Fiber Optic Sensing Types Explained

Have you heard hype about fiber optic sensing?  Do you want a simple summary of the basics without getting swamped by science?

This article explores the different types of types of Fiber Optic Sensing (FOS) and the capabilities they offer.  Types of fiber optic sensing explored include:

• Distributed Acoustic Sensing (DAS)
• Distributed Strain Sensing (DSS)
• Distributed Temperature Sensing (DTS)
• Distributed Temperature & Strain Sensing (DTSS)
• Fiber Bragg Gratings (FBG)

Jump to your area of interest or see our summary table below

Fiber Optic Sensing Summarised:

Fiber optic sensing technology is revolutionising the way we monitor in diverse industries. Distributed fiber optic sensing together with fiber Bragg grating sensors allow fiber optics to offer high sensitivity, reliability, and versatile sensing capability for a wide range of applications including in hazardous and remote environments. Let's delve into the different types of fiber optic sensing technologies and their capabilities:

 

Distributed Acoustic Sensing (DAS):

Distributed Acoustic Sensing turns standard fiber optic cables into a continuous stream of virtual microphones. By analysing microscopic changes in backscattered light, we measure acoustic vibrations along every meter of the fiber with no trackside power or extra hardware required. Because it uses telecoms-grade fiber already resting in the rail corridor, DAS offers a low barrier to adoption with proven reliability in harsh conditions. We at Sensonic specialise in bringing this continuous asset intelligence to global railways. DAS delivers real-time acoustic monitoring enabling the detection of natural hazards such as rockfalls and landslides, security threats such as trespass or cable theft, and allow railways to continuously monitor the performance and safety of their assets over long distances. 

 

 

Distributed Strain Sensing (DSS):

Distributed Strain Sensing measures physical deformation and mechanical tension along the entire length of a fiber. When fixed or embedded directly within an asset, the fiber acts as an extension of the structure itself, reflecting any physical movement or bending of it. Most widely used in structural health monitoring, DSS lets engineers track the continuous integrity of bridges, tunnels, and dams over time. DSS can show structural deformation as it happens, giving maintainers the opportunity to catch potential engineering failures early.

 

 

Distributed Temperature Sensing (DTS):

Distributed Temperature Sensing provides non-stop temperature mapping across miles of fiber optic cable. By interpreting changes in the backscattered light, these systems track thermal shifts even in extreme or hard-to-reach environments. DTS is used for early fire detection in long rail tunnels and for monitoring power grid cables - helping operators optimise energy capacity without risking thermal overload or catastrophic equipment failure.

Distributed Strain & Temperature Sensing (DSTS / DTSS):

This combines the previous two categories monitoring both strain and temperature of the same fiber.

 

 

Fiber Bragg Grating Sensors (FBG):

Whilst distributed sensing reads backscattered light from the whole fiber, FBG in contrast uses short, engineered sections within the glass to create a sensing element at that point. These precise "gratings" reflect very specific light wavelengths, creating a targeted sensor element that reacts to localised strain, temperature, or pressure changes. FBG delivers high-precision, point-specific, measurements for critical systems often operating under harsh conditions.

 

In conclusion, fiber optic sensing technologies offer a powerful and versatile solution for monitoring and analysing physical parameters spanning many industries and applications. Whether it's detecting acoustic signals with DAS, measuring strain and temperature changes with embedded fiber as a sensor, or utilising FBG sensors for precise point measurements, fiber optic sensing continues to drive innovation and efficiency across multiple sectors. With ongoing advancements in fiber optic technology and data processing capabilities and AI, the future holds many more exciting possibilities for enhanced sensing capabilities and expanding the use of fiber optic sensors to deliver increasing value.

Want to find out more? Try these links or contact our team to discuss your specific requirements. 

   Railway Applications of DAS         More about DAS Technology   

What is backscatter / backscattered light?

Backscattered light in fiber optic sensing refers to the light that is reflected or scattered back toward the light source as it travels through the optical fiber. When a light pulse is transmitted through the fiber not all of it emerges at the other end of the fiber. Some of the light passing through the fiber interacts with the fiber's material, causing a portion of the light to scatter back. Any external influences, such as vibrations, temperature changes, strain, or pressure changes the properties of the back-scattered light, allowing for the monitoring of various physical parameters. The physical processes that affects the scattered light are called Rayleigh, Brillouin and Raman scattering.

What are alternative names for fiber optic sensing types?

In addition to the alternate spellings of fiber / fibre around the world, we find many alternate names used to describe the categories of fiber optic sensing. These different names are sometimes born from the history of development, and sometimes it is down to companies wishing to differentiate their own implementation of the technology. This can appear confusing to those outside the fiber optic sensing industry, so here is a handy guide we have collated to try and capture them in one place. If you find others please contact us and we will update it. 

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