In-plane illuminated metallic annular aperture array for sensing application

Abstract

We propose here an application to sensing of annular aperture arrays (AAA). We theoretically investigate the optical properties of the reflective AAA device when illuminated in-plane. The cavity presents almost perfect absorption due to the waveguide mode resonance with strong field localization in the aperture. Additionally, the reflective cavity is modeled to be available for on-chip sensing with a theoretically expected sensitivity of 764 nm∕RIU (refractive index unit , we propose here to investigate the behavior of the electromagnetic field inside coaxial apertures when illuminated in-plane. It appears as a combination of high transmission and planar optics with strong field localization, which should provide a high sensitivity associated to a local interaction with the measured medium. In this Letter, the integration of these nanostructures is considered for embedment in waveguides. Figure 1 presents the schematic view of three periods of the studied structure. It consists of one row of annular holes in a block of gold (Au) embedded on a silicon nitride (Si 3 N 4 ) waveguide. The different parameters are: the periodicity (p), the cut-distance (d 0 ), the inner radius (r i ), the outer radius (r e ) of the circular aperture, and the block metal thickness (d 1 ). The incident medium (Si 3 N 4