How light in glass made the global digital era possible

Since Alexander Graham Bell invented the telephone in the 1870s, much information was transmitted through copper cables: a good solution, but one that had some drawbacks. The farther the telephone signal traveled, in fact, the weaker or more “attenuated” it became.

The engineers working at AT&T, the company founded by Bell, tried for years to solve the problem. To strengthen the signal, they built thicker and more rigid cables, installed coils and amplifiers, and invented thermionic valves (made of thin blown glass). These new technologies proved effective and reliable, and AT&T connected every corner of the United States through these copper cables; in the 1950s it extended the network to the opposite shore of the Atlantic (thus replacing the slow and inadequate nineteenth-century transatlantic telegraph).

Copper wire, however, is able to carry a limited amount of information at a reduced speed. In the 1960s, at STL, the research division of Standard Telephones and Cables, Charles Kao made the discovery that would revolutionize long-distance communications, ushering in the era of optical fiber, the one we live in today.

The importance of this innovation cannot be overstated. All modern communication passes, in one way or another, through optical fiber. Data travel for kilometers in the form of beams of light along strands of glass.

Come la luce nel vetro ha reso possibile l’era digitale globale

An optical fiber is essentially a long glass cable or, more precisely, two long glass cables fitted one inside the other: the inner one is used to transmit information, the outer one ensures that the light reflects and refracts back into the fiber instead of dispersing outward.

Kao's discovery in the 1960s was that light could be sent for tens of kilometers through these fibers provided that the glass was sufficiently transparent.

The problem at the time was that the best optical glass, manufactured using conventional methods, could carry light only for about ten meters. Kao then set out to find an even purer glass and found fused silica glass. He calculated that with this material light could travel for kilometers with almost no signal loss. And since the bandwidth of thin fibers was decidedly greater than that of large copper cables, even an extremely thin strand could carry a much greater amount of information.

The invention of optical fiber was, as happens with most great discoveries, a synthesis of intellectual ability and materials science. These fundamental innovations and their creators are seldom remembered, but Kao was awarded the Nobel Prize in Physics in 2009 and was knighted by Queen Elizabeth II the following year.