Fig. 1. SRS and TMI have conflicting requirements for fiber laser design

Fig. 2. Structure of fiber with variable core diameter and its bending diagram for use in fiber lasers

Fig. 3. Traditional laser pumping wavelength and new pumping waveband for optimized TMI threshold

Fig. 4. Power distribution and normalized B-integral in fiber amplifier under different pump configuration. (a) Power distribution in the amplifier; (b) Normalized B-integral

Fig. 5. Simulation of TMI thresholds in co-pump and counter pump configuration with a pump wavelength of 976 nm

Fig. 6. Simulation results of TMI threshold at different pump wavelengths in co-pump configuration of 30/400 μm amplifiers

Fig. 7. TMI threshold and output Raman power of different fiber amplifiers

Fig. 8. SeeFiberLaser simulation model of continuous fiber oscillator

Fig. 9. Output spectrum of 1080 nm fiber oscillator with different ytterbium-doped fiber lengths. (a) Output spectrum when the ytterbium fiber is 10 m; (b) Output spectrum when the ytterbium fiber is 20 m

Fig. 10. Fiber laser output spectrum at different central wavelengths. (a) Output spectrum when the central wavelength of the FBG is 1050 nm; (b) Output spectrum when the central wavelength of the FBG is 1080 nm

Fig. 11. Simulation results of output spectrum of the fiber laser oscillator employing output coupling fiber Bragg grating (OCFBG) with different reflectivities. (a) The reflectivity is 5%; (b) The reflectivity is 15%

Fig. 12. Output spectrum and resonator power distribution of different fiber lengths at 975 nm and 915 nm pumping. (a) Output spectrum when 975 nm pumped 15 m YDF; (b) Cavity power distribution when 975 nm pumped 15 m YDF; (c) Output spectrum when 915 nm pumped 30 m YDF; (d) Cavity power distribution when 915 nm pumped 30 m YDF

Fig. 13. V values corresponding to different core diameters and NAs

Fig. 14. Multi-parameter optimization iteration and simulation results. (a) Various parameters that need to be iterated; (b) Simulation results under different simulation parameters

Fig. 15. Experimental setup of bi-direction pumped high power fiber laser

Fig. 16. Comparision of the TMI and beam quality of the fiber amplifier employing spindle-shaped ytterbium-doped fiber and uniform ytterbium-doped fiber before and after pumping. TMI of the fiber amplifier employing (a) spindle-shaped ytterbium-doped fiber and (b) uniform ytterbium-doped fiber; (c) beam quality comparision of the fiber amplifier employing spindle-shaped and uniform ytterbium-doped fiber

Fig. 17. Comparison of experimental results between SPF and 25/400 µm CCAF under the same conditions. (a) Beam quality of the output laser with CCAF; (b) Beam quality of the output laser with SPF; (c) Comparison of the spectra of the two fibers at the same output power

Fig. 18. Experimental setup of 981 nm LD pumped 6 kW level oscillating-amplifying integrated fiber laser

Fig. 19. Experimental results of the oscillating-amplifying integrated fiber laser. (a) Power efficiency characteristics; (b) Spectra in different power; (c) Beam quality

Fig. 20. Experimental setup of 981 nm LD pumped 7 kW fiber laser with good beam quality

Fig. 21. Experiment results of the 7 kW fiber amplifier based on counter-pump with pump wavelength of 981 nm. (a) Power efficiency; (b) Spectra in different power; (c) Beam quality

Fig. 22. Experiment results of the high power fiber amplifier employing 27/600 μm fiber. (a) Power efficiency; (b) Spectra in different power; (c) Beam quality

Fig. 23. Integrated multifunctional passive devices for replacing traditional splicing-based multiple passive devices. (a) Fusion splicing of four independent passive devices; (b) Four passive devices integrated on one single passive fiber without fusion points

Fig. 24. Illustration of ytterbium-doped and energy-transfer integrated fiber

Fig. 25. Fabrication of functional passive devices on the passive fiber of ytterbium-doped and energy-transfer integrated fiber

Fig. 26. Gain-resonator integrated design. (a) Gain-resonator integrated design with FBGs directly written into the gain fiber; (b) Gain-resonator integrated design with FBGs written into the passive fiber of the ytterbium-doped and energy transfer integrated fiber

Fig. 27. Fiber laser directly pumped by high power LD without combiner

Fig. 28. Illustration of high power fiber laser based on ytterbium-doped and energy transfer integrated fiber and integrated multifunctional passive devices