Researchers from the Optoelectronics Research Centre (ORC) at University of Southampton and the Centre for Optics, Photonics and Lasers (COPL) at Université Laval, Québec, say they have been able to measure the back-reflection of hollow-core fibers. The results, reported this month in The Optical Society’s journal Optica, indicate that the hollow-core fiber demonstrates back-reflection that is approximately 10,000X lower than conventional fiber.
As the name implies, hollow-core fiber carries light through a hollow core, rather than the silica core common to conventional fibers. The lack of a solid material reduces latency and non-linear effects, making it potentially attractive for a wide variety of applications (for example, watch the video “Advances in hollow-core fiber cable from OFS” or read “Startup Lumenisity unveils hollowcore fiber cables for DWDM applications, new funding” and "High-frequency traders using hollow core fiber: Wall Street Journal"). Such fibers also demonstrate low back-reflection; in fact, Nested Antiresonant Nodeless Fibres (NANFs) developed within the Southampton-led LightPipe research program, exhibit back-reflection too low to measure with conventional instruments.
Researchers at the ORC therefore turned to the measurement experts at COPL to address the problem. The result was the development of an instrument that was capable of providing reliable back-reflection measurements on the hollow-core fibers. Those measurements confirmed that the back-scattering within the Southampton-developed hollow-core fiber is better than four orders of magnitude lower than in standard fibers, which the researchers say was in line with theoretical expectations.
“The experimental confirmation of our theoretical prediction that back-scattering is 10,000X less in our latest hollow-core fibers than in standard all-glass fibers demonstrates their superiority for many fiber-optic applications,” stated Dr. Eric Numkam Fokoua of the ORC. “Moreover, the ability to measure such low back-scattered signal levels is also critical in the development of hollow-core fiber technology itself, in providing a critical route to distributed fault-finding in fabricated hollow-core fibers and cables as needed to drive forward improvements in their manufacturing processes. Existing technology is simply not sensitive enough to work with these radical new fibers and this work demonstrates a solution to this problem.”
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Left: Light propagates through a central hole of the hollow-core fibre. Right: co-author Vincent Michaud-Belleau from COPL, Université Laval.