Study on the transmission properties of sub-wavelength metallic tapered gratings with different-shaped walls

Sub-wavelength metallic tapered gratings with different-shaped slit walls are proposed in this research report. The transmission properties of the gratings have been investigated by finite difference time domain (FDTD) method. The simulation indicates that the transmission spectra strongly depend on the shapes of the slit walls. For TM-polarized light with normal incidence, the transmission coefficient and the bandwidth in the tapered gratings with the concave-parabolic slit walls are larger compared with the gratings with the convex-parabolic walls. For TE polarized light with normal incidence, the simulated results are reverse. In the visible range, the valley positions or peak positions of the transmission spectra are almost unchanged for all the gratings with different-shaped slit walls. The interaction of the electromagnetic (EM) waves on the slit walls with impendence match model has also been proposed in this paper. © 2014, The Optical Society of India.