New model details Brillouin scattering interactions between light and sound waves in polyimide-coated fiber for detecting liquids outside the cladding boundary.
Since light carried by optical fibers cannot reach outside the inner core, it is difficult to use these cheap and flexible tools for the analysis of surrounding media. Fortunately, the same fibers also support the transfer of ultrasonic waves, and the interactions between light and sound waves can be exploited for probing the properties of liquids outside the protective coating.
Building on their previous research, Diamandi et al. extended their model of these light-ultrasound opto-mechanical sensors to include polyimide-coated fibers, which are readily available commercially. The coating gives the fiber some protection, and at the same time provides connectivity for the ultrasonic waves that actually perform the sensing task.
In their experiment, spectra of interaction between light and ultrasound were measured for stretches of fibers in air, ethanol and water. To push the experiment further, spatial mapping of liquids was carried out over a mile-long fiber that was coated in polyimide for its entire length.