Researchers create fiber network that operates at 99.7% speed of light, smashes speed and latency records

Researchers at the University of Southampton in England have produced optical fibers that can transfer data at 99.7% of the universe’s speed limit: The speed of light. The researchers have used these new optical fibers to transfer data at 73.7 terabits per second — roughly 10 terabytes per second, and some 1,000 times faster than today’s state-of-the-art 40-gigabit fiber optic links, and at much lower latency.

The speed of light in a vacuum is 299,792,458 meters per second, or 186,282 miles per second. In any other medium, though, it’s generally a lot slower. In normal optical fibers (silica glass), light travels a full 31% slower. Light actually travels faster through air than glass — which leads us neatly onto the creation of Francesco Poletti and the other members of his University of Southampton team: A hollow optical fiber that is mostly made of air. 

It might seem counterintuitive, transmitting light down fibers made primarily of air, but look around you: If light didn’t travel well through air, then you’d a hard time seeing. It isn’t like researchers haven’t tried making hollow optical fibers before, of course, but you run into trouble when trying to bend around corners. In normal optical fiber, the glass or plastic material has a refractive index, which causes light to bounce around inside the fiber, allowing it to travel long distances, or Remove the glass/plastic and the light just hits the outer casing, causing the signal to fizzle almost immediately. The glass-air interface inside each fiber also causes issues, causing interference and limiting the total optical bandwidth of the link.

The researchers overcame these issues by fundamentally improving the hollow core design, using an ultra-thin photonic-bandgap rim. This new design enables low loss (3.5 dB/km), wide bandwidth (160nm), and latency that blows the doors off normal optic fiber — light, and thus the data, really is travelling 31% faster down this new hollow fiber. To achieve the transmission rate of 73.7 terabits per second, the researchers used wave division multiplexing (WDM), combined with mode division multiplexing, to transmit three modes of 96 channels of 256Gbps. Mode division multiplexing is a new technology that seems to involve spatial filtering — rotating the signals with a polarizer, so that more of fiber can be used. As far as we’re aware, this is one of the fastest ever transmission rates in the lab. 

As for real-world applications, loss of 3.5 dB/km is okay, but it won’t be replacing normal glass fiber any time soon. For short stretches, though, such as in data centers and supercomputer interconnects, these speed-of-light fibers could provide a very significant speed and latency boost.