Fig. 1. Schematic diagrams of single-crystal fibers. (a) Transitional single-crystal fiber^[10]; (b) cladded single-crystal fiber^[11]

Fig. 2. Schematic diagram of crystal fiber growth equipment by micro-pulling-down method. (a) Schematic diagram of the device^[12]; (b) crucibles with various specifications^[14]

Fig. 3. Schematic diagram of the LHPG method device and its principle^[18]

Fig. 4. Schematic diagram of the multi-microporous crucible method. (a) Schematic diagram of the device; (b) cross-sectional view; (c) schematic diagram of single-crystal fiber growth

Fig. 5. Schematic diagram of the energy level structure of Nd³⁺

Fig. 6. 1.8-μm Nd∶YAG single-crystal fiber laser^[33]. (a) Schematic diagram of the device; (b) relationship between output power and pump power in continuous and passive Q-switching modes

Fig. 7. Nd∶YAG single-crystal fiber laser^[7]. (a) Schematic diagram of the device; (b) relationship between output power and pump power in continuous mode; (c) pulse peak power and single-pulse energy in passive Q-switching mode

Fig. 8. Structure diagram of 251-W high-power Yb∶YAG single-crystal fiber laser^[38]

Fig. 9. Relationship between laser output power and pump power of Yb∶Lu₂O₃ single-crystal fiber, the inset is a microscopic image of the single-crystal fiber endface^[41]

Fig. 10. Tm∶YAG single-crystal fiber laser^[42] (a) Schematic diagram of wing pumping; (b) continuous laser output power;

Fig. 11. Tm∶YAP single-crystal fiber laser^[43]. (a) Schematic diagram of single-end pumping device and continuous laser output performance; (b) schematic diagram of double-end pumping device and continuous laser output performance

Fig. 12. Relationship between laser output power and absorbed pump power of Tm∶CaF₂ single-crystal fiber in continuous mode^[44]. (a) 3%Tm∶CaF₂; (b) 4%Tm∶CaF₂

Fig. 13. Ho∶YAG single-crystal fiber laser^[47]. (a) Schematic diagram of the device; (b) physical diagram of the device; (c) relationship between output power and absorbed pump power

Fig. 14. Cascaded Ho∶YAG single-crystal fiber laser^[9]. (a)‒(d) Schematic diagrams of the device; (e) continuous laser output power; (f) corresponding spectra

Fig. 15. Schematic diagram of cooperative up-conversion between adjacent Er³⁺ ions

Fig. 16. Er∶CaF₂ single-crystal fiber laser^[52]. (a) Schematic diagram of the device; (b) laser performance of Er∶CaF₂ single-crystal fiber with different concentrations

Fig. 17. Comparison between Nd∶YAG single-crystal fiber and Nd∶YAG crystals with other geometric shapes^[62]. (a) Relationship between gain and pump power, the inset is a schematic diagram of the test device; (b) influence of different pump powers on spectral gain shift

Fig. 18. Nd∶YAG single-frequency master oscillator power amplifier system^[63]

Fig. 19. Output characteristics of each amplifier. (a) SCF pre-amplifier; (b) first-stage main amplifier; (c) second-stage main amplifier

Fig. 20. Two-stage Nd∶YAG single-crystal fiber MOPA amplification system^[64]. (a) Schematic diagram of the device; (b) output power and extraction efficiency of the second-stage amplification

Fig. 21. High-power linearly polarized continuous-wave single-frequency laser based on Nd∶YAG single-crystal fiber^[7]. (a) Schematic diagram of the device; (b) total output power; (c) output power of the linearly polarized laser; (d) output power of the depolarized laser

Fig. 22. Schematic diagram of double-pass structure Yb∶YAG single-crystal fiber amplifier^[67]

Fig. 23. High-energy ultrashort pulse amplification system with coherent beam combining of two single-crystal fibers^[58]. (a) Schematic diagram of the device; (b) compressed pulse energy and variation of combining efficiency

Fig. 24. Yb∶YAG single-crystal fiber amplifier based on DPA technology^[57]. (a) High-gain amplification stage; (b) high-energy sub-pulse amplification stage

Fig. 25. Multi-stage end-pumped Yb∶YAG single-crystal fiber CPA system^[8]

Fig. 26. CDLHPG system^[85]. (a) Schematic diagram of the principle; (b) end view and side view of the sapphire tube with fused-silica capillary

Fig. 27. LD-pumped glass-cladding Ti∶sapphire crystal fiber laser^[86]. (a) Schematic diagram of the optical path; (b) output power under different pump powers; (c) laser spectra under different pump powers

Fig. 28. Cr⁴⁺∶YAG single-crystal fiber wavelength-scanning laser^[87]. (a) Schematic diagram of the device; (b)‒(d) wavelength tuning and scanning characteristics

Fig. 29. Schematic diagram of the growth of “C4”-type optical fiber by the LPE method^[11]

Fig. 30. “C4”-type optical fiber^[11]. (a) Cross-sectional view; (b) quasi-continuous laser performance

Fig. 31. Gradient-doped Nd∶YAG single-crystal fiber^[90]. (a) Schematic diagram of the growth principle; (b) laser performance

Fig. 32. 1%Yb∶YAG tapered single-crystal fiber^[91]. (a) Physical image; (b) schematic diagram of the small-signal gain test setup;