Whether you’re texting a friend, streaming a movie, or giving instructions to an AI program, there’s a high probability your data is currently taking a trip deep under the ocean.

Submarine cables are the backbone of our digital lives. They bridge continents and carry the vast majority of international internet traffic, powering the cloud services and mobile apps we’ve come to depend on.

Explosive Data Growth

But—and you knew we were going to say this, didn't you?—there's a catch. Our hunger and need for data is exploding. Between high-def video, massive AI models, and billions of connected devices, we are pushing more data than ever through the same fiber-optic pipes.

For years, engineers have squeezed more juice out of their cables by refining how light travels through them. They use methods such as wavelength-division multiplexing and advanced modulation technologies to pack signals tighter, using different wavelengths of light to carry separate signals. But even with all that, we’re still coming up to a wall and regular optical fiber cables are reaching their physical speed limit. There’s only so much room inside a physical cable to add more individual fibers.

What's Better Than One Lane? Four Lanes

NTT have been thinking about this issue and have developed a submarine cable system using 4-core multi-core fiber (MCF). In a nutshell, instead of a single lane for light to travel down, NTT's new design carves out four separate lanes, or cores, inside a single strand of fiber. This effectively quadruples the capacity of the cable without making the glass any thicker.

Multi-core fiber isn't a new concept for NTT; they’ve been researching it for years as part of their Innovative Optical and Wireless Network (IOWN) vision for future networks. What’s different now is that they are moving the initiative from being a promising research and development project to making it into a practical, real-world tool. NTT haven't just pioneered new uses of fiber, they've gone ahead and built an ecosystem of hardware needed to actually deploy it at the bottom of the sea.

It's All In Place

A submarine network is more than just a long wire. It needs specialized equipment to link underwater segments together, connect sea cables to land cables, and eventually plug everything into a shore-side station. Without humdrum components like connectors and junction boxes, even the fastest fiber in the world is just a lab experiment.

NTT has checked every box. Their connectivity lineup includes the 4-core submarine cable itself, specialized joint boxes to bridge the gap between sea and land, and termination frames that allow their cable to plug into the standard equipment already sitting in communication hubs, enabling connection between multi-core fiber and existing conventional optical fiber inside the station.

So what does it all mean?

4 x Capacity

In practical terms, a cable just 20 millimeters thick can now hold up to 48 of these 4-core fibers. That adds up to 192 individual cores—four times the capacity of a traditional cable of the same size. And it's not just a lab experiment; NTT's system has been put through stress tests for the real world and has met the strict optical, mechanical and functional standards required for life on the unforgiving ocean floor.

It's quick, it's tough. It's also a more economical way of sending data. If a single cable can carry four times the traffic, operators can then build high-capacity networks more efficiently. Keeping up with the world’s never-ending demand for bandwidth without breaking the bank.

We often think of digital progress as just being about software or giant data centers, but the physical world is every bit as important. Sending more bits and bytes by reimagining the fiber itself and then building the infrastructure to make it work in the wild.

Innovating a Sustainable Future for People and Planet

For further information, please see this link:
https://group.ntt/en/newsrelease/2026/03/13/260313a.html

If you have any questions on the content of this article, please contact:

Public Relations
NTT IOWN Integrated Innovation Center
https://tools.group.ntt/en/news/contact/index.php

Daniel O'Connor

Daniel O'Connor joined the NTT Group in 1999 when he began work as the Public Relations Manager of NTT Europe. While in London, he liaised with the local press, created the company's intranet site, wrote technical copy for industry magazines and managed exhibition stands from initial design to finished displays.

Later seconded to the headquarters of NTT Communications in Tokyo, he contributed to the company's first-ever winning of global telecoms awards and the digitalisation of internal company information exchange.

Since 2015 Daniel has created content for the Group's Global Leadership Institute, the One NTT Network and is currently working with NTT R&D teams to grow public understanding of the cutting-edge research undertaken by the NTT Group.