University of Illinois teams up with Clemson University to create a wider material range for optical fibers

Urbana, IL--University of Illinois lecturer Peter Dragic and professor John Ballato of Clemson University have demonstrated optical fibers with the lowest recorded Brillouin scattering by using a broader pallet of fabrication materials.

While the crystal structure of optical fibers has become increasingly complex over the years, the materials used to construct them have been stuck in a certain section of the periodic table within a few spaces of silicon (with silica -- SiO₂ -- being the predominant fiber component). But each element and crystal combination has its own unique suite of properties -- different refractive indices, different thermo-optic effects -- and by using these materials in the right combination, specific optical properties can be tailored into the fibers with relatively simple fabrication techniques.

To minimize Brillouin scattering, Dragic and Ballato understood that, relative to silica, they would have to design a fiber with a lower photoelastic constant. A model they had developed led initially from yttrium aluminum garnet (Y₃Al₅O₁₂, or YAG) to sapphire (Al₂O₃) to spinel (MgAl₂O₄) to barium oxide (BaO). With the last three materials, the model suggests that a full removal of Brillouin scattering is possible. Already, the sapphire-derived fibers created by Dragic and Ballato have set records for the lowest observed Brillouin scattering.

The materials used in conventional fibers are limited in a large part by limitations inherent to conventional chemical vapor deposition (CVD) methods. “There may also be a role played by the classic human condition whereby something done the same way for decades can paralyze creativity,” Dragic and Ballato write in an article in the Journal of this month's American Ceramic Society. “From a materials perspective, modern optical fibers are boring.”

To expand the materials pallet, Ballato’s fabrication team at Clemson University created fibers using a molten-core approach -- a radically simple technique, especially when compared to recent research on photonic-crystal fibers (PCFs), which contain complex structural waveguides. But, unlike PCF fabrication, the molten-core approach could be adopted by small companies. “It’s not something that requires a huge investment to implement commercially,” Dragic says.

Based on their model for crystals and glasses, Dragic will suggest new materials to study. After considering specific adjustments to optimize the molten-core process (temperatures and dimensions among other things), Ballato will have a demonstration fiber boxed and ready to send to Illinois within a week or two. Dragic tests the fibers, checking for Brillouin scattering and other phenomena and properties, and after processing the data with their model, he can suggest even better materials to try. “It’s all predictable and designable,” he says. “It’s not like we say, let’s just make something and see what happens.”