A Local Nanofiber-Optic Ear

The development of acoustic sensors that are compact, have simple read-out mechanisms, and have geometries that enable them to be inserted/embedded deep in materials is of great interest for acoustic-based imaging technologies and novel analytical instruments. Fiber-optic-based detectors are the most logical choice to satisfy these demands, but scaling down the size to sub-micrometer dimensions and uncovering transduction mechanisms that can be more robust than interferometric techniques in dynamic environments has been challenging. In this work, we demonstrate a non-interference-based acoustic ear that utilizes the movement of plasmonic nanoparticles embedded in the near field of a nanofiber optic. The modulated optical signal induced by sound waves can be read-out through transmission through the nanofiber or by tracking the scattering of the nanoparticles in the far field. By utilizing a thin, compressible cladding on the nanofibers, acoustic intensities of <10^–8 W/m² can be detected by the devices over an interaction area of <4 μm², representing a measured acoustic power at the sensor of 10^–21 W. With the ability to modify the mechanical properties of the cladding, change the size of the plasmonic nanoparticle, and alter the guided wavelength, the performance of this platform is highly tunable and ideal for compact, deep-body acoustic probes