Microsoft Scales Up Hollow Core Fiber Production

Creating better fiber is a non-trivial task. Today’s G.652/G.657 single-mode fiber has proven to be remarkably resilient and scalable for decades to come, with vendors delivering terabit-level speeds over long-haul distances and CableLabs asserting it has demonstrated coherent optics to go up to 50 Tbps over the same media.

Over the past few years, hollow core fiber (HCF) has emerged as a next-generation medium for AI Data Centers to deliver higher speeds at shorter distances with lower latencies and less power by using a glass hollow tube with a center full of air instead of the traditional solid glass core in service today. By transmitting laser light through air instead of solid glass, increasing transmission speeds by 47% and cutting latency by 33%, while enabling the use of more optical wavelengths in the future for more bandwidth. Lower signal loss also means that fewer repeaters are needed, translating to lower energy usage.

Small amounts of hollow core fiber have been produced and deployed over the past five years for reducing latency between offices or data centers at short distances while manufacturers have worked to improve the media’s loss characteristics to equal or exceed those of traditional fiber.

Microsoft has signaled that it has met that improvement goal and is bringing HCF into large-scale production for use in its Azure data centers. The company published its “Broadband optical fibre with an attenuation lower than 0.1 decibel per kilometer” paper in Nature on September 1, 2025, exceeding the industry norm of 0.14 dB per kilometer, followed by a September 23, 2025, blog post by Microsoft that it is establishing additional HCF production with Corning and Heraeus Covantis.

The “industrial scale-up of HCF production,” as the blog describes it, will go to supply Microsoft’s Azure data centers to help increase capacity, resiliency, and speed for its customers in the near-term and will likely stimulate other manufacturers to ramp up their offerings as well. Lightera has been working with Nokia and Digital Realty to use its HCF product, and this summer announced a family of tools with Furukawa Electric for HCF and multi-core splicing.

Microsoft’s Hollow Core Fiber winding onto a spool during the manufacturing process. Source: Microsoft.

Microsoft is no stranger to HCF. It made the strategic decision to acquire Lumenisity in 2022 and launched its first HCF fabrication factory in the UK to expand production and drive longer-term HCF research, prototyping and testing. In 2024, the company said it planned to deploy 15,000 kilometers of HFC across the Azure network in a two-year period to support AI connectivity.

To be sure, there is plenty of work ahead in moving HCF from a specialized technology into mainstream usage, including building a cadre of fiber technicians skilled in working with and splicing the media, available tools and standards for installing and working with HCF, and understanding the potential quirks and issues of the medium when compared to single strand fiber.

Under the announced industrial production agreement, Azure engineers “are working alongside Corning and Heraeus to operationalize Microsoft manufacturing process intellectual property (IP), deliver targeted training programs, and drive the yield, metrology, and reliability improvements required for scaled production,” according to the Microsoft blog post. The collaborations are “foundational” to a growing standardized global ecosystem to support HCF glass preform/tubing supply, fiber production at scale, and cable and connectivity for deployment into carrier-grade environments.