Half he announced Petala new one transoceanic submarine cable which aims for a technological record: it will be the first system capable of offering a petabit capacity over a transoceanic distance. The cable will connect the Atlantic coast of France to the United States for an overall development of approximately 7,000 kmand is expected in service in 2029.
According to what was stated, Petal will offer a capacity double that of the best transoceanic cables currently in operationwithout however requiring a proportional increase in electrical power or physical infrastructure.
Submarine cables are the least visible but most critical layer of internet infrastructure: according to Meta estimates, approximately 99% of intercontinental data traffic – messaging, calls, video content and streaming – passes through fiber optic cables laid on the ocean floor.
The distinctive element of Petal is the adoption, for the first time on a transoceanic scale, of multi-core fiber technology. The cable will use 2 core fiber in a 24 fiber pair systemwith a capacity equivalent to that of a traditional 48-pair fiber system, thus reaching 1 petabit per second (1 Pbps, equal to 1,000 terabits per second) on the transatlantic route.
The transition to multi-core fiber comes at the end of an evolution path of the sector which, from the introduction of erbium-doped fiber amplifiers (EDFA) in the 1980s, passed through coherent optical transmission and uncompensated dispersion designs in the 2010s, technologies that had allowed capacity increases of up to ten times, until the so-called Shannon limit was reached.
To overcome this limitation, the industry had subsequently moved towards spatial division multiplexing (SDM), increasing the number of fiber pairs per cable: a path that Meta has already followed with the Marea (8 fiber pairs), Amitié (16 pairs) and, more recently, Anjana (24 pairs) cables, the latter being the first transatlantic system to achieve 0.5 Pbps.
To further double capacity, the company evaluated three alternative routes: further increase the number of fibers up to 48 pairs, expand the optical transmission band using the L band (as already done with the PLCN cable), or adopt a solution based on 2-core fibre. Meta chose the latter option.
The transition from single core fiber to double core fiber involves two sets of problems mainexplains Meta. The first concerns the maintaining low attenuation of the signal while maintaining the standard physical dimensions of the fiber, including the 125 micrometer external diameter; problem solved through the use of very high purity synthetic silica in the production of the preform. The second concerns the reduction of interference (crosstalk) between the two nucleiachieved by precisely controlling the refractive indices of the cores with respect to the surrounding material and by making the optical signals travel in opposite directions within the same fiber, so as to reduce crosstalk to practically unmeasurable levels.
Even the repeatersthe devices that amplify the signal along the cable route (about a hundred over a 7,000 km stretch), they required a redesign. Petal’s single-body repeater integrates amplification of 96 fiber cores using a Fan-In/Fan-Out (FIFO) interface that temporarily splits the 2-core fiber into two single-core fibers for amplification, then recombines them.
This solution, combined with an SDM pump-sharing architecture), allows maintaining the typical efficiency of single core amplification while doubling the overall capacity, remaining within the power limits foreseen by current power equipment (up to 18 kV), thus avoiding the need for a redevelopment of the entire underwater ecosystem for higher voltages.
Petal is made by Meta in collaboration with NECsystem supplier, responsible for the design, production and installation of the cable, and with Sumitomo Electric Industrieswhich provides multi-core fiber. The French landing point on the Atlantic coast, including the land interconnection to the European network, will instead be managed in collaboration with the French operator Orange.
