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Fiber cables made of air move data at 99.7 percent the speed of light

Researchers say they have created fiber cables that can move data at 99.7 percent of the speed of light, all but eliminating the latency plaguing standard fiber technology. There are still data loss problems to be overcome before the cables could be used over long distances, but the research may be an important step toward incredibly low-latency data transmissions.

Although optic fibers transmit information using beams of light, that information doesn't actually go at "light speed." The speed of light, about 300,000 km/s, is the speed light travels in a vacuum. In a medium such as glass, it goes about 30 percent slower, a mere 200,000 km/s."[L]ight propagates 31% slower in a silica glass fibre than in vacuum, thus compromising latency," notes a paper published Sunday in Nature Photonics, titled "Towards high-capacity fibre-optic communications at the speed of light in vacuum."
The research team from the University of Southampton in England solved this problem by taking the glass out of the glass fiber. This results in a "hollow-core photonic-bandgap fibre," which is made mostly of air yet still allows light to follow the path of the cable when it twists and turns.
The methods used by the researchers result in data loss of 3.5 dB/km, an impressively low number considering its incredibly low latency. However, that data loss is still too high for long-range communications. For now, these cables won't be used to wire up Internet Service Provider networks or for transatlantic cables.The cable uses wide-bandwidth channels to send 37 streams of 40 gigabits per second each, with an aggregate transmission capacity of 1.48Tbps. Even with the current rate of data loss, the researchers say the cable technology is adequate for "short reach low-latency applications," such as future exaflop-speed supercomputers and "mega data centres.""For longer transmission distances, additional work is needed to further reduce surface scattering loss and to achieve the sub-0.2 dB km," the researchers wrote.
Although this wasn't described in the paper, one of the researchers told ExtremeTech that the cable's throughput actually goes up to 73.7Tbps, "using wave division multiplexing (WDM), combined with mode division multiplexing, to transmit three modes of 96 channels of 256Gbps."