Optical fiber gas sensors

Our society is increasingly demanding measurement and control instruments of all kinds, whether for safety, comfort or product quality control.

The risks associated with gas production, storage and transport are widespread, and have a direct impact not only on the environment, but also on health. Gas sites therefore need to be protected by gas sensors to prevent any risk of explosion or exposure to noxious effluents in the event of an accidental leak. In practice, measuring systems such as electrochemical sensors, pellistors or optical sensors using infrared or ultraviolet absorption are often bulky, complex or energy-consuming, requiring electrical wiring that is often difficult to install. They are therefore ill-suited to measurements in large enclosed spaces (vast industrial sites, road tunnels, underground parking lots, etc.) or along gas pipelines, which are currently unprotected. For these applications, fiber optic sensors offer a potential unmatched by other technologies.

These sensors have all the advantages inherent in the use of fiber optics. Among these, the most decisive for gas detection are their immunity to electromagnetic interference, their resistance to high temperatures and chemical corrosion, and their ability to address multiple measurement points simultaneously. However, an optical fiber is not intrinsically sensitive and selective to a gas. In practice, it is therefore necessary to associate a sensitive layer with the optical fiber, on which the gas will adsorb and cause a physical change (change in temperature, change in pressure, generation of a mechanical stress, change in density) that can be measured by the optical fiber. Of course, this sensitive layer must meet a certain number of conditions to ensure that the overall sensor (optical fiber + sensitive layer) functions correctly. The combination of a suitable sensitive material and the optical fiber is the key to the finesse of fiber optic gas sensors.

The aim of this dossier is to present the physical principles of the main configurations of fiber optic gas sensors, and then to look at concrete applications such as the detection of hydrogen, oxygen, methane or carbon dioxide.