Fig. 1. Basic structure of OTDR

Fig. 2. Basic structure of POTDR

Fig. 3. Basic structure of Φ-OTDR

Fig. 4. Basic structure of OFDR

Fig. 5. Basic structure of Sagnac interferometer

Fig. 6. Basic structure of Mach-Zehnder interferometer

Fig. 7. Basic structure of Michelson interferometer

Fig. 8. Sagnac and Mach-Zehnder compound interferometer

Fig. 9. Structure of positioning system

Fig. 10. Structure of defense-zone system

Fig. 11. Structure of Defense-zone hybrid positioning system

Fig. 12. Net hanging system

Fig. 13. Buried system

Fig. 14. Laying mode of vibration sensing fiber optic cable for water depth ＞1.5 m and ＜4 m tributaries

Fig. 15. Submarine seismic fiber optic cable system