Fig. 1. Experimental setup of 978-nm ultrashort cavity DBR single-frequency fiber laser^[29]

Fig. 2. Experimental setup of short linear cavity Yb³⁺-doped single-frequency phosphate fiber laser^[11]

Fig. 3. Experimental setup of single-frequency amplifier^[31]

Fig. 4. Output power and backward power versus pump power^[34]

Fig. 5. Experimental setup of 1120 nm linearly-polarized DBR single-frequency fiber laser^[12]

Fig. 6. Schematic diagram of linearly frequency-modulated pulsed single-frequency fiber laser at 1083 nm^[39]

Fig. 7. Experimental setup of single-frequency all-fiber pulsed MOPA^[40]

Fig. 8. Structural diagram of 1.6 μm linearly-polarized DBR single-frequency fiber laser^[14]

Fig. 9. Schematic of high-power single-frequency Er³⁺/Yb³⁺ co-doped fiber amplifier^[48]

Fig. 10. Output power of high-power EYDFA pumped by 940 nm laser^[48]

Fig. 11. Output power versus pump power with input auxiliary power of 0, 200, 400, 500, and 600 mW^[49]

Fig. 12. Experimental setup diagram of intensity noise suppression of single-frequency fiber laser based on SOA and optoelectronic negative feedback^[52]

Fig. 13. Experimental setup diagram of frequency noise suppression of single-frequency fiber laser based on SOA and optical feedback^[56]

Fig. 14. Schematic diagram of 100-Hz-level-linewidth single-frequency fiber laser^[57]

Fig. 15. Laser linewidth of self-injection locked single-frequency fiber laser^[58]

Fig. 16. Experimental setup of self-injection locked tunable single-frequency fiber laser^[61]

Fig. 17. Structural diagram of multi-wavelength passively Q-switched single-frequency fiber laser^[65]

Fig. 18. Structural diagram of single-frequency MOPA laser based on single-mode pulse^[66]

Fig. 19. Simulated and experimental results of output powers versus pump power for different pump wavelengths^[15]

Fig. 20. Diagram of single-frequency Tm³⁺-doped silica fiber laser based on cascaded SMS fiber devices^[10]

Fig. 21. Experimental setup diagram of four-stage single-frequency Tm³⁺-doped fiber amplifier^[71]

Fig. 22. Power of 1950 nm linear polarization single-frequency fiber laser versus pump power at 1610 nm^[75]. Inset: PERs at different output powers

Fig. 23. Diagram of two-stage power amplifier^[82]. Inset: cross-section of gain fiber and picture of experimental device

Fig. 24. Diagram of 1200 nm Ho³⁺-doped single-frequency ZBLAN fiber laser^[89]

Fig. 25. Schematic diagram of DFB single-frequency laser^[88]