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New hollow-core fiber outperforms glass, pushing data closer to light speed [techspot.com]:

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What just happened? A Microsoft-backed research team has set a new benchmark for optical fiber performance, developing a hollow-core cable that posts the lowest optical loss ever recorded in the industry, according to findings published in Nature Photonics. The milestone comes after years of effort by Lumenisity, a spinout from the University of Southampton's Optoelectronics Research Center, now operating under Microsoft's wing following an acquisition in 2022.

This novel fiber, utilizing [theregister.com] a design known as double-nested antiresonant nodeless fiber (DNANF), exhibits an attenuation of just 0.091 dB/km at the 1,550-nm wavelength. For comparison, today's best silica fibers bottom out at roughly 0.14 dB/km – a figure that has remained relatively unchanged since the 1980s.

Francesco Poletti, who co-authored the research paper and helped invent the design, told The Register that the development ranks as "one of the most noteworthy improvements in waveguided optical technology for the past 40 years."

The main draw behind hollow-core fiber is the medium: while standard optical fiber guides photons through solid glass, limiting signal speed to just under 200 million meters per second, the hollow variant lets light travel through air, which increases velocity closer to the maximum of 300 million meters per second.

More speed means lower latency – an especially important metric for moving data between cloud datacenters and accelerating mobile network performance. However, earlier hollow-core designs suffered high energy loss (over 1 dB/km), restricting practical use to short and specialized links.

The DNANF fiber counters this by using concentric, micron-thin glass tubes acting as tiny mirrors, bouncing light through an air core while suppressing unwanted transmission modes. Tests conducted on kilometer-scale spools confirmed attenuation below the critical 0.1 dB/km mark using multiple measurement methods, including optical time-domain reflectometry.

The researchers report that loss remained under 0.2 dB/km across a 66-terahertz spectral band – significantly more bandwidth and flexibility than conventional fibers can offer. They also measured chromatic dispersion at levels seven times lower than those of legacy architectures, which could simplify transceiver designs and reduce network energy costs. "So you need to amplify less," Poletti explained. "It can lead to greener networks if this is how you want to exploit it."

Microsoft's acquisition [tomshardware.com] of Lumenisity in 2022 signaled its intention to move hollow-core technology from academic circles into real-world infrastructure. Initial iterations achieved losses of 2.5 dB/km – respectable but uncompetitive with legacy glass fiber. Through ongoing development, Microsoft confirmed to Network World that approximately 1,200 kilometers of the new fiber are already carrying live cloud traffic. At the 2024 Ignite conference, CEO Satya Nadella announced plans to deploy 15,000 kilometers of DNANF fiber across Azure's global backbone within two years, aiming to support the explosive growth in AI workloads.

While the technology promises transmission speeds up to 45 percent faster than current solid-core options and holds the potential for five to ten times wider bandwidth, certain hurdles remain. Scaling production will require new manufacturing tools, and the fiber must undergo international standardization processes before entering mass-market use – a milestone that could take around five years. Still, the latest results mark the first time fiber that carries light through air has outpaced and outperformed the glass it was engineered to replace – a watershed moment for telecom and cloud infrastructure.

Original Submission