Submarine cables from Calais

Submarine cables from Calais

Today, Calais is best known as the French terminus of the Channel Tunnel. But, in the world of submarine cables, Calais is also known for the tunnel between the Alcatel Submarine Networks plant and the port. “Our factory is one of the biggest in the world and has been making submarine cables for 120 years” says factory manager Patricia Boulanger with some pride. ASN currently belongs to Finnish telecommunications group, Nokia.

Most of the 600,000km of cable produced in Calais to date was loaded via this tunnel. The ASN fleet of cableships is operated by Louis Dreyfus Armateurs. “ASN has six ships. Three cable layers (Île de Sein, Île de Batz and Île de Bréhat) and three cable repair vessels (Peter Faber, Lodbrog and Île d’Aix). We’re very happy with our ships and with LDA, our operator. The fleet is well suited to our needs, although changes are made as our needs change. A case in point is the recent cable laying project in Alaska where the crew and the shore team had to develop innovative solutions to overcome location-specific challenges.”

Cable layers come to Calais to load hundreds of kilometres of ASN cable at a time into their tanks. “Our production numbers are impressive; every year, we use the equivalent, by weight, of two Eiffel towers of steel for the metal braid that protects our fibre optic cables.”


Plant-side entrance to ASN cable tunnel, Calais harbour (© Mer et Marine – Caroline Britz)

Cable layer Île de Bréhat (© Michel Floch)

Cable repair vessel Peter Faber (© Michel Floch)

With a diameter of just 250µm — the thickness of, say, medium-gauge plastic sheeting — the optical fibre is a technological marvel. Submarine cables transmitting data between continents at higher and higher speeds criss-cross every ocean and sea. While long the preserve of telecoms majors, today the leading clients for submarine cables are over-the-top companies providing web-based services — led by giants like Google, Apple, Facebook and Amazon — that are now deploying their own inter-continental networks to transmit data ever faster. As a result, the ASN plant at Calais is fairly buzzing. ASN offers a turnkey service, working closely with ASN Greenwich in the UK, which specialises in repeaters, branching units and related items.


Optical fibres (diameter: 250 µm) for a submarine cable (© Alcatel Submarine Networks)


“Each cable of each network is different, if only to accommodate local conditions. One of the first steps in any submarine cable project is a detailed survey of the seabed along the proposed route.” This work is performed by survey vessels that collect data on water depth, seabed features, temperature profiles, and so on. “After reviewing the survey results and the client’s needs, we design the network, choose the types of cables and obtain permits to build the landing stations that provide connections to terrestrial networks.”

Local seabed conditions dictate the number and types of layers needed to protect the fibre optic core. “The fragile core must be protected. But first, we colour-code the fibres so that they can be correctly identified in the event of repairs. Next, we assemble the core and feed it into a stainless steel buffer tube containing a blocking compound to minimise fibre ageing due to the presence of hydrogen. Next comes a layer of steel braid to protect the core against the high pressures encountered in deep water, the thickness of the braid depending on the depth of immersion, followed by a conducting copper tube with an outer insulating sheath. “Different types of outer protection are used, depending on the anticipated hazards and conditions.


Colour-coding optical fibres (© ASN)

Cable cross-section. Note multiple layers of protection (© ASN)

Protective layers for different seabed conditions (© ASN)


The next step is to assemble great lengths of cable, complete with repeaters. The cable is then coiled down in the plant’s storage drums ready to be loaded. “Every cable is custom made with extreme attention to every detail. Each join and each layer of protection must be faultless.” After the network has been laid, its propagation performance is tested. “Once the network has been commissioned, we provide network maintenance.”


Cable assembly area (© Mer et Marine – Caroline Britz)

Coiling cable in a tank (© ASN)

View over sheave while laying a cable (© ASN)

A cable plough is lowered into the water (© ASN)

Plough on seabed ready to lay and bury a cable (© ASN)

A repeater goes into the water (© ASN)

Laying a shore end (© ASN)

Shore end on beach (© ASN)


The 400 or so people who work at ASN’s Calais plant are proud of their know-how. “We work in a highly specialised field with demanding technical requirements at every level, from line operators to our 60-strong R&D department.” To ensure that everyone has the required skills, we have our own on-site training centre “which helps us to maintain our ties with the community as we continue to employ and train local people where possible”.

While the submarine cable market is both cyclical and highly competitive, ASN Calais has good contracts in its orderbook. “First, there’s the 12,000-km Brusa network between Brazil and the United States, then the Ace network linking Europe and South Africa. The Brusa network will be laid by the Île de Bréhat and the Île de Sein.” Africa currently offers the brightest prospects, followed by Asia and the Pacific where a number of projects aim to bring Internet connectivity to far-flung islands and archipelagos.

“Naturally, we’re always prospecting for new business. But we’re also looking for new applications and ways to diversify our skills.” To supplement its work in fibre optic submarine cables, ASN is keeping a close eye on the offshore oil & gas sector. “We have laid cables to several offshore rigs and learned a great deal about this type of client and their requirements.” Indeed, a team of ASN engineers has developed services tailored specifically to the sector’s needs. “In 2014, we acquired the Norwegian company Optoplan, a provider of sensors and 4D permanent reservoir monitoring solutions.” By placing acoustic sensors above pockets of hydrocarbons, subsea resources can be monitored in real time as it is exploited.

Original by Caroline Britz published on 11 December 2017. Translated and adapted by Steve Dyson.