Which cable was the first?
Asking for the first fiber optic cable has no clean answer, because the phrase can mean several different things. Glass fibers that carried images for medical instruments existed in the 1950s. Fiber with low enough loss to carry a telephone call over a useful distance appeared in 1970. The first fiber systems carrying live public traffic came in 1977. The first fiber cable under an ocean entered service in 1988. Different sources point to different points on this list, and several researchers and companies contributed to each.
What matters most for the story is what happened once the cable became a communications system, and why it suited digital data so well.
Why digital and light fit together
A fiber link works by switching a light source on and off, or varying it very quickly, to represent ones and zeros. Because a clean pulse of light is either present or absent, digital signaling copes well with the small distortions and noise that build up along a cable. The earliest telephone systems on copper were analog, and engineers had begun converting speech to digital pulses by the 1960s, using pulse-code modulation. Fiber arrived at a time when the telephone network was already becoming digital, and the two developments reinforced each other.
A standard system in the late 1970s sent data at tens of millions of bits per second over each fiber, which was a large improvement over the copper cables it replaced. A typical early design used a light-emitting diode or semiconductor laser at one end, a length of glass fiber, and a photodiode at the other. Along long routes, regenerators received a weakening signal, cleaned it up and sent it on again.
Early service
In 1977, telephone systems in the United States and Britain began carrying live calls over fiber between exchanges in cities. Bell Laboratories had tested a system in Atlanta in 1976, and General Telephone and Electronics reported a commercial link in Long Beach, California, in 1977. These first routes covered only a few miles, but they showed that the glass and the transmitters were reliable enough for service. Through the early 1980s, telephone companies laid long-distance fiber between cities, and in the 1980s, single-mode fiber with a lower-loss design replaced the multimode type used in many early systems.
Undersea cables
Telephone and telegraph cables had crossed the oceans since the nineteenth century, first with the electric telegraph and later with coaxial cables carrying voice circuits, beginning with the TAT-1 cable in 1956. Fiber promised more capacity with fewer repeaters. The first transatlantic fiber cable, TAT-8, began service in 1988, linking North America with Britain and France. Its capacity was in the range of tens of thousands of simultaneous voice circuits, much more than the last coaxial cable. Transpacific fiber cables followed soon after.
Such cables are laid by specialized ships and buried in shallow water to protect them from fishing gear and anchors. Today, most international internet traffic travels through these undersea routes rather than via communications satellites, which are used more for remote areas and for mobile or broadcast links.
Amplifiers and multiplexing
Two later advances sharply raised the capacity of fiber. Optical amplifiers, built by doping a section of fiber with the element erbium, were developed in the late 1980s by groups including David Payne’s team at the University of Southampton and Emmanuel Desurvire’s at Bell Laboratories. They boost a light signal directly, with no need to convert it to electricity first. Wavelength division multiplexing sends several colors of light at once through the same fiber, with each color carrying its own data stream. Together, these made it possible for a single strand to carry far more than the first systems, and the capacity of installed fiber could be raised by upgrading the equipment at each end without replacing the cable.
Shared credit
Many names appear in accounts of the first fiber optic cable. Charles Kao and George Hockham made the proposal that glass could be clear enough, researchers at Corning made the first low-loss fiber, and teams at Bell Laboratories, the British Post Office, and companies in Japan and elsewhere developed lasers, cable designs, splicing methods and complete systems. Capturing the achievement as a single invention misses how much depended on each part working together.
Effects on the internet
The internet’s growth in the 1990s depended on the large amount of capacity that fiber provided. Backbone links between cities and countries moved from megabits to gigabits per second. Fiber later reached more homes and businesses directly. Whatever the exact date one assigns to the first cable, fiber’s real importance was its ability to scale as demand for data grew.