Expanded bandwidth yields a transmission rate of 402 terabits per second
An international team of researchers have smashed the world record for fiber optic communications through commercial-grade fiber. By broadening fiber’s communication bandwidth, the team has produced data rates four times as fast as existing commercial systems—and 33 percent better than the previous world record.
The researchers’ success derives in part from their innovative use of optical amplifiers to boost signals across communications bands that conventional fiber optics technology today less-frequently uses. “It’s just more spectrum, more or less,” says Ben Puttnam, chief senior researcher at the National Institute of Information and Communications Technology (NICT) in Koganei, Japan.
Puttnam says the researchers have built their communications hardware stack from optical amplifiers and other equipment developed, in part, by Nokia Bell Labs and the Hong Kong-based company Amonics. The assembled tech comprises six separate optical amplifiers that can squeeze optical signals through C-band wavelengths—the standard, workhorse communications band today—plus the less-popular U-, L-, S-, E-, and O-bands. (E- and O- bands are in the near-infrared; while S-band, C-band, L-, and O-bands are in what’s called short-wavelength infrared.)
All together, the combination of O, E, S, C, L, and U bands enables the new technology to push a staggering 402 terabits per second (Tbps) through the kinds of fiber optic cables that are already in the ground and underneath the oceans. Which is impressive when compared to the competition.
“The world’s best commercial systems are 100 terabits per second,” Puttnam says. “So we’re already doing about four times better.” Then, earlier this year, a team of researchers at Aston University in the Birmingham, England boasted what at the time was a record-setting 301 Tbps using much the same tech as the joint Japanese-British work—plus sharing a number of researchers between the two groups.
Puttnam adds that if one wanted to push everything to its utmost limits, more bandwidth still could be squeezed out of existing cables.
“If you really push everything, if you filled in all the gaps, and you had every channel the highest quality you can arrange, then probably 600 [Tbps] is the absolute limit,” Puttnam says.
Getting to 402 Tbps—or 600
The “C” in C-band stands for “conventional”—and C-band is the conventional communications band in fiber optics in part because signals in this region of spectrum experience low signal loss from the fiber. “Fiber loss is higher as you move away from C-band in both directions,” Puttnam says.
For instance, in much of the E-band and O-band, the same phenomenon that causes the sky to be blue and sunsets to be pink and red—Rayleigh scattering—makes the fiber less transparent for these regions of the infrared spectrum. And just as a foggy night sometimes requires fog lights, strong amplification of signals can be all the more significant when the fiber is less transparent than it is for the comparatively high-transparency C-band.
“The world’s best commercial systems are 100 terabits per second. We’re already doing about four times better.”—BEN PUTTNAM, NICT
Previous efforts to increase fiber optic bandwidths have often relied on what are called doped-fiber amplifiers (DFA)—in which an optical signal enters a modified stretch of fiber that’s been doped with a rare-earth ion like erbium. When a pump laser is shined into the fiber, the dopant elements in the fiber are pushed into higher energy states. That allows photons from the optical signal passing through the fiber to trigger a stimulated emission from the dopant elements. The result is a stronger (i.e. amplified) signal exiting the DFA fiber stretch than the one that entered it.
Bismuth is the dopant of choice for the E band. But even bismuth DFAs are still just the least-bad option for boosting E-band signals.They can sometimes be inefficient, with higher noise rates, and more limited bandwidths.
So Puttnam says the team developed a DFA that is co-doped with both bismuth and germanium. Then they added to the mix a kind of filter developed by Nokia that optimizes the amplifier performance and improves the signal quality.
“So you can control the spectrum to compensate for the variations of the amplifier,” Puttnam says.
Ultimately, he says, the amplifier can still do its job without overwhelming the original signal.New Fiber Optics Tech Smashes Data Rate Record Expanded bandwidth yields a transmission rate of 402 terabits per second
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