Northern Sweden—Bornholm—Berlin: New gigabit fibre-optic cable can transfer three petabits per second

Illustration: GlobalConnect

We will shift into higher gear next year when GlobalConnect starts transporting data through a new mega-capacity cable that stretches 2500 kilometres of fibre from Luleå in northern Sweden all the way to Berlin.

The cable consists of a total of 192 fibres. On certain stretches on land, the number is even higher.

“We can support a traffic of three petabits per second. The limitation is not in the raw fibre, but in the optical transport systems used to direct the network traffic. We have significantly upgraded this transport system over the past two years,” says Anders Saaby, CTO of GlobalConnect, which supplies fibre-optic connections in the Nordic region.

When his colleague Anders Poulsen, who is head of projects and in charge of the project, started working in the telecommunications industry, speed and capacity in the telephone network were calculated according to how many conversations could be going on at the same time. Today, the unit of measurement has been converted into streaming devices.

“Today, the unit of measurement is the number of Netflix users watching video in HD. The new cable has a capacity equivalent to 640 million Netflix users watching HD video at the same time,” says Anders Poulsen.

GlobalConnect is nearing completion of the excavation work on Bornholm. The new mega cable is expected to be ready in the autumn of 2022. Illustration: GlobalConnect

The capacity of the cable is expected to be around three petabits per second. The cable is a single-mode G652D fibre, and there are 192 fibres in a tube.

“With the new cable, we can deliver up to 400 Gbit/s connections from the town of Nørre Nebel on Jutland’s west coast to Stockholm without having to continuously reinforce them with more active equipment along the way,” says Anders Saaby.

The route runs on land, under sea, and via several islands in the Baltic Sea.

“It is absolutely central that the route is as direct as possible, as distance can be translated directly to latency of the fibre. The line is—despite a bit of a zigzag—the most direct possible route through the eastern part of the Nordic region,” says Anders Saaby.

Bornholm will become a hub for the west

Several of Ingeniøren’s readers have wondered why GlobalConnect has chosen to lay the large mega cable across Bornholm instead of choosing the sea route and thus avoiding costly excavation work on the granite island.

“There are two reasons. In part, Bornholm is an important hub northwards to Sweden, westwards to Denmark and southwards to Germany. At the same time, we want to limit the distance of the submarine cables, as there is a certain attenuation in an optical fibre over distance,” says Anders Saaby.

On Bornholm, the new mega cable is connected to Jutland’s west coast as a landing point for several overseas connections to North America.

Other than on Bornholm, the mega cable also goes ashore on Öland and Gotland on the way from Stockholm to Bornholm.

“Fibre has a certain maximum distance before one has to actively amplify and boost the signal. That reinforcement should preferably take place on land, as otherwise we would have to use a different type of submarine cable with underwater reinforcement. That type of long-distance submarine cable has less capacity, so we want to avoid that,” says Anders Poulsen.

Roadmap for 800 Gbit/s

It is not the optical fibre itself that increases the capacity of the connection. It is the technological upgrades of the active equipment, such as the optical transport system and the amplifiers that boost the signal along the way.

“The latest transport platform is geared for connections between 100 Gbit/s and 400 Gbit/s. We have already tested 600 Gbit/s and have a roadmap ready for up to 800 Gbit/s. This type of a generational leap occurs every five to 10 years, and the raw optical fibre can keep up with that,” says Anders Saaby.

He points to the increased precision of the lasers that fire light into the fibre, and the ability to work around noise and attenuation as the main technological advances in recent years.

The new mega cable has a life expectancy of up to 30 years.

“The cable is depreciated over 25–30 years, but some technologies are so new that we do not yet have experience with how long the service life really is. But in our experience, the cables can last longer than assumed,” says Anders Saaby.

The existing submarine cables within Denmark, between Denmark and Germany, and between Denmark and Sweden have broken just three to four times in the last twenty years. When the fibre is installed on land, a duct is first placed in a trench, and the fibre is then jetted into it. This is not the case at sea, where ducts and fibres are laid together.

“As a starting point, the fibre should preferably be laid one meter down in the seabed. It depends on the conditions of the seabed, and around the cliffs of Bornholm the cable is laid on top of the seabed and is then protected,” says Anders Poulsen.

The sea can cause a big headache

He says that the most challenging part of the project is at sea.

“There are so many considerations that need to be taken into account by authorities and other stakeholders when we are in open waters. Here, the Danish authorities must be commended on a process that is much more flexible than in Sweden and Germany.”

Right now, the project is in full swing, and it is expected that the cable can be put into use within a year, in the autumn of 2022.

“We are working everywhere right now. We are almost done on Bornholm. Because the route is so long, we conduct work as parallel as possible. Time is a crucial factor, as we already have customers for the cable,” says Anders Saaby.

The project has a budget of EUR 50 million, i.e. about DKK 371 million.

With the prospect of another long winter with video conferences and the coronavirus, Anders Saaby emphasizes that it is not the fibre connections that are the main cause of the time pressure.

“I want to guarantee that we do not become the bottleneck. The capacity of fibre-optic cables, optical transport networks, and service platforms is so well designed that we are ready for a new pandemic,” says Anders Saaby.