A method to obtain large transmission of light through a nano-metallic slit bordered by nano trenches is demonstrated theoretically. The model is based on the composite diffraction of evanescent waves (CDEW) theory and utilizes a single trench design to effectively convert free-space light into surface plasma waves (SPW). The effectiveness is confirmed by the finite difference time domain (FDTD) method. The SPW loss due to scattering by the trench is also analyzed. It is found that when the width of the trench is slightly larger than λspp/2, the SPW becomes localized and resonates at the bottom edges performing as a dipole-like radiation source. At this time, the propagating SPW suffers from high scattering loss. Trenches can be used to enhance the transmission of a nano-scaled slit while simultaneously preserving high conversion efficiency and low scattering loss. A nano-scaled slit bordered by 10 pairs of trenches can be enhanced by a factor as high as 16. It is determined that a device designed to have a large clear aperture of 15 μm would have an advantage in terms of alignment.
- Diffraction theory
- Surface plasma waves