3-D intensity profile of reflected infrared light from MIT-made mirror fibers. MIT photo

Scientists at MIT's Research Laboratory of Electronics (RLE) and Center for Materials Science and Engineering (CMSE) in 1998 initially developed the photonic bandgap fiber, which has a hollow core surrounded by a highly confining reflective surface dubbed "the perfect mirror".

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.

As an MIT graduate student, Fink was instrumental in creating the "perfect mirror." The team reported their latest findings in the 12 December 2002 issue of Nature.

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

The materials are layered in alternating thicknesses to create a hollow pre-form--a scaled-up version of the final fiber. When the pre-form 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 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.

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. Hart said 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 require 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, the Francis Wright Davis Professor of Physics.

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