Enhanced optical transmission of non-coaxial double-layer gold nano-slit with slanted sidewall arrays

We present the numerical investigation of the optical transmission through the non-coaxial double-layer gold nano-slit with slanted sidewall arrays by using the finite-difference time-domain (FDTD) method. It is found that there mainly exist three resonant peaks in the transmission spectra and the transmission behaviors are strongly dependent on the lateral displacement, the slit widths, the layer separation and the thickness of the film. Based on the field distribution, we show that the two short wavelength transmission peaks are characterized as the surface plasmon resonance, while the long wavelength transmission peak is characterized as the localized waveguide resonance.