Smart optical fibers could save lives

Laser light beams, commonly used for surgery, can harm you if they escape from their enclosures. But now, MIT researchers have designed smart optical fibers which can monitor their status while the laser is doing its magic inside you and shut it down if a fiber wall is about to break.

Lasers are now commonly used for surgery. With them, you can recover a better sense of vision. Or a tumor inside your body can be eliminated. But these laser light beams, which are currently enclosed inside optical fibers, can harm you if they escape from their enclosures. But now, according to Technology Review, MIT researchers have designed smart optical fibers which can monitor their status while the laser is doing its magic inside you and shut it down if a fiber wall is about to break. So far, the technology is only working in labs, but it could be used for medical applications in a few years.

This new technology has been developed by MIT researcher Yoel Fink, associate professor of materials science. Here is how it works.

Fink's fibers channel a high-powered laser through a hollow core lined with a high-quality mirror. To detect incipient breaks, researchers in Fink's lab have surrounded the mirror with a semiconducting material whose electrical conductivity changes with temperature. These conductivity changes can be detected by metal wires that run the length of the fiber. When the conductivity changes abruptly, the wires signal the fault and a controller can automatically shut down the laser.
To fabricate the fibers, which are just over one millimeter thick, Fink starts with a cylindrical "preform" that has the exact geometry of the completed fiber, but is much thicker. This form is then heated and drawn out into a much longer, thinner fiber. A 30-centimeter-long preform can make a one-kilometer-long fiber.

Below is a figure extracted from a research paper published by Physical Reviews Letters under the name "Complete Modal Decomposition for Optical Waveguides" (Vol. 94, Article 143902, April 14, 2005). Here are two links to the abstract and to the full paper (PDF format, 4 pages, 451 KB).

Smart optical fibers -- example #1

Here are the "measured and reconstructed intensity distributions for the short-fiber case. The circle in the near-field images represents the location of the fiber core-cladding interface. The two circles in the far-field images represent the location of the first and second zeros of a far-field image of a uniformly distributed field having the shape and extent of the fiber core.

But the researchers have other ideas about how this technology could be used.

Optical fibers with integrated electronics could be made sensitive not just to heat, as in laser applications, but also to light, vibration, and perhaps chemicals, says Fink. Farther in the future, "smart" fibers, capable of sensing, information processing, and data storage, could be woven into fabric.

Here is an illustration extracted from another paper published by Nature under the title "Metal-insulator-semiconductor optoelectronic fibres" (Vol. 431, Pages 826-829, October 14, 2004). Here are two links to the abstract and to the full paper (PDF format, 4 pages, 285 KB).

Smart optical fibers -- example #2

Here you can see "a woven spectrometric fabric. The fabric consists of interleaved threads, 400 to 500-micrometers-thick, chosen from our device fibres. The visual appearance of the fabric, specifically the range of exhibited colours, is a result of the tight control exerted over the optical properties of the produced fibres.

When will we see practical applications coming from Fink's lab? Probably sooner than you think. Ask your dentist in about a few years and you might be surprised...

Sources: Kevin Bullis, Technology Review, November 8, 2005; and various web sites

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