TE-polarized beam shaping by a subwavelength metal slit: Finite-difference at frequency-domain simulations

We present the beam-shaping effect by using a subwavelength slit perforated in the metal with engineered surface. The incident waves with transverse electric (TE) polarization are considered. As the metal is dressed with a dielectric film, the guided TE mode is excited and can be modulated by the periodically fabricated nano-objects on the dielectric or on the metal. By modifying the resonance condition of the guided mode, the beam collimating, focusing and splitting can be observed at the output of the slit. The study provides another way to manipulate light diffraction at nano-scale without the help of surface plasmons. Our results are based on the numerical simulations by using a compact finite-difference at frequency-domain method, the algorithm of which is also given in detail.