Infinera claims to have achieved the first 700 Gb/s transatlantic transmission over a single wavelength. The milestone marks the optical vendor’s latest trial of its Infinite Capacity Engine 6 (ICE 6) coherent optics on a production network.

The trial was conducted over the 6,600 kilometer Marea submarine cable, which stretches from Virginia Beach, Virginia to Bilbao, Spain. Completed in 2017, the sub-sea cable is among the most advanced ever deployed, and has since become the benchmark by which network vendor’s optics are measured.

“MAREA is the highest performing cable system in the world because it was specifically optimized for maximum capacity per fiber pair. It utilizes a large area, low-loss optical fiber type based on a pure silica core,” explained Steve Grubb, global network optical architect at Facebook, which operates several fiber pairs on the Marea cable. “Every vendor of submarine transponder equipment has trialed its transponder technology on this cable.”

It was over this cable that Infinera trialed its forthcoming ICE 6 coherent optics, achieving 30 Tb/s of total capacity and a peak line rate of 700 Gb/s on a single fiber pair. However, this is what Infinera is referring to as its “hero rate.” Under real-world conditions, the peak line rate across the transatlantic span diminished to between 650 Gb/s and 450 Gb/s with a total capacity of 28 Tb/s.

According to Pierre Mertz, a submarine networking engineer and fellow at Infinera, ICE 6 is pushing up against the "Shannon limit," which describes the theoretical bandwidth limit for a given cable. He explained that Infinera was able to achieve this by using lower baud rates. This is also partially why Infinera’s specified deployable line rate is given as a range instead of an absolute.

Baud rates are a measure of symbols per second. As a general rule, the higher the baud rate, the higher the peak line rate can go. However, Mertz explains that higher spectral efficiency can also be achieved by lowering the baud rate.

“The result is an optimal 450 Gb/s per wave in order to achieve 28 Tb/s in total,” he explained. “This is a really interesting result because it means that as a submarine network operator starts to fill the cable, they can operate at high data rates like 650 Gb/s, that are less spectrally efficient but more cost effective on an interface basis… And then as the cable utilization increases, they can switch to a lower data rate and higher spectral efficiency.”

In other words, Infinera can achieve a peak deployable line rate of 650 Gb/s, but the per wavelength line rate would have to be tuned down to achieve the maximum total capacity of the fiber of 28Tb/s.

Rob Shore, SVP of marketing at Infinera, told SDxCentral the performance demonstrated in this trial represents a considerable uptick in performance since the company’s latest trial in June where the company demonstrated 700 Gb/s transmission over 1,460 kilometers on Windstream’s network.

The production-ready transceivers used in the Marea trial are able to achieve 60% to 70% higher performance compared to the prototype modules, he said. “If we were to redo those terrestrial trials, you would see increased reaches of anywhere between 60% and 100%."

Infinera isn’t the first network operator to trial its coherent optics on the Marea submarine cable. However, it is a little tricky to make an apples-to-apples comparison of the various vendor’s performance as the constrains employed by their respective optics aren’t always broken out.

Both Ciena and Cisco have trialed their 800 Gb/s and 400 Gb/s capable coherent optics over the last year and a half. The most recent being Ciena, which trialed its WaveLogic 5 Extreme optics in October of last year. However, the company didn't disclose details of the trial.

“We were satisfied with the results, as we saw tangible benefits in the time it took to enable the spectrum of channels, as well as improvements in spectral efficiency on this open cable design,” said Brian Lavallée, senior director of marketing for Ciena’s 5G, packet, and submarine networking solutions.

Meanwhile, Cisco undertook a similar trial a little over a year ago using its Network Convergence System 1004 (NCS 1004) operating at 400 Gb/s to achieve 26.4 Tb/s of total capacity.