Complex photonic manufacturing may be getting easier due to a novel use of 3D printing.

Image: University of Southampton

One technology I did not expect to benefit from 3D printing was the manufacturing of optical fibers used in fiber-optic cables. It is difficult to imagine how a tiny, chemically, and optically complex glass fiber could be made using a 3D-additive manufacturing process. Well, that's not quite what's happening.

To understanding why 3D printing is an important piece of the process, let's first look at how optical fibers are currently made; the process involves two main manufacturing steps: preform and drawing.

Preform: The preform starts out as a hollow glass jacket tube. The jacket tube is heated and specially formulated silicon dioxide is deposited on the interior. The chemical brew gives the finished fiber specific optical qualities. The jacket tube eventually becomes a solid, with the deposited silicon dioxide becoming the core of the optical fiber. This Discovery Channel video explains the process.

Image: Max Planck Institute

Drawing process: The now solid preform is transferred to a vertical drawing system similar to the diagram to the right and the image at the beginning of the article. The furnace heats the preform to 2000 degrees Celsius. The molten glass is then carefully drawn through the equipment, measured, coated, and wound on a spool.

In single-mode fiber, the core diameter is 10 micrometers, and the cladding diameter is 100 micrometers. Multimode optical fibers have a core diameter of 50 micrometers and a cladding diameter of 125 micrometers.

It is a lot more complicated than what I described, but at least this should allow us to understand why researchers at the University of Southampton's Optoelectronics Research Center are using 3D-printing techniques to fabricate optical fibers.

3D printing simplifies the preform process

From the video, one can see the resultant chemical composition of the core becomes uniform throughout the preform; however, there are situations where it would be nice to alter the shape and composition of the finished optical fiber along its length. This is where 3D-printing comes into play.

"We will design, fabricate and employ novel Multiple Materials Additive Manufacturing (MMAM) equipment to enable us to make optical fibre preforms (both in conventional and microstructured fibre geometries) in silica and other host glass materials," said Professor Jayanta Sahu of the Optoelectronics Research Center in the press release. "Our proposed process can be utilised to produce complex preforms, which are otherwise too difficult, too time-consuming, or currently impossible to be achieved by existing fabrication techniques."

If understood correctly, "impossible" refers to the fact that current technology only allows for a uniform depositing of the formulated silicon dioxide. MMAM (3D-additive process) offers the researchers the chance to vary the composition along the length of the preform as it is being created, which in turn alters the characteristics of the optical fiber.

The ability to create preforms with a complex internal structure will be welcomed by manufacturers, as the industry is moving towards even more complex microstructured optical fibers called photonic bandgap fibers.

Professor Sahu talked to Martin Rowe of EE Times about hollow-core fiber (photonic bandgap fiber). "Take an example of hollow-core fiber where the light is being guided in the central air region, and hence more light can be transmitted in such fibers as compared to a solid core fiber," mentioned Sahu. "In hollow-core fiber, communications can be made faster than SMF 28 because light travels faster in air than in silica glass, the material used in SMF 28."

Rowe then asked Sahu about his plans for MMAM. "Initially, basic fiber characterisations on spectral attenuation, dispersion, strength, doping concentration and profile, and laser efficiency will be made to establish the technology," said Sahu. "Once the technology has been established, we will then validate the fibers in real devices, for example, in a transmission experiment."

The hope for this research

In the University of Southampton press release, Professor Sahu stated, "We hope our work will open up a route to manufacture novel fibre structures in silica and other glasses for a wide range of applications, covering telecommunications, sensing, lab-in-a-fibre, metamaterial fibre, and high-power lasers. This is something that has never been tried before and we are excited about starting this project."

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