Fiber-optic communication

A fiber-optic line is a thread of glass, about the width of a human hair, that holds light in the way a pipe holds water. The core is glass of one refractive index; a cladding of slightly lower index wraps it, so a ray travelling at a shallow angle keeps striking the boundary and keeps reflecting perfectly back inside — total internal reflection — instead of leaking out. Flash a laser on and off at the near end and the flashes travel the whole length; a detector at the far end reads them back as ones and zeros. Because you can flash light billions of times a second, a single fiber carries an enormous river of information.

Copper carries signals as electrical current, and current fades and picks up interference; long lines needed repeaters every kilometre or two and could only carry so many calls at once. Glass fiber changed the arithmetic entirely: far higher capacity, immunity to electrical noise, and — once it was pure enough — repeaters tens of kilometres apart instead of every mile. Essentially all long-distance telephony and the entire backbone of the internet run on light in glass. The undersea cables that stitch the continents together are fiber. Without low-loss fiber there is no cheap, global, high-bandwidth network.

Fiber is the physical spine of the connected world: transoceanic cables, the links between data centers, and increasingly the line into the home. It made bandwidth cheap enough that streaming video, cloud computing, and instant global communication became ordinary. The same drive for flawless glass and precise light-guiding also gave medicine the endoscope and the surgical laser delivery fiber, and gave sensing a family of fiber instruments that measure strain, temperature, and rotation. All of it rests on Kao's insight that the limit was dirt, not nature.