Subsea Cables & Internet Infrastructure

Long haul fibre optic bandwidth ranges from a few terabits per second into the low thirties with the equipment and operating expense sharply rising as transmission rates go up. Repeatered subsea cables generally lie in the 12 to 25 Tbps window with most spatial division multiplexing deployments pushing 12 to 20 Tbps whereas the traditional 6 to 8 pair coherent optics deployments transmit at least 20 Tbps or higher per strand.  The key factor determining the optical transmission rate is attenuation, which refers to the fact that a photon or wavelength's intensity or energy diminishes as it travels through fibre optic glass or any other medium. Light is scattered, reflected backwards or absorbed. Other variables that affect transmission rates include the number of distinct wavelength bands (dense wave division multiplexing) that can serve as distinct optical channels in a given spectrum range (usually the C band). The more channels, the higher the transmission rate. Chromatic dispers...

The Japanese National Institute of Information and Communication set a single fibre pair transmission record of 22.9 petabits last November. To achieve it, multicore was combined with multiple frequency bands including the standard C-band, L-band (in limited production use today), and S-band. The C-band is the work horse of optical infrared transmission with a wavelength range of 1530-1550 nanometers. These wavelengths experience the least attenuation in a glass medium; they are also ideal for erbium-doped optical amplifiers. The L-band includes the 1565 to 1625 nanometer range. Its attenuation in glass is the second lowest. Arelion has used L-band in its US East Coast network. At least one Pacific cable has used L-band as well. I believe it is PLNC which connects HK to the US. The S-band ranges from 1460 to 1515 nanometers. The 'S' stands for short band. It has the third lowest attenuation in glass. The Japanese combined these three bands with a 38 core fibre strand which they...