Fig. 1. Schematic diagram of MCVD technique^[31]

Fig. 2. Schematic diagram of MCVD combined sol-doping^[32]

Fig. 3. Schematic diagram of MCVD system with vapor phase doping^[33]

Fig. 4. Schematic diagram of DND manufacturing fiber^[34]

Fig. 5. Schematic diagram of the REPUSIL process^[31]

Fig. 6. Fabrication procedure of RE-doped silica glasses and fibers by sol-gel combined high temperature sintering^[36]

Fig. 7. Schematic diagram of laser sintering RE-doped silica powder^[37]

Fig. 8. Schematic diagram of glass phase-separation technology^[39]

Fig. 9. Single-frequency DBR Nd³⁺-doped silica fiber laser at 930 nm^[44]. (a) Experimental setup; (b) laser spectrum; (c) output power

Fig. 10. Watt-level single-frequency tunable MOPA Nd³⁺-doped fiber laser operating at 915‒937 nm^[45]

Fig. 11. Single-frequency DBR Nd³⁺-doped silica fiber laser at 910 nm^[58]. (a) Experimental setup; (b) laser spectrum, the inset is the longitudinal characteristic; (c) output power

Fig. 12. 920 nm passively mode-locked Nd³⁺-doped fiber laser with 207 MHz fundamental repetition rate^[61]. (a) Experimental setup; (b) pulse train; (c) laser spectra, the inset is the measurement result of 2 h spectrum stability; (d) radio frequency (RF) spectra, the inset is the RF spectrum from 0 to 5 GHz; (e) autocorrelation curve; (f) output power

Fig. 13. Single-frequency DBR laser based on commercial Yb406 Yb³⁺-doped silica fiber^[67]. (a) Experimental setup; (b) output power, the inset is the power stability in 10 min time span; (c) laser spectra, the inset is the laser spectrum in 3 nm span

Fig. 14. Structure comparison of single-frequency DBR cavity. (a) Conventional DBR cavity; (b) monolithic single-frequency DBR cavity

Fig. 15. Monolithic single-frequency DBR laser based on photosensitive Yb³⁺-doped silica fiber^[71]. (a) Experimental setup, the inset is the photograph of the monolithic cavity; (b) transmission spectra of HR-FBG and LR-FBG; (c) output power

Fig. 16. Dissipative soliton mode-locked laser with 3.3 GHz fundamental repetition rate by high absorption Yb³⁺-doped silica fiber^[72]. (a) Experimental setup; (b) structure of the dispersive dielectric mirror (DDM), the Ta₂O₅-SiO₂ multilayer coating designed and deposited onto the end facet of the fiber ferrule segment; (c) group velocity dispersion and transmissivity of the DDM versus wavelength between 970 nm and 1100 nm; (d) laser spectra versus pump power; (e) RF spectrum

Fig. 17. Dual-frequency DBR 1.5 μm fiber laser based on Er³⁺-doped silica fiber^[76]. (a) Experimental setup; (b) reflective spectra of high- and low-reflection superimposed fiber Bragg gratings; (c) laser output power; (d) verification of dual-wavelength laser single frequency operation using a scanning Fabry‒Pérot interferometer; (e) frequency spectrum of the two-wavelength beating signal within 1 GHz span

Fig. 18. Highly Er³⁺-doped silica fiber developed by Shanghai Institute of Optics and Fine Mechanics via MCVD combined sol-gel doping method^[32]. (a) Radial refractive index profile, the inset shows micrograph of fiber end-face; (b) distribution of Al and Er elements in the end-face; (c) core absorption coefficient; (d) propagation loss

Fig. 19. Monolithic single-frequency fiber laser at 1540 nm based on photosensitive Er³⁺/Yb³⁺ co-doped silica fiber^[80]. (a) Experimental setup; (b) single longitudinal mode characteristic measured by Fabry‒Pérot interferometer; (c) laser spectrum

Fig. 20. Passively mode-locked Er³⁺-doped fiber laser at 1.5 μm with 5 GHz fundamental repetition rate^[86]. (a) Experimental setup; (b) laser spectra, the inset shows the magnification of the optical spectrum in 0.3 nm range; (c) RF spectra, the inset shows the RF spectra from 0 to 12 GHz

Fig. 21. Schematic of single-frequency DFB fiber laser at 2.0 μm^[91]

Fig. 22. Monolithic single-frequency DBR fiber laser at 2.0 μm^[92]. (a) Experimental setup; (b) transmission spectra of high- and low-reflection fiber Bragg gratings; (c) output power

Fig. 23. Single-frequency DBR fiber laser at 1908-2050 nm based on commercial Tm³⁺-doped silica fiber^[93]. (a) Cavity structure;

Fig. 24. Single-frequency DBR fiber laser at 2.0 μm based on commercial Tm³⁺-doped silica fiber^[94]. (a) Experimental setup; (b) laser spectra, the inset show the laser spectrum in 2 nm range; (c) output power

Fig. 25. Single-frequency DBR fiber laser at 2.0 μm^[96]. (a) Structure diagram; (b) photo of laser adiabatic package; (c) photo of the laser prototype