Since optical fibers have become almost necessary for operating devices such as thermometers, acting like sensors by detecting changes in pressure etc. For structures like gas pipelines and bridges, using optical fibers for this technique has become quite important.
Researchers from the École polytechnique fédérale de Lausanne (EPFL) have developed a new method that allows optical fibers to identify whether the materials they’re in contract with are in liquid state or solid state. The fibers produce a sound wave from a light beam that is present inside the fiber. The research was conducted by the Group for Fibre Optics (GFO) from EPFL’s School of Engineering, which is run by Luc Thévenaz and was published recently in the journal Nature Communications.
Optical fibers are extremely thin and made up of glass, light is transmitted through this glass and varies depending on the four parameters: intensity, phase, polarization and wavelength. These parameters change when the temperature changes, or when the fiber is stretched, the fiber can detect these changes by acting like a sensor.
Up until now it has not been possible to get a hold of what kind of materials are present around the fiber without having the light escape the fiber. The method developed by the EPFL research team uses a sound wave which is produced inside the fiber. This hyper frequency wave bounces off of the fiber’s walls repeatedly. The echo produced depends on the material that the wave comes into contact with.
The echo leaves behind an imprint on the light wave that can be analysed by scientists after the beam exits the optical fiber, thereby giving an idea about the fiber’s surroundings. The research team did immerse the fibers in liquids like alcohol and water, and then left them out in the air. Their method was successful in identifying the materials around the fibers each time.
“Each wave impulse is generated with a slight time lag. And this delay is reflected upon the beam’s arrival. If there were any disturbances along the way, we can both see what they were and determine their location”, explained Thévenaz. “Our technique will make it possible to detect water leakages, as well as the density and salinity of fluids that come into contact with the fiber. There are many potential applications”, he added.