Water propagation blocking properties of submarine optical fiber cables

Abstract A transit transmission system for a long‐distance digital transmission line using a submarine optical fiber cable is expected to be used at water depth of 8000 m and transit distance of 40 km. This paper introduces a fundamental design for a submarine optical‐fiber cable for deep‐sea use, which can block water propagation within the cable if it is cut accidentally on the sea bed. Evaluations of the water‐blocking properties and signal transmission characteristics of the cable are presented also. The water propagation in the cable can be approximated by the stationary laminar flow of viscous fluid in a capillary tube. The distance of the water propagated is proportional to 0.5 power of the water pressure and 0.3 to 0.5 power of time. The transmission loss of the prototype submarine optical cable (with the water propagation blocking properties) is less than 0.04 dB/km. The propagation of water within the cable is estimated to be less than 800 m per month at water depth of 8000 m. This shows that the cable has practical application.