In today’s hyper-connected world, it’s easy to forget that the backbone of the global internet isn’t floating in the cloud — it’s lying on the ocean floor. Subsea fibre optic cables are the key piece of infrastructure which propels digital communication, carrying over 95% of international data to connect continents.
How many fibre optic cables are in the ocean?
As of 2025, there are over 600 active and planned undersea internet cables spanning the globe. They collectively stretch more than 1.4 million kilometres (nearly 870,000 miles), enough to circle the Earth more than 35 times. The ocean’s fibre optic network links major data hubs like New York, London, Tokyo, and Sydney, while also increasingly reaching into developing regions to help bridge the global digital divide. You can explore this network on the interactive Subsea Cable Map by TeleGeography.
What’s inside a subsea fibre optic cable?
Although these cables play a critical role in global connectivity, their size might surprise you. Most subsea fibre optic cables measure just 17 to 25 millimetres in diameter (roughly the size of a garden hose). This compact design is made possible by the thin optical fibres at their core, each about the diameter of a human hair.
Here’s a closer look at the key components that make up these vital links in the global internet infrastructure:
- Optical Fibre – Ultra-thin strands of glass that transmit data as pulses of light, enabling high-speed communication across continents.
- Insulation – Multiple layers of polyethylene (PE) and other protective materials shield the fibres from water, pressure, and environmental damage.
- Strength Members – Steel wires or similar reinforcements provide tensile strength to withstand deep-sea pressure, seabed movement, and marine life.
- Conductor – A copper or aluminium tube runs alongside the fibres, supplying electrical power to the repeaters spaced along the cable’s length.
- Repeaters (Optical Amplifiers) – Positioned at regular intervals, these devices boost the light signal to maintain data integrity over thousands of kilometres.
Laying and maintaining the cables
Laying fibre optic cables in the ocean is a major engineering feat. Specialised ships known as cable-layers carefully place cables on the ocean floor along mapped routes. These vessels are equipped with cable carousels, tensioners, and dynamic positioning systems that precisely unwind and place the cable; sometimes a plough is used to bury it in the seabed for protection.
Maintenance is equally complex. When faults occur, remotely operated vehicles (ROVs) are dispatched to locate and repair the damage. In significant cases, cable ships recover sections of the cable to the surface for inspection and testing. Damaged sections are cut away, and the remaining functional cable is sealed to prevent water ingress. The ship then retrieves the cable ends with a grapnel or other specialised tools, reels them in with motorised drums, and splices in a new section of cable.
In a wireless world, do these cables matter?
In an age dominated by 5G, Wi-Fi 6, and satellite internet, it’s easy to assume that the world is going fully wireless. But the internet is still very much wired — especially when it comes to global connectivity.
While satellites are essential for remote or underserved regions, they cannot match the performance of fibre, which offers lower latency, higher bandwidth, and greater resilience, which are critical for today’s digital economy. Whether you’re streaming a film, backing up data to the cloud, or conducting a cross-border business deal, chances are your data is traveling through a cable on the ocean floor, not bouncing off a satellite in space.
Fujikura and the global fibre ecosystem
While we don’t manufacture submarine cables, our fibre optic expertise has a significant impact on the global fibre optic landscape. Subsea cables may carry data across oceans, but they rely on robust terrestrial networks to deliver that data to homes, businesses, and data centres, which is where we come in.
As a leading innovator of fibre optic cable technology, we help enable the high-speed, high-capacity networks that power everything from local broadband to international cloud infrastructure. Our contributions include advanced optical fibre cables, fusion splicing equipment, and connectivity solutions that are essential for building and maintaining resilient fibre networks on land (the critical link between the ocean floor and the end user).
It’s remarkable to consider that the internet, something we rely on every day for work, communication, entertainment, and innovation, depends on thousands of miles of glass strands laid across the ocean floor. These subsea fibre optic cables enable a level of global connectivity that would have seemed impossible just a few decades ago.
While the technology will continue to evolve, the need for fast, reliable, and scalable networks will remain constant. That’s where we come in – solutions such as our next generation Wrapping Tube Cable with SpiderWeb Ribbon delivers industry-leading fibre density for telcos, which enables them to build networks faster and with less cost. Click here to learn more about our end-to-end optical networking solutions.
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