Microsoft Azure scales Hollow Core Fiber (HCF) production through outsourced manufacturing
Introduction As cloud and AI workloads surge, the pressure on datacenter (DC), Metro and Wide Area Network (WAN) networks has never been greater. Microsoft is tackling the physical limits of traditional networking head-on. From pioneering research in microLED technologies to deploying Hollow Core Fiber (HCF) at global scale, Microsoft is reimagining connectivity to power the next era of cloud networking. Azure’s HCF journey has been one of relentless innovation, collaboration, and a vision to redefine the physical layer of the cloud. Microsoft’s HCF, based on the proprietary Double Nested Antiresonant Nodeless Fiber (DNANF) design, delivers up to 47% faster data transmission and approximately 33% lower latency compared to conventional Single Mode Fiber (SMF), bringing significant advantages to the network that powers Azure. Today, Microsoft is announcing a major milestone: the industrial scale-up of HCF production, powered by new strategic manufacturing collaborations with Corning Incorporated (Corning) and Heraeus Covantics (Heraeus). These collaborations will enable Azure to increase the global fiber production of HCF to meet the demands of the growing network infrastructure, advancing the performance and reliability customers expect for cloud and AI workloads. Real-world benefits for Azure customers Since 2023, Microsoft has deployed HCF across multiple Azure regions, with production links meeting performance and reliability targets. As manufacturing scales, Azure plans to expand deployment of the full end-to-end HCF network solution to help increase capacity, resiliency, and speed for customers, with the potential to set new benchmarks for latency and efficiency in fiber infrastructure. Why it matters Microsoft’s proprietary HCF design brings the following improvements for Azure customers: Increased data transmission speeds with up to 33% lower latency. Enhanced signal performance that improves data transmission quality for customers. Improved optical efficiency resulting in higher bandwidth rates compared to conventional fiber. How Microsoft is making it possible To operationalize HCF across Azure with production grade performance, Microsoft is: Deploying a standardized HCF solution with end-to-end systems and components for operational efficiency, streamlined network management, and reliable connectivity across Azure’s infrastructure. Ensuring interoperability with standard SMF environments, enabling seamless integration with existing optical infrastructure in the network for faster deployment and scalable growth. Creating a multinational production supply chain to scale next generation fiber production, ensuring the volumes and speed to market needed for widespread HCF deployment across the Azure network. Scaling up and out With Corning and Heraeus as Microsoft’s first HCF manufacturing collaborators, Azure plans to accelerate deployment to meet surging demand for high-performance connectivity. These collaborations underscore Microsoft’s commitment to enhancing its global infrastructure and delivering a reliable customer experience. They also reinforce Azure’s continued investment in deploying HCF, with a vision for this technology to potentially set the global benchmark for high-capacity fiber innovation. “This milestone marks a new chapter in reimagining the cloud’s physical layer. Our collaborations with Corning and Heraeus establish a resilient, global HCF supply chain so Azure can deliver a standardized, world-class customer experience with ultra-low latency and high reliability for modern AI and cloud workloads.” - Jamie Gaudette, Partner Cloud Network Engineering Manager at Microsoft To scale HCF production, Microsoft will utilize Corning’s established U.S. facilities, while Heraeus will produce out of its sites in both Europe and the U.S. "Corning is excited to expand our longtime collaboration with Microsoft, leveraging Corning’s fiber and cable manufacturing facilities in North Carolina to accelerate the production of Microsoft's Hollow Core Fiber. This collaboration not only strengthens our existing relationship but also underscores our commitment to advancing U.S. leadership in AI innovation and infrastructure. By working closely with Microsoft, we are poised to deliver solutions that meet the demands of AI workloads, setting new benchmarks for speed and efficiency in fiber infrastructure." - Mike O'Day, Senior Vice President and General Manager, Corning Optical Communications “We started our work on HCF a decade ago, teamed up with the Optoelectronics Research Centre (ORC) at the University of Southampton and then with Lumenisity prior to its acquisition. Now, we are excited to continue working with Microsoft on shaping the datacom industry. With leading solutions in glass, tube, preform, and fiber manufacturing, we are ready to scale this disruptive HCF technology to significant volumes. We’ll leverage our proven track record of taking glass and fiber innovations from the lab to widespread adoption, just as we did in the telecom industry, where approximately 2 billion kilometers of fiber are made using Heraeus products.” - Dr. Jan Vydra, Executive Vice President Fiber Optics, Heraeus Covantics 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. The collaborations are foundational to a growing standardized, global ecosystem that supports: Glass preform/tubing supply Fiber production at scale Cable and connectivity for deployment into carrier‑grade environments Building on a foundation of innovation: Microsoft’s HCF program In 2022, Microsoft acquired Lumenisity, a spin‑out from the Optoelectronics Research Centre (ORC) at the University of Southampton, UK. That same year, Microsoft launched the world’s first state‑of‑the‑art HCF fabrication facility in the UK to expand production and drive innovation. This purpose-built site continues to support long‑term HCF research, prototyping, and testing, ensuring that Azure remains at the forefront of HCF technology. Working with industry leaders, Microsoft has developed a proven end‑to‑end ecosystem of components, equipment, and HCF‑specific hardware necessary and successfully proven in production deployments and operations. Pushing the boundaries: recent breakthrough research Today, the University of Southampton announced a landmark achievement in optical communications: in collaboration with Azure Fiber researchers, they have demonstrated the lowest signal loss ever recorded for optical fibers (<0.1 dB/km) using research-grade DNANF HCF technology (see figure 4). This breakthrough, detailed in a research paper published in Nature Photonics earlier this month, paves the way for a potential revolution in the field, enabling unprecedented data transmission capacities and longer unamplified spans. ecords at around 1550nm [1] 2002 Nagayama et al. 1 [2] 2025 Sato et al. 2 [3] 2025 research-grade DNANF HCF Petrovich et al. 3 This breakthrough highlights the potential for this technology to transform global internet infrastructure and DC connectivity. Expected benefits include: Faster: Approximately 47% faster, reducing latency, powering real-time AI inference, cloud gaming and other interactive workloads. More capacity: A wider optical spectrum window enabling exponentially greater bandwidth. Future-ready: Lays the groundwork for quantum-safe links, quantum computing infrastructure, advanced sensing, and remote laser delivery. Looking ahead: Unlocking the future of cloud networking The future of cloud networking is being built today! With record-breaking [3] fiber innovations, a rapidly expanding collaborative ecosystem, and the industrialized scale to deliver next-generation performance, Azure continues to evolve to meet the demands for speed, reliability, and connectivity. As we accelerate the deployment of HCF across our global network, we’re not just keeping pace with the demands of AI and cloud, we’re redefining what’s possible. References: [1] Nagayama, K., Kakui, M., Matsui, M., Saitoh, T. & Chigusa, Y. Ultra-low-loss (0.1484 dB/km) pure silica core fibre and extension of transmission distance. Electron. Lett. 38, 1168–1169 (2002). [2] Sato, S., Kawaguchi, Y., Sakuma, H., Haruna, T. & Hasegawa, T. Record low loss optical fiber with 0.1397 dB/km. In Proc. Optical Fiber Communication Conference (OFC) 2024 Tu2E.1 (Optica Publishing Group, 2024). [3] Petrovich, M., Numkam Fokoua, E., Chen, Y., Sakr, H., Isa Adamu, A., Hassan, R., Wu, D., Fatobene Ando, R., Papadimopoulos, A., Sandoghchi, S., Jasion, G., & Poletti, F. Broadband optical fibre with an attenuation lower than 0.1 decibel per kilometre. Nat. Photon. (2025). https://doi.org/10.1038/s41566-025-01747-5 Useful Links: The Deployment of Hollow Core Fiber (HCF) in Azure’s Network How hollow core fiber is accelerating AI | Microsoft Azure Blog Learn more about Microsoft global infrastructureThe Deployment of Hollow Core Fiber (HCF) in Azure’s Network
Co-authors: Jamie Gaudette, Frank Rey, Tony Pearson, Russell Ellis, Chris Badgley and Arsalan Saljoghei In the evolving Cloud and AI landscape, Microsoft is deploying state-of-the-art Hollow Core Fiber (HCF) technology in Azure’s network to optimize infrastructure and enhance performance for customers. By deploying cabled HCF technology together with HCF-supportable datacenter (DC) equipment, this solution creates ultra-low latency traffic routes with faster data transmission to meet the demands of Cloud & AI workloads. The successful adoption of HCF technology in Azure’s network relies on developing a new ecosystem to take full advantage of the solution, including new cables, field splicing, installation and testing… and Microsoft has done exactly that. Azure has collaborated with industry leaders to deliver components and equipment, cable manufacturing and installation. These efforts, along with advancements in HCF technology, have paved the way for its deployment in-field. HCF is now operational and carrying live customer traffic in multiple Microsoft Azure regions, proving it is as reliable as conventional fiber with no field failures or outages. This article will explore the installation activities, testing, and link performance of a recent HCF deployment, showcasing the benefits that Azure customers can leverage from HCF technology. HCF connected Azure DCs are ready for service The latest HCF cable deployment connects two Azure DCs in a major city, with two metro routes each over 20km long. The hybrid cables both include 32 HCF and 48 single mode fiber (SMF) strands, with HCFs delivering high-capacity Dense Wavelength Division Multiplexing (DWDM) transmission comparable to SMF. The cables are installed over two diverse paths (the red and blue lines shown in image 1), each with different entry points into the DC. Route diversity at the physical layer enhances network resilience and reliability by allowing traffic to be rerouted through alternate paths, minimizing the risk of network outage should there be a disruption. It also allows for increased capacity by distributing network traffic more evenly, improving overall network performance and operational efficiency. Image 1: Satellite image of two Azure DC sites (A & Z) within a metro region interconnected with new ultra-low latency HCF technology, using two diverse paths (blue & red) Image 2 shows the optical routing that the deployed HCF cables take through both Inside Plant (ISP) and Outside Plant (OSP), for interconnecting terminal equipment within key sites in the region (comprised of DCs, Network Gateways and PoPs). Image 2: Optical connectivity at the physical layer between DCA and DCZ The HCF OSP cables have been developed for outdoor use in harsh environments without degrading the propagation properties of the fiber. The cable technology is smaller, faster, and easier to install (using a blown installation method). Alongside cables, various other technologies have been developed and integrated to provide a reliable end-to-end HCF network solution. This includes dedicated HCF-compatible equipment (shown in image 3), such as custom cable joint enclosures, fusion splicing technology, HCF patch tails for cable termination in the DC, and a HCF custom-designed Optical Time Domain Reflectometer (OTDR) to locate faults in the link. These solutions work with commercially available transponders and DWDM technologies to deliver multi-Tb/s capacities for Azure customers. Looking more closely at a HCF cable installation, in image 4 the cable is installed by passing it through a blowing-head (1) and inserting it into pre-installed conduit in segments underground along the route. As with traditional installations with conventional cable, the conduit, cable entry/exit, and cable joints are accessible through pre-installed access chambers, typically a few hundred meters apart. The blowing head uses high-pressure air from a compressor to push the cable into the conduit. A single drum-length of cable can be re-fleeted above ground (2) at multiple access points and re-jetted (3) over several kilometers. After the cables are installed inside the conduit, they are jointed at pre-designated access chamber locations. These house the purpose designed cable joint enclosures. Image 4: Cable preparation and installation during in-field deployment Image 5 shows a custom HCF cable joint enclosure in the field, tailored to protect HCFs for reliable data transmission. These enclosures organize the many HCF splices inside and are placed in underground chambers across the link. Image 5: 1) HCF joint enclosure in a chamber in-field 2) Open enclosure showing fiber loop storage protected by colored tubes at the rear-side of the joint 3) Open enclosure showing HCF spliced on multiple splice tray layers Inside the DC, connectorized ‘plug-and-play’ HCF-specific patch tails have been developed and installed for use with existing DWDM solutions. The patch tails interface between the HCF transmission and SMF active and passive equipment, each containing two SMF compatible connectors, coupled to the ISP HCF cable. In image 6, this has been terminated to a patch panel and mated with existing DWDM equipment inside the DC. Image 6: HCF patch tail solution connected to DWDM equipment Testing To validate the end-to-end quality of the installed HCF links (post deployment and during its operation), field deployable solutions have been developed and integrated to ensure all required transmission metrics are met and to identify and restore any faults before the link is ready for customer traffic. One such solution is Microsoft’s custom-designed HCF-specific OTDR, which helps measure individual splice losses and verify attenuation in all cable sections. This is checked against rigorous Azure HCF specification requirements. The OTDR tool is invaluable for locating high splice losses or faults that need to be reworked before the link can be brought into service. The diagram below shows an OTDR trace detecting splice locations and splice loss levels (dB) across a single strand of installed HCF. The OTDR can also continuously monitor HCF links and quickly locate faults, such as cable cuts, for quick recovery and remediation. For this deployment, a mean splice loss of 0.16dB was achieved, with some splices as low as 0.04dB, comparable to conventional fiber. Low attenuation and splice loss helps to maintain higher signal integrity, supporting longer transmission reach and higher traffic capacity. There are ongoing Azure HCF roadmap programs to continually improve this. Performance Before running customer traffic on the link, the fiber is tested to ensure reliable, error-free data transmission across the operating spectrum by counting lost or error bits. Once confirmed, the link is moved into production, allowing customer traffic to flow on the route. These optical tests, tailored to HCF, are carried out by the installer to meet Azure’s acceptance requirements. Image 8 illustrates the flow of traffic across a HCF link, dictated by changing demand on capacity and routing protocols in the region, which fluctuate throughout the day. The HCF span supports varying levels of customer traffic from the point the link was made live, without incurring any outages or link flaps. A critical metric for measuring transmission performance over each HCF path is the instantaneous Pre-Forward Error Correction (FEC) Bit Error Rate (BER) level. Pre-FEC BERs measure errors in a digital data stream at the receiver before any error correction is applied. This is crucial for transmission quality when the link carries data traffic; lower levels mean fewer errors and higher signal quality, essential for reliable data transmission. The following graph (image 9) shows the evolution of the Pre-FEC BER level on a HCF span once the link is live. A single strand of HCF is represented by a color, with all showing minimal fluctuation. This demonstrates very stable Pre-FEC BER levels, well below < -3.4 (log 10 ), across all 400G optical transponders, operating over all channels during a 24-day period. This indicates the network can handle high-data transmission efficiently with no Post-FEC errors, leading to high customer traffic performance and reliability. Image 9: Very stable Pre-FEC BER levels across the HCF span over 20 days The graph below demonstrates the optical loss stability over one entire span which is comprised of two HCF strands. It was monitored continuously over 20 days using the inbuilt line system and measured in both directions to assess the optical health of the HCF link. The new HCF cable paths are live and carrying customer traffic across multiple Azure regions. Having demonstrated the end-to-end deployment capabilities and network compatibility of the HCF solution, it is possible to take full advantage of the ultra-stable, high performance and reliable connectivity HCF delivers to Azure customers. What’s next? Unlocking the full potential of HCF requires compatible, end-to-end solutions. This blog outlines the holistic and deployable HCF systems we have developed to better serve our customers. While we further integrate HCF into more Azure Regions, our development roadmap continues. Smaller cables with more fibers and enhanced systems components to further increase the capacity of our solutions, standardized and simplified deployment and operations, as well as extending the deployable distance of HCF long haul transmission solutions. Creating a more stable, higher capacity, faster network will allow Azure to better serve all its customers. Learn more about how hollow core fiber is accelerating AI. Recently published HCF research papers: Ultra high resolution and long range OFDRs for characterizing and monitoring HCF DNANFs Unrepeated HCF transmission over spans up to 301.7km
