Predicting Signal Degradation in Submarine Communication Cables

Researchers analyze signals from subsea experiments to determine the performance of submarine communication cables with optimum efficiency

Lying on the seabed is an interconnected system of submarine communication cables carrying signals for such ubiquitous modern technologies as the internet.

Spanning the vastness of oceans, these cables allow for telecommunications between continents. Though difficult, the ability to predict and measure cable performance is necessary for efficiently upgrading the system.

Jean-Christophe Antona leads a group of researchers at Alcatel Submarine Networks, France, that propose a quality of transmission estimator for the design, upgrade and interconnection of submarine cables. Antona will present the group’s performance estimator at the Optical Fiber Communication Conference and Exhibition (OFC), to be held 8-12 March 2020 at the San Diego Convention Center, California, U.S.A.

“Speed is key when you design a submarine system, because you need to optimize a myriad of parameters related to physics, cost, deployment and material constraints,” Antona said.

To determine how to best optimize these systems, the researchers performed transmission studies to measure how the effective noise varies with a number of different parameters, such as signal power. Aside from the expected signals, they found an additional source of noise previous models have overlooked, which scales proportionally with distance and accounts for up to 10% of the total noise along a line. The characteristics of the noise appear in agreement with recent spectral analyses of guided acoustic wave Brillouin scattering.

They observed this using the generalized droop model, a method for determining the total droop impact of different noise sources developed and validated by the group. According to this model, the overall droop from a cascade of noise sources is a product of the individual droops.

“A consequence is that the optical signal-to-noise ratio (OSNR) degrades faster and faster as distance increases,” said Antona. “This phenomenon is all the more important if the distance is long or the signal-to-noise ratio is low, as in typical submarine space-division multiplexing.”

“From this simple rule, the OSNR can be accurately modeled from the knowledge of individual OSNR degradations caused by independent sources of noise,” he said. “With such an approach, we can therefore use simple, available models to estimate the OSNR terms associated with each propagation effect independently, then combine them using the generalized droop model.”

This method reduces the problem from a complex, time-consuming process down to simple multiplication.

With the generalized droop model, the group was able to estimate independent contributions to OSNR and use them to accurately predict transceiver performances for over 100 subsea experiments of a typical submarine fiber with distances ranging from 1,522 to 16,203 kilometers.

These results and additional research will be presented onsite at OFC 2020.

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