Fig. 1. High-power 1018 nm fiber lasers (Ⅰ). (a) Non-wavelength-stabilized LD pumped 805 W and 240 W/(μm²·sr) 1018 nm fiber laser using 30/250 μm YDF^[36]; (b) bidirectionally pumped 1150 W and 289 W/(μm²·sr) 1018 nm fiber laser using 30/250 μm YDF^[38]

Fig. 2. High-power 1018 nm fiber lasers (Ⅱ). (a) Linearly polarized 616 W and 491 W/(μm²·sr) 1018 nm fiber laser using specially made 32/260 μm ring-up-doped YDF^[40]; (b) 1330 W and >1100 W/(μm²·sr) 1018 nm fiber laser^[16]

Fig. 3. Possible features for further suppressing ASE and parasitic oscillation. (a) 32/260 μm ring-up-doped YDF^[40]; (b) refractive-index profile of the 50/400 μm homemade YDF that offered 10 kW output^[3]; (c) device for suppressing the inner reflections that feedback to spurious lasing, and its effect^[48]; (d) comparison between the hybrid-structure and traditional oscillator structures^[46]

Fig. 4. Examples of tandem-pumped high-power ytterbium-doped fiber lasers. (a) IPG’s 1018 nm tandem-pumped 10 kW fiber laser^[23]; (b) a qusi-continuous-wave 6.8 kW 1071 nm fiber laser tandem-pumped by 1030 nm thin-disk laser^[53]; (c) a 836 W fiber laser tandem-pumped by 1018 nm fiber laser^[54]

Fig. 5. High-power ytterbium-doped fiber lasers tandem-pumped by 1018 nm fiber lasers (Ⅰ). (a) A 5448 W 1080 nm fiber laser using 30/250 μm YDF^[56]; (b) a 3079 W 1080 nm fiber laser using homemade 25/250 μm YDF^[57]; (c) a 4.2 kW 1070 nm fiber laser using chirped tilt fiber Bragg gratings ^[59]; (d) a 5220 W 1070 nm fiber laser using homemade 30/250 μm YDF^[58]

Fig. 6. High-power ytterbium-doped fiber lasers tandem-pumped by 1018 nm fiber lasers (Ⅱ). (a) Results of a 9.01 kW 1080 nm fiber laser using homemade 50/350/400 μm triple-cladding YDF; (b) results of a 20 kW tandem-pumped fiber laser using homemade YDF

Fig. 7. Tandem-pumped 1 kW narrow-linewidth tunable fiber laser spanning from 1060 nm to 1090 nm^[62]

Fig. 8. Tandem-pumped high-power random fiber lasers. (a) 3 kW system random fiber seed and three-stage amplification experimental system structure diagram, and corresponding spectral evolution ^[75]; (b) 4 kW system random fiber seed and two-stage amplification experimental system structure diagram, and corresponding spectral evolution ^[76]

Fig. 9. System structure, power, linewidth, and spectral evolution of a cascade pumped 5 kW random fiber laser using bandpass filters to suppress SRS ^[77]

Fig. 10. Schematic diagram, power, and spectrum of a 3.89 kW hybrid gain Raman fiber laser with a bidirectional LD pumped MOPA structure ^[87]

Fig. 11. Tandem-pumped high-power Raman fiber lasers. (a) Schematic diagram, power, and spectrum of 1018 nm and LD hybrid bidirectional pumping 3.7 kW hybrid gain Raman fiber laser^[88]; (b) structure, power, and spectrum of 1018 nm cascade pumped 5 kW hybrid gain Raman fiber laser