Asymmetric plasmonic grating for optical sensing of thin layers of organic materials

In this paper the performance of an optical organic sensor based on a plasmonic grating immersed in an asymmetric dielectric environment is investigated. Metal gratings offer the possibility to tailor the spectral response, in dependence of the geometrical parameter settings and variation of the refractive index of the surrounding media. It is then possible to obtain a reflection spectrum displaying a sharp dip that can be efficiently exploited to improve the detection of small quantities of organic materials. In particular, using a finite difference time domain (FDTD) based method, we demonstrate that the designed plasmonic grating, made of gold strips placed on a silicon substrate and covered by a generic organic material (analyte), exhibits an improved sensitivity for the detection of the overlayer thickness (analyte quantity). Nevertheless, this plasmonic sensor can also be used to determine the typology of the generic organic layer in dependence of the refractive index change.