14 Oct 2004
Optical fibers containing layers of conducting, semiconducting and insulating materials are unveiled in this week's Nature.
Scientists at the Massachusetts Institute of Technology (MIT) have created novel optoelectronic fibers that contain metal, insulator and semiconductor layers. The fibers can be woven into a "spectrometric fabric" that could be used in devices such as photodetectors, and might also have applications in light-sensitive materials for clothing (Nature 431 826).
Yoel Fink and colleagues at MIT began by arranging a crystalline conductor (tin), an amorphous semiconductor (arsenic-selenium) and an insulator (polyetherimide) into a preform about 20 centimeters long. The three components all have different refractive indices but similar melting temperatures, which means they can be processed under the same conditions.
The preform comprises a hollow air core, surrounded by a so-called omnidirectional or "perfect" dielectric mirror that is formed from eight pairs of alternating layers of arsenic-selenium and polyetherimide. Such a mirror -- which was first demonstrated by Fink and co-workers in 1998 -- is able to reflect light from all angles and with all polarizations, like an ordinary mirror, but it can also be tuned to only reflect at certain wavelengths.
The fibers are able to detect light along their length and if modified -- by introducing a special photoconducting glass cylinder into the core -- can generate an electrical response when illuminated. When woven into a fabric with a grid structure, the device is capable of localising point sources of light. Furthermore, the direction of incoming light could be determined if layers of the fabric were overlapped.Author