Combining types of strain measurements reduces noise, allowing for ultra-sensitive applications

Brillouin fiber strain sensors are useful for providing absolute measurements of strain in a material. However, their utility is limited in situations where strain changes at high frequencies, as time delay complicates the localization of the signal source. By combining four different strain measurements, Joseph Murray and Brandon Redding introduced a solution for the localization problem and improved the measurement sensitivity of ultra-low noise strain signals more than an order of magnitude compared to previous methods.

Using both a Stokes probe and an anti-Stokes probe to each measure the gain and the phase of the strain, the researchers combined the four measurements into a single output. Because each individual measurement has a different noise dependence, their combined value has a much lower background noise overall, while maintaining the sensitivity to strain. Because Brillouin sensing systems typically only feature one probe rather than the two here, the possibility of this type of noise reduction is precluded.

In testing the technique, they were able to clearly localize the strain signal with very low noise.

“Brillouin-based sensing has some unique and quite attractive features. It was rather disappointing that this type of sensing appeared to be not nearly as useful as we had hoped for these higher frequency strain regimes,” Murray said. “It was really exciting when we had the insight that we could overcome this limitation by combining Stokes and anti-Stokes interactions.”

Currently, Murray and Redding are working on additional optimizations to suppress noise even further. The technique has a wide variety of potential applications, from ensuring buildings are structurally sound, to using the bending of fibers to determine the shape of soft materials, like tissue.

Source: “Combining Stokes and anti-Stokes interactions to achieve ultra-low noise dynamic Brillouin strain sensing,” by Joseph B. Murray and Brandon Redding, Applied Physics Photonics (2020). The article can be accessed at https://doi.org/10.1063/5.0024121 .