Inside Submarine Cables: Construction, Powering, and Repair Explained

Submarine cables form the backbone of the internet, carrying more than 90% of international voice and data traffic; without them, the global network would be limited to local connections.

Physical Structure

Like terrestrial fiber, the core of a submarine cable is a hair‑thin glass fiber, but it is encased in robust armor and includes a remote power conductor that delivers electricity to underwater repeaters.

System Composition

The submarine cable system consists of two main parts: shore‑side equipment and underwater equipment.

Underwater equipment: the cable itself, optical amplifiers/repeaters, and branching units.

Shore‑side equipment: cable termination units, remote power supply units, monitoring devices, network management gear, and grounding systems.

Power Supply to Repeaters

Because optical signals attenuate over long distances, repeaters are placed at intervals to amplify the light. In the ocean, these repeaters receive power through the remote power conductor, which carries high‑voltage (several kilovolts), low‑current DC—typically around 1 A.

Armor Protection

Submarine cables face threats from ship anchors, natural disasters, and even marine life. Armor thickness varies with depth: shallow waters require heavy armoring to resist anchors, while deep‑water cables may have minimal armor, with diameters under 20 mm.

Underwater Repeaters

Repeaters are large cylindrical units mounted on cable‑laying ships. Their size limits the number of fiber cores that can be housed in a cable, because more fibers require larger repeaters and higher power.

Shore‑Side Power Equipment

The shore station contains DC converters that generate several‑kilovolt DC, arranged with N+1 redundancy. Monitoring interfaces display real‑time voltage levels. Backup batteries and diesel generators provide power during outages.

Landing Station and Network Integration

When the cable reaches land, it connects to termination equipment, then to patch panels and finally to data‑center transmission gear, completing the link between continents.

Repair Process

Repairing a submarine cable is a complex operation. Engineers first locate the fault with an OTDR instrument, then dispatch an ROV to cut the damaged section. The cable ends are brought aboard a ship for precise splicing of each fiber strand.

After splicing, the repaired segment is lowered back to the seabed, and a high‑pressure water jet creates a trench to bury the cable, a step also performed by the ROV.

These procedures ensure that a single cable can operate for decades without intervention, sustaining the global internet infrastructure.