All About Glass

You are here

On a Thread of Glass: Optical Fibers for Communication

All About Glass

I have heard a ray of the sun laugh and cough and sing!
    — Alexander Graham Bell

It was a bright idea: use sunlight to transmit the human voice. In 1880, American innovator Alexander Graham Bell tried it, using a thin, flexible mirror to reflect a light beam onto a distant receiver. His voice caused the mirror—and the reflected light—to vibrate. The receiver detected the light’s vibrations and turned them back into sound.

Bell’s photophone worked, but it wasn’t practical. Rain, smoke—anything in the atmosphere—scattered the unprotected light signal. Bell’s idea languished. Instead of sunlight, microwaves and radio waves - which are less affected by the atmosphere - became the media of choice.

As the demand for communication grew, the problem with microwaves and radio waves became apparent: they couldn’t carry enough information. Shorter-wavelength light could carry more. Eventually, Bell’s idea of optical communication resurfaced, as did the problem of how to protect the light.

drawing optical fiber

Light can carry a lot of information, but it needs something to guide it. Mirrors and lenses had been tried, but had proved impractical. There seemed only one choice: glass fibers.

The problem was that fibers made from ordinary glass absorbed too much of the light signal. In 1964, Charles Kao, an engineer at Standard Telecommunications Laboratories in England, made a critical calculation. If the impurities were removed from glass, enough of the signal would get through to make an optical communication system a reality. Around the world, scientists raced to purify glass and use it to make optical fiber.

Corning Glass Works already had the world’s purest glass: fused silica. Physicist Robert Maurer decided to use it to form the cladding, or skin, of the fiber. With the help of chemist Peter Schultz and physicist Donald Keck, he made the fiber’s core from fused silica with the added element titanium. The “extra” element changed the optical properties of the core glass in a way that ensured that the light would be totally reflected inside the fiber.

On an August day in 1970, Keck set out to measure the latest prototype. When he looked at the end of the fiber through a microscope, the light was so bright, he said, that “it hit me in the eye.” That first low-loss optical fiber sparked the telecommunications revolution—and catapulted us into the Information Age.

The Corning Museum of Glass
This article was originally published in Innovations in Glass, 1999, pp. 42–43.

Published on October 25, 2011