Power-efficient undersea SDM systems

Abstract

Undersea submarine cable transmission systems are characterized by fixed and limited electrical power supplies. Electrical power is provided by a DC voltage applied across the cable from power feed equipment (PFE) located at the terminal ends and is used to power all optical amplifiers throughout the entire link which may be many thousands of kilometers. Because of the limited nature of electrical power, the concept of power efficiency is very important. In fact, power efficiency drives the recent design trend in undersea systems to spatial division multiplexing (SDM), increasing fiber counts in submarine cables. We examine here efficiency maximization via system modeling primarily with respect to the optimal generalized signal-to-noise ratio (GSNR). We explore dependences on system aspects such as capacity metric, link length, span loss, and fiber attenuation. We compare three different measures of efficiency based on total amplifier optical output power, total pump power, and overall cable capacity predicted by application of a pump sharing model and the resulting electrical-to-optical conversion efficiency levels predicted. Several capacity metrics are also studied and compared ranging from the theoretical Shannon capacity limit to a fitting of a real-time transponder. We evaluate optimal link GSNR values that maximize the various efficiency definitions as a function of link length, as well as optimal span loss values for a fixed link distance.