Single-core hollow fiber for data center interconnects

Single-core hollow-core fiber (HCF) offers ultra-low latency and high-speed interconnects for modern data centers by guiding light through an air-filled core instead of solid glass.

Design and Operation

Single-core hollow-core fiber replaces the solid glass core of conventional single-mode fiber (SMF) with a central air or gas-filled channel, surrounded by a microstructured glass cladding. Light is confined using photonic bandgap or anti-resonant effects, rather than total internal reflection in glass. Common designs, such as the “revolver” anti-resonant structure, feature a central air core encircled by thin silica tubes, keeping over 99% of the optical mode in air, which dramatically reduces interaction with glass and associated latency .

Performance Advantages

• Lower Latency: Light travels faster in air (refractive index ~1.0) than in silica glass (~1.5), resulting in 30–47% lower latency compared to SMF. Typical HCF latency is around 1.5–3.33 µs/km, versus 2.0–4.9 µs/km for conventional SMF . This is critical for AI workloads, high-frequency trading, and distributed computing across multiple data centers.
• Reduced Nonlinear Effects: Minimal light-glass interaction reduces optical distortions, improving signal quality and allowing higher optical power without thermal damage .
• Low Loss: Modern HCF designs have achieved losses below 0.2 dB/km, approaching or even surpassing high-quality SMF, enabling longer interconnect distances without amplification .
• High Bandwidth and PMD Stability: HCF supports high-speed links (800G/1.6T fabrics) with polarization mode dispersion (PMD) values below 0.1 ps/√km, suitable for hyperscale data center interconnects .

Applications in Data Centers

HCF is increasingly deployed in AI and cloud data centers to interconnect geographically distributed facilities. For example, Microsoft has implemented HCF between Azure data centers in Europe, and hyperscale operators are using it to reduce latency for AI model training and real-time data synchronization . Its low-latency and high-bandwidth characteristics make it ideal for:

• AI and high-performance computing clusters
• Financial trading networks
• Quantum communication links
• Edge computing and 5G/6G infrastructure

Challenges and Considerations

While HCF offers significant advantages, adoption is limited by manufacturing complexity, cost, and the need for specialized splicing and handling techniques. However, advances in nested anti-resonant designs and improved fabrication have made single-core HCF increasingly practical for production deployments .

Summary

Single-core hollow-core fiber represents a major advancement over conventional SMF for data center interconnects, providing ultra-low latency, low loss, and high bandwidth. Its air-guided design enables faster light propagation, reduced nonlinearities, and longer reach, making it particularly valuable for AI, cloud, and hyperscale data center networks where every microsecond counts .