Light beamed through fiber can be used to test and monitor fiber networks. It is also increasingly being used as a sophisticated sensor for the world around the fiber cable.
On the surface, an optical fiber seems like an unassuming piece of modern infrastructure: A glass thread, about the thickness of a human hair, carrying pulses of light across vast distances. For decades, fibers have been threaded beneath city streets, across mountain passes, and under oceans, serving as the backbone of global communications.
But to Stuart Bausor, who leads the fiber sensing product team at Viavi Solutions, these fibers are more than a highway for data: They are sensors as well. With the right tools, the world’s fiber networks can be repurposed to hear footsteps, detect ground movement, feel shifts in temperature, and even tell when ice has started to form on a cable.
“If 5G is the neural conduction of the digital age and AI the super brain, fiber sensing serves as the quietly growing peripheral nerves,” Chinese researchers wrote in a paper on fiber sensing published last month in IEEE ComSoc Technology News.
The technology isn’t new, but it is gaining new momentum as fiber deployments proliferate and as companies across a wide range of verticals look for smarter, more holistic ways to monitor and protect critical infrastructure — both fiber networks themselves, and other infrastructure like pipelines, railways, and more. The reach of fiber sensing is significant: Up to 50 kilometers from a single point for vibration detection, according to Bausor, and up to 80 kilometers for temperature and strain sensing. And the resolution is quite fine, especially considering the distances involved: “Even at 50 to 80 kilometers, we’re still giving you resolution [of] maybe one to four meters, depending on the length of the fiber,” Bausor said.
While the foundation of fiber sensing will be familiar to telecom network engineers, the uses to which fiber sensing are being put extend far beyond telecom networks.
From OTDR to environmental sensor
Fiber sensing technology builds on Optical Time Domain Reflectometer (OTDR) principles, familiar to any fiber engineer.
“Inherently, it is an OTDR technology — so it’s very similar to the technology we use for monitoring optical networks,” Bausor said. “We take an instrument, and we plug it into the end of a fiber, we send light into it, and we then look at the backscatterings that come back from that.”
However, the resulting analysis is slightly different than traditional OTDR, which focuses on checking signal integrity and pinpointing fiber faults or breaks. For fiber sensing, Bausor said, “We look at different concepts of how the light comes back that allows us to then effectively deduce different insights related to temperature of the fiber, strain of the fiber and also vibrations along the fiber. Those three elements can then really open up a story to what’s actually happening, not only on the fiber but also in the environment that the fiber is in as well.”
The fiber itself becomes a distributed sensor with multiple capabilities.
What Fiber Sensing Can Do
Fiber sensing, also known as distributed fiber sensing (DFS), falls into three primary sensing capabilities, Bausor explained: Temperature, strain, and vibration. These can be applied across a wide variety of use cases. Each one requires a slightly different underlying technology.
- Temperature (Distributed Temperature Sensing, or DTS): Raman scattering produces temperature-related changes in photons that, when precisely measured, can accurately determine the temperature at any given location along a fiber, including increases and decreases. Temperature data can reveal whether buried cables are at risk of exposure, whether concrete around embedded fibers is curing properly, or if there is a fire near the fiber.
- Strain: (Distributed Temperature and Strain Sensing, or DTSS): Brillouin scattering is used to detect compression and elongation along the fiber, allowing subtle stresses to be detected that don’t show up in traditional OTDR testing. Bausor highlighted real-world threats such as wind-induced oscillations (aeolian vibrations) or icing on aerial cables, both of which can lead to long-term wear and potential failure. By measuring strain values, operators could intervene before a cable snaps.
- Vibration (Distributed Acoustic Sensing, or DAS): This is not to be confused with DAS as in Distributed Antenna System, or acoustic as in audible signals. “It’s really around monitoring vibration,” said Bausor. “Anything that creates a vibration, anything that moves, effectively — that fiber with a distributed acoustic sensing interrogator connected … will effectively detect it and identify it.” That means being able to pick up footsteps, vehicles, digging, the opening of gates or lifting of manhole covers, up to 25 meters away for vehicles and 10 meters for people or wildlife. “We can actually discriminate walking, driving, digging, [or] manhole lid lift autonomously within our software,” he added. And the software can be trained to identify, and then ignore, the patterns associated with passing wildlife.
There is only one catch: In order to use fiber as a sensor, it can’t also be used for data service. Viavi’s fiber sensing solution requires a single dark fiber to be dedicated to sensing. Coexistence with live traffic is a goal (one that Viavi is working on) but not yet a reality. That means the assets being monitored have to be valuable enough to justify the cost of an extra fiber that can’t be used for data transmission.
How fiber sensing is being used
Fiber sensing technology is already in use for perimeter security, border monitoring, and pipeline protection. Fibers can be tagged with latitude and longitude for integrated geospatial mapping that allows multi-modal surveillance: An alert from a DFS system could, for example, prompt activation of surveillance cameras or direct a drone to a specific location.
One of the most valuable use cases for fiber sensing is for monitoring and protection of the subsea cables that provide more than 99% of the world’s intercontinental data connectivity. According to the International Cable Protection Committee (ICPC), of the roughly 150–200 cable faults that are recorded around the world annually, between 70% to 80% are from accidental damage, most often caused by fishing or anchoring. Because vibrations travel even better in water than through the ground, Bausor said, fiber sensing can be used to track, and then to notify, ships that kilometers away in order to prevent anchor strikes.
Telecom cables aren’t the only ones that run underwater and need monitoring and protection. Offshore wind farms, for example, rely on special flexible or “dynamic” electrical cables to bring power to land. As much as 80-90% of offshore wind farm projects have experienced a cable-related fault, which can take millions of dollars and 3-5 months to repair. Dedicating a fiber to reduce that risk pays for itself, Bausor said.
The use of fiber sensing is being explored outside of cable infrastructure monitoring as well. In 2024, fiber sensing was the basic for a detection and early warning system for volcanic eruptions at the Reykjanes Peninsula on Iceland’s southwestern edge, one of the most seismically active areas of the world. Researchers from the California Institute of Technology worked with Icelandic scientists and a local telecommunications company, Ljósleidarinn, to deploy DAS through unused fibers.
The technology is also used for fire detection in warehouses, airplane hangars or industrial settings, or even for wildfire detection purposes. Earlier this year, the Chicago Transit Authority’s board approved a 12-month pilot program for fiber sensing from DAS company Sensonic, to enable real-time detection of trackside intrusions and fallen objects along the rail corridor. Researchers at Cornell University even created a compression shirt with embroidered optical fibers, aimed at patients with breathing issues, that can provide real-time respiratory rate monitoring.
Grand View Research has estimated that the size of global distributed fiberoptic sensor market was at nearly $1.5 billion last year, and that it’ll grow at more than 11% percent per year to reach more than $2.8 billion by 2030. What’s driving the growth? In part, more awareness among industries and corporations of fiber-sensing capabilities. Bausor also credits both fiber proliferation — there is simply more fiber in the ground and inside buildings and industrial environments, than ever before — and the desire for fiberoptic network owners to monetize their assets by potentially providing utilities, rail companies or governments with fiber-sensor data.
“Distributed fiber optic sensors are distinguished by their ability to monitor extensive areas with a single fiber, offering significant advantages over traditional point sensors,” Grand View wrote. “Their immunity to electromagnetic interference and harsh environmental conditions makes them suitable for deployment in challenging settings, including subsea pipelines, tunnels, and power grids.”
Data centers are another potential environment where fiber is already densely deployed and the temperature and vibration are critical environmental conditions that must be constantly monitored for safe and efficient operations. “These are passive systems — we’re only putting light into fiber — so they can go into combustible environments, they can go into wherever that fiber is,” Bausor said. That could mean fibers running through cooling systems, or providing environmental insights as part of interconnections between data center campuses.
Integrating sensor information
Viavi sees its competitive edge in the integration of fiber sensing with its existing optical network monitoring system (ONMSi) platform, Bausor said, and also its ability to combine both DFS and traditional network monitoring in a single platform, with existing customers having the ability to add DFS capabilities via modules. The company began exploring the technology back in 2017 — prompted by network operator customers who wanted to understand how the condition of fibers were impacting network performance — and made a full commercial launch of DFS capabilities last year.
The combination of optical network monitoring and DFS is a unique proposition; otherwise the market which is largely divided between exclusive sensing companies and exclusive network monitoring companies. “Viavi is the only one really in the market that’s sort of bringing those two worlds together as a single solution,” Bausor said, adding: “The key element is looking at relationships between network performance and any of that temperature change, strain change, or acoustic change.” By correlating events, operators can move from reactive troubleshooting to predictive maintenance — or proactive protection.
With more fiber available, adoption is widening
Fiber sensing itself is not brand new; early applications date back to the oil and gas industry, where it has been used for monitoring pipelines and storage facilities in hazardous environments. Grand View said that the oil and gas segment accounted for the largest revenue share of the fiber sensing market in 2024; in terms of capabilities, temperature sensing accounted for more than 45% of market revenues. Nearly 31% of fiber sensing revenues came from North America.
But adoption is widening quickly, as Grand View’s projections reflect. Governments are directing more attention to the protection of national or international infrastructure, including fiber networks themselves, urged on by trade groups. Telecom and utilities (which often also provide fiber broadband service) are showing high levels of interest, although adoption isn’t widespread just yet. “The vastness and the speed and the growth of the data center market is really driving a key focus on sensing as well,” Bausor said.
As to timing, Bausor suggested widespread adoption is closer than many think. “We’re engaged at a very high level in a number of key customers [for whom] sensing is at the forefront of their future directives of innovation, development and protection of their assets,” he said. He suggested the value proposition will hinge on whether operators see sensing as a way to reduce downtime, protect assets, or even monetize networks by selling data to other industries. “I think we’re very close to those business cases being contextualized,” he said.
If adoption does accelerate, the world’s vast installed base of fiber could double as a distributed nervous system: Detecting threats, predicting failures, and feeding valuable data to operators and other stakeholders. The trajectory echoes one that is also being seen in wireless networks: In a 6G context, wireless networks are already being seen as potential vehicles for joint communication and sensing. DFS shows that the same concept is already being applied to fiber networks, to deliver situational awareness of the surrounding environment, alongside connectivity. And that could make fiber a multi-purpose tool that both is critical infrastructure, and protects critical infrastructure.
