Scientists ride new fiber wavelengths for terabit speed

  • A team of researchers got to terabit speeds using E- and S-band spectrum over a single optical fiber

  • Historically, C-band was the exclusive spectrum used within fiber to transmit data

  • The method might not be employed anytime soon, but using the additional E- and S-bands could increase fiber network capacity years from now

Fiber research is heading into uncharted waters. A team of scientists in the U.K. recently hit a new speed record using wavelength bands that aren't usually used in fiber optic systems.

In partnership with the National Institute of Information and Communications Technology (NICT) in Japan and Nokia Bell Labs in the U.S., Aston University researchers were able to transfer data at a rate of 301,000,000 megabits per second using a single standard optical fiber. To put this into perspective, that’s over a million times faster than the average download speed of 242.4 Mbps in the U.S.

In very simple terms, fiber strands operate by sending waves of light through fiber optic glass to transmit data. It’s how many of us get our internet today. Historically, C-band was the exclusive spectrum used within fiber to transmit data, but L-band usage is becoming more commonplace.

One day, networks will need more capacity than those bands can provide. “When we think of a fiber strand, we always kind of imagine it's a limitless amount of capacity you can put in there,” Dell’Oro analyst Jimmy Yu told Fierce Network. “But it's actually fixed by the frequency band that you can use.”

The team at Aston University came up with an optical amplifier and an optical processing unit that can access the E- and S-bands. Those devices allow them “to control the light within a particular band or a particular wavelength,” explained Aston professor Ian Phillips. Essentially, the new wavelength bands are like sending different colors of light down the optical fiber.

The technology used to achieve these speeds is aimed at the backbone of the network, but Phillips said using the S- and E-bands to increase the capacity of the core could potentially “ripple down” broadband distribution networks and eventually, bring higher capacity for fiber-to-the-home.

Yu said it’s a new trend among researchers to find ways to increase the amount of spectrum that's available within a single strand of fiber. Just like in the airwaves, there’s additional spectrum available to carry more data on a single strand.

This could be important for companies like hyperscalers who lease long-distance fiber strands from telecom operators. “You're paying some fixed amount for that fiber strand, but if you could put more and more capacity on it, then your inherent costs go down and you don't need to lease another fiber strand,” Yu told Fierce Network.

Amplifier nitty gritty

Often, high-power Erbium-Doped Fiber Amplifiers (EDFAs) and multi-way splitters are used in fiber networks for downstream traffic. The EDFA is based on the rare earth element Erbium.

The amplifiers used at Aston University have similar operating principles to EDFAs, Phillips told Fierce, but they use different rare earth elements doped into the fiber core to amplify signals. For example, Thulium is used in the S-band of the optical spectrum, while Bismuth-Doped Fiber Amplifiers (BDFAs) are used in the E-band.

Aston researchers also have an active research project investigating “Discrete and distributed Raman amplification,” Phillips said, which uses a different amplification technique and has the advantage of working in different optical bands.

Importantly, amplifier technology is not yet used in PON networks. Dell’Oro analyst Jeff Heynen said vendors are currently still working on the upstream wavelength utilization for 50G PON, and there are efforts underway to develop 100G and 200G PON variants.

According to Phillips, there have been a number of research projects to get Wavelength Division Multiplexing (WDM)-PON implemented, but the technology’s price tag has limited progress. “The wavelength processor would currently be considered expensive and unnecessary if related to the current design principles,” he added.

Phillips noted there have been a few WDM-PON experiments where researchers have investigated the wavelength selective switch (an optical processor), but he thinks “it is unlikely to be adopted in PON in near term, at least.”

What’s new here?

Although 301 terabits is impressive, the speed achievement itself is not especially rare. Phillips said the work around enhancing fiber optic speeds is “a slow evolution where every year, somebody improves it by 10 to 20%.”

Other records have been set through different methods of improving fiber capacity. In Japan, NICT set a speed record of 22.9 petabits per second using multi-core fiber and the C- and L-bands. Most optical fiber has a single core, or single piece of glass that can transmit data. In that case, NICT transmitted signals over 19 cores within an optical fiber.

The real news from the Aston experiment is the use of the S- and E-band spectrum, and especially through the use of a standard single fiber optic cable.

Most of the fiber that’s already in use is standard telecommunications fiber called SMF-28. That means a lot of these new multi-core fiber or multi-mode fibers would need to be installed — “and installing fiber is a very expensive process,” Phillips said. “You've got a choice to install a new fiber or try and increase the capacity on the carbon fiber. This technique, in principle, would allow us to use the existing infrastructure.”

That said, actually adopting these new methods and technologies is a long process. And like many things, "it will come down to economics," meaning there needs to be a business case for systems suppliers and telecom providers to adopt them. It could be years before we actually see the E- and S-bands used on real-life telecom networks.

In the meantime, the team at Aston is continuing their research, including improving performance on fiber optic lines. Additionally, Phillips said they’re looking at other optical bands — “There’s a U-band as well, which is above the L-band,” he noted — and trying to get further improvements and transmission performance in those bands.