Glass carries the internet because of a seventeenth-century optics principle, a 1550 nm valley in silica's absorption curve, and a family of amplifiers that happen to work on erbium. This is the physics of how light stays in the wire, why it fades, and how DWDM turns one strand into eighty parallel highways.
Fiber-Optics
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Fiber Optics: From Total Internal Reflection to DWDM -
Undersea Cables: The Internet's Physical Layer The internet's intercontinental backbone is about 1.5 million kilometers of garden-hose-thick fiber on the seabed — how it's built, powered at 15 kV from shore, broken 200 times a year, repaired by grapnel, and increasingly owned by hyperscalers.