Profile of an ultrasonic wave in a polyimide-coated fiber. Source: Diamandi, London, Bashan and Zadok
Light carried by optical fibers cannot reach outside the inner core, making it difficult to use these flexible tools for the analysis of surrounding media. However, these materials also support the transfer of ultrasonic waves, which can be exploited to analyze the properties of liquids outside of the fiber, but only if its polymer protective coating is first removed.
This barrier to the deployment of light-ultrasound optomechanical sensors was surmounted by the use of commercially available polyimide-coated fibers. The coating gives the fiber some protection while providing connectivity for the ultrasonic waves that affect the sensing task.
To test the efficacy of this sensing solution, researchers from Israel’s Bar-Ilan University measured the spectra of interaction between light and ultrasound for stretches of fibers in air, ethanol and water. Spatial mapping of liquids was also carried out over a 1.6 km long polyimide-coated fiber. Results correctly identified and located segments of fiber that were immersed in ethanol and water with a resolution of 100 m.
The new approach to optical fiber sensing through a coating should be of practical application in the oil and gas sector, desalination systems and chemical processing. The research is published in APL Photonics.
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