Light Goes on a Bender

Massachusetts Institute of Technology researchers have developed a new type of cable that can quickly and efficiently shoot light over long distances and around sharp bends.

At optical wavelengths, networking vendors use nonmetallic “dielectric” coaxial cable – made of silica or another crystalline material – because conventional cables absorb too many signals. The technology works well, except for two big problems: polarization (the orientation of the light waves) changes between the points where the light enters and exits the cable, causing coupling problems for devices such as switches and routers. Additionally, light inside a dielectric cable cannot bend in a radius of less than 3 millimetres, complicating installation.

MIT researchers designed their cable to solve both problems. The technology uses a new kind of mirror, composed of dielectric materials that reflect light for all polarizations and from all angles with very little loss. In the new cable, light shoots down a hollow dielectric core until it reaches its destination.

“It’s a perfect mirror,” says John Joannopoulos, the Francis Wright Davis professor of physics at MIT who led the research team. “You get out of it what you put into it, since light retains its polarization.” The cable can also be bent into tight corners.

To visualize how the cable works, think of a sheet of plywood that has been shaped into a long, hollow tube. But instead of wood, imagine the tube is composed of alternating layers of dielectric materials that form a mirror. An empty passage for the light lies at the tube’s core.

According to Joannopoulos, the new cable can offer as much as 1,000 times the bandwidth of a standard optical cable. The technology also eliminates the need for optical signal amplification, which will be a significant money saver. Consider that conventional optical cables require amplification approximately every 50 kilometres. A submarine cluster of four amplifiers costs a cool US$1 million or so apiece, so on a 500-kilometre cable run the newer cable technology could save users some US$10 million – and that doesn’t include the expenses involved in installing, maintaining or powering the amplifiers. “The potential for savings is enormous,” Joannopoulos says.

To explore the cable’s commercial potential, Joannopoulos and his fellow researchers have cofounded OmniGuide Communications. The company, based in Cambridge, Mass., is backed by Ray Stata and Mukesh Chatter, a pair of veteran investors in telecommunications-oriented start-ups.

But bringing the cable to market at a competitive cost may prove the technology’s undoing. The cable structure is highly complex, and OmniGuide will be entering uncharted manufacturing territories.