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

The enhanced middle-infrared light transmission through Au/SiO
x
N
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
x
N
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
x
N
y
/Au cascaded structure. Simultaneously, a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO
2.1
N
0.3
/Au cascaded structure with small refractive index (1.6) than in Au/ SiO
0.6
N1/Au cascaded structure with large refractive index (1.8). When the thickness of SiO
x
N
y
changes from 0.2 to 0.4 µm, 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
x
N
y
/Au cascaded structure with a thin dielectric film (0.2 µm), with the increase of SiO
x
N
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.