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New technique could enable the creation of a variety of fiber-based electronic and photonic devices.
By David L. Chandler
What do saltwater taffy and smart textiles have in common? Until recently, probably nothing. But scientists at the Massachusetts Institute of Technology (MIT) have found a way to “pull” fibers—in a manufacturing process akin to making taffy—that makes it possible to add light- and sound-sensitive materials to synthetic fabrics.
Researchers have succeeded in making a fine thread that functions as a diode, a device at the heart of modern electronics. This feat, made possible by a new approach to a type of fiber manufacturing known as fiber drawing, could open up possibilities for fabricating a variety of electronic and photonic devices within composite fibers, using a variety of materials.
The findings, part of a doctoral research project in materials science, have been published in the journal Proceedings of the National Academy of Sciences. The work was carried out in Dr. Yoel Fink’s research group. Fink is professor of materials science and director of the Research Laboratory of Electronics at MIT.
How it’s different
Fiber drawing techniques are used to produce the optical fibers behind much of today’s broadband communications, but these techniques have been limited to materials that can partially melt and stretch like taffy at the temperatures being used for drawing the fibers. The new work demonstrates a way of synthesizing new materials during the fiber-making process, including materials whose melting points are far higher than the temperatures used to process the fibers. The simple proof-of-concept demonstration carried out by the MIT researchers could open the door to an array of sophisticated devices based on composite fibers.
All previous work on fiber-drawing ended up with the same materials that were there to begin with, just in a different shape. In this method, researchers report, new materials are formed during the drawing process.
Fiber drawing involves preparing a “preform” of materials, such as a large glass rod resembling an oversized model of the fiber to be produced. This preform is heated until it reaches a taffy-like consistency and then pulled into a thin fiber. The materials comprising the preform remain unchanged as its dimensions are drastically reduced. The resulting fiber was a simple but functional diode—a sort of one-way valve for electrical current, allowing electrons to flow through it in only one direction.
Where it could lead
Because the physical arrangements placed in the preform are preserved in the drawn fiber, it should ultimately be possible to incorporate more complex electronic circuits within the structure of the fiber itself. Such fibers might find uses as sensors for light, temperature or other environmental conditions, according to the researchers’ reports, or the fibers could then be woven and used to make a solar-cell fabric, for example.
Fink says his research group has been working for more than a decade on expanding the kinds of materials and structures that can be incorporated into fibers. He says that despite the rapid progress made in the last few decades in various forms of electronics, “there has been little progress in advancing the overall functionality and sophistication of fibers and fabrics.”
The group’s research, he says, has stemmed from the basic question, “How sophisticated can a fiber be?” Over the years they have incorporated more and more materials, structures and functions into fibers. But one of the biggest limitations has been the set of materials that could be incorporated into the fibers; this new work has greatly expanded that list. The work shows that it is possible, Fink says, “to use the fiber draw as a way to synthesize new materials. It’s the first time this has been demonstrated anywhere.”
Such fibers might have uses in new photonic circuits, which use light beams to perform functions similar to those carried out by flowing electrons in electronic circuits. While this experiment produced 15 individual diode devices in the fiber, each separate from the others, Fink says that through continuing research, “We think you could probably do hundreds” and even interconnect them to form electronic circuits.
But don’t take just their word for it
Professor John Ballato, director of the Center for Optical Materials Science and Engineering Technologies at Clemson University, Clemson, S.C., says, “There has been growing international interest in semiconducting optical fibers over the past few years. Such fibers offer the potential to marry the optoelectronic benefits of semiconductors, [which] we know from the silicon photonics and integrated circuit worlds, with the light guidance and long path lengths of optical fibers.” The new MIT work is particularly significant, he says, because of “the utilization of the fiber as a micro solid-state chemical reactor to realize materials that are not generally amenable to direct fiber fabrication.”
Ballato, who was not involved in this research, adds that a similar technique has been used to produce reactions using gases, but that to the best of his knowledge, “this is the first … to extend this concept to the solid state, where indeed a more bountiful opportunity exists to achieve a wider range of materials.” The process is so flexible and has the potential to be used with such a range of materials, he says, that “it can be considered an important step to a ‘fiber that does everything’—creates, propagates, senses and manipulates photons, electrons [and] phonons.