Fig. 1. Schematic of the first Brillouin ring laser^[21]

Fig. 2. Simplified schematic of narrow-linewidth BFL with pump frequency tracking circuit^[23]

Fig. 3. Simplified schematic of narrow-linewidth BFL with resonance tracking circuit^[24]

Fig. 4. Actively stabilized Brillouin fiber ring laser^[42]

Fig. 5. Configuration of Brillouin/erbium fiber laser^[26]

Fig. 6. (a) Optical spectra and (b) Output power of Brillouin/erbium fiber laser with different 980 nm pump power^[26]

Fig. 7. Single-mode multi-resonance-cavity BEFL^[44]

Fig. 8. Configuration of compact BEFL based on Bi-based erbium-doped fiber^[46]

Fig. 9. Configuration of single-mode BEFL based on BP pre-amplification^[48]

Fig. 10. Configuration of ultra-short-ring-cavity compact BEFL^[49]

Fig. 11. Configuration of all-polarization-maintained ultra-short-ring-cavity compact BEFL^[32]

Fig. 12. Heterodyne setup for compact BEFL linewidth measurement^[34]

Fig. 13. Heterodyne beat spectrum of compact BEFL^[34]

Fig. 14. 25-km-delayed self-heterodyne spectrum of compact BEFL and the fitting curves^[35]

Fig. 15. Heterodyne setup of two compact BEFLs^[50]

Fig. 16. Heterodyne beat note of two compact BEFLs^[50]

Fig. 17. Phase noise spectra of compact BEFL and BP^[51]

Fig. 18. Phase noise spectra of compact BEFL and RIO laser diode^[50]

Fig. 19. Ulta-low phase noise of compact BEFL^[32]

Fig. 20. Optical power of compact BEFL versus BP power^[33]

Fig. 21. Optical power of compact BEFL versus 980 nm pump power^[33]

Fig. 22. SBS threshold of EDF against fiber length at different linear gain^[50]

Fig. 23. Configuration of fast tuning BEFL^[54]

Fig. 24. Frequency modulating amplitude of the BEFL against the modulation voltage amplitude^[55]

Fig. 25. Brillouin gain spectra of the EDF with different driving voltages^[55]

Fig. 26. Fast-tuning stabilities of (a) compact BEFL and (b) narrow-linewidth LD

Fig. 27. Experimental setup for calibrating fiber-optic hydrophone^[58]

Fig. 28. (a) Frequency response of acoutic pressure sensitivity and (b) phase noise spectra of the fiber-optic hydrophone^[58]

Fig. 29. Configuration of BOTDA based on BEFL^[59]

Fig. 30. Time-domain signals of BOTDA using BEFL^[59]