Fiber-Optic Communications

In 1987, both Eli Yablonvitch and Sajeev John got together to discuss research that both had previously discovered. Eli Yablonvitch was an electrical engineer at Bell Communications Research in Red Bank, New Jersey. Yablonvitch was known for refining a laser that would become a mainstay of fiber-optic communications. Sajeev John is a Harvard graduate student who worked on a thesis inspired by Philip Anderson of Princeton.

The two agreed that the name of their idea should be called a photonic band gap. Phontonic crystals have the regular lattice structure of natural crystals. Their purpose is to try and trap light without destroying it. The trick is to not kill the photons but to tame them, by allowing light out when you want. Microchips are made of semiconductors and a semiconductor is a band gap. A band gap makes is possible to control the flow of electricity in a chip. In order to make light chips, you need the photonic equivalent of silicon: a material that can trap light. "You need a way of trapping the light so there are no escape channels," says John.

It was until 1997, when European investigators succeed in trapping light in a random material. Diederik Wiersma and his colleagues used a powder of gallium arsenide. The laser could not penetrate a layer of powder even when the layer was less than a hundredth of an inch thick. It was indeed the very first time that anyone had trapped light, but as they knew, microchips cannot be made out of powder.

Yablonovitch was in his office on day in October 1986, "I started drawing crisscrossing lines, and everywhere the lines crossed I put a heavier mark. Before I knew it I had drawn a checkerboard. And then I said, 'Well, I might as well do it in three dimensions.'" This later became known as Yablonovitch's "eureka moment." He realized that what he had drawn was a crystal structure that might trap light through interference. Interference happens when two light waves of the same wavelength meet.

The Bragg reflection is when light waves pass through one plane but is reflected back by the next plan. All waves that interfere constructively intensify the reflected light. Yablonovitch found that if you could design a crystal that Bragg-reflected light now which direction is was coming from, you would have built a trap. Finding a way to build this crystal was the hardest project. The wavelength of