Extraordinary optical transmission: Role of the slit width in 1D metallic grating on higher refractive index substrate

• Higher Refractive index substrate is used.
• Extraordinary optical transmission results are correlated with near- and far-field analysis.
• Application as ultrafast photodetectors, biosensing and sub-wavelength photolithography.

We present a detailed analysis of the excitation of surface plasmon polaritons (SPPs) and associated extraordinary optical transmission (EOT) when a plane wave is incident at normal on a 1D metallic grating fabricated on higher refractive index GaP substrate. A simple method is introduced to estimate the EOT by measuring the 0th order transmission spectra obtained through the plasmonic grating structures with varying grating slit width for a fixed period and the thickness of the gold (Au) film in which the grating is formed. For an optimum Au film thickness, a slit width of slightly less than half and greater than one-third of the periodicity of 770 nm in the grating device yields a maximum EOT value. Such grating devices support only a fundamental plasmonic mode because the profile/shape of the slit in the grating device is more like a sinusoidal nature. Far-field and near-field modelling results also support the far-field results obtained through the experiment. The optimal grating devices have many applications in real world.

Schematic of transmission through a 1D grating with metallic thickness t slit width a and periodicity Λ. Vertical arrows indicate the incident (green), reflected (blue) and transmitted (red) light at each interface in the slit of the gratings. The structure is illuminated with p- or s-polarized light from the substrate side and corresponding backward and forward scattered modes are shown. (right) Relative transmission (for p-polarized and s-polarized light of 1D grating devices of period Λ = 770 ± 7 nm, with different slit.Figure optionsDownload as PowerPoint slide