Phononic and photonic crystals for sensing applications

TLDR: In this article, the authors proposed a method to determine properties of the fluid such as its nature, concentration or temperature, employing specific features in the photonic and phononic transmission spectra.

Abstract: Photonic and phononic crystals provide a novel and alternative platform for sensing material properties with high sensitivity. The sensor aims to determine properties of the fluid such as its nature, concentration or temperature, employing specific features in the photonic and phononic transmission spectra. The dependence of such frequency dips or peaks where the transmission takes place is correlated to material properties, specifically to the acoustic or optical refractive index through the light and sound velocity of the fluid. Looking at both phononic and photonic behaviors within one single platform increases the ability to determine the fluid properties by cross correlating the optical and acoustic data. The capability of the concept is demonstrated through two different structures for which different specific applications can be reached. The first one is made of a two-dimensional crystal constituted of infinite cylindrical holes in a silicon substrate where one row of holes oriented perpendicular to the propagation direction is filled with a liquid. In the second one, the transmissions of optical and acoustic waves are normally impinging upon a periodic perforated silicon plate where the embedded medium is a liquid. Finally, we introduce acoustic metamaterials made of hollow pillars deposited on a plate for sensing purposes. Such crystals can exhibit confined whispering gallery modes around the hollow parts of the pillars. Filling the hollow parts with a fluid gives rise to new localized modes, which depend on the physical properties and height of the fluid. In all the investigated cases, we show an ultra-sensitivity to the light and sound velocities for different fluids, considered as the analyte, depending on their nature, concentrations or temperature.