Microsoft Scales Hollow-Core Fiber for AI Data Centers With Corning and Heraeus After Setting a 0.091 dB/km Fiber-Loss Record
Microsoft is moving hollow-core fiber from pilot to production for Azure, partnering with Corning and Heraeus after a research team recorded the lowest optical-fiber loss ever measured, 0.091 dB/km.
Overview
Microsoft is moving hollow-core fiber (HCF) from pilot deployments toward volume production for its Azure network. In late September 2025 the company named Corning and Heraeus as manufacturing partners to build what it calls a resilient, global supply chain for the technology, as reported by Data Center Dynamics. The push follows a research result, published in the journal Nature Photonics, that recorded the lowest signal loss ever measured in an optical fiber, according to Network World.
The move matters because networking, not raw compute, is increasingly the constraint on AI data centers, where light has to shuttle between racks, halls, and neighboring buildings with as little delay as possible.
What Hollow-Core Fiber Is
Conventional optical fiber carries light through a solid glass core. Hollow-core fiber instead guides light through an air-filled channel, as described by SDxCentral. Microsoft’s version uses a design called double nested antiresonant nodeless fiber (DNANF), which confines light in the central void using thin nested glass membranes, according to The Register.
Because light travels faster through air than through glass, Microsoft says HCF delivers up to 47 percent faster data transmission and approximately 33 percent lower latency than conventional single-mode fiber, as reported by Data Center Dynamics. The company also claims up to three times the bandwidth of standard fiber, and says signals can travel about 33 kilometers before needing amplification, compared with roughly 15 to 20 kilometers for standard fiber, according to IEEE Spectrum.
The Loss Record
The technical result underpinning the effort is a sharp reduction in attenuation, the rate at which a signal fades as it travels. Microsoft’s research team reported a best result of 0.091 dB/km, below the roughly 0.14 dB/km that has long been a practical floor for conventional silica fiber, according to Network World. The team also kept the loss below 0.1 dB/km across an 18-terahertz slice of spectrum and reported a sevenfold reduction in chromatic dispersion compared with conventional fiber, Network World reported.
The Register noted that the team “managed 0.091 dB km−1 in their best result, though Poletti noted that the average loss was slightly higher,” and that the design is promising transmission speeds 45 percent faster than what is possible with solid-core fiber, per The Register. The concept traces to Francesco Poletti, a University of Southampton researcher who co-founded Lumenisity, the university spinout behind the fiber, The Register reported.
From Pilot to Live Traffic
The work has already moved out of the lab. Microsoft’s pilot “involved over 1,200 km of fibre, now installed underground and actively carrying live traffic,” according to Network World. Chief Executive Satya Nadella announced at the company’s 2024 Ignite conference a plan to deploy 15,000 kilometers of the fiber across the Azure network, Network World reported. Earlier real-world routes include a 40-kilometer Comcast link in Philadelphia and a 45-kilometer euNetworks deployment in London, according to Network World.
In one test installation, Microsoft ran hybrid cables carrying 32 hollow-core strands alongside 48 single-mode strands over two routes of more than 20 kilometers each, according to IEEE Spectrum. “We can deliver signals to the recipient with much fewer distortions and in a faster time,” Poletti told IEEE Spectrum.
The Production Deals
Scaling from pilot routes to a global network requires manufacturing capacity that Microsoft does not have in-house. Under the September 2025 agreements, Microsoft will work with Corning to ramp up HCF production at Corning’s U.S. facilities, while German-based Heraeus will produce the fiber from sites in both Europe and the U.S., as reported by Data Center Dynamics.
“This milestone marks a new chapter in reimagining the cloud’s physical layer,” said Jamie Gaudette, partner cloud network engineering manager at Microsoft, according to Data Center Dynamics.
A Parallel Bet on MicroLEDs
Hollow-core fiber is not Microsoft’s only optical project. In March 2026 the company detailed a separate interconnect that replaces lasers with microLEDs; early lab testing indicated the system could consume about 50 percent less energy than conventional laser-based optical links, according to SDxCentral. The system pairs commercially available microLEDs with “imaging fiber,” a cable containing thousands of microscopic cores that carry parallel streams of light, and was developed at Microsoft Research in Cambridge, U.K., with the Azure and Microsoft 365 teams and the Taiwanese chipmaker MediaTek, SDxCentral reported.
Microsoft expects the microLED interconnect to reach commercial availability by late 2027, according to SDxCentral. The project drew on Lumenisity, which Microsoft acquired in 2022, SDxCentral reported. Doug Burger, a technical fellow and corporate vice president at Microsoft Research, and Frank Rey, general manager of Azure hyperscale networking at Microsoft, were among those credited on the work, alongside Vince Hu, a corporate vice president at MediaTek, according to SDxCentral.
What We Don’t Know
Broad availability remains years out. The Register reported that data center operators may be able to purchase and install the technology in around five years’ time, once it has gone through international standardization, per The Register. With further refinement, the team says the design could eventually support five to ten times wider bandwidth, though that potential is unproven, The Register reported. Microsoft has not disclosed the cost of the fiber relative to conventional cable, nor a firm timeline for reaching the full 15,000-kilometer Azure target.
Analysis
The common thread across both projects is a shift in where data center engineers spend their optimization budget. As AI clusters grow to tens of thousands of accelerators, the distance and delay between compute nodes become a limiting factor, and both lower-latency fiber and lower-energy interconnects attack that constraint from different angles. Hollow-core fiber targets the longer links between halls and buildings, where its speed and low loss reduce the need for signal amplification; the microLED interconnect, by Microsoft’s account, aims at shorter, denser connections inside a facility where energy per bit dominates.
The production agreements are the more consequential near-term signal. A record loss figure is a laboratory achievement; contracting Corning and Heraeus to manufacture the fiber at volume is a bet that the economics work at hyperscale. Whether hollow-core fiber becomes a mainstream data center building block or stays a Microsoft-specific advantage will depend less on the physics, which now appears settled, and more on manufacturing yield, cost, and the standardization work that The Register flags as the gating step.