Professor Charles Kao launching light from a laser into an early optical fibre at STL, Harlow © Nortel
If anyone can lay claim to having rewired the planet it is Professor Charles Kao. The first person to propose a practical optical fibre communication system, he helped to lay the technological foundations for the internet. Last year’s Nobel Prize was one of a long line of accolades and awards for this electrical engineer. On 17 June he will be honoured once more by The Royal Academy of Engineering at a special event marking 50 years of lasers and their applications. Michael Kenward talked to people who know him and his work.
When Professor Charles Kao collected his share of the 2009 Nobel Prize for Physics, it was not his first visit to Stockholm to shake hands with the King of Sweden at an awards ceremony. It also happened in 1979, when he shared the LM Ericsson International Prize with Robert D. Maurer “for fundamental contributions to the long-distance transmission of information through optical fibres”. As the IEEE reported at the time, “Kao has demonstrated the possibility of using glass fibres for telecommunication, while Maurer has had a decisive part in the development of such fibres.”
It might seem odd that Kao collected an ‘engineering’ award 30 years before receiving the ultimate accolade for scientific achievement. Engineering usually follows science in such things. But there is no Nobel Prize for engineering and the physics prize rarely lands in the hands of someone whose science set out to change the face of technology rather than science. Rare too is the award of the Nobel prize for work that happened in a company laboratory. Kao, who did his prize winning work in the mid 1960s at Standard Telecommunication Laboratories (STL) at Harlow in Essex, really must have done something striking to have caught the attention of the Nobel Foundation.
Wave studies in Woolwich
Kao had arrived at Standard Telephones and Cables (STC) a part of ITT, from his first degree at Woolwich Polytechnic, now the University of Greenwich. Kao travelled from Hong Kong to Woolwich, then famous for its defence establishment and not much else, to study electrical engineering. Born in Shanghai in 1933. Kao’s family had moved to Hong Kong when he was a teenager. Like many Asian youngsters after him, Kao decided to come to the UK to study. With his degree behind him, he worked as a graduate engineer for STC’s Woolwich factory on millimetre wave transmission.
In 1960, Kao moved into the company’s research and development operations at STL in Harlow, initially conductiong “routine R&D”. Kao’s boss encouraged the young engineer to study for a doctorate while working at STL. He registered at University College London and within two years he had completed his dissertation on ‘quasi-optical waveguides’.
When Kao started his career in telecommunications, telephones were still a relative luxury for many people. Apart from making voice calls, just about the only other thing that most people could do on a telephone line was to operate a telex machine.
In the 1960s, new applications and a growing demand for telecommunications were putting pressure on telephone networks. Engineers sought ways to increase the capacity of telephone systems, especially long-distance links. At the time, telecoms engineers thought that the best approach was to build networks of microwave towers. When the traffic had to go underground and in exchanges, microwave waveguides – carefully engineered hollow metal ‘pipes’ – would have a much higher capacity of bandwidth, than the copper cables they would replace.
“When we increased the frequency of the carrier, we could get the carrier to carry more information,” Kao told Robert Colburn in an interview for the IEEE History Center in 2004. An alternative approach, and one that could get even more bandwidth, would be to move even higher up the frequency spectrum into optical frequencies. Around the time that Kao was working on his PhD, Theodore Maiman demonstrated the first functioning laser in 1960.
Dr Charles Kao receives the Academy’s Prince Philip medal from HRH The Duke of Edinburgh in 1996 for “his pioneering work which led to the invention of optical fibre and for his leadership in its engineering and commercial realisation; and for his distinguished contribution to higher education in Hong Kong”.
Lasers were still exotic research devices when Kao started research in telecommunications. Telecoms engineers did not, at first, take them seriously as something they could use in day-to-day operations. As Kao’s wife, Gwen, said on his behalf in last year’s Nobel address: “In 1960, optical lasers were in their infancy, demonstrated at only a few research laboratories, and performing much below the needed specs. Optical systems seemed a non-starter. Charles still thought the laser had potential though. He said to himself: ‘How can we dismiss the laser so readily? Optical communication is too good to be left on the theoretical shelf.’
Kao was the first person to think seriously about replacing copper with glass as a carrier of telecommunications traffic. Everyone said that glass was a hopeless medium: light would scatter and lose intensity before it could travel far enough to be a practical telecoms channel. Kao and George Hockham, the theoretician in the team, thought otherwise and set to work on the idea in 1965.
One challenge they faced was to find a source of light that they could send down optical fibres. Kao talks of working with “a laser that dies every few hours”. This is where Peter Selway (now an Academy Fellow), who had joined the lab in 1963, entered the picture. Then in charge of a group at STL that was working on semiconductor lasers, Selway met Kao in 1968. “We were developing light sources”, says Selway, “aware of interesting but mysterious doors down the corridor that were labelled ‘Optical Communications’.”
The two worked together when Kao not only asked for some lasers but turned up at Selway’s door with a set of specifications for light sources. Kao wanted something that was about two micrometres square and that would work continuously at room temperature, delivering a few milliwatts for at least 10,000 hours. These were the early days of semiconductor lasers. Selway could offer something ¼ millimetre wide, 100times too big. They had to cool their lasers with liquid nitrogen: even then the devices heated up and could only deliver short pulses. They also typically only lasted for a few hours. Kao would not take ‘no’ for an answer. “He correctly forecast that we would solve these problems and that he would get what he wanted. However, at the time we thought he was little bit crazy”, says Selway.
Kao could produce specifications for light sources because he took an analytical approach to his engineering. Looking at the challenge from a system viewpoint, he analysed the telecommunications network and calculated what it would take to replace copper with optical fibre. Knowing the spacing between repeaters in existing networks, Kao calculated how far light had to travel between repeaters if optical communication was to compete with conventional techniques. He concluded that fibre stood a chance if light losses were below 20 decibels per kilometre.
In 1966, Kao and Hockham published their first paper, Dielectric-fibre surface waveguides for optical frequencies. Hockham had worked on theoretical aspects of optical fibres while Kao studied light losses. Gwen Kao recounts that the paper appeared in July 1966 – the date now regarded as the birthday of optical fibre communication.
The paper certainly covered many of the issues that went on to become key aspects of optical telecoms. Kao and Hockham put forward the idea of cladding the core of the glass fibre, the part that carried the light, with a sheath of glass with a lower refractive index, confining the light in the core. They also laid out the losses expected of optical fibres and the foundations for the use of ‘single-mode fibre’.
On the way to achieving those goals, Kao’s team had to grapple with problems such as light coming out of the fibre as it went round corners and the effect of water vapour on fibres. “It took us nearly three years to complete the fundamental research to make sure that everything on the chemical and on the material science side was proven,” said Kao “I think it was a very respectable bit of detective work as well as good theory and good fundamentals.”
A major task for Kao was to persuade the telecommunications industry that his idea wasn’t far-fetched and to ensure that fibres could be made in industrial quantities. This part of the jigsaw began to fall into place in 1970, when Corning demonstrated a fused silica fibre waveguide with a loss of 17 dB/km. This put it in the right ballpark as far as Kao was concerned. By making 100 metres of fibre, Corning had also paved the way for commercial production.
The significant role that Corning played in the success of fibre optics explains why Kao shared the LM Ericsson International Prize in 1979 with Robert Maurer, who worked for the glass company. By then glass waveguides had achieved attenuations below 1 dB/km.
Kao realised that he had to sell the very idea of optical communications. Surprised by how much he was ‘giving away’, some urged secrecy on Kao. As Selway says: “Charles said, ‘No, it will get nowhere unless we get more people involved’.” Gwen Kao recalls that: “He said that until more and more jumped on the bandwagon, the use of glass fibres would not take off. He had tremendous conviction in the face of widespread scepticism.”
Kao talked about his ideas to anyone who would spare him time. Some laboratories listened politely and did nothing. There was more enthusiasm in Japan than in the USA, Selway recalls, but there was no mad scramble to commercialise optical fibre. Gwen Kao recalls that it took time: “The global telephony industry is huge, too large to be changed by a single person or even a single country, but he [Kao] was persistent and his enthusiasm was contagious, and slowly he converted others to be believers.”
Fortunately, Kao found a receptive audience near to home. The predecessor of British Telecom (BT), the Government owned Post Office, was an early enthusiast for optical fibres. Following Kao’s lead, the business set up an research and development team, as did the Ministry of Defence and Southampton University which, to this day, is at the forefront of research into optical communications.
In the mid 1970s, BT opted to build a wholly digital telephone network built around optical fibre. By 1995, optical fibre carried more than 90% of BT’s traffic. Research and development continued apace throughout the 1970s, with the first fibre optic cables to carry live traffic coming into operation in April 1977.
Today, networks of hundreds of millions of kilometres of optical fibres crisscross the planet, over land and under the oceans. Transmission capacity has risen – from 45megabit per second in 1976 to tens of terabits per second. The first trans-Pacific copper telephone cable could handle 91simultaneous phone calls. Today’s optical cables can handle more than 1.6billion simultaneous calls.
Passing the baton
Kao’s technical achievements gained him professional recognition and numerous awards which inevitably eclipsed the many things he did later. He went on to play a major part in the development of university education in Hong Kong. In 1970, he took time out from STL to set up an electronics department at the Chinese University of Hong Kong. Then, in 1974, it was back to ITT, this time in the USA as director of research. In 1987, Kao returned to Hong Kong as the third vice-chancellor of the Chinese University, a job he held until he retired in 1996. He wanted to create a university that, in line with the growth of Hong Kong itself, could hold its own internationally.
Selway’s view is that had Kao not gone into industrial research he would have made a good professor. “He wasn’t a hand-waving engineer. He wanted to understand the maths.” Kao wanted rigour in his engineering.
Kao also advised the Hong Kong Government on education and technology and became involved in projects on environmental issues. He then went on to create what he called his third career, when he set up his own company to specialise in technology transfer. Throughout all this work he was called upon for advice on optical telecoms.
By the time the call came from the Nobel Foundation, the onset of Alzheimer’s disease had prevented Kao from playing a full role in the celebrations. But he had already seen his ideas change the face not just of telecoms but also of society.
Kao’s impact on his chosen domain, telecommunications, matched that of another Nobel Laureate, Guglielmo Marconi. Exactly a century before Kao, Marconi shared the physics prize with Karl Ferdinand Braun “in recognition of their contributions to the development of wireless telegraphy”.
Some argue that Kao’s discovery was as important as Marconi’s. His thinking was genuinely original. In research, ideas often arise because the time is right. Jeff Hecht, author of City of Light: The Story of Fiber Optics, sometimes described as the ‘bible’ of optical communications, believes that Kao was different: “I would argue that had Charles Kao not asked the right question and believed the answer so strongly that he campaigned for it, fibre optics would likely have been a couple of decades behind the current state of the art, and our global telecommunications network would be far more clogged and costly than today’s fibre optic network.”
The true test of Kao’s breakthrough, a word that is, for once, justified, will be in the longevity of optical communications. “It is hard to think of anything that will replace fibre,” says Selway. Kao agrees: “I cannot think of anything that can replace fibre optics,” he told Radio Television Hong Kong. “In the next 1,000 years, I can’t think of a better system. But don’t believe what I say, because I didn’t believe what experts said either.”
Film of the Nobel Prize Awards can be seen at: http://nobelprize.org/nobel_prizes/physics/laureates/2009/kao-lecture.html
Ingenia is grateful to the IEEE History Center, Rutgers University, New Brunswick, NJ, USA for permission to quote from an oral history interview of Professor Kao conducted in 2004 by Robert Colburn, Research Coordinator.