Published by: Research & Development Department, Technologie Optic.ca Inc., November 2025

Introduction

Modern data centers need lightning-fast communication links, and even small delays can hurt performance. Traditional fiber-optic cables send data through solid glass cores, which slows light by about 30% compared to air. In practice, standard fiber adds roughly 5 microseconds of latency per kilometer. A new solution is emerging: hollow-core fiber (HCF), which uses an air-filled core. By letting light travel through air, HCF cuts latency dramatically – roughly 30–50% lower delay over the same distance than conventional glass fiber. This innovation promises ultra-low latency links between data centres, pushing network performance closer to the speed of light.

Application Context

Inter-data-centre communication is critical for cloud computing, financial trading, and other real-time services. Companies often maintain multiple data centres that must mirror databases or share workloads in real time, so every microsecond of network delay matters. Some industries have even resorted to microwave radio links to beat fiber latency, sacrificing capacity for speed. Hollow-core fiber offers a compelling alternative: it provides fiber-optic reliability and high bandwidth while significantly reducing latency. Trials have shown around a one-third drop in latency on metropolitan links using HCF – for example, a 40 km hollow-fiber circuit delivered about 33% lower round-trip time than the same route on standard fiber. Such improvements are significant for data centre interconnects (DCI), where links often span tens or hundreds of kilometers.

Lower latency between data centres means faster data replication, more responsive cloud applications, and better performance for distributed computing. A cluster of servers split between sites can communicate more efficiently when connected by HCF links, almost as if they were in one location. This can especially benefit high-frequency trading networks (where nanoseconds can influence profits) and enable more seamless collaboration between distant cloud data centres.

Fundamentals of Hollow-Core Fiber

HCF resembles ordinary fiber in appearance, but its operation is very different. Instead of a solid silica core, it has a hollow core filled with air and is surrounded by a ring of engineered glass structure in the cladding. This design uses reflective optical effects to confine light in the empty core, essentially forming a tiny air tunnel for the signal. Because light travels through air nearly as fast as in a vacuum (~3×10⁸ m/s versus ~2×10⁸ m/s in glass), signals in a hollow-core fiber move much faster than in standard fiber. In practical terms, standard fiber introduces about 5 µs of delay per km, while HCF only adds on the order of 3.3–3.5 µs/km. Over long distances, these savings accumulate into milliseconds of reduced latency.

Another benefit of HCF’s design is the reduced interaction between light and material. In a traditional fiber, light can scatter and disperse as it travels through glass, causing signal loss and distortion at high power. In hollow-core fibers, light mostly travels in air, so attenuation is minimized and optical distortions are virtually eliminated. In short, HCF acts as an ultra-clear, high-speed pipeline for light signals.

Technical Insights and Developments

Years of R&D have brought hollow-core fiber to the cusp of practical use. A major breakthrough came in 2024 when researchers demonstrated an HCF with only ~0.09 dB/km of signal loss – better than the best conventional fiber (~0.14 dB/km). This record-low loss, achieved by a Microsoft and University of Southampton team, shows that hollow fibers can now match or exceed standard fibers in core performance. One big implication is that fewer optical amplifiers are needed on long HCF routes, potentially cutting the number of amplification sites and reducing network costs and complexity.

Real-world tests have verified HCF’s advantages. Comcast in the U.S. reported roughly one-third lower latency on a 40 km hollow-core link compared to an equivalent glass-fiber link. Similarly, European provider euNetworks deployed a 45 km HCF to connect two London data centres, demonstrating the technology’s readiness for live network traffic. These early deployments prove that HCF can integrate with existing infrastructure and deliver the promised latency gains without sacrificing data-carrying capacity.

Industry players are now investing heavily in hollow-core fiber. Microsoft, for example, acquired HCF manufacturer Lumenisity and plans to install 15,000 km of hollow-core fiber in its Azure cloud backbone to accelerate global data connectivity.

Advantages of HCF for Inter-Data-Centre Links

• Ultra-Low Latency: Propagating through air yields roughly 30–50% less latency per kilometer. This provides a significant edge in latency-critical operations like high-speed trading and distributed databases.
• High Data Capacity: Hollow-core fibers can carry huge volumes of data with minimal distortion. Greatly reduced nonlinear effects allow higher signal power and more wavelength channels without performance degradation.
• Low Signal Loss: The newest HCF designs have attenuation on par with or even below that of top silica fibers. This enables longer links between data centres with fewer signal boosters (amplifiers) needed along the way.

Limitations and Challenges

• Complex Manufacturing: Building HCF is difficult and currently costly. It requires extremely precise fabrication of microscopic glass structures, so production is not yet as scalable or economical as standard fiber.
• Integration & Handling: Special techniques are required to splice or connect HCF with traditional fiber systems without high losses. Also, hollow-core fibers are somewhat more sensitive to bending and physical stress, so installation must follow stricter handling guidelines to avoid performance degradation.

Conclusion

Hollow-core fiber is poised to transform inter-data-centre connectivity by slashing transmission delays without sacrificing bandwidth. Early deployments have shown that hollow-core links can seamlessly integrate with existing networks and deliver on their latency promises. As the technology matures and production becomes more efficient, HCF will likely be adopted first in high-value, latency-critical routes – for example connecting major data centres and financial exchanges. Over time, broader use of hollow-core fiber could become a cornerstone of next-generation networks, effectively shrinking distances through near light-speed communication. Ultra-low latency inter-data-centre links using hollow-core fiber offer a promising solution to meet the growing demand for speed in our digital world.