Hollow Core Fibre Matures

Hollow core enjoys 33% lower latency than standard solid core single mode fibre. Moreover, it offers at least 50% more bandwidth because a much wider spectrum band can be used. In contrast, solid glass is hobbled by high attenuation outside the C and L bands. A final advantage is hollow core exhibits little chromatic dispersion. Single mode fibre is bedeviled by polar mode and chromatic dispersion. In each case, the speed of light through glass varies sufficiently by wavelength to blur the signal by the time it reaches the far end. The coherent optics revolution was largely about using digital signal processing to unscramble the signal or more precisely to use physics to work backwards and infer the original, pristine signal.

But hollow core technology until now has been stymied by very high optical attenuation. This simply means the light fades rapidly as it passes through the hollow core. The light is absorbed rapidly by the surrounding glass border due to the absence of refraction. In solid fibre cores light bounces off the border and back into the core. In hollow core this internal reflection is absent.

Recently Microsoft-owned Lumensity developed a new design that achieves attenuation 30% lower than standard solid core single mode fibre. Below .1 db/km at 1550 nanometers. This breakthrough means that hollow core is no longer a niche application limited to 20 kilometers or less, but a real candidate to replace the current generation of single mode fibre. Here is the link to the Nature Photonics publication detailing the performance tests: https://lnkd.in/dynyEzBT.

At this point the remaining challenge is to reduce cost via large scale production. Azure is determined to deploy hollow core fibre in its global network to dramatically improve its performance and also trigger the large scale production required to fully exploit the economies of scale. If costs can be brought down to levels comparable with single mode fibre, then we might have an optical network revolution

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