Subsea Cables & Internet Infrastructure

Lasers produce coherent light. This means the electromagnetic waves have the same frequency, move in the same direction, and their phase repeats in a regular pattern. The practical implication is that the laser light remains in a tight, focused band as opposed to spreading over time. This prevents the signal strength or optical power from rapidly diminishing. However, in telecommunications, coherent optics is more than just laser light. It has two key ingredients, advanced modulation schemes that use combinations of amplitude and phase to create higher bandwidth. The other component are digital processing chips (DSPs). Laser light is subject to nonlinear errors due to chromatic and polar dispersion. The DSPs can detect these errors and recover the original pristine signal. Digital signal processing detects nonlinear errors using mathematical algorithms called forward error correction. 

A fibre optic subsea cable is encased in a polyethylene sheath. Most damage due to fishing trawlers, current abrasion, and anchors occurs in water depths 1,000 meters or less. Hence cables laid or buried in shallow waters are usually single or double armored to protect them. The armor consists of galvanized or stainless steel wires wrapped around the white polyethylene layer. Galvanized steel wire has a zinc coat that resists salt water corrosion. While armor does protect against abrasion and small mechanical forces, it is not strong to prevent the cable being torn by sea floor trawler net or a dropped or moving anchor.