Subsea Cables & Internet Infrastructure

If you have ever heard someone say they bought a quarter or half fibre pair, it means they bought the right to use a slice of laser spectrum to create transport services. Think of spectrum as clay and optical waves as the finished product. The spectrum seller places a filter on a fibre pair that ensures the buyer only gets the purchased frequencies. A quarter fibre pair means they get 25% of the pair's total usable spectrum. Similarly, for a half fibre pair.  In general, the minimum commercial purchase is 560 Gigahertz. The amount of usable bandwidth depends on the modulation or encoding scheme. Complex encoding schemes generate more zeros and ones than simple ones. And they cost proportionally more. Using standard Ciena gear, you can squeeze about 2.5 terabits of usable capacity out of the 560 Ghz allotment. Below is the basic topolgy. Richard Norris of Ciena (2025 Suboptic Spectrum Working Group) created the slides.  Spectrum is like any other service. You can lease or buy i...

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.