Breaking News: META Building First Petabit Trans-Atlantic Cable Using Two Optical Cores

Facebook is deploying the first deep sea 1 Petabit per second fibre optic cable with two optical cores per fibre strand. A core is the optical transmission path in a fiber strand. Standard fiber has one core. The cable will connect North America to Europe and will land in Virginia Beach, and in Bordeaux, France (where the Amitié cable also comes ashore). So it will effectively link Ashburn Equinix to Paris. It is likely Facebook will use the existing cable landing stations serving Marea and Dunant at Virginia Beach. Similarly, in Bordeaux the 1 petabit cable is likely to use the Amitié CLS.

Today the highest capacity communication cable in service across the Atlantic or any ocean for that matter is the half petabit Anjana, another META project. It has 24 fibre pairs operating at 20 Tbps per pair. Shannon's law tells us that a fibre pair operating at 20 Tbps is pretty close to full spectral efficiency.  Hence boosting per pair output is a dead end if the goal is to raising total throughput. So to reach 1 Pbps requires either a 48 fibre pair system or using the C and L optical spectrum bands or deploying multicore fibre glass as opposed to the standard single core fibre.

Now a 48 fibre pair system adds significant weight and cost. It is complex and expensive to thread 48 fibre pairs through an optical amplifier. Moreover, META and Google had a bad experience with the C & L band approach deployed on their PLCN cable. The manufactured cable proved to be so structurally weak that it was at serious risk of breaking when being lifted out of the sea for repairs. Subcom was forced to replace several thousand kilometers of this cable due to this problem. Shortly afterward, Tyco sold Subcom to Cerberus Capital Management. 

In contrast, NEC has been developing and researching multicore subsea fibre and amplifiers since at least 2021 with several successful field tests in recent years using spooled fibre and amplifiers. So the technological maturity of multicore probably played a key role in Facebook choosing NEC's two core optical fibre for the petabit throughput project. Multicore fibre have been historically bedeviled by optical cross talk. Light escapes each core and interferes with neighboring cores, a kind of mutual optical pollution. However, NEC has shown its two core product meets the key performance requirements for subsea cables. NEC accomplished this by doing two things. It places the two cores far enough apart in the fiber strand to minimize mode field overlap. In addition, a special barrier region with a  very low refractive index is placed between the two modes. A lower refractive index means the light bends less as it traverses the glass. Less bending means less light bleeding out of the cores. NEC has also developed power efficient optical amplifiers for its two core product and these amplifiers can be powered from one end of the cable. This enhances uptime and less power consumption cuts operating costs.😊

Map of META's New 1 Terabit Trans-Atlantic Cable




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