 272 W, respectively

Fig. 16. Photo of photonic crystal fiber end face and laser amplification performance. (a) SEM photograph of large mode area PCF with 75 μm core diameter; (b) average pulse amplification power versus pump power

Fig. 17. Development of LMA-PCF fabricated by sol-gel method