This week marks the death of Sir Charles Kuen Kao, one of modern networking’s pioneers. He died on Sunday 23 September 2018, aged 84. Born in Shanghai in 1933, Charles Kao moved later to Hong Kong where he completed his secondary education. He came to the UK to gain a Bachelor of Engineering degree. In later years, he would be diagnosed with Alzheimer’s, and created a foundation to promote awareness and brain-care activities.
Work on the physics of fiber
Here he joined Standard Telecommunications Laboratories (STL), the research arm of Standard Telephone and Cables (STC), part of ITT. Here in July 1966, he released (alongside G. A. Hockham), the seminal paper on Dielectric-fiber surface waveguides for optical frequencies. (Although STC published a press-release on Communication by Guided Light earlier in the year). This paper covers a lot of the primary issues that are present (even today) with fibre optic transmissions. These include losses from the dielectric media (the fibre itself), from bends, and dispersion. The paper covers both theoretical and experimentally deduced data which today provide the fundamental elements of fibre transmission.
The challenge of optical loss
But, at the time, optical fibers failed to meet the primary constraint, primarily that of loss. In 1966 fiber optic cables typically provided a signal reduction of 1,000db/km or more. Kao determined that the level should be less than 20db/km. So the race was on to develop the low-loss fibre optics to deliver this. The development of new fibers was a bigger challenge than you think, as the decibel scale is logarithmic, meaning the difference between 1,000 and 20 is not 500x, but 10e48 times.
In 1969, Kao discovered that Silica blocks would produce a loss of less than 10db/km. From that discovery, it didn’t take long before Corning was producing fibre optic cables with less than 4db/km loss (a 50% improvement), delivering them in 1972.
Turning theory into reality
From here, the work now focused on turning this into the reality of delivering information via fibre optic cables. In 1973, STC provided a commercial connection using fibre optics. This replaced a damaged co-axial cable from a radio mast with a fibre connection. This used one of fiber’s most compelling advantages, which was resistance to electrical and magnetic fields. (A lightning strike destroyed the previous copper co-axial cable, so not having a metallic path was an advantage)
Later on, in 1977, STC worked on an experimental delivery of a 140Mb/s fibre optic cable between Hitchin and Stevenage. Over 9km long, this used multi-mode fibre. The route required the development of fibre optic cable splices, connections, and electro-optical transfers for the six regeneration points.
The challenge of covering longer distances and reducing the number of regeneration points meant overcoming the “noise” introduced by multi-mode fibre. Noise causes dispersion, and is defeated primarily by a move to single mode fibres. Single-mode fiber means that the light is channelled through a smaller tube, effectively corralling it into a single path. This avoids the smearing of the light signal that occurs with multi-mode fibre, where each track taken from the source is a slightly different distance depending on the angle of bounce inside the fibre.
This move led to another trial, this time across Loch Fyne in Scotland, in 1980. In 1985, the first international subsea fibre optic cable was laid between the UK and Belgium. Just three years later, in 1988, the TAT8 cable was laid across the Atlantic as the first transoceanic fibre cable. Providing a significant increase in bandwidth between the UK and the USA, providing 280Mb/s of bandwidth.
The impact of extra bandwidth
The provision of a dedicated T1 link (1.5Mb/s) between Cornell University (Ithaca, New York, United States) and CERN, (Geneva, Switzerland) funded by IBM allowed Tim Berners-Lee to have a direct connection to the NSFnet, and allowing for the development of the World Wide Web.
Awarded a Nobel Prize for Physics
Kao’s work on the underlying physics of optical fibres gained recognition with the award of the Nobel Prize for Physics in 2009. His contribution was for:
for groundbreaking achievements concerning the transmission of light in fibers for optical communication
Technically, Kao received half of the prize. Willard Boyle and George Smith shared the other half, for their work on using charge-coupled devices as sensors. Mobile phone cameras are probably now the most significant use of charge-coupled devices.
A worldwide recognition
Posthumously, many leading news outlets recognised Sir Charles Kao’s work. These news outlets show the impact that instant global communication on fibre optic networks has in our society today.
Sources:
The Comet, (the local newspaper that covers Stevenage and Hitchin) (Sir Charles Kao: Inspiration for 1977 Stevenage-Hitchin Fibre optic trial dies).
The South China Morning Post (Hong Kong mourns passing of Nobel Prize winner and father of fibre optics, Charles Kao, 84).
The New York Times (Charles Kao, Nobel Laureate Who Revolutionized Fiber Optics, Dies at 84).
BBC (Sir Charles Kao: Fibre optics genius passes away).
