Overview
Charles Kuen Kao (1933–2018) demonstrated in 1966 that the attenuation of light in glass fibre was caused by impurities rather than by any intrinsic property of glass, and specified the purity required for practical long-distance optical communication. He shared the 2009 Nobel Prize in Physics. Every submarine cable and fibre network in the world rests on that finding.
What You Need
- Lived: 1933–2018, China, worked in Britain, the US and Hong Kong
- Anchor year: 1966 — the fibre attenuation paper
- Strand: canon
Steps
The problem as it stood
Optical fibres of the early 1960s lost about 1,000 decibels per kilometre — a signal was gone within metres. The consensus was that this was intrinsic to glass, making optical communication a non-starter over any useful distance.
What he actually did
Kao, at Standard Telecommunication Laboratories in Harlow, analysed the sources of loss and showed the dominant term was absorption by impurities — particularly iron and other transition metals — not scattering intrinsic to the material. He specified the target: below 20 dB per kilometre, which he argued was achievable with sufficiently pure silica.
How it worked
Separating intrinsic loss from extrinsic loss changes the problem from a physical limit into a purification target. Corning reached 17 dB/km in 1970; modern fibre achieves around 0.2 dB/km, meaning light travels tens of kilometres before needing amplification.
What it made possible
The physical layer of the modern internet. Intercontinental submarine cables, backbone networks and fibre to the home all depend on it — and streaming video, which moves far more data than broadcasting ever did, is only economic because fibre capacity is effectively enormous.
What happened to him
He became vice-chancellor of the Chinese University of Hong Kong, shared the 2009 Nobel Prize, and was diagnosed with Alzheimer's disease around the time of the award. He died in 2018.
Where the credit landed
Kao is properly credited and Nobel-recognised, and his contribution is frequently described as inventing fibre optics, which it was not — fibres existed and Narinder Singh Kapany had demonstrated image transmission through bundled fibres in the 1950s. Kao's contribution was the diagnosis that made low-loss fibre a target worth pursuing, which is a different and arguably harder kind of insight.
Pro Tips
- He reframed a supposed physical limit as a purification problem.
- Modern fibre reaches ~0.2 dB/km, against ~1,000 dB/km in the early 1960s.
- He did not invent optical fibre; he showed low-loss fibre was possible.
Knowledge Base
What You'll Learn
The most valuable result here was a diagnosis, not a device.
Why streaming needed fibre
Broadcasting sends one signal to everyone, so its cost is independent of audience size. Streaming sends a separate stream to every viewer, so cost scales with the audience — an approach that is absurd unless bandwidth is extraordinarily cheap. Fibre is what made it cheap enough. The economic inversion at the end of this corpus, from one-to-many to one-to-one delivery, rests directly on Kao's finding.
Where This Fits
This guide covers one specific part of the history of media technology. The wider picture — how each link in the chain from capture through transmission to display was actually built, who built it, and why the credit so often landed somewhere else — is in A History of Broadcast Technology: The Chain From Capture to Screen, which frames the discipline as a whole and links out to the detailed guides underneath it, including this one. If you are starting from scratch rather than solving a specific problem, read that first and come back here.
FAQ
Q: Did Charles Kao invent fibre optics?
A: No. Optical fibres already existed and had been used for image transmission. Kao showed in 1966 that their high loss came from impurities rather than from glass itself, and specified the purity needed for practical long-distance communication.
Q: How much better is modern fibre?
A: Early 1960s fibre lost roughly 1,000 decibels per kilometre. Corning reached 17 dB/km in 1970 and modern fibre achieves about 0.2 dB/km.