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Submarine optical cables placed on the seabed are easily to suffer from damage and interference in submarine environment. In order to ensure the safety of submarine optical cable, distribution fiber-optic sensing technology is used for submarine optical cable safety monitoring. In the method, long submarine optical cables firstly are divided into several parts, then optical signals and ambient sounds in each part are collected and analyzed, finally the interference types and sources are judged based on signal above through the system host. Fiber optic sensing methods, which is mainly divided into scattering fiber optic sensing and reflective grating sensing, will affect the effectiveness of submarine optical cable safety monitoring greatly. Common scattering optical fiber sensing methods include optical time domain reflection (OTDR), polarized optical time domain reflection (POTDR), phase-sensitive optical time domain reflection (Phase-OTDR) and Brillouin optical time domain reflection (BOTDR), which all have the disadvantages of short range, low resolution. Reflective grating sensing for monitoring requires a large signal bandwidth and is costly. Consequently, a novel sensing method is proposed in this paper, which combines multiple sensing techniques such as Phase-OTDR, POTDR and BOTDR with frequency division multiplexing (FDM), wavelength division multiplexing (WDM) and time division multiplexing (TDM).
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