MIT Researchers Create Photonic Bandgap Fiber

CAMBRIDGE, Mass., Jan. 10 --MIT researchers have created a low-loss optical fiber that may lead to advances in medicine, manufacturing, sensor technology and telecommunications.

Scientists and members of MIT's Research Laboratory of Electronics and Center for Materials Science and Engineering developed the photonic bandgap fiber, which has a hollow core surrounded by a highly confining reflective surface -- dubbed "the perfect mirror" when MIT researchers invented it in 1998. The team reports on their findings in the Dec. 12 issue of Nature.

The fiber conducts an intense stream of laser light that would melt traditional fiber-making materials.

"Due to the efficient confinement of light in the hollow core, enabled by the mirror surface, we are able to utilize materials that would normally be damaged under such intense illumination conditions," said team leader Yoel Fink, assistant professor of materials science and engineering. Fink was intrumental in creating the "perfect mirror" as an MIT graduate student.

To create the fiber, the researchers identified a pair of materials that have very different optical properties yet soften at the same temperature.

These materials are layered in alternating thicknesses to create a hollow preform -- a scaled-up version of the final fiber. When the preform is fed into a furnace and drawn into a fiber, the layers reduce in thickness to micrometer dimensions, resulting in a mirror that confines light to the hollow core.

The transmission window is determined by the layer thickness and thus can be scaled to target a wide range of wavelengths.

Tens of meters of fiber with "transmission losses ... orders of magnitude lower than those of the constituent materials" demonstrate that "low attenuation can be achieved through structural design rather than high-transparency material selection," the authors wrote.

A Powerful Beam
The researchers chose to concentrate on the transmission of 10.6-micron light because there are "no good fibers at this wavelength, and yet very strong, low-cost lasers exist at this wavelength that may be useful for a variety of applications," said co-author Shandon D. Hart, a graduate student in the Department of Materials Science and Engineering. The new fiber would allow a carbon dioxide laser's high power to be transmitted over longer distances than are possible today.

Possible applications include medical treatments that necessitate high-power delivery, such as surgery or facilitating the breakup of kidney stones, and medical diagnosis requiring broadband infrared transmission such as detecting cancerous cells with spectroscopy. For manufacturing and materials processing, the fiber may in the future transmit sufficient laser light to cut metal. Another potential spectroscopic application involves the construction of a fiber optic sensor.

"The significance of this work is that it clearly demonstrates a key attribute of photonic bandgap fibers, namely the ability to achieve lower losses than their index-guided counterparts," said co-author John D. Joannopoulos, professor of physics at MIT.

In addition to Fink, Joannopoulos and Hart, authors include RLE research scientist Burak Temelkuran and materials science and engineering graduate student Gilles Benoit.

Their work is funded by the Defense Advanced Research Projects Agency Quantum Information Science and Technology Program/Army Research Office, the National Science Foundation (NSF), the US Department of Energy and an NSF graduate research fellowship. It was also supported by the Materials Research Science and Engineering Center program of the NSF and made use of MRSEC shared facilities.

For more information, visit: www.mit.edu