Enhanced middle-infrared light transmission through Au/SiOxNy/Au aperture arrays

The enhanced middle-infrared light transmission through Au/SiO_xN_y/Au aperture arrays by changing the refractive index and the thickness of a dielectric layer was studied experimentally. The results indicated that the transmission spectrum was highly dependent on the refractive index and the thickness of SiO_xN_y. We found that the transmission peaks redshifted regularly along with the refractive index from 1.6 to 1.8, owing to the role of surface plasmon polaritons (SPP) coupling in the Au/SiO_xN_y/Au cascaded structure. Simultaneously, a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO_2.1N_0.3/Au cascaded structure with small refractive index (1.6) than in Au/ SiO_0.6N1/Au cascaded structure with large refractive index (1.8). When the thickness of SiO_xN_y changes from 0.2 to 0.4 ¿m, the shape of transmission spectrum exhibits a large change. It was found that a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO_xN_y/Au cascaded structure with a thin dielectric film (0.2 ¿m), with the increase of SiO_xN_y film´s thickness, the transmission peak gradually widened and disappeared finally. This effect is useful in applications of biochemical sensing and tunable integrated plasmonic devices in the middle-infrared region.