Study coordinated by Unicamp also brought together researchers from Stanford University
Study involving the calculation of the transmission capacity limits of future underwater fiber optic systems, coordinated by professor Darli Mello, from the Department of Communications of the Faculty of Electrical Engineering and Computer Science (FEEC) at Unicamp, gave rise to the article “Capacity Limits of Space-Division Multiplexed Submarine Links Subject to Nonlinearities and Power Feed Constraints”, to be presented in March at the Optical Fiber Communications Conference (OFC), an event organized annually by the Optical Society of America (OSA) and held this year in California (USA) . This is the main world-class meeting in the area of optical fiber communication, which should have more than ten thousand participants this year.
The article, whose first author is scientific initiation student Omar Domingues from FEEC, has as co-authors, in addition to the professor, Reginaldo Silva, representative of the national company Padtec de Campinas, one of the leaders in optical communications technology, researcher Sercan Arik and Professor Joseph Kahn, one of the greatest experts in optical communications worldwide, both from Stanford University (USA). The project was carried out in FEEC's COMLAB laboratory, coordinated by professor Dalton Arantes, and had the support of Fapesp.
The publication presents an analysis of the capacity of underwater fiber optic links and proposes a method to evaluate the theoretical limits of data transmission capacity of these systems.
The challenges
With the proliferation of data centers In countries on all continents, data traffic over the Internet has grown exponentially, threatening exhaustion of the transmission capacity of optical fibers currently available in terrestrial and submarine cables, used in pairs to send and return signals. This exponential growth is close to making existing systems unfeasible and requires the study of solutions. The installation of new cables would be a possibility, although expensive, especially when it comes to submarine cables, installed on the bottom of the oceans, which, in addition to supporting a smaller number of fiber pairs, have much higher costs than terrestrial systems.
Another complication of submarine links is that the signal has to be amplified every approximately 50 km. To achieve this, the amplifiers placed there must be powered by an electrical current, conducted through a copper cable that runs parallel to the optical fibers throughout the entire mileage, which can reach up to 15 thousand km. As energy consumption and dissipation occurs throughout this circuit, the system must be subjected to an adequate electrical starting potential that, in addition to being high enough to guarantee the reliability of the signals, does not degrade the electrical and mechanical properties of the cable.
In terrestrial systems this problem does not exist because the amplifiers are supplied locally without the need for an axial electrical conductor. Therefore, the electrical power system in submarine cables must guarantee the power necessary to supply all amplifiers.
The problem, emphasizes Darli, is that the need for an increasing number of fibers in the cables requires a sufficiently high supply voltage at the end to guarantee adequate amplifications in order to preserve the signals throughout the entire system.
In view of this, the professor explains: “Our study focused on discovering what is the maximum capacity that a submarine optical fiber system can support, given the cable's electrical supply restrictions. In current systems, as the quantity of fibers is doubled, their capacities also double. But a situation will reach such that, if there is not sufficient electrical power in the system, this variation will no longer be linear and will increase less, for example, only 30%”. The work therefore consisted, through the use of numerical methods, of evaluating the theoretical limit in increasing the transmission capacity of a submarine system that finds limitations in the electrical energy supply equipment.
perspectives
In existing systems, the technology used is not yet sufficient to reach the theoretical capacity limit that is being calculated in the study, which may be achieved in the medium term with the advancement of technology. The results presented in the article should help network designers to choose the most appropriate set of techniques to achieve capacity, considering issues of cost and complexity.
In this sense, the same group of researchers has just produced paper to be submitted to a journal in which they evaluate transmission technologies. The professor summarizes: “In the work to be presented at OFC, we calculated the theoretical capacity limit depending on the electrical power supply restrictions. In this second article, we suggest the best technologies to reach these limits.”
