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Researchers used 3-D printing to make preforms for a step-index fiber (a) and a structured preform (b). These preforms were then placed in a draw tower (right) to make the final optical fiber. [Image: John Canning, University of Technology Sydney]

The entire global telecommunications network, not to mention the ever-expanding Internet-of-Things (IOT), is tied together with string—silica optical fiber. Manufacturing this crucial connector is a laborious process, one that a research team in Australia believes it may have re-invented.

Researchers at the University of Technology Sydney and the University of New South Wales have demonstrated a way to 3-D print a glass preform for fabricating glass optical fiber (Opt. Lett., doi: 10.1364/OL.44.005358). This method, according to the team, simplifies fiber production as well as enabling both novel fiber designs and applications.

The art of drawing fiber

Silica optical fiber has a multitude of applications, but it’s expensive and labor-intensive to make. It comprises two parts: the fiber core that carries light, and the cladding that traps the light in the core as it travels through the fiber. In order to minimize loss and keep the light trapped in the core, the fiber core must have a higher refractive index than the fiber cladding.

Conventional methods of constructing the preform through which optical fiber can be drawn require spinning a hollow tube of glass with a carefully controlled refractive index profile on a lathe over a heat source. It’s essential that the fiber geometry is precisely centered during this process.

3-D printing the preform instead is thus a very attractive alternative—one that several members of the Australian team have been working toward for a while. Several years ago, the team successfully demonstrated the first fiber drawn from a 3-D-printed polymer preform. Applying this additive-manufacturing technique to glass, however, presents a tricky manufacturing challenge, as 3-D printing glass requires temperatures of more than 1900 °C.

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Researchers shone green light through the final optical fiber and measured loss. The orange inset shows a fiber cross-section. [Image: John Canning, University of Technology Sydney]

Printing glass

To apply the approach to glass, the team behind the latest study added silica nanoparticles into the photo-curable resin. The researchers then used direct-light projection (DLP) to 3-D print the cladding preform with UV light at 385 nm, and poured a clever mixture of polymer and silica nanoparticles—this time doped with germanosilicate—into the hollow, cylindrical preform. The addition of the germanosilicate to the core resin upped the refractive index.

To overcome the heat quandary, the researchers applied a thermal debinding process. The debinding sloughs off the polymer and other impurities, leaving the silica nanoparticles behind, which are held together by intermolecular forces. Kicking up the heat even more, the researchers then fused the nanoparticles into a solid structure that could be inserted into a draw tower to be molded into the optical fiber. According to the team, the end result was the first silica fibers drawn from 3-D-printed preforms.

Scattering and next steps

To test the quality of the first-of-its-kind fiber, the researchers shone 532-nm green light through 2 meters of both single-mode and multimode fiber—and measured significant loss. But while the team concedes that there is “considerable scope to improve the transmission properties of this fiber,” the researchers also believe that the relative ease with which the fiber was created could make the technique a game changer for future fiber fabrication.

In particular, the team suspects that this new method could enable the production of incredibly complex multicore and multi-shaped fiber designs for previously unrealizable applications. According to a press release accompanying the work, the researchers are interested in partnering with a fiber manufacturer to improve and eventually commercialize the technology.