Deeper dive — What is hollow core fiber?

U.K. operator BT recently made headlines when it revealed trials of an advanced optical technology known as hollow core fiber (HCF). At the time, the company touted HCF as a potential tool to help slash network costs and enable advanced use cases with latency-sensitive requirements. But what exactly is hollow core fiber, how might it change the game and when?

BT’s trial partner Lumenisity is a key player in the HCF market and has been deploying HCF in production networks in North America and Europe for the past four years. Tony Pearson, Lumenisity’s business development director, told Fierce the fundamental idea behind hollow core is that light travels faster through air than glass. Thus, as the name implies, HCF cables have been designed to have an air-filled center channel which is surrounded by a ring of glass tubes. Generally, a cross-section of a hollow core cable looks a bit like honeycomb with a hole in the middle.

Pearson explained HCF has been around for about 20 years, but until now has been plagued by high loss and other performance issues. Thus far, Lumenisity has been able to get the loss per kilometer down to around 1 decibel (compared to around 0.2 dB/km for traditional single mode fiber), but Pearson said the physics indicate it should be able to reduce the loss even further. To do this, it’s looking to process improvements in how it manufactures its cables.

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Lumenisity is in the midst of building a new fabrication facility in the U.K. and expects to be in production there by Q1 2022. Once that’s up and running, he said, it can do additional development work, with the goal of nearing or achieving loss performance equivalent to glass fiber in the 2023 timeframe.

Why it matters

But even once it reaches this milestone, Pearson said the goal isn’t to compete with glass fiber. Instead, HCF is meant to do things traditional fiber can't.

He explained HCF’s ability to minimize chromatic dispersion allows more wavelengths to be launched into a single fiber without interwave mixing, meaning operators can launch more channels for higher capacity. This characteristic also means there’s no need for digital signal processors to compensate for chromatic dispersion, allowing transceivers to become simpler and cheaper, ultimately reducing the cost of a given route. Higher power can also be used since HCF minimizes scattering, which, assuming the same loss as glass fiber, would provide a longer reach.

A range of players have expressed interest in the technology, including carriers, high-frequency traders and the gaming industry. Pearson said hyperscalers are particularly keen since HCF has the potential to extend the range of availability zones around data centers without a drop in latency performance.

To make these benefits a reality, “there’s only loss left to conqueror, and we’re working on that,” Pearson said.