Specialty fiber draws renewed interest

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The days of booming demand for transmission fibers such as SMF-28, dispersion-shifted fiber, and nonzero dispersion-shifted fiber are a distant memory. New network builds are few and large fiber production facilities have closed their doors. In contrast, optical fiber for specific if limited applications has gained more interest from government, industry, and academia.

True, specialty fiber benefited from the telecom bubble, especially from the market for erbium-doped fiber amplifiers. That market has collapsed, although telecommunications still commands a share of the specialty fiber market. Defense, aerospace, oil exploration, medical, and research applications have been the recent stars. Opportunities continue for specialty products such as polarization-maintaining fiber, doped fiber, high-numerical-aperture fiber, dispersion-compensating fiber, photosensitive fiber, and holey fiber.Th 128253

In a closed-line process, a preform is made by modified chemical vapor deposition (MCVD). Several layers of ultra-high-purity glass are deposited inside a substrate tube. The composition of each layer is precisely controlled so the refractive index profile of the deposited glass is a scaled-up version of the optical fiber. The tube is then collapsed and jacketed into a preform with the desired core-to-clad ratio. Optical fiber is drawn from the preform in a draw furnace. MCVD is suited for rapid prototyping as well as large-scale manufacturing. Photo courtesy of Nufern.

A February gathering of the specialty fiber community at Boston University's Photonics Center highlighted some of the recent trends and opportunities. The workshop was organized as part of the Photonics Technology Access Program (PTAP), which is administered by the Optoelectronics Industry Development Association (OIDA) for the two sponsors: the National Science Foundation and Defense Advanced Research Projects Agency.

Marko Slusarczuk, the OIDA project coordinator, says that the goal was to encourage dialog between system researchers and fiber fabricators. From a potential users point of view, the ideal specialty fiber for a research project can be difficult to obtain, and researchers are often left trying to come up with a set of specifications that will satisfy a range of needs to justify the expense of drawing the fiber. Manufacturers, on the other hand, are reluctant to produce a fiber for which there is very little demand.

A useful dialog between users and suppliers is critical if both are to capitalize on existing markets and create new ones. As Bryce Samson, director of business development at fiber maker Nufern, says, there are "lots of niche markets relatively untapped by specialty fiber."

Differences among the custom products from each specialty fiber company are significant, in contrast to the more standardized fibers for optical networks. During the bubble, the revenues for these transmission fibers were high and the margins were good for companies such as Corning, OFS, Sumitomo, and Alcatel. Specialty fiber is a different game.

According to Samson, what distinguishes specialty fiber manufacture is the amount of engineering that must be invested for each unique fiber application without any guarantee on the volume of product that will be ordered. Hence, the value of the PTAP meeting for Samson, where the goal was to help develop target performance ranges that still provide researchers with what they need and manufacturers with the kind of volume that comes with multiple applications.

The results can be quite rewarding if a specialty fiber can find widespread application. Nufern, for example, is helping develop high-power fiber lasers based on double-clad fiber technology. The company believes its fiber lasers can replace Nd:YAGs in industrial cutting/welding/marking and have military applications as well, as witnessed by the 155-W fiber amplifier recently demonstrated by Northrop Grumman. Holey fiber, based on photonic bandgap technology, is another exciting field, says Samson.

Jim Harrington, a professor in the department of ceramic and materials engineering at Rutgers University—and well-known researcher in the field of fibers and sensing—is also much taken with what he terms "strange fiber." His work, along with that of many established and startup fiber companies, focuses on fibers with holes, either microstructure or single-hole.

Harrington sees these holey fibers as having excellent uses in temperature, chemistry, and radiometric sensing. Power delivery over single-hole fiber is his current interest since the structure seems to have advantages for pulsed energy delivery from a CO2 laser for medical or dental applications.

One lesson that specialty fiber makers seem to have learned from the telecom experience is that they can succeed if they take advantage of diverse markets, work hard on new innovations, and keep the lines of communication open.

Conard Holton is chief editor of WDM Solutions and executive editor of Laser Focus World. He can be reached at 603-891-9161 or cholton@pennwell.com.

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