Fig. 1. Schematic diagram of different narrow-linewidth seed sources. (a) Phase modulated single frequency laser seed source; (b) narrow-band filtered superfluorescent seed source; (c) random fiber laser seed source; (d) narrow-linewidth multi-longitudinal-mode oscillator seed source

Fig. 2. Time-domain signals of self-pulse at different time scales and powers. (a) Laser threshold self-pulse at the scale of microsecond; (b) laser threshold self-pulse at the scale of ten nanoseconds; (c) laser self-pulse with higher power at the scale of microsecond; (d) laser self-pulse with higher power at the scale of ten nanoseconds^[35]

Fig. 3. Test results of oscillating cavity constructed by different bandwidths OC-FBGs in time domain ^[35]

Fig. 4. Time-domain characteristic of oscillator with different cavity lengths at different scale when the output power is 18.25 W. (a) At microsecond scale; (b) at nanosecond scale^[35]

Fig. 5. Schematic diagram of self-pulse suppression experiment (a) without and (b) with spatially coupled F-P cavity

Fig. 6. Schematic diagram of complex oscillator cavity with all-fiber configuration

Fig. 7. High power laser spectra based on different oscillator cavities. (a) Laser spectra after amplification of single oscillator cavity; (b) laser spectra after amplification of complex oscillator cavity^[35]

Fig. 8. SRS suppression of 1 kW narrow line width fiber laser with and without CTFBG

Fig. 9. Schematic diagrams of optical paths of (a) ordinary oscillator cavity seed source, (b) complex oscillator cavity seed source, (c) long complex oscillator cavity seed source, and (d) amplifier stage^[51]

Fig. 10. Schematic diagram of narrow-linewidth single stage MOPA configuration laser system based on complex cavity oscillator seed source^[52]

Fig. 11. Schematic diagram of optical path of 1045-nm narrow-linewidth fiber laser

Fig. 12. Schematic diagram of the optical path of a 3.3 kW narrow-linewidth fiber laser

Fig. 13. Structural diagram of the “seed-amplifier sharing pump”

Fig. 14. The variation of line width under different pumping methods