Hollow-Core Fiber: Lower Latency for AI and DCI — Ready for Data Centers?
Hollow-core fiber (HCF) guides light through an air core instead of solid glass. Light in air travels about 47% faster than in silica, so every kilometer saves about 1.5 µs of one-way delay. A 2025 research fiber of the DNANF design reached 0.091 dB/km at 1,550 nm, lower than the 0.14 dB/km record for solid-core fiber. The gain matters on metro and data center interconnect (DCI) routes of tens of kilometers. Inside a data center hall, links are short, so standard OS2 and multimode cabling remain the practical choice.
How Hollow-Core Fiber Works
A standard single-mode fiber has a solid glass core about 9 µm across. A hollow-core fiber has an air core, about 29 µm in the published DNANF design, surrounded by thin glass membranes. DNANF stands for double nested antiresonant nodeless fiber: nested glass tubes around the core reflect light back into the air, so very little light travels in glass.
| Standard single-mode (OS2) | Hollow-core (DNANF, research 2025) | |
|---|---|---|
| Core | Solid silica | Air |
| Loss at 1,550 nm | ~0.2 dB/km typical; 0.14 dB/km record | 0.091 dB/km measured |
| Low-loss window (<0.2 dB/km) | about 26 THz | 66 THz |
| Chromatic dispersion | reference | about 6× lower |
| Speed of light | about 2/3 of c | close to c (about 45–47% faster) |
Figures from the 2025 Nature Photonics paper and the research group's release. Typical OS2 loss is a general value; check the cable datasheet.
Latency: What 47% Faster Means
Light needs about 4.9 µs per km in silica and about 3.34 µs per km in air. The difference is about 1.56 µs per km, one way (derived from the speed of light and a typical silica group index of about 1.468).
| Link (example) | Length | One-way saving |
|---|---|---|
| Row-to-row in a hall | 100 m | about 0.16 µs |
| Campus between buildings | 10 km | about 16 µs |
| Metro DCI | 80 km | about 125 µs |
All rows are derived examples. Put another way: for the same latency budget, a data center can sit about 47% farther away on HCF. That is why the first users are cloud operators linking sites for AI training and inference, not data center halls.
Is It Ready for Data Centers?
- Inside the hall: not needed yet. A 0.16 µs saving on 100 m is far smaller than the latency of one switch hop. Short links are limited by optics and switches, not by fiber speed.
- DCI and metro: early deployments. The latency and loss gains add up over tens of kilometers, and lower loss means fewer amplifiers.
- Interconnect is different. HCF needs specialist splicing and connection to standard single-mode fiber at each end. It does not use today's MPO patching in the same way, and it is not covered by the IEC/TIA connector standards used for OS2.
- Cost and supply. HCF is made in small volumes compared with standard single-mode fiber.
For links inside the data center, plan structured OS2 or multimode cabling as before. See OS2 vs OM4 vs OM5 and the 802.3dj guide. For new switch architectures, see co-packaged optics.
Frequently Asked Questions
What is hollow-core fiber?
An optical fiber that guides light through an air core surrounded by a glass microstructure, instead of through solid glass.
How much faster is hollow-core fiber?
Light travels about 45–47% faster than in standard fiber. That saves about 1.5 µs of one-way delay per kilometer.
What is DNANF?
Double nested antiresonant nodeless fiber, a hollow-core design. A 2025 research fiber of this type measured 0.091 dB/km at 1,550 nm.
Should I use hollow-core fiber inside my data center?
Usually not yet. Links inside a hall are short, so the latency saving is a fraction of a microsecond. Standard OS2 and multimode cabling remain the practical choice.
Can hollow-core fiber use MPO connectors?
Not in the same way as standard fiber today. HCF links are usually spliced to standard single-mode fiber at each end, and the standard MPO cabling is on that side.
Huawellux Single-Mode Cabling
Huawellux does not supply hollow-core fiber. We build OS2 single-mode and multimode MPO trunks, cords and harnesses for the links inside and between data center halls, to order. Huawellux can also supply bend-insensitive fiber.
Huawellux's specification for MPO and MTP® assemblies (identical for both) is insertion loss ≤0.35 dB for single-mode and multimode, with return loss >60 dB single-mode (OS2, APC) and >30 dB multimode (OM3/OM4/OM5). LC and SC patch cords are listed at insertion loss ≤0.35 dB and return loss ≥50 dB (single-mode UPC), ≥60 dB (single-mode APC) and >30 dB (multimode). Every Huawellux product receives end-face visual inspection under a 400x video microscope and is tested for insertion loss (IL) and return loss (RL) before it ships. Interferometric end-face geometry (fiber height, coplanarity, end-face angle and radius) is checked by sample-based testing in standard production, and 100% interferometer testing of a batch is available on request. Dust caps are fitted on every connector, and a formal test report is available on request.
Huawellux replies to inquiries within 24 hours. Custom orders typically take 1–5 business days to complete production, with final timing confirmed case by case in the quotation. For special/custom requirements, MOQ is 2 km of fiber length. Standard listed patch cords have no formal MOQ. The sample fee is credited against the bulk order.
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