The shimmering fibers shown below combine the strength of a polymer and the exquisite reflectivity of an omnidirectional mirror. They were made by MIT researchers led by Yoel Fink, an assistant professor of materials science and engineering [Science, 296, 510 (2002)]. The work opens avenues for tailoring the external optical properties of polymer fibers that could be used as telecommunications filters or to code fabrics or paper.

	FINK RESEARCH GROUP/MIT

Omnidirectional mirrors reflect light coming from all angles and polarizations. They can be constructed from multiple layers of transparent, nonconducting materials with very different indexes of refraction. Such mirrors are typically fragile, however, and restricted to planar geometries.

Putting these mirrors onto fibers requires matching the optical and thermomechanical properties of the components, Fink says. The fibers shown are made from poly(ether sulfone) and arsenic triselenide, which have quite different indexes of refraction but deform and start flowing at the same temperature.

The fibers are drawn from a preform--a thick core of poly(ether sulfone) surrounded by 21 alternating layers of poly(ether sulfone) and arsenic triselenide. Because of the thermochemical matching, the preform retains its organization when heated. These particular fibers reflect in the infrared region and in parts of the visible region. The colors are due to optical interference, akin to the sheen of a thin oil layer on a puddle of water, Fink explains.

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