Hollow core fiber marks a turning point in fiber technology. But first, there are obstacles to overcome
In Sept, 2025, Microsoft Azure announced it is scaling its hollow core fiber (HCF) production by outsourcing manufacturing to Corning and Heraeus. It made clear that the tech giant is quite serious about its commitment to high-capacity fiber innovation, despite its deep focus on AI — or especially because of it.
Microsoft’s HCF play
If you followed the developments in the nascent HCF space, you’d know that Microsoft has been noodling with HCF R&D for quite some time now.
At Ignite 2024, CEO Satya Nadella stated that the technology delivers “absolute breakthroughs” in terms of speed, bandwidth, and power efficiency compared to conventional fibers.
The frenzy around hollow core fiber is not just marketing fluff. Physicists at the University of Southampton in U.K. have shown that HCF exhibits 35% less attenuation and 45% faster signal transmission compared to standard glass fibers.
The Azure team, testing Microsoft’s HCF solution over 1,200 Km of fiber last year, achieved 0.091 dB per kilometer of transmission loss, the lowest ever recorded — and a far cry from the 0.14 dB/km of fiber networks.
“This low fiber loss is absolutely critical for data center to data center connectivity, and we now have production routes of hollow fiber running. In fact, we’re going to add 15,000 additional kilometers planned over the next 24 months,” Nadella said.
The planned 15,000 km of HCF route will lay the groundwork to deploy “end-to-end” HCF solution across Azure’s global network and achieve better speeds and lower latency to feed the hungry cloud and AI workloads in data centers.
Breaking a 40 year deadlock
Optical fiber cables carry Internet around the world. They have a solid glass core that guides light signals through with the help of the core’s high refractive index. Hollow core fiber takes it to the next level by swapping out the solid glass core with an air-filled one nested inside walls made from ultra-thin glass membranes. As air is more transparent, photons travel faster through this hollow center, while the surrounding glass membranes keep the signals moving through without scattering. This amounts of faster transfers — and more importantly, very low data loss which is critical for AI and high-performance computing (HPC).
This allows fiber players to sidestep a problem that has existed for four decades, signal loss and attenuation leading to performance plateau in optical fibers. Even the best fibers in the market need amplification every 12 kms or so.
The high transmission and reduced loss of HCF can prove transformative for next-generation applications like AI and remote data centers. However, the performance gain can significantly boost many other technologies as well, including 5G/6G networks, quantum computing, defense communications, IoT smart cities, and high-frequency trading.
Challenges and barriers
Scala Data Centers, Lightera, and Nokia tag-teamed in November to conduct an HCF test in Sao Paulo. With optical testing and certification equipment from Viavi, the trio tested AccuCore HCF, Lightera’s hollow core fiber optic cable solution, demonstrating 32% reduction in latency. The data transmission speeds are close to “the speed of light”, the companies claimed.
“A 32% reduction in latency time, verified using commercially available 400G high end measurement equipment such as those from Viavi solutions, adds significant weight to this test,” said Andre Champavere, fiber optic measurement and sensing expert, in a LinkedIn comment. As for the OTDR [Optical Time Domain Reflectometer] characterization of HCF fibers, it is somewhat specific (very low backscatter level, high reflective peaks at SMF/HCF hybrid connections), but it can work.”
But before HCF becomes a medium of long-haul connectivity, an obstacle course of challenges lay ahead for HCF players. HCF cables have delicate microstructures which make handling and splicing a nightmare. The thin walls of the cables are prone to collapse, and as a result, sensitive to bending. It demands tight thermal control, sub-micron alignment, and precise humidity management for manufacturing, installation and splicing
So, when an HCF cable breaks in the field, repairing becomes just as tricky. For one, there is a limited window by which the fibers need to be spliced back together.
“You cannot leave it open for weeks or months,” Mario Simard, product line manager at Viavi said in a webinar. “If there’s pressure differential, you can get some contaminant inside the fiber,” he added.
Currently, the solid core and hollow core infrastructures are not directly compatible. “You have to have an adapter from glass to air to connect the HCF to a system or to a test instrument,” Simard noted. Even so, adapter loss can lead to a poor-quality link.
As with any new technology, HCF too faces a lack of standardized Method of Procedure (MoP) and shortage of skilled professionals which further complicates test and monitoring.
The condition demands specialized testing techniques and parameters, including non-standard (OTDR) settings, additional test wavelengths, and new post-processing analysis algorithms. Best practices, like testing the attenuation profile and chromatic dispersion are also critical to avoid surprises in the field.
Hollow core fiber is still in its early stages, but one thing is clear: hyperscalers and internet service providers (ISPs) are taking interest and gradually deploying it in select parts of the network to augment performance where there is demand. Side by side, test suppliers are also working on the challenges behind the scenes, so that when HCF becomes pervasive, companies have a loaded arsenal of test equipment and industry standards to leverage. Even though that’s still a few years away, testing vendors are falling back on their decades of fiber testing expertise to engineer new testing solutions that will make HCF a commercial reality in the future.
