“Dielectric-fibre Surface Waveguides for Optical Frequencies,” published by Charles K. Kao and George Hockham in 1966, established the theoretical foundation for fiber optic communication. This paper demonstrated that glass fibers could transmit light over long distances, launching a technological revolution that now carries over 99% of the world’s international data traffic.
Background
By the 1960s, telecommunications networks were straining under increasing demand. Copper cables had limited bandwidth, and radio spectrum was becoming congested. Light, with its vastly higher frequencies, offered theoretically enormous bandwidth—but no practical medium existed for guiding it over long distances.
Early optical fibers existed, but they could only transmit light for about 20 meters before the signal degraded beyond usefulness. Most scientists believed this was an inherent limitation of glass[1].
The Breakthrough
Working at Standard Telecommunication Laboratories (STL) in Harlow, England, Kao and Hockham conducted careful research into why optical fibers lost light so rapidly. Their crucial discovery: the loss was not intrinsic to glass itself but was caused by impurities—primarily metal ions and water.
Their 1966 paper made a revolutionary prediction: if glass could be purified to remove these impurities, optical fibers could achieve losses below 20 decibels per kilometer (dB/km)—making them practical for telecommunications[2].
This was far below the 1,000 dB/km typical of fibers at the time—a 50-fold improvement that seemed almost impossible.
Key Technical Insights
The paper established several fundamental principles:
Single-Mode Fibers
Kao showed that fibers with very small cores (a few micrometers) would support only a single propagation mode, eliminating dispersion problems that degraded signals in larger fibers.
Material Purity
The paper identified specific impurities causing absorption and specified the purity levels required—glass with fewer than one part per million of critical impurities.
Wavelength Selection
Kao determined optimal wavelengths for transmission, avoiding absorption bands where glass naturally attenuates light.
Making It Real
Kao didn’t stop at theory. He traveled worldwide, visiting glass manufacturers and encouraging development of ultra-pure glass. His advocacy sparked an international race:
- 1970: Corning Glass Works produced the first fiber meeting Kao’s specifications
- 1977: First commercial fiber optic telephone system installed in Chicago
- 1988: First transatlantic fiber optic cable (TAT-8)
- 2000s: Fiber replaced copper for most long-distance communication
Modern Fiber Optic Technology
Today’s fiber optic systems far exceed Kao’s initial predictions[3]:
- Loss: Modern fibers achieve 0.2 dB/km—100 times better than Kao’s target
- Bandwidth: A single fiber can carry tens of terabits per second
- Distance: Signals travel thousands of kilometers between amplifiers
- Capacity: Wavelength division multiplexing transmits many signals on one fiber
Impact
Fiber optic communication transformed global telecommunications:
- The Internet: Fiber backbone networks make the modern internet possible
- Transatlantic communication: Submarine cables carry 99% of intercontinental data
- Telephone networks: Long-distance and increasingly local calls travel over fiber
- Cable television: Fiber-to-the-home delivers TV and internet
- Data centers: Fiber connects servers within and between facilities
Nobel Prize
In 2009, Charles Kao received the Nobel Prize in Physics “for groundbreaking achievements concerning the transmission of light in fibers for optical communication.” He shared the prize with Willard Boyle and George Smith, who invented the CCD image sensor.
The Nobel committee noted that Kao’s work “laid the foundation for the fiber-optic networks that today carry most of the world’s communication traffic.”
Sources
- Nobel Prize. “The Nobel Prize in Physics 2009.” Background on fiber optics before Kao.
- Nature. “Kuen Charles Kao (1933–2018).” The breakthrough discovery.
- Wikipedia. “Fiber-optic communication.” Modern technology and applications.