Design and test results of a deep sea optical fiber submarine cable

Long‐distance submarine cable telecommunication systems using low‐loss optical fiber have been investigated more and more extensively. They are expected for international digital trunk because of their economical feature brought by smaller diameter cable and longer repeater spacing as well as large transmission capacity. This paper describes a design concept for deep sea optical submarine cable and proposes a three‐split metal pipe structure as the pressure‐resistant layer against the high water pressure. This structure features good manufacturability of small diameter and thick‐wall metal pipe, particularly cable of long run length. A prototype anti‐water propagation cable was manufactured using the pipe described above and the mechanical and transmission performance was measured in elevated temperatures, pressures, and tensions in the ocean simulator on the land. Also, test operations of the cable laying, holding and recovery on the 7000‐m deep ocean bed were performed. From the results obtained, we find that the estimated loss change is less than 0.02 dB/km, which makes the proposed optical fiber cable structure feasible for deep sea submarine cable system application.