Subsea Cables & Internet Infrastructure

University of Eindhoven in the Netherlands has set up a 4.6 kilometer free space optical link that traverses the city center. Its throughput is 5.7 Tbps. Unfortunately, I don't see signal to noise measurements. Free space lasers suffer from atmospheric turbulence such as rain, fog, and clouds. They work well in outer space. The technology is the basis of the new NASA deep space communications network. Click here for the short paper: https://arxiv.org/pdf/2503.21058v1. 

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...