Submarine Cables

The internet is 99% underwater. Over 400 active cable systems form the physical backbone of global digital trade.

Diagram of a submarine cable cross section

Anatomy of a Cable

A typical deep-ocean cable is barely thicker than a garden hose (about 17-20mm). Despite carrying terabits of data, the optical fibers themselves are the size of a human hair. The rest of the bulk is entirely for protection and power.

  • Optical Fibers: Carrying the actual light signals (DWDM).
  • Copper/Steel Tube: Protects fibers and carries up to 10,000 volts DC to power optical repeaters spaced every 50-100km.
  • Polycarbonate/Aluminum: Water barriers.
  • Steel Armor: Added near shorelines to protect against anchors and fishing nets.

Learn more about landing stations and data centers where these cables terminate.

Cable Capacity vs. Demand

The introduction of Space Division Multiplexing (SDM) has radically shifted the economics of cable laying. Modern cables like Google's Dunant achieve 250 Tbps.

Cable SystemReady for ServiceCapacityMajor Owners
Dunant2021250 TbpsGoogle
Grace Hopper2022340 TbpsGoogle
Amitié2023320 TbpsMeta, Microsoft, Orange
SEA-ME-WE 62025 (Est.)120 TbpsConsortium

Tool: Cable Latency Calculator

Calculate the theoretical minimum latency between two points based on the speed of light in optical fiber (~200,000 km/s, roughly 2/3 the speed of light in a vacuum).

Common Mistakes in Cable Analysis

  • Confusing capacity with lit capacity: A cable might support 250 Tbps, but owners only light pairs (install terminal equipment) as demand requires.
  • Assuming direct paths: Cables follow the seabed topology, avoiding deep trenches and political conflict zones, not the great circle route. Read about choke points.
  • Ignoring repeaters: Optical signals degrade. Deep ocean cables require powered repeaters every ~100km, making power the limiting factor in cable length, not signal.

FAQ

Are cables safe from sharks?

Mostly, yes. While there was brief panic in the 2010s over shark bites, the vast majority (70%+) of cable faults are caused by human activity (fishing trawlers and ship anchors).

Who fixes them?

A specialized fleet of roughly 50-60 cable ships globally operate on standby. When a fault occurs, they sail to the location, grapple the cable off the seabed, splice a repair on deck, and drop it back down. See fault repair data.

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