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Optical Fibers Can Detect Type of Materials Around Them

Updated: Oct 11, 2019

LAUSANNE, Switzerland, July 31, 2018 — Forward stimulated Brillouin scattering (FSBS), because of its resonating transverse acoustic waves, has the potential to facilitate detections in an optical fiber’s surroundings. Researchers have now demonstrated a technique to measure the distributed FSBS spectrum of an optical fiber and retrieve the local acoustic impedance of the surrounding materials.

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The optical fibers are capable of detecting what sort of material or liquid they have come into contact with. Courtesy of EPFL/Desmond Chow.

To test the technique, researchers immersed optical fibers first in water and then in alcohol, before leaving them out in the open air. Each time, the fiber was able to correctly sense the change in its surroundings. According to researchers, the acoustic impedances of water and ethanol obtained by their technique agree well with the reported standard values.

Changes in the fiber’s surroundings are located using a time-based method.

“Each wave impulse is generated with a slight time lag," said professor Luc Thévenaz. "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. For the moment, we can locate disturbances to within around 10 meters, but we have the technical means to increase our accuracy to one meter.” 

According to researchers, until now it has not been possible to determine changes and events in a fiber’s surroundings without light escaping from the fiber and disrupting its path.

The team’s experimental results show that the distributed acoustic impedance measurements of a material are possible using the FSBS optoacoustic interaction, without direct interaction between light and the external material.

“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,” said Thévenaz. "There are many potential applications."

The research was published in Nature Communications (doi: 10.1038/s41467-018-05410-2).

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