New cable guides light through air

17 Jun 2002

Researchers at Massachusetts Institute of Technology (MIT) have proposed a new kind of coaxial cable that may be able to quickly and efficiently shoot light over long distances and around sharp bends while retaining its polarization.

OmniGuide Fiber will guide light through air, and not through silica glass, as is done by today's industry leaders. This will result in lower attenuation, increased power per channel, polarization insensitivity, improved dispersion characteristics.

The all-dielectric coaxial cable may create the kind of fast, high-bandwidth conduit needed for today's Internet applications.

With its ability for higher capacity, this cable may be able to transmit much more information more efficiently and cheaply than current methods. It also could lead to significant miniaturization of integrated optical devices.

"What's important about this is that it has opened a new direction for experimental research that was not possible before," said John D. Joannopoulos, Francis Wright Davis Professor of Physics at MIT and the team leader. "It's important to push along in this direction and see if we can find materials and fabrication approaches that will make this happen.

"We do know if we can do what the theory says, it will happen. This may be a breakthrough in bridging the very different requirements for transmitting infrared and radio frequencies" at opposite ends of the energy spectrum.

In 1998 Joannopoulos and colleagues developed a type of mirror -- dubbed the "perfect mirror" - which reflects light from all angles and polarizations, just like metallic mirrors, but also can be as low-loss as dielectric mirrors.

These researchers then made a tube out of the perfect mirror to create an omnidirectional waveguide. Unlike conventional waveguides, which need to make wide turns to ensure that the light within them does not escape, the omnidirectional waveguide can turn light quickly and efficiently in small spaces.

This would allow a slew of new technological advances in devices such as an optical chip, which cannot now be miniaturized because bending the light's route takes up so much space. In addition, the new waveguide can accommodate a much wider bandwidth of light.

Taking the waveguide a step farther, Joannopolous proposed that the omnidirectional reflector could be fashioned like a conventional coaxial cable, which consists of a tube of metal with a metal core snaking down its center. Coaxial cable is used to transmit radio and microwaves, which have large wavelengths, but it is not good for light energy at the smaller-wavelength, higher-frequency end of the spectrum.

Fiber optic cable was created to fill that need. But light transmitted through fiber optic cable does not maintain its polarization, which is important for certain high-tech applications. Using dielectrical materials instead of metal or fiber optics may bridge both worlds.

"This coaxial omniguide may be able to replace what metal does, and also do the job at wavelengths where metal doesn't work," Joannopoulos said. "And the nice thing about it is that whatever you put in, you get out. This could make a big difference" where polarization is an issue.

The next step is to prototype and test the coaxial omniguide. Joannopolous and colleagues have lauched a new company, OmniGuide Communications Inc. , to explore its practicality.