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Hollow Core Fiber

BT, formerly known as British Telecom has been working with Lumenisity to greatly improve the performance of hollow core fiber. This is fiber that takes advantage of the fact that light travels faster through air than it does through glass. In a hollow core fiber, air fills center tubes surrounded by glass. As can be seen by the picture accompanying this blog, multiple tubes of glass and air are created inside a single fiber creating a honeycomb effect.

There was news about hollow core fiber a decade ago when a lab at DARPA worked with Honeywell to improve the performance of the fiber. They found then that they could create a single straight path of light in the tubes that was perfect for military applications. The light could carry more bandwidth for greater distances without having to be regenerated. By not bouncing through glass, the signal maintained intensity for longer distances. DARPA found the fixed orientation of light inside the tubes to be of great value for communication with military-grade gyroscopes.

Until the recent breakthrough, the hollow tube fiber was plagued by periodic high signal loss when the light signal lost it’s straight-path coherence. Lumenisity has been able to lower signal loss to 1 dB per kilometer, which is still higher than the 0.2 dB loss expected for traditional fiber. However, the lab trials indicate that better manufacturing process should be able to significantly lower signal loss.

The Lumenisity breakthrough comes from the ability to combine multiple wavelengths of light while avoiding the phenomenon known as interwave mixing where different light frequencies interfere with each other. By minimizing signal dispersion, Lumenisity has eliminated the need for digital signal processors that are used in other fiber to compensate for chromatic dispersion. This means repeater sites that can be placed further apart and that require simpler and cheaper electronics.

Lumenisity doesn’t see hollow core fiber being used as a replacement on most fiber routes. The real benefits come in situations that require low latency along with high bandwidth. For example, the hollow core fiber might be used to feed the trading desks on Wall Street. The fiber might improve performance for fiber leaving big data centers.

Lumenisity is building a factory in the U.K. to manufacture hollow core fiber and expects to have it in mass production by 2023.

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