Better Optical Fibers Under High Pressure

Madoka Ono calculated voids in silica glass, which are responsible for scattering of light and degradation of signals. They become much smaller when the glass is quenched at higher pressures. (Source: Hokkaido U.)

Optical fiber data transmission can be signi­ficantly improved by producing the fibers, made of silica glass, under high pressure, researchers from Japan and the US report. Using computer simu­lations, researchers at Hokkaido University, the Penn­sylvania State University, and their industry colla­borators theo­retically show that signal loss from silica glass fibers can be reduced by more than 50 percent, which could drama­tically extend the distance data can be trans­mitted without the need for amplifi­cation.

“Improvements in silica glass, the most important material for optical communi­cation, have stalled in recent years due to lack of understanding of the material on the atomic level,” says Madoka Ono of Hokkaido University’s Research Institute of Electronic Science, RIES. Her research focuses on the properties of non-organic and silica glass by both laboratory experiments and compu­tational analyses. “Our findings can now help guide future physical experi­ments and produc­tion processes, though it will be technically challenging.”

The data signal in optical fibers peters out before reaching its final destina­tion due to light being scattered. Amplifiers and other tools are used to contain and relay the infor­mation before it scatters, ensuring it is delivered success­fully. Scientists are seeking to reduce light scatter, called Rayleigh scattering, to help accelerate data trans­mission and move closer towards quantum communic­ation. Ono and her colla­borators used multiple compu­tational methods to predict what happens to the atomic structure of silica glass under high temperature and high pressure. They found large voids between silica atoms form when the glass is heated up and then cooled down, which is called quenching, under low pressure. But when this process occurs under four giga­pascals, most of the large voids disappear and the glass takes on a much more uniform lattice structure.

Speci­fically, the models show that the glass goes under a physical trans­formation, and smaller rings of atoms are eliminated or pruned allowing larger rings to join more closely together. This helps to reduce the number of large voids and the average size of voids, which cause light scattering, and decrease signal loss by more than fifty percent. The researchers suspect even greater improve­ments can be achieved using a slower cooling rate at higher pressure. The process could also be explored for other types of inorganic glass with similar structures. However, actually making glass fibers under such high pressures at an industrial scale is very difficult.

“Now that we know the ideal pressure, we hope this research will help spur the develop­ment of high-pressure manu­facturing devices that can produce this ultra-transparent silica glass,” Ono says. (Source: Hokkaido U.)

Reference: Y. Yang et al.: Topological pruning enables ultra-low Rayleigh scattering in pressure-quenched silica glass, npj Comp. Mat. 6, 139 (2020); DOI: 10.1038/s41524-020-00408-1

Link: Laboratory of Nanostructured Functional Materials, Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan

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