Lab-on-Fiber Plasmonic Probes for Ultrasound Detection: A Comparative Study

This paper deals with a numerical study on Lab-on-Fiber devices for acoustic (ultrasound) sensing applications. Specifically, four different configurations based on hybrid metallo-dielectric nanostructures-with sub-wavelength dimensions-supporting plasmonic modes are analyzed. A comparison in terms of spectral features and electric field distributions at resonant wavelengths is carried out. For each configuration, sensitivity is evaluated as the reflectivity intensity changes as function of dielectric slab thickness, in the range of a few hundreds of nanometers. We demonstrate that sensitivity can be maximized by exploiting the interplay between different plasmonic modes. The influence of the acousto-optic coefficient is also evaluated. In the plasmonic interaction regime, we find that the acousto-optic effect also contributes to improve the sensitivity performances. Overall, in comparison with Fabry-Perot cavity-based transducers made from same materials and with comparable dimensions, sensitivity enhancement factors of about 3 can be obtained.