Fig. 1. Relay submarine cable transmission system

Fig. 2. Typical OTDR detection curve

Fig. 3. Schematic diagram of C-OTDR system

Fig. 4. Signal comparison diagram before and after filtering

Fig. 5. Different signal power superimposes different pulse signal power light surge diagram

Fig. 6. C-OTDR system based on FSK

Fig. 7. 100 μs pulsed C-OTDR probe light

Fig. 8. C-OTDR detection curve

Fig. 9. Simulation of 25 cross-sea cable transmission system