Short and long range surface plasmon polariton waveguides for xylene sensing.

Nanostructured plasmonic sensors are fabricated as sinusoidal surface plasmon metallic gratings (SPGs) embedded in a functional and porous hybrid sol-gel material, phenyl-bridged polysilsesquioxane (ph-PSQ). The metal layer is in contact with the environment through the sol-gel film, which works as sensitive element, changing its dielectric properties upon interaction with aromatic hydrocarbons. The combination of sensitivity, transparency and patternability offered by ph-PSQs gives the exceptional possibility to fabricate innovative optical sensors with straightforward processes. An embedded SPG is a thin metal slab waveguide, in which the surface plasmon polaritons (SPPs) at the two metal-dielectric interfaces superpose, resulting in two physical coupled modes: the long range SPPs (LRSPPs) and the short range SPPs (SRSPPs). An extended experimental and theoretical characterization of the optical properties of the plasmonic device was performed. The sensor performance was tested against the detection of 30 ppm xylene, monitoring the influence of the target gas on the SPPs modes. A reversible red-shift of the reflectance dips of both LRSPP and SRSPP resonances in the 1.9-2.9 nm range was observed and correlated to the interaction with the analyte. An enhancement in sensitivity associated with the rotation of the grating grooves with respect to the scattering plane (azimuthal rotation) was verified within the experimental errors. Collected data are compatible with theoretical predictions assuming a variation of the film refractive index of 0.011 ± 0.005.

Extraordinary optical transmission in one-dimensional gold gratings: near- and far-field analysis.

One-dimensional arrays of nanoslits fabricated on silicon nitride membranes show extraordinary optical transmission. Optical characterization techniques have been used to characterize the transmission spectra and the near-field optical configuration. Experimental results have been compared with numerical simulations in order to elucidate the different modes of light propagation. Near- and far-field optical distribution is studied as a function of the polarization of light.

Absorption profile modulation by means of 1D digital plasmonic gratings.

Optical simulations of 1D digital plasmonic gratings on a Silicon substrate are performed by means of the Finite Elements Method and a modal analysis. The different mechanisms of transmission of the light are elucidated. The absorption profile in Silicon can be modulated and controlled changing the geometry. Configuration maps allow to determine the different optical regimes. Surface Plasmon Polaritons and cavity-mode resonances are shown to be effectively exploitable to enhance NIR-light absorption in different shallower regions of the underlying Silicon.