Brains that made a difference

Forgive the question but have you had a colonoscopy yet? If the answer is yes, you can thank Charles Kao, Willard S. Boyle and George Smith, who won the 2009 Nobel Prize in Physics. Four decades ago, the men produced key scientific insights that have led to fibre-optic data transmission and digital photography. Those two technologies today exist side by side — or more precisely, one in front of the other — in the endoscopes that are ubiquitous in diagnostic medicine and surgery. Of course, fibre-optic cable is responsible for carrying much of the information, voices and pictures that course around the planet. And "charge-coupled devices", or the guts of digital cameras, have changed the recording of images from a chemical process into an electronic one.

Rarely has a Nobel prize been so indisputably relevant to the ordinary person. Although the discoveries involve important theoretical insights, they both arose from serious wrestling matches with practical problems. In the early 1960s, Kao was an engineer at Standard Telecommunication Laboratories, the research arm of a British telephone company. His assignment was to see whether light might be an alternative to microwaves as a vehicle for transmitting information over long distances. Since light beams sent through the atmosphere were not stable, Kao considered the possibility of using glass as a conduit. While light normally passes through glass and does not go around corners, Kao's work is proof that under the right conditions, those generalities do not hold true. Sometimes light can be kept inside a strand of glass.

This is achieved by exploiting light's tendency to bend when it passes from one transparent medium into another — the phenomenon called "refraction". Kao and other physicists realised that if a beam of light was aimed down a glass fibre that had specific optical properties, the angle at which the light was refracted when it hit the glass-to-air boundary would keep some of the beam inside the fibre, basically bouncing between the walls.

But only 1 per cent remained after travelling a distance of 50 feet. The rest of the beam had been scattered through the glass or absorbed by the atoms and molecules in the glass itself. It seemed hopeless until Kao and a theoretician colleague, George Hockham, made some measurements and calculations. They determined that if the impurities scattering the light rays could be removed from the glass, and if they used a wavelength that the glass molecules could not absorb, then much, much more light would stay inside the fibre. Four years after Kao and Hockham's 1966 paper, Corning Glass Works in the United States produced a strand of glass with the properties the researchers outlined. Today, optical fibres — covered with a coating that prevents a glass-glass interface when they are bundled together — preserve 95 per cent of light at the end of a kilometre.

Kao remarked on the lucky confluence of things. "The material is very cheap, as I went to the most abundant material on Earth," he said. Silicon, the main constituent of glass, is 26 per cent of the planet's crust by weight. Boyle and Smith also exploited silicon. In the 1960s, at Bell Laboratories in New Jersey, they were working on ways to improve memory devices — a way of storing information acquired over time. The goal was to eliminate the annoying echo that sometimes occurred in very-long-distance telephone calls.

They used an array of small squares made from silicon-based semiconductor material. "Semiconductors" are capable of generating an electrical charge, although not as readily as metals and other conductors (hence their name). Electrodes placed nearby can then be used to hold the charges in place and keep them from dispersing. A line of small semiconductor squares called "pixels" outfitted with electrodes were able to hold a row of different charges. If a voltage was then applied to the array in the right fashion, the charges could be moved off the pixels and "read out".

In 1969, Boyle and Smith built a prototype of their device. When they tried it out, however, they noticed it worked much better when the lights were off in the lab. After some pondering, they realised that light falling onto the semiconductor chips was being transformed into electrical energy. With the lab lights off, that interference disappeared. "They realised they had made an imaging device," said Anthony Tyson, who was at Bell Labs with the two men.

By combining the photoelectric effect and the ability to hold and move an entire array of charges in an organised fashion, they created the basis for digital photography. As it turns out, a "charge-coupled device", as these image sensors are called, is 100 times as sensitive as photographic emulsion in detecting light, which makes it perfect for Tyson's present project.

He is director of the Large Synoptic Survey Telescope, slated to start construction next year on a mountaintop in Chile. It will contain a 3 billion-pixel digital camera, the largest in the world. Scheduled for completion in 2015, the LSST will eventually produce an ultra-sensitive film of the sky available for public viewing in real time. "It will be a completely new window on the universe, enabled by the device that Smith and Boyle invented. Already the CCD has produced advances in many fields, from biomedicine to the discovery of cosmic dark energy," Tyson said.