Specialty fibre draws renewed interest

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

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

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 fibre. The tube is then collapsed and jacketed into a preform with the desired core-to-clad ratio. Optical fibre 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 fibre community at Boston University's Photonics Center highlighted some of the recent trends and opportunities. The workshop was organised 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 fibre fabricators. From a potential users point of view, the ideal specialty fibre 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 fibre. Manufacturers, on the other hand, are reluctant to produce a fibre for which there is very little demand.

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

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

According to Samson, what distinguishes specialty fibre manufacture is the amount of engineering that must be invested for each unique fibre 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 fibre can find widespread application. Nufern, for example, is helping develop high-power fibre lasers based on double-clad fibre technology. The company believes its fibre lasers can replace Nd:YAGs in industrial cutting/welding/marking and have military applications as well, as witnessed by the 155-W fibre amplifier recently demonstrated by Northrop Grumman. Holey fibre, 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 fibres and sensing—is also much taken with what he terms "strange fibre." His work, along with that of many established and startup fibre companies, focuses on fibres with holes, either microstructure or single-hole.

Harrington sees these holey fibres as having excellent uses in temperature, chemistry, and radiometric sensing. Power delivery over single-hole fibre 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 fibre makers seem to have learned from the telecoms 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.

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