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Happy 50th birthday, optical fibres for telecoms

In July 1966, Charles Kao looked into glass and saw the future of telecoms

By Richard Chirgwin, 18 Jul 2016

One of the seminal developments in modern telecommunications turns 50 years old this month: the paper that bootstrapped the world of optical fibre communications.

With this publication in the July 1966 issue of Proceedings of the Institution of Electrical Engineers (now the IET), Charles Kao upended then-current research into using lasers for communications.

Researchers already knew lasers could be used for communications, but were convinced the best application was either in free space optics or using some kind of hollow waveguide.

Kao's big contribution to the world we now live in was to determine that if a glass fibre was sufficiently pure, attenuation in it would be low enough to carry a signal far enough to be useful for telecommunications.

As the IEEE relates, Kao was working in the UK's Standard Telephones & Cables (later part of Nortel, while its Australian arm was acquired by Alcatel) under Antoni Karbowiak, who was trying to make plastic optical waveguides.

Kao and other researchers – the IEEE singles out Rudolf Kompfner at Bell Labs – knew it was impurities in the glass that were the problem.

Their paths diverged when Kompfner looked at the best glass then available: finding its attenuation was thousands of decibels per kilometre, he continued with Bell Labs' focus on hollow waveguides, while Kao searched for high-purity materials for fibres.

After Karbowiak left STC to take up a university post in Australia, Kao worked with the University of Sheffield's Harold Rawson on that engineering problem, and with his assistant George Hockham published the 1966 paper.

That sparked an international research effort. Kao's original question to Rawson was whether 20 dB of attenuation per kilometre was feasible; by 1979, Corning was making fibres with 0.2 dB/km attenuation, and fibre's future in the telecommunications network was assured.

Indeed, it's highly likely that Kao's ideas played a part in bringing you this very Reg story.

Kao shared the 2009 Nobel Prize for Physics for his 1966 paper with the inventors of charge-coupled devices (CCDs). ®

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