Optical fibre cables have traditionally been used for high-speed telecommunications. But they have another valuable use in industry — as continuous sensors.

Unlike ‘point sensors’, which measure data at specific locations, continuous sensors turn the entire length of fibre into a sensor capable of monitoring conditions across tens of kilometres in real time.

Folium Sensing co-founder Prof. Balaji Srinivasan traces the science’s roots to the 1980s. At the time, fibre was used to transport data as it minimised data loss and offered high bandwidth. “Whatever is bad for communications — like scattering of light, which causes attenuation (loss) in the fibre as well as external perturbations — turned out to be good for sensing,” he says.

While external vibrations or temperature changes may affect the efficiency of data transmission, they serve as the very signals needed for monitoring. Any existing telecom fibre can be converted into a distributed sensor, equivalent to numerous thermometers or microphones, simply by connecting an instrument to one of its ends.

The instrument sends laser pulses through the fibre and analyses the returning light — much like an echo. This is ‘backscattering’. Folium uses three types of scattering to detect various problems: Rayleigh scattering detects vibrations and acoustics in instances of intrusion or pipeline leaks; Raman scattering is sensitive to temperature for fire detection and power cable monitoring; and Brillouin scattering measures stress or deformation in structures such as bridges and tunnels.

AI/ML models sift through the data to differentiate harmless background noise from critical events, Srinivasan explains. Using the analogy of locating a friend’s voice in a crowd, he adds: “Once trained to an acoustic signature, you can pick it up in the presence of other acoustic signatures.

Folium says the oil and gas industry could benefit the most from the technology — existing fibres can offer round-the-clock monitoring for leaks and illegal excavations. IIT-Madras has built a 100-metre buried pipeline test bed, one of the largest in the world, to simulate various threats. “I can tell between a leak in a pipe or if somebody is using a jackhammer in the vicinity; whether it’s manual digging or an earthmover,” he says. This supplants the need for workers to patrol 50-km stretches on motorbikes daily.

In defence and security, Folium’s technology acts as a quiet ‘sentry’. Srinivasan points out that border areas already have underground fibre cables for surveillance cameras, but intruders can exploit ‘blind’ spots between cameras. Folium’s box can monitor across lengths not possible before.

Unlike cameras or electronic sensors that require power sources — a challenge in remote locations — Folium’s sensors rely on light pulses from a central control room, where power is already available.

Other important uses include monitoring railway tracks for breaks, detecting train movement, and identifying trespassing, including animal crossing; and checking for temperature changes in overhead and underground power cables to prevent degradation of wires or insulation.

In aerospace, Srinivasan has patented a method for monitoring ‘combustion instability’ in jet engines. By tracking the ‘dancing of the flame’ and the acoustics of the combustion chamber, the system can warn pilots before an engine flame-out occurs.

Typically, a single system can monitor up to 100 km, but this can be extended using amplifiers. The world record for such sensing is over 2,200 km. Customers also prefer installing a system every 50 km to maintain the signal and reduce uncertainty.

Folium Sensing is currently engaging with about a dozen potential customers and has a few orders, Srinivasan says.

“The idea resonates well because it provides high-accuracy, real-time intelligence for critical infrastructure without complex field hardware” or having to relay fibre cables.

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Published on March 23, 2026