Our society is using more and more data. There's no escaping it. We're streaming more video, often in 4K, and watching a lot less traditional broadcast TV. We used to save photos, videos, documents, and backups on hard drives; now we save them in the cloud. We don't write letters any more; we send off emails with heavy attachments without a second's thought. It all adds to the rising demand.

But we're not the ones most responsible for the jump in data use. Any idea who is?

It's the machines. More than anything humans do, machines are now talking to other machines, constantly, at scale, and often without any need for us to be in the loop.

Machine-Generated Data

AI systems move information back and forth between data centers to train, refine and compare models. Sensors in factories, transport systems, and cities send continuous streams of data for monitoring and control. Software systems are programmed to synchronize databases, replicas, and logs across regions, to stay consistent. The same data can find itself sent, processed, and sent again, not once, but over and over again. And the volume grows.

Networks Getting Squeezed

Optical fiber is carrying this rising load and engineers have worked hard to increase capacity by packing more signals into a limited range of wavelengths, mainly in what are known as the C and L bands. Doing so relies on extracting more performance from a relatively narrow slice of the optical spectrum, over networks that can span hundreds or thousands of kilometers. At some point, however, we have to face the prospect of reaching a hard ceiling for all the data, above which lies bottlenecks and delays.

NTT’s Science and Core Technology Laboratory Group has been thinking about the problem and wants to do things differently.

A New Information Super-Highway?

Instead of working the same wavelength bands even harder, NTT has been looking at how to use parts of the spectrum that have traditionally been left unused. Think of it as being like a highway system. Until now, engineers have added extra lanes by narrowing them and managing traffic more carefully within a fixed stretch of road. NTT thinks: how about if we don't keep on narrowing the lanes, but start to use this entirely new section of highway that has always been there, just not yet paved or signposted?

The X Factor

By extending transmission into a newly defined X band, beyond the longest wavelengths normally used in optical communications, the Science and Core Technology Laboratory team has been able to demonstrate that existing fiber can carry far more information than previously assumed. Taken together with the short-wavelength S band, they have tested ways of expanding the usable optical spectrum to about 27 terahertz, roughly six times wider than the bands normally used in long-distance systems. Not replacing wavelengths, but extracting additional capacity from what's already there. It's very X-citing.

The team is making deliberate use of a physical effect inside the fiber itself. When very wide bands of signals travel together, optical power naturally shifts from shorter wavelengths to longer ones, a phenomenon known as "inter-channel stimulated Raman scattering." That energy transfer helps longer wavelengths, which normally fade quickly, travel further than they otherwise could.

From Shorter to Longer Wavelengths

In optical systems, longer wavelengths usually suffer higher losses, which is why they have been avoided until now. By taking advantage of the natural power transfer from shorter to longer wavelengths, however, NTT’s researchers were able to compensate for those losses. Optical parametric amplification allows signals to move smoothly between different wavelength ranges. Used together with erbium-doped fiber amplifiers, the standard signal boosters already deployed in networks, this makes it possible to carry signals continuously from the S band through to the new X band within a single system.

The System Works

Before you think it was something just tested in a laboratory, here are some of NTT's real-world results. In transmission tests using standard 80-kilometer repeater spacing, similar to regular terrestrial backbone networks, NTT reached data rates of 189.5 terabits per second over 560 kilometers, roughly equivalent to the distance between Tokyo and Nagoya. Over longer distances of 1,040 kilometers, covering routes comparable to the Tokyo-Nagoya-Osaka corridor, the system was still able to deliver 160.2 terabits per second.

The blistering speed is X-cellent to have, of course, but just as important is the fact that a long-standing constraint has been pushed back. Optical networks have been moving toward a limit defined by how much usable spectrum fiber is able to support; NTT is pointing to a way in which entirely new wavelength regions could be brought into service, over real distances and using existing infrastructure. So perhaps the wavelength limit isn't as fixed as we thought. Maybe we're not running out of optical “room” after all, and future networks still have space to grow. X-ceedingly good news.

Innovating a Sustainable Future for People and Planet

For further information, please see this link:
https://group.ntt/en/newsrelease/2025/08/12/250812a.html

If you have any questions on the content of this article, please contact:
Public Relations
NTT Science and Core Technology Laboratory Group
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.