Fig. 1. Schematic diagram of fiber core temperature measurement by fiber Bragg gratings^[28]

Fig. 2. Experimental setup for measuring internal temperature of fiber laser cores by FBGs^[36]

Fig. 3. Schematic diagram of the fiber laser based on highly reflective FBG and π-phase shift FBG^[37]

Fig. 4. Measured temperature of the fiber core in fiber laser at different pump powers^[37]

Fig. 5. Experimental setup for measuring the temperature of high reflection grating by composite grating^[38]

Fig. 6. Experimental setup for core temperature measurement in single-mode fiber laser amplifier^[51]

Fig. 7. Measurement results of core temperature in single-mode fiber laser amplifier^[51]

Fig. 8. Experimental setup for core temperature measurement in hundredwatt-level few-mode fiber laser amplifier^[52]

Fig. 9. Measurement results of core temperature distribution in hundredwatt-level few-mode fiber laser amplifier^[52]

Fig. 10. Experimental setup for core temperature measurement in kilowatt-level few-mode fiber laser amplifier^[53]

Fig. 11. Measurement results of core temperature in kilowatt-level few-mode fiber laser amplifier^[53]

Fig. 12. Experimental setup for core temperature measurement in fiber laser oscillator^[54]

Fig. 13. Comparison of the fiber core temperature distribution in fiber laser oscillator with (a) 976 nm and (b) 915 nm pump wavelength^[54]

Fig. 14. Experimental setup for core temperature measurement in kilowatt-level few-mode fiber laser oscillator^[57]

Fig. 15. Measurement results of core temperature in kilowatt-level few-mode fiber laser oscillator^[57]

Fig. 16. Experimental setup for core temperature measurement in side-pumped fiber laser^[58]

Fig. 17. Temperature distribution of the gain fiber with different pump schemes^[58]

Fig. 18. Splice thermogenic factor of a fusion point in high power fiber laser^[59]

Fig. 19. Modulated temperature of the gain fiber measured by OFDR^[63]

Fig. 20. Fiber core temperature distribution by (a) thermoelectric-cooled and (b) water-cooled at 20 ℃^[67]