Subsea Cables & Internet Infrastructure

A Chinese team achieved this new world record of 3.2 petabits per second on a single fibre strand using the C, L, and S bands combined with 24 optical cores. So they tripled the usable spectrum on each of the 24 optical highways to get aggregate throughput of 3.2 Tbps. Each core achieved 133 Tbps. It is increasingly common for terrestrial networks to use both C and L bands. For example, Arelion has used the C and L bands because their network routes only consists of one or two fiber pairs. I call it a low fibre count, DWDM-on-steroids approach. The C band is defined as 1530 to 1565 nanometer wavelengths whereas the L band ranges from 1565 to 1625. L band attenuation in standard fiber is only slightly higher than the work horse C band. So L is the natural place to start when expanding the spectrum range to gain more bandwidth. In contrast, the S band has significantly higher attenuation than either C and L band, and consequently, has not been implemented in commercial hardware. S band ...

In a recent interview META subsea engineers suggested their next project would be a 1 Petabit Trans-Atlantic cable. They pointed to three possible ways of accomplishing it: multicore fibre, use of the C and L spectrum bands, and 50 fibre pair SDM. Pros and Cons 1. Multicore is subject to cross talk. Right now the only multicore cable is the Taiwan-Phillipines-US cable scheduled to go live this year. A Google project with NEC as the vendor, it has two cores per fibre strand and 26 Tbps total per fibre strand or 13 Tbps per core. The challenge is cross talk. The light spills from one core to the other and vice versa. Obviously this distorts the signals and at high transmission rates the distortions become greater and greater and the signal-to-noise ratio disintegrates. The advantage of multicore fibre is that no redesigning of the optical amplifiers is required. Since everyone acknowledges that SDM alone is unlikely to surpass the half terabit mark, Google is obviously interested in mult...