Tradeoffs in Optimization of Deepsea Electro-Optical Cables

The efficient use of optical fibers for telemetry in a deepsea tether cable requires that interactions of such telemetry with the total system be examined and carefully optimized. For example, telemetry bandwidth and system power will no longer be closely coupled as they are in a coaxial cable. In the electro-optical (E-O) cable, power cannot ride free on the back of the large dielectric and copper cross sections needed for conventional coaxial telemetry. Instead, power transfer can (and should) be treated independently at the system level—in simple terms of its own penalties and benefits to the total system. The term “optimum” means much more than increased bandwidth; although that can grow by at least an order of magnitude. It also means increased cable strength, reduced cable diameter, more efficient power transfer and longer cable flexure life. To achieve these, it may be necessary to assign multiple roles to critical cable components. For example, the electrical conductor(s) may also be tasked to supply a fraction of the cable’s strength, or to serve as protective enclosures around the optical fiber(s). In this paper design tradeoffs are evaluated for three types of E-O cables—with 1, 2 and 3 electrical conductors.