Near-field plates in the visible-IR regime using rectangular subwavelength apertures

Near-field plates have been proposed to focus electromagnetic radiation to arbitrarily small subwavelength dimension. Here we investigate the use of plasmonic structures for near-field focusing plates in the visible-IR regime. Rectangular subwavelength structures are used to manipulate near-field using rectangular subwavelength apertures. Our simulations show the desired characteristics of equal transmission and a 180 degree phase difference between two apertures of different dimensions. In addition, these structures can be realized using existing techniques, and we demonstrate the fabrication of rectangular apertures with the smallest side of 20 nm in a 300 nm thick gold film.