A team of scientists led by John Badding, a
professor of chemistry at Penn State Univ., has developed the very first
optical fiber made with a core of zinc selenide—a light-yellow compound that
can be used as a semiconductor. The new class of optical fiber, which allows
for a more effective and liberal manipulation of light, promises to open the
door to more versatile laser-radar technology. Such technology could be applied
to the development of improved surgical and medical lasers, better countermeasure
lasers used by the military, and superior environment-sensing lasers such as
those used to measure pollutants and to detect the dissemination of
bioterrorist chemical agents. The team’s research will be published in Advanced
Materials.
“It has become almost a cliché to say that
optical fibers are the cornerstone of the modern information age,” said
Badding. “These long, thin fibers, which are three times as thick as a
human hair, can transmit over a terabyte—the equivalent of 250 DVDs—of
information per second. Still, there always are ways to improve on existing
technology.” Badding explained that optical-fiber technology always has
been limited by the use of a glass core. “Glass has a haphazard
arrangement of atoms,” Badding said. “In contrast, a crystalline
substance like zinc selenide is highly ordered. That order allows light to be
transported over longer wavelengths, specifically those in the
mid-infrared.”
Unlike silica glass, which traditionally is used
in optical fibers, zinc selenide is a compound semiconductor. “We’ve known
for a long time that zinc selenide is a useful compound, capable of
manipulating light in ways that silica can’t,” Badding said. “The
trick was to get this compound into a fiber structure, something that had never
been done before.” Using an innovative high-pressure chemical-deposition
technique developed by Justin Sparks, a graduate student in the Department of
Chemistry, Badding and his team deposited zinc selenide waveguiding cores
inside of silica glass capillaries to form the new class of optical fibers.
“The high-pressure deposition is unique in allowing formation of such
long, thin, zinc selenide fiber cores in a very confined space,” Badding
said.
The scientists found that the optical fibers made
of zinc selenide could be useful in two ways. First, they observed that the new
fibers were more efficient at converting light from one color to another.
“When traditional optical fibers are used for signs, displays, and art,
it’s not always possible to get the colors you want,” Badding explained.
“Zinc selenide, using a process called nonlinear frequency conversion, is
more capable of changing colors.”
Second, as Badding and his team expected, they
found that the new class of fiber provided more versatility not just in the
visible spectrum, but also in the infrared—electromagnetic radiation with
wavelengths longer than those of visible light. Existing optical-fiber
technology is inefficient at transmitting infrared light. However, the zinc
selenide optical fibers that Badding’s team developed are able to transmit the
longer wavelengths of infrared light. “Exploiting these wavelengths is
exciting because it represents a step toward making fibers that can serve as
infrared lasers,” Badding explained. “For example, the military
currently uses laser-radar technology that can handle the near-infrared, or 2
to 2.5-micron range. A device capable of handling the mid-infrared, or over
5-micron range would be more accurate. The fibers we created can transmit
wavelengths of up to 15 microns.”
Badding also explained that the detection of pollutants and environmental
toxins could be yet another application of better laser-radar technology
capable of interacting with light of longer wavelengths. “Different
molecules absorb light of different wavelengths; for example, water absorbs, or
stops, light at the wavelengths of 2.6 microns,” Badding said. “But
the molecules of certain pollutants or other toxic substances may absorb light
of much longer wavelengths. If we can transport light over longer wavelengths
through the atmosphere, we can see what substances are out there much more
clearly.” In addition, Badding mentioned that zinc selenide optical fibers
also may open new avenues of research that could improve laser-assisted surgical
techniques, such as corrective eye surgery.
