In 1966, a young researcher working in a Harlow laboratory published a paper that would transform global communications forever. Charles K. Kao, then head of the electro-optics research group at Standard Telecommunication Laboratories in Harlow, demonstrated that glass fibres could carry light signals over long distances. This discovery laid the foundation for the fibre optic networks that power today's internet.
The Laboratory on the Edge of Town
Standard Telecommunication Laboratories (STL) had moved to Harlow from Enfield in 1959, becoming one of the new town's first major technology employers. The research centre, owned by Standard Telephones and Cables (STC), employed hundreds of scientists and engineers working on cutting-edge telecommunications technology.
Charles K. Kao joined STL in 1963 and was appointed head of the electro-optics research group that same year. When his supervisor Antoni Karbowiak left in December 1964 to take a university chair in Australia, Kao took over the optical communications programme. He was working towards his PhD at University College London whilst conducting his research in Harlow, earning his doctorate in 1965.
Kao met his wife Gwen Wong May-Wun at STL; they married in London in 1959 and raised two children in Harlow, both born during the 1960s whilst the family lived in the town.
The 20 dB/km Threshold
At the time Kao began his work, optical fibres suffered from severe light loss; commonly as high as 1,000 decibels per kilometre. This made them impractical for anything beyond very short distances. Kao and his colleague George Hockham, who had joined STL Harlow in 1961, set out to determine whether the problem was fundamental to glass itself or could be overcome.
In 1965, Kao and Hockham concluded that the fundamental limitation for glass light attenuation was below 20 dB/km, a figure that became the crucial threshold for optical communications to become viable. Kao demonstrated that impurities in the glass material, not fundamental physical effects like scattering, caused the dramatic loss of light transmission. Such impurities, he argued, could be removed.
He identified fused silica (SiOβ) as an ideal candidate for optical communication due to its high purity. In 1969, Kao and M. W. Jones measured the intrinsic loss of bulk-fused silica at 4 dB/km, providing the first evidence of ultra-transparent glass.
Publication and Initial Scepticism
The results were first presented to the Institution of Electrical Engineers in London in January 1966. The paper, titled "Dielectric-fibre surface waveguides for optical frequencies," was published in the Proceedings of the IEE in July 1966. It established the electromagnetic theory and performance parameters still used in fibre optic communications today.
Initial reception was far from enthusiastic. Kao's proposal that glass fibre could be used for long-distance information transfer was widely disbelieved. Professor Charles Midwinter of UCL later told the BBC that "a lot of people just openly laughed at the paper."
Kao himself recounted telling his wife that the project could be "world shaking," only to be met with absolute disbelief. It was not until 1970 that Corning Glass Works finally broke the 20 dB/km barrier, proving Kao's theory correct. By 2017, fibre optic losses had fallen to as low as 0.1419 dB/km.
The Birthplace of a Revolution
STL Harlow is now recognised as the birthplace of optical fibre communications. David Devine of Harlow Museum stated: "What Kao did in Harlow transformed the world and provided a backbone for the internet. He was the father of fiber optics."
Kao's work became the foundation for the internet and World Wide Web. He became known as the "godfather of broadband," the "father of fibre optics," and the "father of fibre optic communications."
Recognition and Return
Kao's contributions earned him the Nobel Prize in Physics in 2009, awarded "for groundbreaking achievements concerning the transmission of light in fibers for optical communication." He shared half the prize, with the other half awarded to Willard Boyle and George Smith for their work on the charge-coupled device.
The following year, Queen Elizabeth II knighted him "for services to fibre-optic communications." His other honours include the Rank Prize for Optoelectronics (1978), the Marconi Prize (1985), the Japan Prize (1996), and election as a Fellow of the Royal Society.
Kao's parents moved to Harlow in 1967 to join him, and his father's ashes were later laid to rest in a Harlow cemetery, cementing the family's connection to the town.
Kao Park: A Lasting Legacy
The original STL site, which later became a Nortel facility after STC was acquired in 1991, has been redeveloped as Kao Park, a science and technology business park named in honour of Charles K. Kao. The park's developers describe it as the site where "Sir Charles Kao and George Hockham made a groundbreaking discovery: data could be transmitted through optical fibers."
Today, Kao Park continues Harlow's technology heritage, housing businesses in the same location where one of the most significant communications breakthroughs of the twentieth century took place. For Harlow residents, it stands as a reminder that world-changing innovation happened not in London or Silicon Valley, but right here in Essex.