Fig. 1. Schematic diagram of OFDR

Fig. 2. Relationship between scan range and spatial resolution of OFDR

Fig. 3. Effect of laser frequency scanning error on spatial resolution for different distances

Fig. 4. Relationship between scanning laser frequency and echo signal, and mapping relationship between echo delay and beat frequency of OFDR. (a) Relationship between scanning laser frequency and echo signal; (b) mapping relationship between echo delay and beat frequency of OFDR

Fig. 5. Schematic diagram of sweep laser generation using optical phase locked control

Fig. 6. Typical results of phase locked control laser scanning. (a) Instantaneous frequency of delay heterodyne beat frequency signal; (b) spectrum of beat frequency signal before and after phase locking; (c) laser instantaneous frequency and frequency error

Fig. 7. System diagram of OFDR controlled by optical phase locking

Fig. 8. Fiber link loss of OFDR controlled by optical phase locking

Fig. 9. Measurement accuracy of optical fiber loss at different distances. (a) 10 km; (b) 100 km

Fig. 10. Optical fiber distributed strain sensing system

Fig. 11. Weighted average signal. (a) Power spectrum; (b) phase spectrum

Fig. 12. Color temperature diagram of strain varying with time and distance, and curve of strain varying with time at specific position. (a) Color temperature diagram of strain varying with time and distance; (b) curve of strain varying with time at specific position