Topology-Based Fiber Ensures Robust Performance Amid Distortions

JOEL WILLIAMS, ASSOCIATE EDITOR
joel.williams@photonics.com
JAKE SALTZMAN, NEWS EDITOR
jake.saltzman@photonics.com

Researchers at the University of Bath fabricated optical fiber that hosts topological supermodes across multiple light-guiding cores. The topological protection of the fibers prevents changes to the structure of the fiber edge modes when the intercore coupling — or how much light can move between each core — changes, such as in the event of a bend or twist.

The fabrication approach targets the need for optical fibers that comprise a network to traverse natural landscapes, where the path is rarely straight and undisturbed. Distortions that result from turns, loops, and bends can cause information to degrade as it moves between sender and receiver, the researchers said.

According to the researchers, information can be compromised when a fiber becomes damaged.

To address this problem and enhance the robustness of fiber-based optical networks, the researchers used topology, which is the mathematical study of quantities that remain unchanged despite continuous distortions to the geometry. By connecting physical phenomena to unchanging numbers, the destructive effects of a disordered environment can be avoided, they said.

Their architecture features several light-guiding cores in a fiber, linked together in a spiral. Light can move between these cores, but becomes trapped within the edge thanks to the topological design. These edge states are protected against disorder in the structure.

“Whenever you fabricate a fiber optic cable, small variations in the physical structure of the fiber are inevitably present,” said Nathan Roberts, a Ph.D. student who led the research. One way to alleviate that, he said, is to ensure the design process is focused on robustness.

“This is where we found the ideas of topology useful,” Roberts said.

“In a telecom’s single-mode fiber, tight bends induce additional loss,” Bath physicist and co-author Anton Souslov told Photonics Media. “This will degrade the signal as it is attenuated more than in a straight fiber.

“In a multicore fiber, however, much less bending will distort the modes, scrambling the intended intensity pattern at the fiber output. One factor that contributes to the scrambling of the modes is the changes in coupling strengths between the cores, the effects of which we can alleviate with our topological design.”

Coupling strengths can change through fabrication, since not every fiber is identical post-fabrication, or through external changes due to expansion or contraction from temperature changes or deformations of the fiber that bring cores closer together or farther apart, Souslov told Photonics Media. Similar levels of variation will distort the output intensity distribution of the team’s topological fiber less than conventional coupled multicore fiber, he said, which might be used for space division multiplexing.

According to Souslov, the fabrication approach is unlikely to have any beneficial effect on attenuation. The team is now looking for industry partners to further develop the concept.

The work received funding from the Engineering and Physical Sciences Research Council, the Royal Society, and the Air Force Office of Scientific Research.

The research was published in Science Advances (www.doi.org/10.1126/sciadv.add3522).